(tender ref. as 10 231) · 2014. 6. 13. · i finalport re for provision of service for fine...
TRANSCRIPT
i
Final Report
for
Provision of Service for Fine Particulate Matter (PM2.5) Sample Chemical Analysis
(Tender Ref. AS 10‐231)
Prepared by:
Prof. Jian Zhen Yu
Dr. X. H. Hilda Huang
Ms. Wai Man Ng
Environmental Central Facility
The Hong Kong University of Science & Technology
Clear Water Bay, Kowloon, Hong Kong
Presented to:
Environmental Protection Department
The Government of the Hong Kong Special Administrative Region
May 2012
ii
Table of Contents
Title Page..................................................................................................................................... i
Table of Contents....................................................................................................................... ii
List of Tables ............................................................................................................................. iii
List of Figures ............................................................................................................................ iv
1. Introduction ...........................................................................................................................1
1.1 Study Objectives .............................................................................................................. 1
1.2 Background ......................................................................................................................1
1.3 Technical Approach..........................................................................................................1
2. Sampling Network.................................................................................................................. 3
2.1 Ambient PM2.5 Monitoring Network................................................................................3
2.2 Ambient PM2.5 Measurements ........................................................................................4
3. Database and Data Validation ...............................................................................................7
3.1 Data File Preparation ....................................................................................................... 7
3.2 Measurement and Analytical Specifications....................................................................7
3.2.1 Precision Calculations and Error Propagation ..........................................................7
3.2.2 Analytical Specifications ...........................................................................................9
3.3 Data Validation............................................................................................................... 15
3.3.1 Sum of Chemical Species versus PM2.5 Mass..........................................................16
3.3.2 Physical and Chemical Consistency.........................................................................19
3.3.2.1 Water‐Soluble Sulfate (SO42‐) versus Total Sulfur (S) ......................................19
3.3.2.2 Water‐soluble Potassium (K+) versus Total Potassium (K) ..............................22
3.3.2.3 Water‐soluble Chloride (Cl‐) versus Total Chlorine (Cl) ...................................25
3.3.2.4 Ammonium Balance.........................................................................................28
3.3.3 Charge Balance .......................................................................................................31
3.3.4 NIOSH_TOT versus IMPROVE_TOR for Carbon Measurements .............................34
3.3.5 Material Balance .....................................................................................................40
3.3.6 Comparison of Collocated Samples ........................................................................45
3.3.7 PM2.5 Mass Concentrations: Gravimetric vs. Continuous Measurements .............47
4. Comparison to the PM2.5 Sampling Campaigns in 2000 ‐ 2001, 2004 ‐ 2005, and 2008 ‐ 2009 .........................................................................................................................................49
5. Summary ..............................................................................................................................56
References ...............................................................................................................................58
iii
List of Tables
Table 1. Descriptions of monitoring sites ..................................................................................3
Table 2. Arrangement of the Partisol samplers in monitoring sites..........................................4
Table 3. Temperature programs of the IMPROVE and the NIOSH protocols. ...........................6
Table 4. Summary of data files for the PM2.5 study (EPD Tender Ref. AS 10‐231) in Hong Kong....................................................................................................................................................7
Table 5. Field blank concentrations of PM2.5 samples collected at MK, CW, WB, TC, TW, and YL sites during the study period in Hong Kong ..........................................................................9
Table 6. Analytical specifications of 24‐hour PM2.5 measurements at MK, CW, WB, TC, TW, and YL sites during the study period in Hong Kong .................................................................12
Table 7. Statistics analysis of sum of measured chemical species versus measured mass on Teflon filters for PM2.5 samples collected at individual sites...................................................18
Table 8. Statistics analysis of sulfate versus total sulfur measurements for PM2.5 samples collected at individual sites......................................................................................................21
Table 9. Statistics analysis of water‐soluble potassium versus total potassium measurements for PM2.5 samples collected at individual sites. .......................................................................24
Table 10. Statistics analysis of water‐soluble chloride versus total chlorine measurements for PM2.5 samples collected at individual sites..............................................................................27
Table 11. Statistics analysis of calculated ammonium versus measured ammonium for PM2.5 samples collected at individual sites. ......................................................................................30
Table 12. Statistics analysis of anion versus cation measurements for PM2.5 samples collected at individual sites......................................................................................................33
Table 13. Statistics analysis of OC and EC determined by NIOSH_TOT and IMPROVE_TOR methods for PM2.5 samples collected at individual sites.........................................................37
Table 14. Statistics analysis of OC and EC determined by IMPROVE_TOT versus IMPROVE_TOR and IMPROVE_TOT versus NIOSH_TOT for PM2.5 samples collected at all sites...................................................................................................................................................39
Table 15. Statistics analysis of reconstructed mass versus measured mass on Teflon filters for PM2.5 samples collected at individual sites. .......................................................................42
Table 16. Average relative biases and average relative standard deviations of concentrations of PM2.5 and selected chemical species for collocated samples. ............................................46
Table 17. Side‐by‐side comparison of the four one‐year studies of PM2.5 samples (in µg/m3) collected during 2000 ‐ 2001, 2004 ‐ 2005, 2008 ‐ 2009, and current 2011 (1/1/2011 ‐ 12/30/2011) period. Carbon concentrations are from the IMPROVE_TOR method. .............52
iv
List of Figures
Figure 1. PM2.5 monitoring sites in Hong Kong for characterization study ...............................3
Figure 2. Scatter plots of sum of measured chemical species versus measured mass on Teflon filter for PM2.5 samples collected at (a) MK, (b) CW, (c) WB, (d) TC, (e) TW, and (f) YL...................................................................................................................................................17
Figure 3. Scatter plots of sulfate versus total sulfur measurements for PM2.5 samples collected at (a) MK, (b) CW, (c) WB, (d) TC, (e) TW, and (f) YL. ...............................................20
Figure 4. Scatter plots of water‐soluble potassium versus total potassium measurements for PM2.5 samples collected at (a) MK, (b) CW, (c) WB, (d) TC, (e) TW, and (f) YL. .......................23
Figure 5. Scatter plots of water‐soluble chloride versus total chlorine measurements for PM2.5 samples collected at (a) MK, (b) CW, (c) WB, (d) TC, (e) TW, and (f) YL. .......................26
Figure 6. Scatter plots of calculated ammonium versus measured ammonium for PM2.5 samples collected at (a) MK, (b) CW, (c) WB, (d) TC, (e) TW, and (f) YL..................................29
Figure 7. Scatter plots of anion versus cation measurements for PM2.5 samples collected at (a) MK, (b) CW, (c) WB, (d) TC, (e) TW, and (f) YL....................................................................32
Figure 8. Comparisons of TC determined by NIOSH_TOT and IMPROVE_TOR methods for PM2.5 samples collected at all sites..........................................................................................34
Figure 9. Comparisons of OC and EC determined by NIOSH_TOT and IMPROVE_TOR methods for PM2.5 samples collected at (a) MK, (b) CW, (c) WB, (d) TC, (e) TW, and (f) YL. .................36
Figure 10. Comparisons of OC and EC determined by (a) IMPROVE_TOT versus IMPROVE_TOR and (b) IMPROVE_TOT versus NIOSH_TOT for PM2.5 samples collected at all sites. .........................................................................................................................................38
Figure 11. Scatter plots of reconstructed mass versus measured mass on Teflon filters for PM2.5 samples collected at (a) MK, (b) CW, (c) WB, (d) TC, (e) TW, and (f) YL. .......................41
Figure 12. Annual average composition (%) of major components including 1) geological material; 2) organic matter; 3) soot; 4) ammonium; 5) sulfate; 6) nitrate; 7) non‐crustal trace elements, and 8) Unidentified material (difference between measured mass and the reconstructed mass) to PM2.5 mass for (a) MK, (b) CW, (c) WB, (d) TC, (e) TW, and (f) YL. ....43
Figure 13. Comparison of annual average concentrations of major components including 1) geological material; 2) organic matter; 3) soot; 4) ammonium; 5) sulfate; 6) nitrate; 7) non‐crustal trace elements, and 8) Unidentified material (difference between measured mass and the reconstructed mass) to PM2.5 mass between individual sites. ..................................44
Figure 14. Comparisons of PM2.5 mass concentrations from gravimetric and continuous measurements at (a) MK, (b) CW, (c) WB, (d) TC, (e) TW, and (f) YL. .....................................48
Figure 15. Comparisons of annual average PM2.5 mass concentrations at MK, TW, and YL sites from 2001 to 2011. The error bars represent one standard variation of the PM2.5 mass concentration measurements over the year. ..........................................................................49
Figure 16. Wind Roses for PM2.5 mass concentrations (µg/m3) at TW site during 2000 ‐ 2001, 2004 ‐ 2005, 2008 ‐ 2009, and 2011. The black concentric circles correspond to winds of 3.5,
v
7, and 10.5 m/s. The blue contour lines correspond to the most frequent 80% of the measured wind speed and direction pairs. .............................................................................50
Figure 17. Wind Roses for PM2.5 mass concentrations (µg/m3) at YL site during 2004 ‐ 2005, 2008 ‐ 2009, and 2011. The black concentric circles correspond to winds of 5, 10, and 15 m/s. The blue contour lines correspond to the most frequent 80% of the measured wind speed and direction pairs. .................................................................................................................. 50
Figure 18. Annual trend of major components of PM2.5 samples collected at (a) MK, (b) TW, and (c) YL..................................................................................................................................53
Figure 19. Annual average concentration levels of (a) sulfur dioxide and (b) oxidants at TW and YL sites from 2000 to 2011. ..............................................................................................54
Figure 20. Annual average concentrations of O3 and CO at Tap Mun AQMS from 2000 to 2011. ........................................................................................................................................55
Figure 21. Monthly average of PM2.5 mass concentrations and chemical compositions for (a) MK, (b) CW, (c) WB, (d) TC, (e) TW, and (f) YL during 2011 PM study. ...................................57
1
1. Introduction
1.1 Study Objectives
The Environmental Central Facility (ENVF) at the Hong Kong University of Science and Technology (HKUST) assisted the Hong Kong Environmental Protection Department (HKEPD) in the analysis of PM2.5 samples acquired over the course of yearlong from January 2011 to December 2011. The objectives of this study were to:
Determine the organic and inorganic composition of PM2.5 and how it differs by season and proximity to different types of emission sources.
Based on the ambient concentrations of certain tracer compounds, determine the contributions of different sources to PM2.5 in Hong Kong.
Investigate and understand the influences of meteorological/atmospheric conditions on PM2.5 episodic events in Hong Kong.
Establish inter‐annual variability of PM2.5 concentration and chemical composition in Hong Kong urban and rural areas.
1.2 Background
The Hong Kong Environmental Protection Department (HKEPD) did not establish or adopt ambient air quality standards for fine suspended particles (FSP) which have aerodynamic diameters less than 2.5 µm (PM2.5) in the year of 2011. However, the Hong Kong government announced new air quality standards which are called Air Quality Objectives (AQOs) on January 17, 2012. In the proposed AQOs, the standards for PM2.5 were implemented with a 24‐hour average of 75 µg/m3 and a yearly average of 35 µg/m3.
This report documents the PM2.5 measurements and data validation for a twelve‐month study from January 2011 to December 2011 in order to get a better understanding on the nature and contribution of sources for air pollution trend analysis. The data will be analyzed to characterize the composition and temporal and spatial variations of PM2.5 concentrations. The main objectives of the study include: 1) establish the trend of PM2.5 concentration and chemical composition by comparing previous 12‐month PM2.5 studies during 2000 and 2001, 2004 and 2005, and 2008 and 2009; 2) explore the contribution of different emission sources to the PM2.5 loading in Hong Kong, and 3) investigate the hypotheses regarding the formation of PM2.5 episodes.
1.3 Technical Approach
During the sampling period from January 2011 to December 2011, 24‐hour PM2.5 mass measurements were acquired once every six days from the roadside‐source‐dominated Mong Kok (MK) Air Quality Monitoring Site (AQMS), the urban Central/Western (CW) and Tsuen Wan (TW) AQMSs, the new town Tung Chung (TC) and Yuen Long (YL) AQMSs, and the suburban Clear Water Bay (WB) Air Quality Research Site (AQRS) which is located on the campus of the Hong Kong University of Science and Technology. Three Partisol particle samplers (Rupprecht & Patachnick, Model 2025, Albany, NY) were used at MK, CW, WB, and TC sites while two Partisol samplers were placed at TW and YL sites to obtain PM2.5 samples on both Teflon‐membrane and QMA 47‐mm filters. All sampled Teflon‐membrane and QMA
2
filters were analyzed for mass by gravimetry by HKEPD’s contractor and then subjected to full chemical analysis, including 1) elemental measurements for atomic number ranging from 11 (Sodium) to 92 (Uranium) using ED‐XRF Spectroscopy; 2) carbon analysis using a Thermal/Optical Carbon Analyzer by both Thermal Optical Transmittance (TOT) and Thermal Optical Reflectance (TOR) methods; 3) Ionic measurements using Ion Chromatography.
3
2. Sampling Network
2.1 Ambient PM2.5 Monitoring Network
24‐hour PM2.5 filter samples were taken at six air quality monitoring sites in Hong Kong once every six days from January 2011 to December 2011. The six sampling sites are shown in Figure 1, representing roadside (MK), urban (CW and TW), new town (TC and YL), and suburban (WB) areas. The names, codes, locations, and descriptions of each site are listed in Table 1.
Figure 1. PM2.5 monitoring sites in Hong Kong for characterization study
Table 1. Descriptions of monitoring sites
Site Name Site Code Site Location Site Description
Mong Kok MK Junction of Lai Chi Kok Road and Nathan Road, Kowloon
Urban roadside in mixed residential/commercial area with heavy traffic and surrounded by many tall buildings
Central/Western CW Rooftop of Sai Ying Pun Community Center, No. 2 High Street, Sai Ying Pun, Hong Kong
Urban, densely populated, residential site with mixed commercial development
Clear Water Bay WB Rooftop of a pump house next to Coastal Marine Lab, HKUST Campus, Clear Water Bay
Clean rural area with little residential and commercial development on the east coast of Sai Kung
Tung Chung TC Rooftop of Tung Chung Health Center, No. 6 Fu Tung Street, Lantau Island
Residential town, within 5 km southeast of HK International Airport
4
Site Name Site Code Site Location Site Description
Tsuen Wan TW Rooftop of Princess Alexandra Community Center, 60 Tai Ho Road, New Territories
Urban, densely populated, residential site with mixed commercial and industrial developments. Located northwest of the MK site
Yuen Long YL Rooftop of Yuen Long District Branch Office Building, 269 Castle Peak Road, New Territories
Residential town, about 15 km southwest of Shenzhen
2.2 Ambient PM2.5 Measurements
A total of 16 Partisol samplers were employed to obtain PM2.5 samples around Hong Kong. The detailed arrangement of the samplers is described in Table 2.
Table 2. Arrangement of the Partisol samplers in monitoring sites.
Location No. of Samplers Collocated Samples
MK AQMS 3 QMA Filters
CW AQMS 3 QMA Filters
WB AQRS 3 Teflon Filters
TC AQMS 3 Teflon Filters
TW AQMS 2
YL AQMS 2
Each Partisol sampler was equipped with an Andersen PM2.5 inlet with Very Sharp Cut Cyclone (VSCC). The samplings were conducted at a flow rate of 16.7 L/min. At this flow rate, a nominal volume of approx. 24.0 m3 of ambient air would be sampled over a 24‐hour period. The Partisol samplers were configured to take either a Teflon‐membrane filter or a QMA filter. For this study, the following filters were chosen: 1) Whatman (Clifton, NJ, USA), PM2.5 membrane, PTFE, 46.2 mm with support ring (#7592204); and 2) Pall Life Sciences (Ann Arbor, MI, USA), 2500QAT‐UP, 47 mm, TissuquartzTM filters (#7202).
The Partisol samplers were operated and maintained by HKEPD’s contractor, PTC International Ltd. with support from the Hong Kong University of Science and Technology (HKUST) throughout the study period. The HKUST was responsible for pre‐ and post‐sampling procedures required for quality assurance and sample preservation. HKUST was also responsible for the mass measurement and analysis on both filter types before and after sampling.
The collected Teflon‐membrane filters were used for mass analysis by gravimetry and elemental analysis (for more than 40 elements with atomic number ranging from 11 to 92) by X‐Ray Fluorescence [Watson et al., 1999]. The collected QMA filters were analyzed for mass by gravimetry, for carbon content by multiple thermal evolution methods, and for chloride (Cl‐), nitrate (NO3
‐), sulfate (SO42‐), water‐soluble sodium (Na+), ammonium (NH4
+), and water‐soluble potassium (K+) by ion chromatography.
5
A major uncertainty in determining carbon concentrations lies in the differentiation of organic and elemental carbon during analysis. EC has been defined as the carbon that evolves after the detected optical signal attains the value it had prior to commencement of heating and the rest of the carbon is considered to be OC [Chow et al., 1993; Birch and Cary, 1996]. The split of OC and EC in the thermal analysis depends on several parameters including temperature setpoints, temperature ramping rates, residence time at each setpoint, combustion atmospheres, and optical signal used. Heating in an inert atmosphere causes certain OC to pyrolyze or char, inflating the EC in the sample. The extent of pyrolysis is affected by different thermal/temperature protocols. A laser is used to overcome this problem by monitoring changes in filter darkness during the thermal evolution process by detecting either filter transmittance (thermal/optical transmittance [TOT] method) or reflectance (thermal/optical reflectance [TOR] method). However, this introduces another problem of inner/near‐surface filter pyrolysis. It is found that pyrolysis occurs both within filter and on the filter surface. TOT method measures light transmittance which goes through the filter and is more likely influenced by the inner filter char while TOR method is more influenced by the charring of near‐surface deposit.
In this study, two analytical protocols ‐ National Institute of Occupational Safety and Health (NIOSH 5040) protocol coupled with TOT method, and the Interagency Monitoring of Protected Visual Environments (IMPROVE) protocol coupled with TOR method are employed to analyze the QMA filters. Table 3 shows the temperature programs of the NIOSH and IMPROVE protocols. Results obtained with the two protocols are compared and evaluated in Section 3.3.4.
6
Table 3. Temperature programs of the IMPROVE and the NIOSH protocols.
Methods’ carrier gas Carbon fractionNIOSH_TOT
temp, time
IMPROVE_TOR*
temp, time
He purge 25 °C, 10 s 25 °C, 10 s
He‐1 OC1 310 °C, 80 s 120 °C, 180 s
He‐2 OC2 475 °C, 60 s 250 °C, 180 s
He‐3 OC3 615 °C, 60 s 450 °C, 180 s
He‐4 OC4 870 °C, 90 s 550 °C, 180 s
He‐5 Cool oven ‐
O2 / He‐1 EC1 550 °C, 45 s 550 °C, 240 s
O2 / He‐2 EC2 625 °C, 45 s 700 °C, 210 s
O2 / He‐3 EC3 700 °C, 45 s 850 °C, 210 s
O2 / He‐4 EC4 775 °C, 45 s
O2 / He‐5 EC5 850 °C, 45 s
O2 / He‐6 EC6 870 °C, 45 s
* The IMPROVE temperature program was used for measurements reported in this work. Another related temperature protocol, termed IMPROVE_A, is typically adopted on DRI Model 2001 carbon analyzers. The IMPROVE_A temperature protocol defines temperature plateaus of 140 °C for OC1, 280 °C for OC2, 480 °C for OC3, and 580 °C for OC4 in a helium (He) carrier gas and 580 °C for EC1, 740 °C for EC2, and 840 °C for EC3 in a 98% He/2% oxygen (O2) carrier gas [Chow et al., 2007]. These temperatures used with the new hardware in DRI Model 2001 better match the sample temperatures experienced in the analysis using the IMPROVE protocol on the previous models of DRI analyzers.
7
3. Database and Data Validation
3.1 Data File Preparation
An electronic database on analytical results is established for Hong Kong PM2.5 data archive. Detailed data processing and data validation are documented in Section 3.3. The data are available on Compact Disc in the format of Microsoft Excel spreadsheets for convenient distribution to data users. The contents of the final data files are listed in Table 4.
Table 4. Summary of data files for the PM2.5 study (EPD Tender Ref. AS 10‐231) in Hong Kong
Category Database File File Description
I. DATABASE DOCUMENTATION
AS 10‐231_ID.xls Defines the field sample names, measurement units, and formats used in the database file
II. MASS AND CHEMICAL DATA
AS 10‐231_PM2.5.xls Contains PM2.5 mass data and chemical data for samples collected by Partisol samplers at six sites once every six days during January 2011 to December 2011
III. DATABASE VALIDATION
AS 10‐231_FLAG.xls contains both field sampling and chemical analysis data validation flags
3.2 Measurement and Analytical Specifications
The measurement/analysis methods are described in Section 2 and every measurement consists of 1) a value; 2) a precision (uncertainty), and 3) a validity. The values are obtained by different analysis methods. The precisions are estimated through standard testing, blank analysis, and replicate analysis. The validity of each measurement is indicated by appropriate flagging in the data base, while the validity of chemical analysis results are evaluated by data validations described in Section 3.3.
A total of 68 sets of ambient PM2.5 samples were received during this study and submitted for comprehensive chemical analyses. For each set of samples, it contains 16 pieces of filters collected at all six sites on one date. These 68 sets of samples include 7 sets of field blanks. 4 out of 6 sites conducted collocated sampling and the collocated samples were used for data validation purpose. All of the 1088 PM2.5 samples acquired are considered valid after data validation and final review.
3.2.1 Precision Calculations and Error Propagation
Measurement precisions are propagated from precisions of volumetric measurements, chemical composition measurements, and field blank variability using the methods of Bevington [1969] and Watson et al. [1995; 2001]. The following equations are used to calculate the prevision associated with filter‐based measurements:
VBM
C iii
−= (1)
8
TQV ×= (2)
iBi
n
oioi BforB
nB σ>= ∑
=1
1 (3)
iBii BforB σ<= 0 (4)
( )iiii BB
n
oiioBB SIGSTDforBB
ni
STDσ >⎥⎥⎦
⎤
⎢⎢⎣
⎡−
−== ∑
=
21
1
2
1 (5)
( )Iiioii BB
n
oBBB SIGSTDfor
ni
SIG ≤⎥⎥⎦
⎤
⎢⎢⎣
⎡== ∑
=
21
1
2σσ (6)
( ) 21
4
22
2
22
⎥⎥
⎦
⎤
⎢⎢
⎣
⎡ −+
+=
V
BM
ViiVBM
Cii
i
σσσσ (7)
21
1
21⎟⎟⎠
⎞⎜⎜⎝
⎛= ∑
=
n
oCRMSi
inσσ (8)
05.0=VVσ (9)
where:
Bi = average amount of species i on field blanks
Bio = the amount of species i found on field blank o
Ci = the ambient concentration of species i
Q = flow rate throughout sampling period
Mi = amount of species i on the substrate
N = total number of samples in the sum
SIGBi = the root mean square error (RMSE), the square root of the averaged sum of the squared σBio
STDBio = standard deviation of the blank
σBi = blank precision for species i
σBio = precision of the species i found on field blank j
σCi = propagated precision for the concentration of species i
σMi = precision of amount of species i on the substrate
σRMSi = root mean square precision for species i
σV = precision of sample volume
9
T = sample duration
V = volume of air sampled
The uncertainty of the measured value and the average uncertainty of the field blanks for each species are used to propagate the overall precision for each blank subtracted concentration value. The final value is propagated by taking the square root of the sum of the squares of the calculated uncertainty and the average field blank uncertainty for each measurement.
3.2.2 Analytical Specifications
The concentrations of field blanks collected during the study are summarized in Table 5 in the unit of µg/filter.
Blank precisions (σBi) are defined as the higher value of the standard deviation of the blank measurements, STDBi, or the square root of the averaged squared uncertainties of the blank concentrations, SIGBi. If the average blank for a species was less than its precision, the blank was set to zero (Eqn 4).
The precisions (σMi) were determined from duplicate analysis of samples. When duplicate sample analysis is made, the range of results, R, is nearly as efficient as the standard deviation since two measures differ by a constant (1.128s = R where s represents the precision).
Table 5. Field blank concentrations of PM2.5 samples collected at MK, CW, WB, TC, TW, and YL sites during the study period in Hong Kong
Concentrations in µg/47‐mm filter
Species
Total No. of Blanks
Field Blank Std. Dev.
(STDBi)
Root Mean Squared Blank
Precision
(SIGBi)
Blank Precision
(σBi)
Average Field Blank
Blank Subtracted
(Bi)
Na+ 48* 0.753 0.464 0.753 ‐0.708 0.000
NH4+ 48 2.200 2.418 2.418 0.344 0.000
K+ 48 0.841 0.474 0.841 0.465 0.000
Cl‐ 48 0.801 0.447 0.801 0.184 0.000
NO3‐ 48 1.270 0.774 1.270 0.431 0.000
SO42‐ 48 4.291 5.484 5.484 0.394 0.000
OC1_TOR 56 0.338 9.435 9.435 0.378 0.000
OC2_TOR 56 3.778 3.673 3.778 6.090 6.090
OC3_TOR 56 3.124 5.530 5.530 5.282 0.000
OC4_TOR 56 1.374 0.201 1.374 1.441 1.441
OC_TOR 56 9.128 0.620 9.128 14.665 14.665
10
Concentrations in µg/47‐mm filter
Species
Total No. of Blanks
Field Blank Std. Dev.
(STDBi)
Root Mean Squared Blank
Precision
(SIGBi)
Blank Precision
(σBi)
Average Field Blank
Blank Subtracted
(Bi)
OC_TOT 56 6.671 1.652 6.671 21.592 21.592
PC_TOR 56 1.640 0.885 1.640 1.913 1.913
PC_TOT 56 0.533 2.393 2.393 0.225 0.000
EC1_TOR 56 1.361 0.393 1.361 0.260 0.000
EC2_TOR 56 0.967 0.384 0.967 0.279 0.000
EC3_TOR 56 0.152 0.107 0.152 0.033 0.000
EC_TOR 56 2.360 0.000 2.360 0.572 0.000
EC_TOT 56 0.001 0.003 0.003 0.001 0.000
TC 56 8.875 0.619 8.875 15.233 15.233
Na 56 0.0871 1.0764 1.0764 0.0771 0.0000
Mg 56 0.2006 0.4561 0.4561 ‐0.4361 0.0000
Al 56 0.1047 1.2078 1.2078 ‐0.1170 0.0000
Si 56 0.5015 0.7024 0.7024 0.1447 0.0000
P 56 0.0168 0.5104 0.5104 0.0072 0.0000
S 56 0.0011 0.5450 0.5450 0.0001 0.0000
Cl 56 0.0801 0.4984 0.4984 0.0211 0.0000
K 56 0.0241 0.0320 0.0320 ‐0.0134 0.0000
Ca 56 0.0955 0.4623 0.4623 0.0229 0.0000
Sc 56 0.0827 0.3834 0.3834 ‐0.2507 0.0000
Ti 56 0.0093 1.1523 1.1523 0.0076 0.0000
V 56 0.0055 0.2183 0.2183 0.0041 0.0000
Cr 56 0.0101 0.7055 0.7055 0.0001 0.0000
Mn 56 0.0389 0.1999 0.1999 0.0320 0.0000
Fe 56 0.0567 0.1109 0.1109 0.0512 0.0000
Co 56 0.0081 0.8177 0.8177 0.0098 0.0000
Ni 56 0.0085 0.2306 0.2306 0.0038 0.0000
Cu 56 0.0202 0.0542 0.0542 0.0212 0.0000
Zn 56 0.0179 0.2433 0.2433 0.0099 0.0000
Ga 56 0.0265 0.1204 0.1204 0.0104 0.0000
Ge 56 0.0276 0.3938 0.3938 0.0157 0.0000
11
Concentrations in µg/47‐mm filter
Species
Total No. of Blanks
Field Blank Std. Dev.
(STDBi)
Root Mean Squared Blank
Precision
(SIGBi)
Blank Precision
(σBi)
Average Field Blank
Blank Subtracted
(Bi)
As 56 0.0000 0.3024 0.3024 0.0000 0.0000
Se 56 0.0000 1.6983 1.6983 0.0000 0.0000
Br 56 0.0169 0.1271 0.1271 ‐0.0267 0.0000
Rb 56 0.0138 0.1296 0.1296 ‐0.0028 0.0000
Sr 56 0.0213 0.4332 0.4332 ‐0.0017 0.0000
Y 56 0.0090 0.3787 0.3787 0.0029 0.0000
Zr 56 0.0393 0.2293 0.2293 ‐0.0464 0.0000
Nb 56 0.0309 0.0414 0.0414 0.0158 0.0000
Mo 56 0.0330 0.4173 0.4173 ‐0.0010 0.0000
Rh 56 0.0589 0.4193 0.4193 0.0585 0.0000
Pd 56 0.0600 0.5305 0.5305 0.0522 0.0000
Ag 56 0.0435 0.6309 0.6309 ‐0.0407 0.0000
Cd 56 0.0556 0.1714 0.1714 ‐0.0468 0.0000
In 56 0.0623 0.4557 0.4557 ‐0.0255 0.0000
Sn 56 0.0770 0.7236 0.7236 0.0575 0.0000
Sb 56 0.0723 1.0310 1.0310 0.1009 0.0000
Te 56 0.1012 0.7929 0.7929 0.1140 0.0000
I 56 0.1153 0.2351 0.2351 ‐0.0050 0.0000
Cs 56 0.2555 1.1224 1.1224 ‐0.7089 0.0000
Ba 56 0.3296 1.5343 1.5343 ‐0.3629 0.0000
La 56 0.3637 1.2352 1.2352 ‐0.0013 0.0000
Ce 56 0.0188 1.2804 1.2804 ‐0.0287 0.0000
Sm 56 0.0358 11.4276 11.4276 ‐0.0176 0.0000
Eu 56 0.0683 21.5164 21.5164 ‐0.0727 0.0000
Tb 56 0.0273 4.3382 4.3382 ‐0.0490 0.0000
Hf 56 0.1565 0.3314 0.3314 ‐0.1740 0.0000
Ta 56 0.0518 0.3314 0.3314 0.0176 0.0000
W 56 0.2789 0.3314 0.3314 0.0887 0.0000
Ir 56 0.0318 23.8755 23.8755 ‐0.0273 0.0000
Au 56 0.0463 47.4197 47.4197 ‐0.0770 0.0000
Hg 56 0.0072 24.6360 24.6360 0.0010 0.0000
12
Concentrations in µg/47‐mm filter
Species
Total No. of Blanks
Field Blank Std. Dev.
(STDBi)
Root Mean Squared Blank
Precision
(SIGBi)
Blank Precision
(σBi)
Average Field Blank
Blank Subtracted
(Bi)
Tl 56 0.0268 1.8523 1.8523 ‐0.0280 0.0000
Pb 56 0.0323 3.4361 3.4361 0.0212 0.0000
U 56 0.0614 0.1912 0.1912 0.0759 0.0000
* The field blank samples collected on January 27, 2011 were not included in calculating dynamic blanks for ionic species since the QMA filters used in January (except for 110131 samples) were from Whatman (Clifton, NJ) and consistently had higher Na+ background.
The analytical specifications for the 24‐hour PM2.5 measurements obtained during the study are summarized in Table 6. Limits of detection (LOD) and limits of quantitation (LOQ) are given. The LOD of an analyte may be described as that concentration which gives an instrument signal significantly different from the “blank” or “background” signal. In this study LOD is defined as the concentration at which instrument response equals three times the standard deviation of the lab blank concentrations. As a further limit, the LOQ is regarded as the lower limit for precise quantitative measurements and is defined as a concentration corresponding to ten times the standard deviation of the lab blank concentrations. The LOQs should always be equal to or larger than the analytical LODs and it was the case for all the chemical compounds listed in Table 6. Both the LODs and LOQs were divided by 24.1 m3, the nominal 24‐hour volume, for the Partisol samplers. The variation of sampling volumes is assumed to be within ±5% of the pre‐set volume.
Table 6. Analytical specifications of 24‐hour PM2.5 measurements at MK, CW, WB, TC, TW, and YL sites during the study period in Hong Kong
Species Analytical Method
LOD (µg/m3)
LOQ (µg/m3)
No. of Values
No. > LOD
% > LOD
No. > LOQ
% > LOQ
Na+ IC 0.0007 0.0024 366 364 99% 364 99%
NH4+ IC 0.0029 0.0098 366 366 100% 366 100%
K+ IC 0.0007 0.0004 366 366 100% 366 100%
Cl‐ IC 0.0007 0.0025 366 320 87% 320 87%
NO3‐ IC 0.0034 0.0016 366 355 97% 355 97%
SO42‐ IC 0.0071 0.0238 366 366 100% 366 100%
OC1_TOR TOR 0.0639 0.2131 366 43 12% 0 0%
OC2_TOR TOR 0.0811 0.2702 366 363 99% 351 96%
OC3_TOR TOR 0.0703 0.2342 366 366 100% 366 100%
OC4_TOR TOR 0.1018 0.3393 366 360 98% 273 75%
13
Species Analytical Method
LOD (µg/m3)
LOQ (µg/m3)
No. of Values
No. > LOD
% > LOD
No. > LOQ
% > LOQ
OC_TOR TOR 0.4082 1.3607 366 366 100% 339 93%
OC_TOT TOT 0.5416 1.8053 366 364 99% 336 92%
PC_TOR TOR 0.1659 0.5528 366 333 91% 277 76%
PC_TOT TOT 0.2725 0.9085 366 321 88% 276 75%
EC1_TOR TOR 0.0541 0.1804 366 366 100% 361 99%
EC2_TOR TOR 0.0418 0.1394 366 366 100% 364 99%
EC3_TOR TOR 0.0333 0.1111 366 362 99% 222 61%
EC_TOR TOR 0.0417 0.1389 366 366 100% 366 100%
EC_TOT TOT 0.0200 0.0666 366 366 100% 366 100%
TC TOR 0.4191 1.3971 366 366 100% 360 98%
Na XRF 0.0149 0.0498 366 362 99% 349 95%
Mg XRF 0.0233 0.0776 366 359 98% 300 82%
Al XRF 0.0124 0.0413 366 365 100% 326 89%
Si XRF 0.0210 0.0700 366 365 100% 333 91%
P XRF 0.0013 0.0043 366 357 98% 335 92%
S XRF 0.0011 0.0035 366 366 100% 366 100%
Cl XRF 0.0018 0.0058 366 361 99% 346 95%
K XRF 0.0017 0.0057 366 366 100% 366 100%
Ca XRF 0.0021 0.0069 366 366 100% 366 100%
Sc XRF 0.0081 0.0270 366 0 0% 0% 0%
Ti XRF 0.0006 0.0021 366 364 99% 344 94%
V XRF 0.0005 0.0016 366 361 99% 349 95%
Cr XRF 0.0008 0.0027 366 268 73% 127 35%
Mn XRF 0.0039 0.0131 366 328 90% 249 68%
Fe XRF 0.0041 0.0137 366 366 100% 365 100%
Co XRF 0.0009 0.0031 366 58 16% 0 0%
Ni XRF 0.0008 0.0028 366 360 98% 246 67%
Cu XRF 0.0016 0.0053 366 366 100% 307 84%
Zn XRF 0.0164 0.0547 366 334 91% 290 79%
Ga XRF 0.0028 0.0093 366 2 1% 0 0%
Ge XRF 0.0015 0.0049 366 72 20% 4 1%
As XRF 0.0000 0.0000 366 240 66% 240 66%
Se XRF 0.0000 0.0000 366 2 1% 2 1%
14
Species Analytical Method
LOD (µg/m3)
LOQ (µg/m3)
No. of Values
No. > LOD
% > LOD
No. > LOQ
% > LOQ
Br XRF 0.0019 0.0063 366 288 79% 240 66%
Rb XRF 0.0017 0.0056 366 115 31% 12 3%
Sr XRF 0.0018 0.0059 366 247 67% 28 8%
Y XRF 0.0017 0.0058 366 6 2% 0 0%
Zr XRF 0.0033 0.0109 366 9 2% 0 0%
Nb XRF 0.0039 0.0130 366 9 2% 0 0%
Mo XRF 0.0027 0.0091 366 42 11% 0 0%
Rh XRF 0.0060 0.0201 366 21 6% 0 0%
Pd XRF 0.0053 0.0175 366 29 8% 0 0%
Ag XRF 0.0042 0.0141 366 1 0% 0 0%
Cd XRF 0.0044 0.0148 366 7 2% 0 0%
In XRF 0.0067 0.0222 366 2 1% 0 0%
Sn XRF 0.0095 0.0318 366 200 55% 22 6%
Sb XRF 0.0090 0.0300 366 132 36% 0 0%
Te XRF 0.0118 0.0394 366 13 4% 0 0%
I XRF 0.0110 0.0366 366 19 5% 0 0%
Cs XRF 0.0367 0.1224 366 0 0% 0 0%
Ba XRF 0.0384 0.1280 366 27 7% 0 0%
La XRF 0.0407 0.1356 366 24 7% 0 0%
Ce XRF 0.0022 0.0072 366 1 0% 0 0%
Sm XRF 0.0038 0.0128 366 9 2% 0 0%
Eu XRF 0.0066 0.0221 366 22 6% 0 0%
Tb XRF 0.0029 0.0096 366 81 22% 8 2%
Hf XRF 0.0161 0.0538 366 0 0% 0 0%
Ta XRF 0.0067 0.0222 366 182 50% 0 0%
W XRF 0.0178 0.0593 366 1 0% 0 0%
Ir XRF 0.0050 0.0165 366 0 0% 0 0%
Au XRF 0.0044 0.0148 366 0 0% 0 0%
Hg XRF 0.0000 0.0000 366 1 0% 1 0%
Tl XRF 0.0034 0.0113 366 0 0% 0 0%
Pb XRF 0.0027 0.0091 366 324 89% 286 78%
U XRF 0.0064 0.0213 366 40 11% 0 0%
15
The number of reported concentrations for each species and number of reported concentrations greater than the LODs and LOQs are also summarized in Table 6. For the 366 valid samples, major ions (including nitrate, sulfate, ammonium, soluble sodium, and soluble potassium), organic carbon, elemental carbon, sodium (Na), magnesium (Mg), aluminum (Al), silicon (Si), phosphorus (P), sulfur (S), chlorine (Cl), potassium (K), calcium (Ca), titanium (Ti), vanadium (V), manganese (Mn), iron (Fe), nickel (Ni), and copper (Cu) were detected (> LOD) in almost all samples (more than 95%). Chloride was detected in 87% of the samples. Several transition metals (e.g. Y, Zr, Nb, Mo, Rh, Pd, Ag, Cd, Hf, W, Ir, Au, Hg, La, Ce, Sm, Eu, and U) were not detected in most of the samples (less than 15%). Species from motor vehicle exhaust such as Br and Pb were detected in 79% and 89% of the samples respectively. V and Ni, which are residual‐oil‐related species, were detected in 99% and 98% of the samples, respectively. This is typical for urban and suburban sites in most regions. Toxic species emitted from industrial sources, such as Cd and Hg, were not detected (2% and 0% of the samples, respectively). Soil‐dust‐related species, including Al, Si, Ca, Ti, and Fe, were found above the LODs in more than 99% of the samples and above the LOQs in more than 89% of the samples.
In general, the analytical specifications shown in Table 6 suggest that the PM2.5 samples collected during the study period possess adequate sampling loading for chemical analysis of those species that are expected from major sources in the region. The detection limits of the selected analytical methods were sufficiently low to establish valid measurements with acceptable precision.
3.3 Data Validation
Three levels of data validation were conducted to the data acquired from the study.
Level I data validation: 1) flag measurements for deviations from procedures; 2) identify and remove invalid values and indicate the reasons for invalid sampling, and 3) estimate precisions from replicate and blank analyses.
Level II data validation examines internal consistency tests among different data and attempts to resolve discrepancies based on known physical relationships between variables: 1) compare a sum of chemical species to mass concentrations; 2) compare measurements from different methods; 3) compare collocated measurements; 4) examine time series from different sites to identify and investigate outliers, and 5) prepare a data qualification statement.
Level III data validation is part of the data interpretation process and should identify unusual values including: 1) extreme values; 2) values which would otherwise normally track the values of other variables in a time series, and 3) values for observables which would normally follow a qualitatively predictable spatial or temporal pattern. External consistency tests are used to identify values in the data set which appear atypical when compared to other data sets. The first assumption upon finding a measurement which is inconsistent with physical expectations is that the unusual value is due to a measurement error. If nothing unusual is found upon tracing the path of the measurement, the value would be assumed to be a valid result of an environmental cause.
Level I data validation was performed and the validation flags and comments are stated in the database as documented in Section 3.1. Level II validation tests and results are
16
described in the following subsections including 1) sum of chemical species versus PM2.5 mass; 2) physical and chemical consistency; 3) anion/cation balance; 4) reconstructed versus measured mass, 5) carbon measurements by different thermal/optical methods, and 6) collocated measurement comparison. For Level III data validation, parallel consistency tests were applied to data sets from the same population (e.g., region, period of time) by different data analysis approaches. Collocated samples collected at four out of the six sampling sites were examined. Comparison of PM2.5 mass concentrations obtained from gravimetric analysis and from 24‐hr average TEOM measurements were also conducted. The level III data validation continues for as long as the database is maintained. For Level II/III data validation in this study, correlations and linear regression statistics were performed on the valid data set and scatter plots were generated for better comparison.
3.3.1 Sum of Chemical Species versus PM2.5 Mass
The sum of the individual chemical concentrations determined in this study for PM2.5 samples should be less than or equal to the corresponding mass concentrations obtained from gravimetric measurements. The chemical species include those that were quantified on both Teflon‐membrane filters and quartz fiber filters. To avoid double counting, chloride (Cl‐), total potassium (K), soluble sodium (Na+), and sulfate (SO4
2‐) are included in the sum while total sulfur (S), total chlorine (Cl), total sodium (Na), and soluble potassium (K+) are excluded. Carbon concentration is represented by the sum of organic carbon and elemental carbon. Unmeasured ions, metal oxides, or hydrogen and oxygen associated with organic carbon are not counted into the measured concentrations.
The sum of chemical species was plotted against the measured PM2.5 mass on Teflon filters for each of the individual sites in Figure 2. Linear regression analysis results and the average ratios of Y over X are both shown in Table 7 for comparison.
None of the 366 sums of species are more than the corresponding PM2.5 mass beyond the reported measurement uncertainties. A strong correlation (R2 = 0.98) was found between the sum of measured species and mass with a slope of 0.81 ± 0.01. The average Y/X ratios indicate that around 80% of the PM2.5 mass can be explained by the measured chemical species.
MK111120 was found to be an outlier in Figure 2a. The PM2.5 mass concentration determined is 67.92 µg/m3 on Teflon filter, 54.79 µg/m3 on QMA filter, 41.86 µg/m3 for reconstructed mass, and 38.05 µg/m3 for sum‐of‐species. However for this sample, good agreements were reached for SO4
2‐ vs. Total S, K+ vs. total K, NH4+ balance, and NIOSH_TOT
TC vs. IMPROVE_TOR TC, suggesting that the chemical analysis results were valid and reliable. Therefore, the large discrepancies found between sum‐of‐species and measured mass might be due to the sampling uncertainties or contamination during sample delivery and/or storage.
17
y = 0.802x + 2.647
R2 = 0.963
0
20
40
60
80
100
0 20 40 60 80 100Measured Mass (ug/m3)
Sum of C
hemical Spe
cies (u
g/m
3 )
(a) Mong Kok (MK)
y = 0.807x + 0.668
R2 = 0.988
0
20
40
60
80
100
0 20 40 60 80 100Measured Mass (ug/m3)
Sum of C
hemical Spe
cies (u
g/m
3 )
(b) Central/Western (CW)
y = 0.799x + 0.105
R2 = 0.987
0
20
40
60
80
100
0 20 40 60 80 100Measured Mass (ug/m3)
Sum of C
hemical Spe
cies (u
g/m
3 )
(c) Clear Water Bay (WB)
y = 0.809x + 0.113
R2 = 0.991
0
20
40
60
80
100
0 20 40 60 80 100Measured Mass (ug/m3)
Sum of C
hemical Spe
cies (u
g/m
3 )
(d) Tung Chung (TC)
y = 0.804x + 0.966
R2 = 0.993
0
20
40
60
80
100
0 20 40 60 80 100Measured Mass (ug/m3)
Sum of C
hemical Spe
cies (u
g/m
3 )
(e) Tsuen Wan (TW)
y = 0.801x + 0.658
R2 = 0.990
0
20
40
60
80
100
0 20 40 60 80 100Measured Mass (ug/m3)
Sum of C
hemical Spe
cies (u
g/m
3 )
(f) Yuen Long (YL)
Figure 2. Scatter plots of sum of measured chemical species versus measured mass on Teflon filter for PM2.5 samples collected at (a) MK, (b) CW, (c) WB, (d) TC, (e) TW, and (f) YL.
18
Table 7. Statistics analysis of sum of measured chemical species versus measured mass on Teflon filters for PM2.5 samples collected at individual sites.
Statistics/Site MK CW WB TC TW YL ALL
n 61 61 61 61 61 61 366
Slope 0.802
(± 0.020)
0.807
(± 0.011)
799
(± 0.012)
0.809
(± 0.010)
0.804
(± 0.009)
0.801
(± 0.010)
0.811
(± 0.005)
Intercept 2.647
(± 0.954)
0.668
(± 0.456)
0.105
(± 0.416)
0.113
(± 0.403)
0.966
(± 0.353)
0.658
(± 0.455)
0.592
(± 0.224)
R2 0.963 0.988 0.987 0.992 0.993 0.990 0.984
AVG mass 43.077 35.364 31.320 35.572 35.298 38.220 36.475
AVG sum 37.178 29.218 25.124 28.901 29.329 31.272 30.170
AVG sum/mass
0.879
(± 0.065)
0.837
(± 0.060)
0.802
(± 0.047)
0.817
(± 0.051)
0.842
(± 0.046)
0.831
(± 0.055)
0.835
(± 0.059)
19
3.3.2 Physical and Chemical Consistency
Measurements of chemical species concentrations conducted by different methods are compared. Physical and chemical consistency tests include: 1) sulfate (SO4
2‐) versus total sulfur (S); 2) soluble potassium (K+) versus total potassium (K), and 3) chloride (Cl‐) versus total chlorine (Cl).
3.3.2.1 Water‐Soluble Sulfate (SO42‐) versus Total Sulfur (S)
SO42‐ is measured by ion chromatography (IC) on QMA filters and total S is measured by x‐
ray fluorescence (XRF) on Teflon filters. The ratio of SO42‐ to S is expected to equal three if all
of the sulfur is present as SO42‐. Figure 3 shows the scatter plots of SO4
2‐ versus total S concentrations for each of the six sites. A good correlation (R2 = 0.96) were observed for all the sites with a slope of 3.02 ± 0.03 and an intercept of ‐0.38 ± 0.13. The average sulfate to total sulfur ratio was determined to be 2.88 ± 0.26, which meets the validation criteria (SO4
2‐
/total S < 3.0).
Good correlations (R2 = 0.92 ‐ 0.98) were found for sulfate/total sulfur in PM2.5 samples collected in individual sites. The regression statistics suggest a slope ranging from 2.95 ± 0.07 to 3.09 ± 0.08 and the intercepts are all kept at relatively low levels. The average sulfate/sulfur ratio, on the other hand, ranges from 2.84 ± 0.24 to 2.91 ± 0.41. Both of the calculations indicate that most of the sulfur was present as soluble sulfate in the atmosphere.
The outlier found in Figure 3a is ascribed to MK110125. The consistency of total S concentrations obtained from the two collocated samples (MK110125SF02T and MK110125PF03T) indicates that the XRF analysis results are reliable. On the other hand, NH4
+ balance and charge balance from the IC analysis results were examined and it suggests the validity of the ionic concentration. Considering the higher mass concentration found on QMA filter than that on Teflon filter and the higher concentrations of K+ and Cl‐ than those of K and Cl, it is suspected that more PM loading was sampled on QMA filter than on Teflon filters for MK110125.
20
y = 3.075x ‐ 0.364
R2 = 0.921
0
5
10
15
20
25
30
0 2 4 6 8 10Sulfur (ug/m3)
Sulfa
te (u
g/m
3 )
(a) Mong Kok (MK)
y = 3.071x ‐ 0.538
R2 = 0.975
0
5
10
15
20
25
30
0 2 4 6 8 10Sulfur (ug/m3)
Sulfate (ug/m
3 )
(b) Central/Western (CW)
y = 2.977x ‐ 0.302
R2 = 0.983
0
5
10
15
20
25
30
0 2 4 6 8 10Sulfur (ug/m3)
Sulfate (ug/m
3 )
(c) Clear Water Bay (WB)
y = 3.089x ‐ 0.496
R2 = 0.962
0
5
10
15
20
25
30
0 2 4 6 8 10Sulfur (ug/m3)
Sulfate (ug/m
3 )
(d) Tung Chung (TC)
y = 2.990x ‐ 0.339
R2 = 0.982
0
5
10
15
20
25
30
0 2 4 6 8 10Sulfur (ug/m3)
Sulfate (ug/m
3 )
(e) Tsuen Wan (TW)
y = 2.952x ‐ 0.310
R2 = 0.967
0
5
10
15
20
25
30
0 2 4 6 8 10Sulfur (ug/m3)
Sulfate (ug/m
3 )
(f) Yuen Long (YL)
Figure 3. Scatter plots of sulfate versus total sulfur measurements for PM2.5 samples collected at (a) MK, (b) CW, (c) WB, (d) TC, (e) TW, and (f) YL.
21
Table 8. Statistics analysis of sulfate versus total sulfur measurements for PM2.5 samples collected at individual sites.
Statistics/Site MK CW WB TC TW YL ALL
n 61 61 61 61 61 61 366
Slope 3.075
(± 0.117)
3.071
(± 0.064)
2.977
(± 0.051)
3.089
(± 0.080)
2.990
(± 0.052)
2.952
(± 0.071)
3.023
(± 0.030)
Intercept ‐0.364
(± 0.478)
‐0.538
(± 0.267)
‐0.302
(± 0.219)
‐0.496
(± 0.336)
‐0.339
(± 0.221)
‐0.310
(± 0.297)
‐0.383
(± 0.128)
R2 0.921 0.975 0.983 0.962 0.982 0.967 0.964
AVG total S 3.668 3.726 3.840 3.752 3.764 3.781 3.755
AVG SO42‐ 10.912 10.907 11.128 11.094 10.914 10.851 10.968
AVG SO42‐/S
2.911
(± 0.407)
2.894
(± 0.215)
2.865
(± 0.199)
2.911
(± 0.254)
2.881
(± 0.173)
2.843
(± 0.244)
2.884
(± 0.259)
22
3.3.2.2 Water‐soluble Potassium (K+) versus Total Potassium (K)
Water‐soluble potassium (K+) is measured by ion chromatography (IC) on QMA filters and the total potassium (K) is measured by x‐ray fluorescence (XRF) on Teflon filters. The ratio of K+ to K is expected to equal or be less than 1. Figure 4 shows the scatter plots of K+ versus total K concentrations for each of the six sites. A good correlation (R2 = 0.94) were observed for all the sites with a slope of 0.95 ± 0.01 and an intercept of 0.03 ± 0.01. The ratio of water‐soluble potassium to total potassium averages at 1.14 ± 0.44.
Good correlations (R2 = 0.90 ‐ 0.95) were found for K+/K in PM2.5 samples collected in individual sites. The regression statistics suggest a slope ranging from 0.90 ± 0.03 to 0.98 ± 0.03 and the intercepts are all kept at relatively low levels. Generally, over 90% of the total potassium is in its soluble ionic form and a few scattered data points might be caused by instrumental and method uncertainties.
23
y = 0.971x + 0.019
R2 = 0.904
0.0
0.5
1.0
1.5
2.0
2.5
0.0 0.5 1.0 1.5 2.0 2.5Total Potassium (ug/m3)
Soluble Po
tassium (u
g/m
3 )
(a) Mong Kok (MK)
y = 0.925x + 0.031
R2 = 0.937
0.0
0.5
1.0
1.5
2.0
2.5
0.0 0.5 1.0 1.5 2.0 2.5Total Potassium (ug/m3)
Soluble Po
tassium (u
g/m
3 )
(b) Central/Western (CW)
y = 0.903x + 0.055
R2 = 0.946
0.0
0.5
1.0
1.5
2.0
2.5
0.0 0.5 1.0 1.5 2.0 2.5Total Potassium (ug/m3)
Soluble Po
tassium (u
g/m
3 )
(c) Clear Water Bay (WB)
y = 0.980x + 0.026
R2 = 0.954
0.0
0.5
1.0
1.5
2.0
2.5
0.0 0.5 1.0 1.5 2.0 2.5Total Potassium (ug/m3)
Soluble Po
tassium (u
g/m
3 )
(d) Tung Chung (TC)
y = 0.930x + 0.046
R2 = 0.938
0.0
0.5
1.0
1.5
2.0
2.5
0.0 0.5 1.0 1.5 2.0 2.5Total Potassium (ug/m3)
Soluble Po
tassium (u
g/m
3 )
(e) Tsuen Wan (TW)
y = 0.973x + 0.033
R2 = 0.946
0.0
0.5
1.0
1.5
2.0
2.5
0.0 0.5 1.0 1.5 2.0 2.5Total Potassium (ug/m3)
Soluble Po
tassium (u
g/m
3 )
(f) Yuen Long (YL)
Figure 4. Scatter plots of water‐soluble potassium versus total potassium measurements for PM2.5 samples collected at (a) MK, (b) CW, (c) WB, (d) TC, (e) TW, and (f) YL.
24
Table 9. Statistics analysis of water‐soluble potassium versus total potassium measurements for PM2.5 samples collected at individual sites.
Statistics/Site MK CW WB TC TW YL ALL
n 61 61 61 61 61 61 366
Slope 0.971
(± 0.041)
0.925
(± 0.031)
0.903
(± 0.028)
0.980
(± 0.028)
0.930
(± 0.031)
0.973
(± 0.030)
0.952
(± 0.013)
Intercept 0.019
(± 0.023)
0.031
(± 0.018)
0.055
(± 0.017)
0.026
(± 0.019)
0.046
(± 0.019)
0.033
(± 0.022)
0.033
(± 0.008)
R2 0.904 0.937 0.946 0.954 0.938 0.946 0.939
AVG total K 0.462 0.468 0.474 0.519 0.480 0.572 0.496
AVG K+ 0.467 0.463 0.483 0.534 0.492 0.590 0.505
AVG K+/K 1.069
(± 0.283)
1.087
(± 0.317)
1.167
(± 0.487)
1.166
(± 0.554)
1.160
(± 0.390)
1.170
(± 3.475)
1.136
(± 0.439)
25
3.3.2.3 Water‐soluble Chloride (Cl‐) versus Total Chlorine (Cl)
Water‐soluble chloride (Cl‐) is measured by ion chromatography (IC) on QMA filters and the total chlorine (Cl) is measured by x‐ray fluorescence (XRF) on Teflon filters. The ratio of Cl‐ to Cl is expected to equal or be less than 1. Figure 5 shows the scatter plots of Cl‐ versus total Cl concentrations for each of the six sites. Moderate correlations (R2 = 0.49 ‐ 0.79) were found for all of the sampling sites. The slopes were larger than unity (1.11 ‐ 2.02) except for the WB site (0.77). The uncertainties of chloride measurements are mainly associated with the volatility of Cl. One one hand, a portion of Cl‐ could be lost during the storage of the QMA filters especially when the aerosol samples are acidic. On the other hand, some Cl would be volatized in the vacuum chamber during XRF analysis. Such losses are more significant when chlorine concentrations are low.
26
y = 1.399x + 0.081
R2 = 0.494
0.0
0.5
1.0
1.5
2.0
0.0 0.5 1.0 1.5 2.0Chlorine (ug/m3)
Chloride
(ug/m
3 )
(a) Mong Kok (MK)
y = 1.168x + 0.050
R2 = 0.690
0.0
0.5
1.0
1.5
2.0
0.0 0.5 1.0 1.5 2.0Chlorine (ug/m3)
Chlorid
e (ug/m
3 )
(b) Central/Western (CW)
y = 0.769x + 0.050
R2 = 0.685
0.0
0.5
1.0
1.5
2.0
0.0 0.5 1.0 1.5 2.0Chlorine (ug/m3)
Chlorid
e (ug/m
3 )
(c) Clear Water Bay (WB)
y = 1.105x + 0.029
R2 = 0.790
0.0
0.5
1.0
1.5
2.0
0.0 0.5 1.0 1.5 2.0Chlorine (ug/m3)
Chlorid
e (ug/m
3 )
(d) Tung Chung (TC)
y = 1.238x + 0.042
R2 = 0.631
0.0
0.5
1.0
1.5
2.0
0.0 0.5 1.0 1.5 2.0Chlorine (ug/m3)
Chloride
(ug/m
3 )
(e) Tsuen Wan (TW)
y = 2.021x + 0.018
R2 = 0.686
0.0
0.5
1.0
1.5
2.0
0.0 0.5 1.0 1.5 2.0Chlorine (ug/m3)
Chlorid
e (ug/m
3 )
(f) Yuen Long (YL)
Figure 5. Scatter plots of water‐soluble chloride versus total chlorine measurements for PM2.5 samples collected at (a) MK, (b) CW, (c) WB, (d) TC, (e) TW, and (f) YL.
27
Table 10. Statistics analysis of water‐soluble chloride versus total chlorine measurements for PM2.5 samples collected at individual sites.
Statistics/Site MK CW WB TC TW YL ALL
n 61 61 61 61 61 61 366
Slope 1.399
(± 0.184)
1.168
(± 0.102)
0.769
(± 0.068)
1.105
(± 0.074)
1.238
(± 0.123)
2.021
(± 0.178)
1.176
(± 0.050)
Intercept 0.081
(± 0.029)
0.050
(± 0.021)
0.050
(± 0.013)
0.029
(± 0.014)
0.042
(± 0.015)
0.018
(± 0.024)
0.054
(± 0.008)
R2 0.494 0.690 0.685 0.790 0.631 0.686 0.599
AVG total Cl 0.089 0.120 0.072 0.073 0.064 0.077 0.083
AVG Cl‐ 0.205 0.191 0.105 0.109 0.122 0.174 0.151
AVG Cl‐/Cl 3.142
(± 5.957)
2.197
(± 2.106)
2.783
(± 3.559)
3.657
(± 8.481)
2.667
(± 2.643)
3.026
(± 3.212)
2.912
(± 4.849)
28
3.3.2.4 Ammonium Balance
To further validate the ion measurements, calculated versus measured ammonium (NH4+)
are compared. NH4+ is directly measured by IC analysis of QMA filter extract. NH4
+ is very often found in the chemical forms of NH4NO3, (NH4)2SO4, and NH4HSO4 while NH4Cl is usually negligible and excluded from the calculation. Assuming full neutralization, measured NH4
+ can be compared with the computed NH4+, which can be calculated in the following
two ways,
Calculated NH4+ based on NH4NO3 and (NH4)2SO4 = 0.29 × NO3
‐ + 0.38 × SO42‐
Calculated NH4+ based on NH4NO3 and NH4HSO4 = 0.29 × NO3
‐ + 0.192 × SO42‐
The calculated NH4+ is plotted against measured NH4
+ for each of the six sites in Figure 6. For both forms of sulfate the comparisons show strong correlations (R2 = 0.98 for ammonium sulfate and R2 = 0.93 for ammonium bisulfate, respectively) but with quite different slopes. The slopes for all of the sampling sites range from 1.04 ± 0.02 to 1.08 ± 0.02 assuming ammonium sulfate, and from 0.59 ± 0.02 to 0.69 ± 0.02 assuming ammonium bisulfate, close to the slope values found in earlier years. The average ratios of calculated ammonium to measured ammonium suggest that ammonium sulfate is the dominant form for sulfate in the PM2.5 over the Hong Kong region.
29
y = 1.063x + 0.208
R2 = 0.978
y = 0.663x ‐ 0.094
R2 = 0.954
0
5
10
15
0 5 10 15Measured Ammonium (ug/m3)
Calculated
Ammon
ium (u
g/m
3 )(a) Mong Kok (MK)
y = 1.039x + 0.212
R2 = 0.983
y = 0.652x ‐ 0.117
R2 = 0.953
0
5
10
15
0 5 10 15Measured Ammonium (ug/m3)
Calculated
Ammon
ium (u
g/m
3 )
(b) Central/Western (CW)
y = 1.085x + 0.063
R2 = 0.974
y = 0.588x + 0.001
R2 = 0.952
0
5
10
15
0 5 10 15Measured Ammonium (ug/m3)
Calculated
Ammon
ium (u
g/m
3 )
(c) Clear Water Bay (WB)
y = 1.077x + 0.052
R2 = 0.964
y = 0.664x ‐ 0.225
R2 = 0.890
0
5
10
15
0 5 10 15Measured Ammonium (ug/m3)
Calculated
Ammon
ium (u
g/m
3 )
(d) Tung Chung (TC)
y = 1.081x ‐ 0.071
R2 = 0.984
y = 0.650x ‐ 0.236
R2 = 0.948
0
5
10
15
0 5 10 15Measured Ammonium (ug/m3)
Calculated
Ammon
ium (u
g/m
3 )
(e) Tsuen Wan (TW)
y = 1.068x ‐ 0.065
R2 = 0.984
y = 0.688x ‐ 0.351
R2 = 0.937
0
5
10
15
0 5 10 15Measured Ammonium (ug/m3)
Calculated
Ammon
ium (u
g/m
3 )
(f) Yuen Long (YL)
Figure 6. Scatter plots of calculated ammonium versus measured ammonium for PM2.5 samples collected at (a) MK, (b) CW, (c) WB, (d) TC, (e) TW, and (f) YL. The calculated ammonium data are obtained assuming all nitrate was in the form of ammonium nitrate and all sulfate was in the form of either ammonium sulfate (data in blue) or ammonium bisulfate (data in brown).
30
Table 11. Statistics analysis of calculated ammonium versus measured ammonium for PM2.5 samples collected at individual sites.
Statistics/Site MK CW WB TC TW YL ALL
n 61 61 61 61 61 61 366
Ammonium Sulfate (blue dots)
Slope 1.063
(± 0.021)
1.039
(± 0.018)
1.085
(± 0.023)
1.077
(± 0.027)
1.081
(± 0.018)
1.068
(± 0.017)
1.066
(± 0.009)
Intercept 0.208
(± 0.106)
0.212
(± 0.092)
0.063
(± 0.107)
0.052
(± 0.137)
‐0.071
(± 0.089)
‐0.065
(± 0.092)
0.078
(± 0.043)
R2 0.978 0.983 0.974 0.964 0.984 0.984 0.977
AVG Mea. NH4+ 4.373 4.454 4.090 4.377 4.385 4.627 4.385
AVG Cal. NH4+ 4.858 4.838 4.500 4.766 4.668 4.874 4.751
AVG Cal./Mea. NH4
+
1.162
(± 0.215)
1.147
(± 0.241)
1.256
(± 0.835)
1.118
(± 0.222)
1.077
(± 0.149)
1.067
(± 0.171)
1.138
(± 0.390)
Ammonium Bisulfate (brown dots)
Slope 0.663
(± 0.019)
0.652
(± 0.019)
0.588
(± 0.017)
0.664
(± 0.030)
0.650
(± 0.020)
0.688
(± 0.023)
0.654
(± 0.009)
Intercept ‐0.094
(± 0.096)
‐0.117
(± 0.098)
0.001
(± 0.080)
‐0.225
(± 0.154)
‐0.236
(± 0.100)
‐0.351
(± 0.122)
‐0.180
(± 0.046)
R2 0.954 0.953 0.952 0.890 0.948 0.937 0.934
AVG Mea. NH4+ 4.373 4.454 4.090 4.377 4.385 4.627 4.385
AVG Cal. NH4+ 2.806 2.787 2.408 2.680 2.616 2.835 2.689
AVG Cal./Mea. NH4
+
0.658
(± 0.144)
0.644
(± 0.150)
0.675
(± 0.496)
0.610
(± 0.147)
0.592
(± 0.107)
0.603
(± 0.124)
0.630
(± 0.237)
31
3.3.3 Charge Balance
For the anion and cation balance, the sum of Cl‐, NO3‐, and SO4
2‐ is compared to the sum of NH4
+, Na+, and K+ in μmoles/m3 using the following equations:
⎟⎟⎠
⎞⎜⎜⎝
⎛++=
−−−
298005.62453.35
2433
/
SONOCl s for anionμmoles/m
⎟⎟⎠
⎞⎜⎜⎝
⎛++=
+++
098.390.2304.1843 KNaNH
ns for catioμmoles/m
The cation equivalents are plotted against the anion equivalents in Figure 7. A strong correlation (R2 = 0.98) was observed for the PM2.5 samples collected at all of the sampling sites. The slopes are expected to be slightly larger than unity since the calculations only accounted for major measured ions and there is a deficiency in cations due to the exclusion of [H+], [Ca2+], and [Mg2+]. Seen from the figure, however, the slopes obtained from individual sites range from 0.95 to 0.96. The difference is most likely caused by the underestimation of chloride and nitrate measurements on QMA filters.
32
y = 0.961x + 0.006
R2 = 0.979
0.0
0.2
0.4
0.6
0.8
1.0
0.0 0.2 0.4 0.6 0.8 1.0Cation Equivalence (umoles/m3)
Anion
Equ
ivalen
ce (u
moles/m
3 )
(a) Mong Kok (MK)
y = 0.949x + 0.002
R2 = 0.992
0.0
0.2
0.4
0.6
0.8
1.0
0.0 0.2 0.4 0.6 0.8 1.0Cation Equivalence (umoles/m3)
Anion
Equ
ivalen
ce (u
moles/m
3 )
(b) Central/Western (CW)
y = 0.956x ‐ 0.005
R2 = 0.982
0.0
0.2
0.4
0.6
0.8
1.0
0.0 0.2 0.4 0.6 0.8 1.0Cation Equivalence (umoles/m3)
Anion
Equ
ivalen
ce (u
moles/m
3 )
(c) Clear Water Bay (WB)
y = 0.961x ‐ 0.003
R2 = 0.980
0.0
0.2
0.4
0.6
0.8
1.0
0.0 0.2 0.4 0.6 0.8 1.0Cation Equivalence (umoles/m3)
Anion
Equ
ivalen
ce (u
moles/m
3 )
(d) Tung Chung (TC)
y = 0.961x ‐ 0.008
R2 = 0.990
0.0
0.2
0.4
0.6
0.8
1.0
0.0 0.2 0.4 0.6 0.8 1.0Cation Equivalence (umoles/m3)
Anion
Equ
ivalen
ce (u
moles/m
3 )
(e) Tsuen Wan (TW)
y = 0.955x ‐ 0.008
R2 = 0.989
0.0
0.2
0.4
0.6
0.8
1.0
0.0 0.2 0.4 0.6 0.8 1.0Cation Equivalence (umoles/m3)
Anion
Equ
ivalen
ce (u
moles/m
3 )
(f) Yuen Long (YL)
Figure 7. Scatter plots of anion versus cation measurements for PM2.5 samples collected at (a) MK, (b) CW, (c) WB, (d) TC, (e) TW, and (f) YL.
33
Table 12. Statistics analysis of anion versus cation measurements for PM2.5 samples collected at individual sites.
Statistics/Site MK CW WB TC TW YL ALL
n 61 61 61 61 61 61 366
Slope 0.961
(± 0.018)
0.949
(± 0.011)
0.956
(± 0.017)
0.961
(± 0.018)
0.961
(± 0.012)
0.955
(± 0.013)
0.957
(± 0.006)
Intercept 0.006
(± 0.006)
0.002
(± 0.004)
‐0.005
(± 0.005)
‐0.003
(± 0.006)
‐0.008
(± 0.004)
‐0.008
(± 0.004)
‐0.002
(± 0.002)
R2 0.979 0.992 0.982 0.980 0.990 0.989 0.984
AVG Σcation 0.273 0.278 0.264 0.274 0.273 0.289 0.275
AVG Σanion 0.268 0.267 0.245 0.260 0.255 0.268 0.261
AVG Σanion/Σcation
0.987
(± 0.112)
0.963
(± 0.069)
0.934
(± 0.080)
0.963
(± 0.076)
0.921
(± 0.059)
0.914
(± 0.076)
0.942
(± 0.084)
34
3.3.4 NIOSH_TOT versus IMPROVE_TOR for Carbon Measurements
Carbon concentrations were determined for the collected PM2.5 samples by both NIOSH_TOT and IMPROVE_TOR methods. The total carbon (TC) concentrations obtained from NIOSH_TOT and IMPROVE_TOR reach an excellent agreement (Figure 8), giving credence to the validities of the analysis results from both methods. The comparison results of OC and EC determined by both methods for individual sites are shown in Figure 9. Generally, EC concentrations derived by NIOSH_TOT method were much lower than those by IMPROVE_TOR method. The difference in EC obtained by these two protocols has been well‐documented and is primarily a result of protocol‐dependent nature of correction of charring of OC formed during thermal analysis [e.g., Chow et al.,2004; Chen et al., 2004; Subraminan et al., 2006]. Seen from the results, the average ratios of NIOSH_TOT EC to IMPROVE_TOR EC for samples from individual sampling sites range from 0.38 ± 0.13 to 0.64 ± 0.46. No correlation was found between NIOSH_TOT EC and IMPROVE_TOR EC for samples collected at Mong Kok site, which have very high EC loading on the QMA filters.
y = 1.013x + 0.228
R2 = 0.979
0
10
20
30
40
0 10 20 30 40
TC by NIOSH_TOT, ug/m3
TC by IM
PROVE_TO
R, ug/m
3
Figure 8. Comparisons of TC determined by NIOSH_TOT and IMPROVE_TOR methods for PM2.5 samples collected at all sites.
35
y = 1.009x + 3.190
R2 = 0.757
0.0
10.0
20.0
30.0
0.0 10.0 20.0 30.0OC by IMPROVE_TOR (ug/m3)
OC by
NIOSH
_TOT (ug/m
3 )
(a) Mong Kok (MK)
y = 0.100x + 4.010
R2 = 0.020
0.0
10.0
20.0
30.0
0.0 10.0 20.0 30.0EC by IMPROVE_TOR (ug/m3)
EC by NIOSH
_TOT (ug/m
3 )
y = 1.146x + 0.908
R2 = 0.870
0.0
10.0
20.0
30.0
0.0 10.0 20.0 30.0OC by IMPROVE_TOR (ug/m3)
OC by
NIOSH
_TOT (ug/m
3 )
(b) Central/Western (CW)
y = 0.338x + 0.382
R2 = 0.524
0.0
10.0
20.0
30.0
0.0 10.0 20.0 30.0EC by IMPROVE_TOR (ug/m3)
EC by NIOSH
_TOT (ug/m
3 )
y = 1.214x + 0.328
R2 = 0.908
0.0
10.0
20.0
30.0
0.0 10.0 20.0 30.0OC by IMPROVE_TOR (ug/m3)
OC by
NIOSH
_TOT (ug/m
3 )
(c) Clear Water Bay (WB)
y = 0.288x + 0.164
R2 = 0.666
0.0
10.0
20.0
30.0
0.0 10.0 20.0 30.0EC by IMPROVE_TOR (ug/m3)
EC by NIOSH
_TOT (ug/m
3 )
36
y = 1.226x + 0.596
R2 = 0.913
0.0
5.0
10.0
15.0
20.0
25.0
30.0
0.0 5.0 10.0 15.0 20.0 25.0 30.0OC by IMPROVE_TOR (ug/m3)
OC by
NIOSH
_TOT (ug/m
3 )
(d) Tung Chung (TC)
y = 0.324x + 0.347
R2 = 0.663
0.0
10.0
20.0
30.0
0.0 10.0 20.0 30.0EC by IMPROVE_TOR (ug/m3)
EC by NIOSH
_TOT (ug/m
3 )
y = 1.158x + 1.077
R2 = 0.919
0.0
5.0
10.0
15.0
20.0
25.0
30.0
0.0 5.0 10.0 15.0 20.0 25.0 30.0OC by IMPROVE_TOR (ug/m3)
OC by
NIOSH
_TOT (ug/m
3 )
(e) Tsuen Wan (TW)
y = 0.392x + 0.287
R2 = 0.581
0.0
10.0
20.0
30.0
0.0 10.0 20.0 30.0EC by IMPROVE_TOR (ug/m3)
EC by NIOSH
_TOT (ug/m
3 )
y = 1.239x + 0.941
R2 = 0.898
0.0
5.0
10.0
15.0
20.0
25.0
30.0
0.0 5.0 10.0 15.0 20.0 25.0 30.0OC by IMPROVE_TOR (ug/m3)
OC by
NIOSH
_TOT (ug/m
3 )
(f) Yuen Long (YL)
Z
y = 0.293x + 0.559
R2 = 0.644
0.0
10.0
20.0
30.0
0.0 10.0 20.0 30.0EC by IMPROVE_TOR (ug/m3)
EC by NIOSH
_TOT (ug/m
3 )
Figure 9. Comparisons of OC and EC determined by NIOSH_TOT and IMPROVE_TOR methods for PM2.5 samples collected at (a) MK, (b) CW, (c) WB, (d) TC, (e) TW, and (f) YL.
37
Table 13. Statistics analysis of OC and EC determined by NIOSH_TOT and IMPROVE_TOR methods for PM2.5 samples collected at individual sites.
Statistics/Site MK CW WB TC TW YL ALL
n 61 61 61 61 61 61 366
NIOSH_TOT OC versus IMPROVE_TOR OC
Slope 1.009
(± 0.074)
1.146
(± 0.058)
1.214
(± 0.050)
1.226
(± 0.049)
1.158
(± 0.045)
1.239
(± 0.054)
1.207
(± 0.023)
Intercept 3.190
(± 0.661)
0.908
(± 0.328)
0.328
(± 0.236)
0.596
(± 0.310)
1.077
(± 0.285)
0.941
(± 0.368)
0.862
(± 0.148)
R2 0.757 0.870 0.908 0.913 0.919 0.898 0.887
AVG IMPROVE_TOR
OC 8.094 4.918 3.905 5.125 5.435 5.727 5.534
AVG NIOSH_TOT OC 11.360 6.546 5.068 6.877 7.371 8.037 7.543
AVG TOT_OC/TOR_OC
1.475
(± 0.269)
1.384
(± 0.276)
1.303
(± 0.314)
1.331
(± 0.276)
1.411
(± 0.243)
1.459
(± 0.356)
1.394
(± 0.296)
NIOSH_TOT EC versus IMPROVE_TOR EC
Slope 0.100
(± 0.091)
0.338
(± 0.042)
0.288
(± 0.027)
0.324
(± 0.030)
0.392
(± 0.043)
0.293
(± 0.028)
0.467
(± 0.018)
Intercept 4.010
(± 0.793)
0.382
(± 0.172)
0.164
(± 0.075)
0.347
(± 0.129)
0.287
(± 0.200)
0.559
(± 0.148)
0.013
(± 0.095)
R2 0.020 0.524 0.666 0.663 0.581 0.644 0.648
AVG TOR_OC 8.481 3.709 2.431 3.654 4.238 4.606 4.520
AVG TOT_OC 4.861 1.634 0.863 1.529 1.949 1.911 2.124
AVG TOT_OC/TOR_OC
0.637
(± 0.463)
0.465
(± 0.154)
0.380
(± 0.125)
0.485
(± 0.247)
0.480
(± 0.157)
0.466
(± 0.205)
0.486
(± 0.262)
38
Comparisons were made between methods using same thermal protocol but with different optical detection for charring correction, and methods using different thermal protocols but with the same optical detection (Figure 10). Results show that the way how to perform charring correction is the major cause for the EC concentration difference while the impact from the temperature program plays a minor role. This result agrees with the findings in a recent publication [Wu et al., 2012] which also concluded that measurements by the IMPROVE_TOR and NIOSH_TOT protocols are not comparable.
y = 1.192x + 0.537
R2 = 0.920
0.0
5.0
10.0
15.0
20.0
25.0
30.0
0.0 5.0 10.0 15.0 20.0 25.0 30.0OC by IMPROVE_TOR (ug/m3)
OC by
IMPR
OVE_TO
T (ug/m
3 )
(a)
y = 0.604x + 0.160
R2 = 0.772
0.0
5.0
10.0
15.0
20.0
25.0
30.0
0.0 5.0 10.0 15.0 20.0 25.0 30.0EC by IMPROVE_TOR (ug/m3)
EC by IM
PROVE_TO
T (ug/m
3 )
y = 0.950x ‐ 0.031
R2 = 0.960
0.0
5.0
10.0
15.0
20.0
25.0
30.0
0.0 5.0 10.0 15.0 20.0 25.0 30.0OC by NIOSH_TOT (ug/m3)
OC by
IMPR
OVE_TO
T (ug/m
3 )
(b)
y = 1.067x + 0.626
R2 = 0.8100.0
5.0
10.0
15.0
20.0
25.0
30.0
0.0 5.0 10.0 15.0 20.0 25.0 30.0EC by NIOSH_TOT (ug/m3)
EC by IM
PROVE_TO
T (ug/m
3 )
Figure 10. Comparisons of OC and EC determined by (a) IMPROVE_TOT versus IMPROVE_TOR and (b) IMPROVE_TOT versus NIOSH_TOT for PM2.5 samples collected at all sites.
39
Table 14. Statistics analysis of OC and EC determined by IMPROVE_TOT versus IMPROVE_TOR and IMPROVE_TOT versus NIOSH_TOT for PM2.5 samples collected at all sites.
Method
Statistics
IMPROVE_TOT
versus
IMPROVE_TOR
IMPROVE_TOT
versus
NIOSH_TOT
OC EC OC EC
n 366 366 366 366
Slope 1.192 ± 0.018 0.604 ± 0.017 0.950 ± 0.010 1.067 ± 0.027
Intercept 0.537± 0.121 0.160 ± 0.091 ‐0.031 ± 0.090 0.626 ± 0.072
R2 0.920 0.772 0.960 0.810
AVG (X) 5.534 4.520 7.543 2.124
AVG (Y) 7.132 2.891 7.132 2.891
AVG (Y/X) 1.305 ± 0.193 0.669 ± 0.326 1.071 ± 0.188 1.481 ± 0.435
40
3.3.5 Material Balance
Major PM components can be classified into seven categories including: 1) geological material, which can be estimated by (1.89 × [Al] + 2.14 × [Si] + 1.4 × [Ca] + 1.43 × [Fe]); 2) organic matter, which can be estimated from OC concentration as [OM] = 1.4 × [OC]; 3) soot which can be represented by EC concentration; 4) ammonium sulfate (1.38 × [SO4
2‐]); 5) ammonium nitrate (1.29 × [NO3
‐]); 6) non‐crustal trace elements; 7) Unidentified material. Considering the large uncertainty in Na measurement by XRF, soluble sodium is used in calculation instead of total sodium. Therefore, the reconstructed mass is calculated by the following equation,
[Reconstructed Mass]
= 1.89 × [Al] + 2.14 × [Si] + 1.4 × [Ca] + 1.43 × [Fe]
+ 1.4 × [OC]
+ [EC]
+ 1.38 × [SO42‐]
+ 1.29 × [NO3‐]
+ [Na+]
+ trace elements excluding Na, Al, Si, Ca, Fe, and S
The reconstructed mass is plotting against the measured mass in Figure 11. A strong correlation (R2 = 0.98) is observed between the reconstructed mass and measured mass with a slope of 0.90 ± 0.01. Different from the comparison made between sum of chemical species and measured mass (Figure 2), the major uncertainty of the reconstructed mass is due to the estimation of organic matter (OM). Generally, the concentration of OM is determined by multiplying the OC concentration by an empirical factor. In this study, a value of 1.4 was applied to this factor. It is worth noting that the [OM]/[OC] ratio is site dependent. The [OM]/[OC] ratio of freshly emitted aerosols is smaller than that of the more aging (oxygenated) aerosols. Since the conversion factor is kept constant for calculation in this study, it can be seen that the average ratio of reconstructed mass to measured mass has the highest value for MK site, which is a roadside station and the dominant air mass is more freshly generated.
MK111120 was found to be an outlier in Figure 11a and the possible underlying causes were discussed in Section 3.3.1.
41
y = 0.887x + 3.307
R2 = 0.963
0
20
40
60
80
100
0 20 40 60 80 100Measured Mass (ug/m3)
Recon
structed
Mass (ug/m
3 )
(a) Mong Kok (MK)
y = 0.875x + 1.216
R2 = 0.988
0
20
40
60
80
100
0 20 40 60 80 100Measured Mass (ug/m3)
Recon
structed
Mass (ug/m
3 )
(b) Central/Western (CW)
y = 0.887x ‐ 0.063
R2 = 0.988
0
20
40
60
80
100
0 20 40 60 80 100Measured Mass (ug/m3)
Reconstructed Mass (ug/m
3 )
(c) Clear Water Bay (WB)
y = 0.899x + 0.024
R2 = 0.994
0
20
40
60
80
100
0 20 40 60 80 100Measured Mass (ug/m3)
Reconstructed Mass (ug/m
3 )
(d) Tung Chung (TC)
y = 0.893x + 0.876
R2 = 0.993
0
20
40
60
80
100
0 20 40 60 80 100Measured Mass (ug/m3)
Recon
structed
Mass (ug/m
3 )
(e) Tsuen Wan (TW)
y = 0.881x + 0.773
R2 = 0.991
0
20
40
60
80
100
0 20 40 60 80 100Measured Mass (ug/m3)
Reconstructed Mass (ug/m
3 )
(f) Yuen Long (YL)
Figure 11. Scatter plots of reconstructed mass versus measured mass on Teflon filters for PM2.5 samples collected at (a) MK, (b) CW, (c) WB, (d) TC, (e) TW, and (f) YL.
42
Table 15. Statistics analysis of reconstructed mass versus measured mass on Teflon filters for PM2.5 samples collected at individual sites.
Statistics/Site MK CW WB TC TW YL ALL
n 61 61 61 61 61 61 366
Slope 0.887
(± 0.023)
0.875
(± 0.012)
0.887
(± 0.013)
0.899
(± 0.009)
0.893
(± 0.010)
0.881
(± 0.011)
0.896
(± 0.006)
Intercept 3.307
(± 1.065)
1.216
(± 0.494)
‐0.063
(± 0.451)
0.024
(± 0.370)
0.876
(± 0.382)
0.773
(± 0.463)
0.682
(± 0.249)
R2 0.963 0.988 0.988 0.994 0.993 0.991 0.984
AVG Mea. Mass
43.077 35.364 31.320 35.572 35.298 38.220 36.475
AVG Rec. Mass
41.500 32.170 27.726 32.003 32.401 34.459 33.376
AVG Rec./Mea.
Mass
0.982
(± 0.071)
0.926
(± 0.068)
0.883
(± 0.051)
0.904
(± 0.048)
0.929
(± 0.048)
0.915
(± 0.057)
0.923
(± 0.065)
The annual average composition (%) of the major components to the PM2.5 mass is shown in Figure 12 for individual sites. The unidentified mass for MK, CW, WB, TC, TW, and YL is 3.7%, 8.8%, 11.3%, 9.7%, 7.7%, and 9.0% of the measured mass, respectively. Overall, the reconstructed mass agrees with the measured mass within approx. 12%.
43
Geological4%
Nitrate6%
Unidentified4%
Trace Element3%
NH4+10%
Na+1%
K1%
Soot20%
Organics26%
Sulfate25%
(a) Mong Kok (MK) Average Mass = 43.08 µg/m3
Geological5%
Nitrate7%
Unidentified9%
Trace Element4%
NH4+13%
Na+1%
K1%
Soot10%
Organics19%
Sulfate31%
Average Mass = 35.36 µg/m3(b) Central/Western (CW)
Geological5%
Nitrate3%
Unidentified11%
Trace Element4%
NH4+13%
Na+2%
K2%
Soot8%
Organics17%
Sulfate35%
Average Mass = 31.32 µg/m3(c) Clear Water Bay (WB)
Sulfate32%
Organics20%
Soot10%
K1%
Na+1%
NH4+12%
Trace Element4%
Unidentified10%
Nitrate5%
Geological5%
Average Mass = 35.57 µg/m3(d) Tung Chung (TC)
Geological5%
Nitrate5%
Unidentified8%
Trace Element3%
NH4+12%
Na+1%
K1%
Soot12%
Organics22%
Sulfate31%
Average Mass = 35.30 µg/m3(e) Tsuen Wan (TW)
Sulfate29%
Organics21%
Soot12%
K1%
Na+1%
NH4+12%
Trace Element3%
Unidentified9%
Nitrate7%
Geological5%
Average Mass = 38.22 µg/m3(f) Yuen Long (YL)
Figure 12. Annual average composition (%) of major components including 1) geological material; 2) organic matter; 3) soot; 4) ammonium; 5) sulfate; 6) nitrate; 7) non‐crustal trace elements, and 8) Unidentified material (difference between measured mass and the reconstructed mass) to PM2.5 mass for (a) MK, (b) CW, (c) WB, (d) TC, (e) TW, and (f) YL.
44
Annually MK had the highest PM2.5 loading while WB had the lowest (Figure 13). For all of the six sites, OM and sulfate were two most abundant components followed by ammonium and soot (EC by IMPROVE_TOR method). The EC concentration was highest in MK and lowest in WB, which is consistent with the natures of the sampling sites. The concentrations of ammonium, geological materials, and trace elements didn’t vary much across all six sites.
0
5
10
15
20
25
30
35
40
45
50
MK CW WB TC TW YL
PM2.5 C
oncentration
(ug/m3)
Trace Element
Nitrate
Sulfate
K
Na+
NH4+
Soot
Organics
Geological
Measured Mass
Figure 13. Comparison of annual average concentrations of major components including 1) geological material; 2) organic matter; 3) soot; 4) ammonium; 5) sulfate; 6) nitrate; 7) non‐crustal trace elements, and 8) Unidentified material (difference between measured mass and the reconstructed mass) to PM2.5 mass between individual sites.
45
3.3.6 Comparison of Collocated Samples
Collocated samplings were conducted in MK and CW sites on Teflon filters, and in WB and TC sites on QMA filters. The comparison of the collocated samples serves as part of the quality assurance efforts for the PM study with the purpose of determining the reproducibility of the sampling and analytical methods.
The data used for this comparison were subject to a data screening procedure including two steps. First, species that can be quantified (concentration > LOQ) more than 70% of the time will be included. Second, if either of the values in one pair of samples is below the LOQ, the whole pair of samples will be removed from the data set.
Bias and precisions were computed for collocated comparisons on PM2.5 and selected chemical species with the screened data set. The equations used are as below,
2ii
iYX
C+
= (10)
%100)(
% ×−
=i
iii
C
XYRB (11)
∑=
×−=
n
i i
ii
C
XY
nRB
1
%100)(1% (12)
2
%% iRBRSD = (13)
∑=
=n
iiRSD
nRSD
1
2%1
% (14)
where:
Xi = ambient air concentration of sample i measured at sampler X, µg/m3
Yi = ambient air concentration of sample i measured at collocated sampler Y, µg/m3
n = number of paired samples
%RB = percent relative bias
%RSD = percent relative standard deviation
The method for comparison used in this analysis gives a measure of the overall precision of the PM study, i.e. the sampling stage and the analytical stage are combined. The results (Table 16) show that the average relative biases of the concentrations of PM2.5 and selected chemical species for collocated samples are below 10%. It suggests that the precision of the PM sampling/analytical methods are acceptable.
46
Table 16. Average relative biases and average relative standard deviations of concentrations of PM2.5 and selected chemical species for collocated samples.
No. of Paired Samples
Average Relative Bias (%RB)
Average Relative Standard Deviation (%RSD)
PM2.5_Teflon 122 ‐0.430 1.664
PM2.5_QMA 122 1.973 14.235
Na+ 121 ‐0.444 11.793
NH4+ 122 ‐0.254 6.564
K+ 121 3.393 13.978
Cl‐ 100 1.446 28.029
NO3‐ 112 7.706 22.378
SO42‐ 122 1.091 5.404
TOR_OC 115 0.258 9.389
TOR_EC 122 0.642 16.366
Al 111 2.117 5.843
Si 114 3.089 7.296
K 122 1.098 3.570
Ca 122 2.822 6.887
Ti 118 1.847 13.528
V 117 ‐0.825 11.453
Mn 86 2.439 9.193
Fe 122 3.584 5.401
Ni 79 1.928 10.271
Cu 108 4.270 7.546
Zn 102 1.574 6.739
Pb 94 0.668 6.029
47
3.3.7 PM2.5 Mass Concentrations: Gravimetric vs. Continuous Measurements
Continuous monitoring of PM2.5 concentrations by TEOMs (tapered element oscillating microbalance) is carried out at a few locations in Hong Kong, including in MK, CW, TC, TW, and YL sites. A beta gauge particulate monitor (Model 5030 SHARP, Thermo Scientific) has been set up in HKUST site for continuous monitoring of PM2.5 concentrations since May 2011. Comparisons of PM2.5 mass concentrations from gravimetric measurement and 24‐hr average TEOM/beta gauge measurement were conducted. The results are presented in both time‐series plots and scatter plots (Figure 14). Uncertainties of TEOM/beta gauge are assumed to be 5% of concentration. The two measurements show good agreement (R2 = 0.79 ‐ 0.94) with slopes ranging from 0.7 to 1.2. No prominent outliers were found in the results from all six sampling sites.
0
20
40
60
80
100
120
1/13/2011
2/13/2011
3/13/2011
4/13/2011
5/13/2011
6/13/2011
7/13/2011
8/13/2011
9/13/2011
10/13/2011
11/13/2011
12/13/2011
PM2.5 C
onc., ug/m
3
Measured Mass
TEOM
(a) Mong Kok (MK)
y = 0.711x + 7.645
R2 = 0.786
0
20
40
60
80
100
120
0 20 40 60 80 100 120Measured PM2.5 mass, ug/m3
TEOM PM
2.5 m
ass, ug/m
3
0
20
40
60
80
100
120
1/13/2011
2/13/2011
3/13/2011
4/13/2011
5/13/2011
6/13/2011
7/13/2011
8/13/2011
9/13/2011
10/13/2011
11/13/2011
12/13/2011
PM2.5 C
onc., ug/m
3
Measured Mass
TEOM
(b) Central/Western (CW)
y = 1.068x ‐ 0.498
R2 = 0.933
0
20
40
60
80
100
120
0 20 40 60 80 100 120Measured PM2.5 mass, ug/m3
TEOM PM
2.5 m
ass, ug/m
3
0
20
40
60
80
100
120
1/13/2011
2/13/2011
3/13/2011
4/13/2011
5/13/2011
6/13/2011
7/13/2011
8/13/2011
9/13/2011
10/13/2011
11/13/2011
12/13/2011
PM2.5 C
onc., ug/m
3
Measured Mass
Beta Gauge
(c) Clear Water Bay (WB)
y = 1.163x ‐ 2.608
R2 = 0.939
0
20
40
60
80
100
120
0 20 40 60 80 100 120Measured PM2.5 mass, ug/m3
Beta Gauge
PM
2.5 m
ass, ug/m
3
48
0
20
40
60
80
100
120
1/13/2011
2/13/2011
3/13/2011
4/13/2011
5/13/2011
6/13/2011
7/13/2011
8/13/2011
9/13/2011
10/13/2011
11/13/2011
12/13/2011
PM2.5 C
onc., ug/m
3Measured Mass
TEOM
(d) Tung Chung (TC)
y = 0.861x + 2.130
R2 = 0.886
0
20
40
60
80
100
120
0 20 40 60 80 100 120Measured PM2.5 mass, ug/m3
TEOM PM
2.5 m
ass, ug/m
3
0
20
40
60
80
100
120
1/13/2011
2/13/2011
3/13/2011
4/13/2011
5/13/2011
6/13/2011
7/13/2011
8/13/2011
9/13/2011
10/13/2011
11/13/2011
12/13/2011
PM2.5 C
onc., ug/m
3
Measured Mass
TEOM
(e) Tsuen Wan (TW)
y = 0.832x + 5.434
R2 = 0.863
0
20
40
60
80
100
120
0 20 40 60 80 100 120Measured PM2.5 mass, ug/m3
TEOM PM
2.5 m
ass, ug/m
3
0
20
40
60
80
100
120
1/13/2011
2/13/2011
3/13/2011
4/13/2011
5/13/2011
6/13/2011
7/13/2011
8/13/2011
9/13/2011
10/13/2011
11/13/2011
12/13/2011
PM2.5 C
onc., ug/m
3
Measured Mass
TEOM
(f) Yuen Long (YL)
y = 0.815x + 5.370
R2 = 0.886
0
20
40
60
80
100
120
0 20 40 60 80 100 120Measured PM2.5 mass, ug/m3
TEOM PM
2.5 m
ass, ug/m
3
Figure 14. Comparisons of PM2.5 mass concentrations from gravimetric and continuous measurements at (a) MK, (b) CW, (c) WB, (d) TC, (e) TW, and (f) YL.
49
4. Comparison to the PM2.5 Sampling Campaigns in 2000 ‐ 2001, 2004 ‐ 2005, and 2008 ‐ 2009
A side‐by‐side comparison of the four year study of PM2.5 samples collected during 2000 ‐ 2001, 2004 ‐ 2005, the whole year of 2009, and current 2011 period is shown in Table 17 [Chow et al., 2002, 2006, 2010]. In this study, two additional sites (CW and TC) were added while the rural HT site was replaced by the suburban WB site.
MK, TW, and YL sites were picked out for annual trend observation. The annual average PM2.5 concentrations observed at these three sites were all found to decrease from 2005 to 2009 and then increase slightly in current study (Figure 15). The circular pollution wind maps as a function of PM2.5 mass concentrations were plotted for TW site during the four sampling campaign periods and for YL site during the three sampling periods (Figures 16&17). Wind data at King’s Park was used to represent TW site while wind data at Lau Fau Shan was used to represent YL site. The color‐coded PM2.5 concentrations (in µg/m
3) were averaged for different wind speeds (given by the radius with 1 m/s resolution) and wind directions (given by the angle with 10 degree resolution). The black concentric circles correspond to winds of 3.5, 7, and 10.5 m/s for TW sites and 5, 10, and 15 m/s for YL site. The blue contours correspond to the most frequent 80% of the measured wind speed and direction pairs. It can be seen from the results that throughout the years, the prevailing winds are easterly (northeasterly in winter and southeasterly in summer) while a small portion are westerly winds. High PM2.5 concentrations were usually associated with winds coming from the north, suggesting the important role of air pollutant transport from regions outside Hong Kong.
0
10
20
30
40
50
60
70
80
90
MK TW YL
PM2.5 C
oncentration
s (ug/m
3 )
2001 2005 2009 2011
Figure 15. Comparisons of annual average PM2.5 mass concentrations at MK, TW, and YL sites from 2001 to 2011. The error bars represent one standard variation of the PM2.5 mass concentration measurements over the year.
50
Figure 16. Wind Roses for PM2.5 mass concentrations (µg/m3) at TW site during 2000 ‐ 2001, 2004 ‐ 2005, 2008 ‐ 2009, and 2011. The black concentric circles correspond to winds of 3.5, 7, and 10.5 m/s. The blue contour lines correspond to the most frequent 80% of the measured wind speed and direction pairs.
Figure 17. Wind Roses for PM2.5 mass concentrations (µg/m3) at YL site during 2004 ‐ 2005, 2008 ‐ 2009, and 2011. The black concentric circles correspond to winds of 5, 10, and 15 m/s. The blue contour lines correspond to the most frequent 80% of the measured wind speed and direction pairs.
51
Measured species were grouped into six categories described in Section 3.3.5 for better comparison (Figure 18).
At MK and TW, ammonium and sulfate concentrations increased from the first year study to the second year study, decreased in the third year study and increased again in the fourth year study. Compared to the 3rd year study, ammonium concentrations increased by 28.5% and 34.2% at MK and TW, respectively, during the 4th year study. At YL, the concentrations of these two species were at a lower level during the third year study compared to the second year study, but increased again in the fourth year study.
Nitrate concentrations trended similarly at both MK and TW. Nitrate kept increasing during the first three one‐year studies but decreased in the 4th year study by 12.7% and 11.6% for MK and TW sites, respectively. At YL site, however, nitrate decreased from the 2nd year study to the 3rd year study but increased again by around 7% in the 4th year study.
OC concentrations increased consistently across the MK, TW, and YL sites in the 4th year study by 29.2%, 24.2%, and 18.5%, respectively, compared to the 3rd year study. However, the EC concentrations exhibited different trends. EC decreased quite significantly (approx. 20%) at MK while increased by 12.7% and 32.1% at TW and YL, respectively.
From 2009 to 2011, the concentrations of water‐soluble potassium (K+) increased by 46.2 ‐ 50.8% across the three sites suggesting that the impact of biomass burning and/or long‐range transport of vegetative burning emissions on the Hong Kong region may become more important. Crustal materials (Al, Si, Ca, and Fe) generally trended down in the 2001 ‐ 2009 period but increased by 51.0%, 90.7%, and 91.5% at MK, TW, and YL sites, respectively. On the other hand, non‐crustal element concentrations increased by 3.5 ‐ 20.3% in the 4th year study compared to the 3rd year study.
52
Table 17. Side‐by‐side comparison of the four one‐year studies of PM2.5 samples (in µg/m3) collected during 2000 ‐ 2001, 2004 ‐ 2005, 2008 ‐ 2009, and current 2011 (1/1/2011 ‐ 12/30/2011) period. Carbon concentrations are from the IMPROVE_TOR method.
2001 2001 2001 2005 2005 2005 2005 2009 2009 2009 2009 2011 2011 2011 2011 2011 2011 MK TW HT MK TW YL HT MK TW YL HT MK CW WB TC TW YL
Teflon Mass 58.281 34.122 23.658 53.023 38.593 41.310 28.437 41.600 30.612 31.781 24.105 43.077 35.364 31.320 35.572 35.298 38.220 Quartz Mass 62.502 37.280 25.848 54.868 40.748 43.908 29.643 45.924 34.003 36.343 25.945 47.922 39.841 35.893 39.811 40.558 42.895
Cl‐ 0.256 0.138 0.143 0.283 0.126 0.264 0.124 0.312 0.175 0.213 0.298 0.205 0.191 0.105 0.109 0.122 0.174 NO3‐ 1.653 1.343 0.708 2.404 1.635 2.864 0.762 2.809 2.031 2.419 1.508 2.452 2.389 0.934 1.897 1.795 2.590 SO4= 9.502 9.172 8.641 12.840 13.174 13.910 11.906 10.414 10.481 11.041 9.657 10.912 10.907 11.128 11.094 10.914 10.851 NH4+ 3.174 2.965 2.157 4.400 4.070 4.617 3.059 3.402 3.268 3.470 2.631 4.373 4.454 4.090 4.377 4.385 4.627 Na+ 0.398 0.397 0.679 0.423 0.362 0.375 0.527 0.320 0.211 0.262 0.380 0.431 0.452 0.510 0.413 0.404 0.402 K+ 0.457 0.492 0.403 0.479 0.486 0.562 0.433 0.278 0.308 0.365 0.259 0.467 0.463 0.483 0.534 0.492 0.590 OC 16.642 8.690 4.226 11.177 6.932 7.235 3.921 6.262 4.376 4.834 2.697 8.094 4.918 3.905 5.125 5.435 5.727 EC 20.288 5.371 1.682 14.115 6.258 6.194 2.277 10.661 3.760 3.488 1.206 8.481 3.709 2.431 3.654 4.238 4.606 TC 36.911 14.041 5.890 25.284 13.181 13.420 6.190 16.912 8.124 8.310 3.892 16.550 8.604 6.313 8.756 9.649 10.309 Al 0.1139 0.1146 0.1094 0.1408 0.1414 0.1448 0.1223 0.0986 0.0828 0.0913 0.0828 0.1942 0.2008 0.1990 0.2009 0.1910 0.2114 Si 0.4778 0.3870 0.3489 0.3469 0.3141 0.3221 0.2546 0.2485 0.1853 0.2073 0.1685 0.3981 0.4209 0.3980 0.4079 0.3888 0.4349 P 0.0092 0.0050 0.0028 0.1886 0.1950 0.1917 0.1747 0.0225 0.0237 0.0229 0.0225 0.0194 0.0163 0.0150 0.0158 0.0163 0.0155 S 3.4886 3.3789 3.0534 4.3005 4.5835 4.5622 4.2099 3.3471 3.4305 3.4535 3.1650 3.6677 3.7263 3.8399 3.7518 3.7641 3.7813 Cl 0.1169 0.0874 0.1432 0.1391 0.0758 0.1590 0.0709 0.1037 0.0568 0.0941 0.0799 0.0889 0.1203 0.0720 0.0726 0.0640 0.0774 K 0.5517 0.5858 0.4892 0.4678 0.5080 0.5631 0.4551 0.3064 0.3281 0.3828 0.2780 0.4619 0.4677 0.4740 0.5192 0.4797 0.5722 Ca 0.1705 0.1262 0.1024 0.1082 0.0896 0.0891 0.0652 0.1102 0.0729 0.0738 0.0626 0.1298 0.1209 0.0914 0.0959 0.1006 0.1111 Ti 0.0092 0.0088 0.0079 0.0109 0.0102 0.0114 0.0062 0.0109 0.0084 0.0097 0.0062 0.0128 0.0118 0.0106 0.0138 0.0117 0.0156 V 0.0134 0.0137 0.0117 0.0190 0.0237 0.0195 0.0167 0.0175 0.0182 0.0144 0.0177 0.0146 0.0150 0.0119 0.0139 0.0206 0.0139 Cr 0.0010 0.0009 0.0006 0.0017 0.0015 0.0017 0.0014 0.0014 0.0012 0.0016 0.0011 0.0021 0.0020 0.0022 0.0022 0.0021 0.0024 Mn 0.0128 0.0124 0.0077 0.0170 0.0158 0.0170 0.0123 0.0127 0.0113 0.0127 0.0087 0.0214 0.0214 0.0174 0.0226 0.0186 0.0215 Fe 0.2692 0.1871 0.1219 0.2579 0.1858 0.1996 0.1190 0.2343 0.1325 0.1552 0.0947 0.2958 0.1978 0.1582 0.2094 0.1932 0.2215 Co 0.0001 0.0001 0.0002 0.0001 0.0001 0.0001 0.0002 0.0002 0.0002 0.0001 0.0002 0.0005 0.0005 0.0003 0.0004 0.0003 0.0004 Ni 0.0055 0.0054 0.0047 0.0061 0.0071 0.0068 0.0050 0.0049 0.0052 0.0044 0.0050 0.0050 0.0050 0.0042 0.0048 0.0064 0.0049 Cu 0.0113 0.0090 0.0052 0.0110 0.0104 0.0113 0.0065 0.0210 0.0188 0.0167 0.0169 0.0252 0.0215 0.0225 0.0226 0.0207 0.0234 Zn 0.1794 0.1743 0.1087 0.2399 0.2186 0.2381 0.1727 0.1579 0.1343 0.1600 0.1177 0.2156 0.2364 0.1948 0.2909 0.1936 0.2188 Ga 0.0004 0.0004 0.0005 0.0018 0.0030 0.0024 0.0026 0.0003 0.0004 0.0003 0.0004 0.0003 0.0002 0.0002 0.0002 0.0001 0.0001 As 0.0046 0.0055 0.0042 0.0053 0.0063 0.0084 0.0043 0.0012 0.0010 0.0016 0.0006 0.0043 0.0046 0.0053 0.0050 0.0046 0.0058 Se 0.0021 0.0022 0.0020 0.0003 0.0004 0.0005 0.0004 0.0003 0.0004 0.0004 0.0006 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 Br 0.0129 0.0127 0.0121 0.0106 0.0099 0.0116 0.0108 0.0172 0.0148 0.0143 0.0174 0.0172 0.0170 0.0190 0.0159 0.0156 0.0171 Rb 0.0036 0.0043 0.0032 0.0020 0.0025 0.0029 0.0019 0.0010 0.0011 0.0015 0.0008 0.0011 0.0013 0.0014 0.0015 0.0014 0.0016 Sr 0.0013 0.0011 0.0011 0.0011 0.0011 0.0015 0.0015 0.0017 0.0019 0.0020 0.0015 0.0030 0.0032 0.0030 0.0027 0.0029 0.0030 Y 0.0001 0.0001 0.0002 0.0004 0.0004 0.0004 0.0003 0.0003 0.0004 0.0003 0.0004 0.0002 0.0002 0.0004 0.0002 0.0003 0.0004 Zr 0.0006 0.0006 0.0005 0.0016 0.0013 0.0007 0.0010 0.0010 0.0008 0.0011 0.0010 0.0006 0.0002 0.0003 0.0004 0.0004 0.0006 Mo 0.0005 0.0005 0.0007 0.0015 0.0011 0.0017 0.0012 0.0007 0.0006 0.0007 0.0005 0.0016 0.0012 0.0011 0.0011 0.0013 0.0009 Pd 0.0012 0.0017 0.0011 0.0019 0.0014 0.0016 0.0020 0.0006 0.0007 0.0008 0.0005 0.0016 0.0018 0.0023 0.0021 0.0019 0.0018 Ag 0.0011 0.0017 0.0014 0.0013 0.0020 0.0018 0.0012 0.0010 0.0007 0.0008 0.0007 0.0003 0.0002 0.0003 0.0002 0.0001 0.0001 Cd 0.0019 0.0023 0.0022 0.0022 0.0021 0.0025 0.0018 0.0008 0.0007 0.0007 0.0005 0.0006 0.0005 0.0005 0.0006 0.0004 0.0007 In 0.0018 0.0020 0.0014 0.0009 0.0010 0.0017 0.0011 0.0005 0.0005 0.0005 0.0005 0.0003 0.0003 0.0005 0.0006 0.0003 0.0002 Sn 0.0188 0.0203 0.0116 0.0131 0.0188 0.0162 0.0084 0.0107 0.0101 0.0100 0.0091 0.0131 0.0122 0.0125 0.0135 0.0120 0.0154 Sb 0.0046 0.0049 0.0038 0.0042 0.0027 0.0039 0.0033 0.0009 0.0009 0.0014 0.0015 0.0080 0.0074 0.0068 0.0075 0.0067 0.0087 Ba 0.0267 0.0170 0.0086 0.0106 0.0081 0.0068 0.0053 0.0031 0.0031 0.0024 0.0026 0.0167 0.0108 0.0087 0.0104 0.0101 0.0108 La 0.0131 0.0087 0.0130 0.0105 0.0081 0.0082 0.0112 0.0036 0.0034 0.0040 0.0053 0.0164 0.0156 0.0146 0.0163 0.0132 0.0165 Au 0.0003 0.0005 0.0004 0.0003 0.0006 0.0002 0.0003 0.0000 0.0000 0.0001 0.0002 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 Hg 0.0001 0.0002 0.0001 0.0000 0.0003 0.0001 0.0001 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 Tl 0.0001 0.0001 0.0001 0.0002 0.0001 0.0000 0.0003 0.0000 0.0001 0.0001 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 Pb 0.0664 0.0726 0.0576 0.0478 0.0498 0.0624 0.0432 0.0405 0.0406 0.0437 0.0399 0.0597 0.0604 0.0626 0.0630 0.0599 0.0671 U 0.0001 0.0002 0.0002 0.0013 0.0011 0.0017 0.0018 0.0008 0.0007 0.0007 0.0010 0.0040 0.0035 0.0040 0.0038 0.0038 0.0035
53
0
5
10
15
20
25
Geological OC So
otNH4+ Na
+ K
Sulfate
Nitrate
Trace Elem
ent
PM2.5 C
oncentration
s (ug/m
3 )2001 2005 2009 2011(a) Mong Kok (MK)
0
5
10
15
20
25
Geological OC So
otNH4+ Na
+ K
Sulfate
Nitrate
Trace Elem
ent
PM2.5 C
oncentration
s (ug/m
3 )
2001 2005 2009 2011(b) Tsuen Wan (TW)
0
5
10
15
20
25
Geological OC So
otNH4+ Na
+ K
Sulfate
Nitrate
Trace Elem
ent
PM2.5 C
oncentration
s (ug/m
3 )
2005 2009 2011(c) Yuen Long (YL)
Figure 18. Annual trend of major components of PM2.5 samples collected at (a) MK, (b) TW, and (c) YL.
54
Annual average concentrations of certain gaseous pollutants were further examined in an attempt to understand more about the underlying causes leading to the increase in OC and ammonium sulfate, which are the two main contributors to the PM elevation. TW and YL sites were chosen since the monitoring data are more complete for these two sites.
Figure 19 shows the annual trends of sulfur dioxide, which is the precursor of sulfate, together with the oxidant level at TW and YL from 2000 to 2011. Peak values of both SO2 and Ox (sum of O3 and NO2) were observed for 2004 ‐ 2005 and they corresponded to the highest SO4
2‐ concentrations at both the TW and YL sites among the studied periods. The SO2 and Ox concentration levels in the period of 2008 ‐ 2009 were comparable to those in 2011. Assuming similar meteorological conditions in both periods (precipitation is important sink of sulfate but the data is not available to the project team), the amounts of sulfate formed locally were expected to be comparable. The increase of sulfate in 2011 compared to 2008 ‐ 2009 might then be attributed to pollutant transport from outside‐Hong Kong region.
0
10
20
30
40
50
60
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
Year
Ox C
onc., ppb
Tsuen Wan
Yuen Long
(b) Oxidants (Ox = O3 + NO2)
0
2
4
6
8
10
12
14
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
Year
SO2 Co
nc., pp
b
Tsuen Wan
Yuen Long
(a) Sulfur Dioxide (SO2)
Figure 19. Annual average concentration levels of (a) sulfur dioxide and (b) oxidants at TW and YL sites from 2000 to 2011.
To briefly investigate the impact of outside‐Hong Kong transport on the pollution level in Hong Kong, the annual average concentrations of O3 and CO at Tap Mun (TM) AQMS were examined (Figure 20). O3 serves as a tracer for regional transport in places where NOx emissions are low. CO is a well‐known combustion tracer. Due to its relatively long lifetime, CO can also be an indicator for long‐range transport. The TM AQMS is chosen for inspecting the annual trend of O3 and CO since it is a rural background/transport site located on a remote island off the northeast coast of Hong Kong, with little local combustion sources. The O3 concentrations in all four studied periods were at similar levels while the CO concentration increased in the 2nd year (2004‐2005) study compared to the 1st year (2000‐2001) study, decreased by approx. 20% in the 3rd year (2008‐2009) study, and then increased again to the level of 2004 ‐ 2005 in this study (year 2011). This variation suggests that transport of air pollutants from regions outside Hong Kong was more significant in 2011 than in the period of 2008 ‐ 2009, in some way supporting the contention that the increase of PM (more specifically, OC and sulfate) might partially be caused by regional transport.
55
0
5
10
15
20
25
30
35
40
45
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
Year
O3 C
onc., p
pb
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
CO Con
c., p
pm
O3, ppb
CO, ppm
Figure 20. Annual average concentrations of O3 and CO at Tap Mun AQMS from 2000 to 2011.
56
5. Summary
During the period from January 1, 2011 to December 31, 2011, a PM2.5 sampling campaign was conducted every sixth day in Hong Kong at six sites representing air quality at roadside, urban, new town, and suburban areas. A total of 366 samples (61 samples for each site) were collected from the Mong Kok (MK), Central Western (CW), Clear Water Bay (WB), Tung Chung (TC), Tsuen Wan (TW), and Yuen Long (YL) sites. The highest annual average PM2.5 mass of about 43.1 µg/m3 was measured at the roadside MK site. The lowest annual average PM2.5 mass of about 31.3 µg/m3 was found at the suburban WB site, which is slightly lower than the newly proposed HK AQO annual 24‐hour PM2.5 standard of 35 µg/m
3.
Two levels of validation were performed on the complete data set. Reconstructed mass and measured mass were highly correlated with correlation coefficients (R2) ranging from 0.96 to 0.99. It further supports the validity of both gravimetric analysis and chemical measurements. The reconstructed mass averagely explains approx. 90% of the measured PM2.5 mass.
Sulfate is the most abundant component in the PM2.5 across the five sites (28.4 ‐ 35.5%) except for MK (25.3%, lower than that of OC). Nitrate concentrations as measured in the quartz filters were much lower than those of sulfate, contributing approx. 3.0 ‐ 6.8% to the total mass at all sites. Ammonium was reasonably balanced by sulfate and nitrate and it was suggested to exist dominantly as ammonium sulfate over the Hong Kong region. Both OC and EC concentrations were consistently higher at MK than at the other five sites. The lowest average EC value was found at WB site, which is in a relatively clean area with little commercial development.
Monthly average PM2.5 concentration and chemical composition for each of the individual site are shown in Figure 21 in order to examine the seasonal trends of the different air pollutants. The results suggest that the entire Hong Kong region experienced higher PM2.5 concentrations in winter months (Jan, Feb, Nov, and Dec) while the summer months (Jun, Jul, and Aug) usually have lower PM levels. The meteorological conditions play an important role in this situation. In winter time, the northerly and northeasterly winds prevail, bringing in air pollutants from mainland China. During summer, wind directions change to southerly and southeasterly and the clean marine air helps to dilute air pollutants in Hong Kong.
The elevated PM2.5 concentrations were mainly caused by increasing concentrations of sulfate, organics, and nitrate. Both sulfate and organics can be linked to regional transport from the Pearl River Delta (PRD) region or even super‐regional transport from outside PRD region. It suggests that sulfate and organics from secondary sources contribute significantly to the PM2.5 mass loading in Hong Kong. The concentration variation of nitrate, on the other hand, might be caused by regional transport together with local formation which is temperature‐dependent.
Unlike the other five sites, the concentrations of EC at MK exhibited little seasonal variations, suggesting that EC at MK is dominantly from local sources (e.g. vehicle exhausts). The reduction in EC levels at MK from 2001 to 2011 indicates control measures of vehicular emissions are effective over the years.
57
0
10
20
30
40
50
60
70
80
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
PM2.5 C
oncentration
(ug/m
3 )
Trace Element
Nitrate
Sulfate
K
Na+
NH4+
Soot
Organics
Geological
PM2.5
(a) Mong Kok (MK)
0
10
20
30
40
50
60
70
80
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
PM2.5 C
oncentration
(ug/m
3 )
Trace Element
Nitrate
Sulfate
K
Na+
NH4+
Soot
Organics
Geological
PM2.5
(b) Central/Western (CW)
0
10
20
30
40
50
60
70
80
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
PM2.5 C
oncentration
(ug/m
3 )
Trace Element
Nitrate
Sulfate
K
Na+
NH4+
Soot
Organics
Geological
PM2.5
(c) Clear Water Bay (WB)
0
10
20
30
40
50
60
70
80
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
PM2.5 C
oncentration
(ug/m
3 )
Trace Element
Nitrate
Sulfate
K
Na+
NH4+
Soot
Organics
Geological
PM2.5
(d) Tung Chung (TC)
0
10
20
30
40
50
60
70
80
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
PM2.5 C
oncentration
(ug/m
3 )
Trace Element
Nitrate
Sulfate
K
Na+
NH4+
Soot
Organics
Geological
PM2.5
(e) Tsuen Wan (TW)
0
10
20
30
40
50
60
70
80
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
PM2.5 C
oncentration
(ug/m
3 )
Trace Element
Nitrate
Sulfate
K
Na+
NH4+
Soot
Organics
Geological
PM2.5
(f) Yuen Long (YL)
Figure 21. Monthly average of PM2.5 mass concentrations and chemical compositions for (a) MK, (b) CW, (c) WB, (d) TC, (e) TW, and (f) YL during 2011 PM study.
Seen from the evaluation of variations of PM2.5 mass concentrations and major PM components at different sites, sulfate, nitrate, and OC increased to different extents during the period of 2009 ‐ 2011. These pollutants can be generated from both primary and secondary sources, and they can be formed locally or transported from outside Hong Kong region.
58
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