chemical compositions of pm2.5 at two non-urban sites from … · 2020-05-15 · 2334 blaszczak et...
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Aerosol and Air Quality Research, 16: 2333–2348, 2016 Copyright © Taiwan Association for Aerosol Research ISSN: 1680-8584 print / 2071-1409 online doi: 10.4209/aaqr.2015.09.0538
Chemical Compositions of PM2.5 at Two Non-Urban Sites from the Polluted Region in Europe Barbara Błaszczak1*, Wioletta Rogula-Kozłowska1, Barbara Mathews1, Katarzyna Juda-Rezler2, Krzysztof Klejnowski1, Patrycja Rogula-Kopiec1 1 Institute of Environmental Engineering of the Polish Academy of Sciences, 41-819 Zabrze, Poland 2 Warsaw University of Technology, Faculty of Environmental Engineering, 00-653 Warsaw, Poland ABSTRACT
The study presents the analysis of measurement results for the ambient mass concentrations of fine particulate matter (PM2.5), PM2.5-bound carbonaceous matter (OC, EC) and water-soluble ions (Cl–, NO3
–, SO42–, Na+, NH4
+, K+, Ca2+, Mg2+). The 24-h PM2.5 samples were collected in the heating and non-heating seasons at two regional background sites in Southern Poland in 2011–2013. The percentage of the secondary organic and inorganic matter in PM2.5 was calculated.
Over the whole measurement period, the mean PM2.5 concentration was 31.56 µg m–3 and 24.92 µg m–3 in Racibórz and Złoty Potok, respectively. Regardless of the season, the total carbon percentage in PM2.5 was comparable at both sites and amounted ~40%. There were no visible seasonal variations in the secondary organic carbon (SOC) share in PM2.5. The mean percentage of the primary organic carbon (POC) in PM2.5 was higher than the SOC percentage at both locations. The mean contribution of the water-soluble ions in the PM2.5 mass was lower than the TC percentage, with values 20.35% (Złoty Potok) and 33.56% (Racibórz). The total share of the secondary ions (SO4
2–, NO3– and NH4
+) in PM2.5 was comparable in both measurement periods.
It was shown that PM2.5 at regional background sites in Southern Poland is significantly different than at similar stations across Europe. It is reflected by higher concentrations of PM2.5 and its main components and lower percentage of the secondary ions in the PM2.5 mass. The carbonaceous matter percentage in PM2.5 is higher than in other parts of Europe. Keywords: PM2.5; Organic carbon; Secondary ions; Regional background sites; Southern Poland. INTRODUCTION
The recent interest has been focused on the chemical composition of particulate matter (PM), especially carbonaceous fractions and water-soluble ions, as they have predominant contribution to the PM2.5 mass (according to Directive 2008/50/EC: “fine PM; shall mean particulate matter which passes through a size-selective inlet as defined in the reference method for the sampling and measurement of PM2.5, EN14907, with a 50% efficiency cut-off at 2.5 µm aerodynamic diameter”) (Rogula-Kozłowska et al., 2014; Zhang et al., 2014; Zhao et al., 2015).
Elemental carbon (EC), inorganic/carbonated carbon (IC/CC) and organic carbon (OC) constitute the total content of carbonaceous matter, i.e., total carbon (TC), in PM (Seinfeld and Pandis, 2006). IC can be found in the crustal matter, present mainly in the coarse particles, so IC content * Corresponding author.
Tel.: +48 32 271 64 81; Fax: +48 32 271 74 70 E-mail address: [email protected]
in PM2.5 can be neglected. Although EC is believed to be solely of primary origin, OC can be either primary or secondary (Jones and Harrison, 2005; Saylor et al., 2006; Plaza et al., 2011). Primary organic carbon (POC) is formed during incomplete combustion of organic materials and emitted mainly as very fine particles (Jones and Harrison, 2005). Mechanical processes, such as abrasion of tire rubber, as well as biological sources, i.e., emission of plant spores and pollen, vegetation debris, give rise to POC related to coarse PM (PM2.5–10, ambient particles with aerodynamic diameters from 2.5 to 10 µm) (Castro et al., 1999). Secondary organic carbon (SOC) comes from condensation of semi-volatile organic vapours onto the particle surfaces and via atmospheric photo-oxidation reactions of precursor gases, such as terpene (Yang et al., 2011). The SOC content in the air is related to the emission of its precursors, whose amounts are expected to increase due to human activities (IPCC, 2007). The climatic conditions also have impact on the ambient SOC concentrations, as SOC production increases during periods with high photochemical activity (clear sky without clouds or fog present, high O3 levels) (Saylor et al., 2006; Rogula-Kozłowska and Klejnowski 2013).
Organic aerosols make an important part of the PM mass.
Blaszczak et al., Aerosol and Air Quality Research, 16: 2333–2348, 2016 2334
The EEA report (2013) shows that, on average, organic substances make ~30% of the PM2.5 concentration and ~20% of the PM10 concentration measured at regional background stations in Europe. The same report also reveals that the secondary inorganic aerosol (SIA) constitutes ~35% of the PM10 concentrations and ~50% of the PM2.5 concentrations. Sulphate (SO4
2–), nitrate (NO3–) and ammonium (NH4
+) are reported to be the major SIA components (Deshmukh et al., 2010; Błaszczak et al., 2016).
SIA is produced in the atmosphere through (photo-) chemical reactions of gaseous precursors (such as NOx, SO2, or NH3) that may react with O3 and other reactive molecules (including radicals) to form mainly ammonium nitrate (NH4NO3), ammonium sulphate ((NH4)2SO4), and ammonium bisulphate (NH4HSO4). The SIA formation strongly depends on the atmospheric conditions and availability of its precursor gases. First, ammonia neutralizes sulphuric acid to ammonium bisulphate (NH4)HSO4 and ammonium sulphate (NH4)2SO4. The remaining NH3 may also react with nitric acid to ammonium nitrate (NH4NO3) (Squizzato et al., 2012; Pay et al., 2012). Moreover, nitrate and sulphate can easily react with the sea salt and crustal aerosols in the atmosphere that is poor in ammonia. It results in the formation of calcium and sodium sulphate (respectively: CaSO4 and Na2SO4), as well as calcium and sodium nitrate (respectively: Ca(NO3)2 and NaNO3) in the coarse particles (Seinfeld and Pandis, 2006; Squizzato et al., 2012).
To assess the percentage of the secondary matter in PM, it is particularly important to have information on the concentrations of its components at the regional background stations (Minguillón et al., 2012; Squizzato et al., 2012). The air quality degradation caused by PM in polluted areas is often characterized by high ambient concentrations of the regional background aerosols. There is not much data on the PM2.5 concentrations and chemical composition available in Eastern Europe (EMEP, 2013). The data on the PM properties and chemical composition in Poland is even more incomplete (Rogula-Kozlowska et al., 2012, 2014).
Southern Poland, where both stations are located, is one of the most industrialized and polluted areas in Europe (EEA report, 2013; Rogula-Kozłowska et al., 2014). Therefore, in order to clarify the chemical characteristics of the regional background aerosols in this region of Poland, PM2.5 collected from Racibórz and Zloty Potok was analysed for its main compounds, i.e., carbonaceous matter (EC, OC) and water-soluble ionic species. The seasonal and spatial variations were also investigated. Furthermore, the secondary organic and inorganic aerosol (SOA and SIA) concentrations, were also discussed. METHODS Research Area
Fine PM was sampled at two regional background sites located in Southern Poland, i.e., Racibórz and Złoty Potok. Fig. 1 presents the geographical location of both sampling sites.
The station located in Złoty Potok constitutes the regional background point for the Silesia Province. Its
nearest surroundings consist of meadows and arable fields. There are also a few chalets and a forester’s houses heated with coal at a 150 m distance from the station.
In Racibórz, the research was conducted on the outskirts of the town. Its nearest surroundings are constituted by arable fields. The national road no. 45 is located ~100 m west of the station. The closest loose residential land development is located ~100 m west of the station.
Southern Poland belongs to the regions of Poland with the highest degree of urbanization and pollution of all the components of the environment. The unique position of coal as an energy source, especially in power generation sector, is the reason why large amounts of gaseous and particulate pollutants are emitted to the atmosphere. Moreover, an important threat to air quality are also numerous industrial plants (e.g., cocking plants, iron works, waste incineration plants), as well as public and individual transport (Rogula-Kozłowska, 2014; Rogula-Kozłowska et al., 2014). The region is also charged with low-level emission sources, in particular fossil fuel combustion in households and local boiler-room (Rogula-Kozłowska et al., 2014).
The above considerations explain the specificity of both considered stations. Even though selected regional background sites are far away from any large energy production and industrial sources, both measurement points could be affected by the municipal emission and the pollutant inflow from the surrounding urban and industrial areas (Pastuszka et al., 2010). Sampling and Chemical Analysis
24-h PM2.5 samples were collected during the field campaigns carried out under the framework of two research projects. The campaigns covered two distinct seasons: the heating and non-heating ones of 2011–2012 (Racibórz) and 2013 (Złoty Potok) (Table 1). The year division was caused by differences in the air temperatures and the resulting energy consumption. In Poland, the increased energy demand in the heating season (October–March) results in the increase in the PM emissions from the fossil fuel combustion and biomass burning (Rogula-Kozłowska et al., 2014). The meteorological conditions during the study were typical for study area and were presented in Table 1.
The 24-h PM2.5 samples were taken with low-volume PNS-15 samplers (Atmoservice) and were collected on quartz fibre filters. Before and after the exposure, the filters were conditioned in a weighing room (48 h; relative humidity: 45 ± 5%; air temperature: 20 ± 2°C). They were weighed on the Mettler Toledo microbalance (resolution: 2 µg). The mass concentration of PM2.5 was determined with the gravimetric method in accordance with the standard of PN-EN 14907: 2006.
A 1.5-cm2 piece was cut out from each filter and was analysed for the OC and EC contents. The remaining part of the filter was analysed for the contents of Cl–, NO3
–, SO4
2–, Na+, NH4+, K+, Ca2+, and Mg2+.
For analyses of the OC and EC contents in the 24-h PM2.5 samples, thermal-optical carbon analyzer was used (Sunset Laboratories Inc.; “eusaar 2” protocol). The ion contents in water extracts were determined with a Metrohm
Blaszczak et al., Aerosol and Air Quality Research, 16: 2333–2348, 2016 2335
Fig. 1. Location of the measurement sites.
ion chromatograph (Herisau Metrohm AG, Swiss). The details of measurement methods were specified elsewhere (e.g., Rogula-Kozłowska et al., 2014). RESULTS AND DISCUSSION PM2.5 Concentrations and Major Components
The results obtained in present study were compared with the data from selected regional background stations in Europe (Tables 2 and 3). The data on the PM concentrations and chemical composition in Europe are collected within the framework of the European Monitoring and Evaluation Programme (EMEP) (http://ebas.nilu.no). They are reported by the EU member countries to the European Commission and collected in the open-access database of the European Environment Agency (EEA), i.e., AirBase (http://www.eea.eu ropa.eu/data-and-maps/data/airbase-the-european-air-quality-database-7). The research on the chemical composition of PM2.5 at background stations in Europe is usually carried out in a random way (selected days of the month) or it concerns folded weekly samples. In fact, the German Melpitz station is the only institution where the investigations of the concentrations of anions, cations and carbon are conducted in the 24-h PM samples over the whole year (Tørseth et al.,
2012). The mean 24-h PM2.5 concentrations were higher and more
diverse in Racibórz (4.04–217.49 µg m–3) than in Złoty Potok (7.23–120.80 µg m–3). The mean PM2.5 concentration in the whole measurement period equaled 24.92 and 31.56 µg m–3, respectively in Złoty Potok and Racibórz. Therefore, at both stations located in southern Poland, the exposure reduction target (18 µg m–3), as well as exposure concentration obligation (20 µg m–3), had not been met (Directive 2008/50/EC, Annex XIV). Moreover, in the case of Racibórz, the limit value for yearly averaged PM2.5 concentrations (25 µg m–3) had been exceeded; mean PM2.5 concentration at Zloty Potok was very close to the limit value. Thus, the obtained results indicate a serious problem in terms of exposure of the residents to fine PM and signal the need to take actions aimed at improving the air quality of the considered areas.
When compared to the values observed at regional background stations in Europe, the PM2.5 concentrations in both considered stations were high. At the background stations in Europe, relatively high PM concentrations are normally observed in the regions exposed to the strong influence of the natural aerosol sources, e.g., desert dust (Rodríguez et al., 2002; Pederzoli et al., 2010; EMEP, 2013). Both considered locations were not affected by such
Blaszczak et al., Aerosol and Air Quality Research, 16: 2333–2348, 2016 2336
Table 1. PM2.5 sampling periods and selected meteorological parameters during the sampling campaigns.
Location Measuring period Season Samples (n) Meteorological parameters
T [°C] RH [%] P [hPa]
Złoty Potok 1 Jan–31 Mar 2013 Heating 87 –2.06a 84.59 976.99 20 Apr–31 Jul 2013 Non-heating 84 16.38 71.26 979.99
Racibórz
6 Jan–31 Mar 2011 Heating 31 –1.20b 83.12 986.40 20 Apr–31 Jul 2011 Non-heating 50 14.60 78.44 981.96 5 Jan–31 Mar 2012 Heating 41 –2.63 84.61 987.87 20 Apr–31 Jul 2012 Non-heating 52 15.29 75.91 981.00
T - air temperature; RH - relative humidity; P - atmospheric pressure. The meteorological data was taken from Regional Inspectorate of Environmental Protection (RIEP) in Katowice website concerning air quality monitoring in Silesian Province (http://monitoring.katowice.wios.gov.pl/). a at station in Zloty Potok. b at the station in Wodzisław Śląski (the nearest RIEP`s station to Racibórz).
sources. Taking into account the location of Racibórz and Złoty Potok in Southern Poland, the seasonal variations in the PM2.5 concentrations revealed that the concentrations were determined mainly by the variations in anthropogenic emission, especially municipal (low-level) emission (Rogula-Kozłowska et al., 2012, 2014). Moreover, the impact of meteorological conditions is crucial, especially in winter - when the low height of the missing layer and frequent temperature inversions prevent from pollutants propagation in the atmosphere (Juda-Rezler et al., 2011; Rogula-Kozłowska et al., 2014; Reizer and Juda-Rezler, 2016).
The mean concentrations of the main PM2.5 components in Złoty Potok and Racibórz were higher (similarly to the PM2.5 concentrations) than the values observed at other sites in Europe (Tables 2 and 3). This finding particularly concerned carbon compounds, which were the dominant PM2.5 component at both measurement stations in Southern Poland. What is more, it was also a dominant PM2.5
component in the Central and North-East Poland (Zielonka and Puszcza Borecka, respectively). The percentage of the three dominant ions (SO4
2–, NO3– and NH4
+, a group known as secondary ions (SI) (Galindo et al., 2013; Moroni et al., 2015) in the PM mass in Poland was either lower (see values for Waldhof, Neuglobsow, Cabauw-Zijdeweg, Risoe, or Auchencorth Moss) or comparable (see values for Üto, Iskrba, Ispra, or Montseny).
It seems that the PM air pollution pattern for background locations in Southern Poland is different in comparison to the locations in other parts of Europe. Its specificity results from the different chemical characteristics of PM2.5 in this region and concerns low SI percentage and high TC percentage in the fine PM mass. It corresponds with the conclusions included in the previous works of the authors, which showed that in cities of Southern Poland the main reasons for these differences are biomass burning and fossil fuel combustion in residential sector (Pastuszka et al., 2010; Juda-Rezler et al., 2011; Klejnowski et al., 2012; Rogula-Kozłowska et al., 2012, 2014). One of the reasons for the presence of very high PM2.5 concentrations and the differences in the PM2.5 chemical composition are also specific conditions that affect both measuring stations. Złoty Potok and Racibórz, differently from the regional background stations located in other parts of Europe (Table 2 and 3), throughout the
year, and mostly in the heating season, remain under the influence of air masses originating from the polluted regions of Upper Silesia and South-Eastern parts of Europe (Juda-Rezler et al., 2011; Rogula-Kozłowska et al., 2014; Błaszczak et al., 2015; Reizer and Juda-Rezler, 2016).
Carbonaceous Compounds. SOC and POC Contributions
The OC and EC measurements in Racibórz and Złoty Potok demonstrated that the TC composition at these two sites was fairly comparable (Table 4). However, the EC and OC concentrations were relatively higher and more diverse in Racibórz, where their 24-h values ranged from 0.14 to 14.93 µg m–3 (EC; mean value: 1.96 µg m–3) and from 1.38 to 102.48 µg m–3 (OC; mean value: 12.08 µg m–3). In Złoty Potok, the 24-h concentrations of EC and OC were 0.30–9.86 µg m–3 (mean value: 1.48 µg m–3) and 2.06–50.96 µg m–3 (mean value: 8.58 µg m–3), respectively.
The 24-h concentrations of carbonaceous compounds in Złoty Potok and Racibórz demonstrated a strong seasonal variability, with higher values in the heating season and more reduced levels in the non-heating season (Table 4). The differences can be attributed to the changes in the emission profile (domestic and public heating combustion devices were generally not in operation from April to September) and unfavourable meteorological conditions (low height of the mixing layer, frequent temperature inversions) that prevented the pollutant dispersion and removal (Yang et al., 2011; Rogula-Kozłowska et al., 2012). Importantly, the extremely high 24-h concentrations were observed in January and February and were associated with the periods when very high PM2.5 mass concentrations occurred. In such cold winter months the activity of local emission sources of PM increases, especially in the case of biomass burning and fossil fuel combustion in domestic furnaces and in small local heating plants.
Regardless of the season, the TC percentage in PM2.5 was comparable at both stations. The mean values were 39.59% for Złoty Potok and 41.52% for Racibórz (Table 4). The TC percentage values in PM2.5 were mainly determined by the variations in the OC share in the PM2.5 mass (mean values: between ~28% in the non-heating season in Złoty Potok and ~40% in the heating season in Racibórz). The OC percentage values in the PM2.5 mass were higher at
Blaszczak et al., Aerosol and Air Quality Research, 16: 2333–2348, 2016 2337
Tab
le 2
. Mea
n ye
arly
con
cent
rati
ons
of P
M2.
5 an
d it
s m
ain
com
pone
nts
at r
egio
nal b
ackg
roun
d st
atio
ns in
Eur
ope.
Sou
rce
Loc
atio
n S
tatio
n P
erio
d C
once
ntra
tion
s (m
ean
valu
es in
the
mea
suri
ng p
erio
d) [
µg
m–3
] P
M2.
5O
CE
CS
O42–
N
O3–
NH
4+ N
a+C
l– K
+
Mg2+
C
a2+
this
stu
dy
Zlo
ty P
otok
(PL
) R
B
2013
24
.92
8.58
1.
482.
301.
360.
690.
240.
12
0.06
0.
03
0.04
th
is s
tudy
R
acib
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(PL
) R
B
2011
,201
2 31
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12.0
8 1.
963.
643.
061.
660.
281.
35
0.12
0.
03
0.04
A
irba
sea
Pus
zcza
Bor
ecka
(P
L)
RB
; EM
EP
20
11
12.7
93.
42
0.58
2.11
1.43
0.78
0.30
0.14
0.
11
0.02
0.
08
Air
base
Z
ielo
nka
(PL
) R
B
2011
16
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4.25
0.
881.
781.
461.
080.
120.
14
0.10
0.
01
0.10
A
irba
se
Wal
dhof
(D
E)
RB
20
12
11.4
52.
41
0.30
1.98
2.70
1.38
0.17
0.17
0.
10
0.02
0.
03
EB
AS
Mel
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(D
E)
RB
; EM
EP
20
12
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97
0.49
0.67
0.59
1.20
0.09
0.10
0.
08
0.01
0.
09
Air
base
N
eugl
obso
w (
DE
) R
B; E
ME
P
2012
10
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2.52
0.
321.
952.
061.
240.
170.
13
0.09
0.
02
0.03
A
irba
se
Sch
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slan
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RB
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EP
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1.47
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910.
860.
600.
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02
0.04
0.
01
0.03
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34
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0.04
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BA
Sb
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(FI
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B; E
ME
P
2011
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-0.
330.
280.
240.
280.
05
0.23
0.
22
0.02
E
BA
S R
ucav
a (L
V)
RB
; EM
EP
20
09
16.7
4-
-0.
760.
41-
0.50
0.25
0.
10
0.03
0.
26
EB
AS
Har
wel
l (U
K)
RB
; EM
EP
20
12
12.8
4-
-0.
590.
491.
091.
240.
53
0.05
0.
14
0.57
A
irB
ase
Auc
henc
orth
Mos
s (U
K)
RB
; EM
EP
20
11
4.72
--
1.08
0.92
0.58
0.42
0.74
0.
05
0.04
0.
05
EB
AS
Iskr
ba (
SI)
R
B; E
ME
P
2010
11
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3.38
0.
380.
880.
080.
820.
040.
04
0.12
0.
02
0.07
E
BA
S Is
pra
(IT
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B; E
ME
P
2010
17
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5.88
1.
270.
750.
831.
390.
110.
55
0.33
0.
02
0.06
E
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(ES
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ME
P
2007
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1.74
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170.
880.
250.
750.
130.
08
0.10
0.
03
0.09
A
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a M
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; EM
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20
11
16.2
21.
68
0.22
3.25
0.14
0.89
0.12
0.06
0.
11
0.02
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Blaszczak et al., Aerosol and Air Quality Research, 16: 2333–2348, 2016 2338T
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Blaszczak et al., Aerosol and Air Quality Research, 16: 2333–2348, 2016 2339
Table 4. Mean ambient concentrations (± standard deviations) of EC, OC, TC, SOC and POC and mass contributions of EC, OC, TC, SOC and POC to PM2.5, OC in EC, EC in TC and SOC and POC in OC, at two regional background sites – Racibórz and Złoty Potok.
Compound Unit Racibórz Złoty Potok
Heating season Non-heating season Heating season Non-heating seasonEC/PM2.5 % 6.93 ± 2.40 5.27 ± 1.88 7.03 ± 2.67 4.92 ± 1.19 OC/PM2.5 % 39.72 ± 9.48 32.64 ± 8.54 38.76 ± 9.67 28.24 ± 5.60 TC/PM2.5 % 46.64 ± 11.42 37.91 ± 9.77 45.79 ± 12.06 33.15 ± 6.29 OC/EC - 6.01 ± 1.33 6.68 ± 1.98 5.81 ± 1.07 5.92 ± 1.23 SOC µg m–3 8.21 ± 10.07 1.52 ± 0.93 4.75 ± 3.55 1.67 ± 0.82 POC µg m–3 14.33 ± 11.38 3.18 ± 2.20 7.78 ± 4.84 2.82 ± 0.90
SOC/OC % 30.66 ± 13.99 35.57 ± 17.27 35.46 ± 12.99 36.68 ± 12.41 POC/OC % 69.34 ± 13.99 64.43 ± 17.27 64.54 ± 12.99 63.32 ± 12.41
SOC/PM2.5 % 12.08 ± 6.45 11.64 ± 7.13 13.36 ± 4.99 10.57 ± 4.76 POC/PM2.5 % 27.64 ± 9.56 21.00 ± 7.34 25.40 ± 9.66 17.66 ± 4.06
EC - elemental carbon; OC - organic carbon; TC - total carbon (TC = EC + OC); SOC - secondary organic carbon; POC - primary organic carbon.
both locations in the heating season than in the non-heating one. Nonetheless, a relatively high OC percentage in the PM2.5 mass was also observed in the non-heating season.
The finding is agreed with similar studies (Plaza et al., 2011; Pio et al., 2011; Zhang et al., 2014) and indicates that biological matter and secondary organic aerosol (SOA) could have been important OC sources in Racibórz and Złoty Potok. There was also a seasonal variation for the EC/PM2.5 ratio. However, it was less significant than the one discovered for OC/PM2.5.
The 24-h OC/EC ratios in PM2.5 revealed a broad range of values from 3.61 to 14.03 and from 3.06 to 9.25, respectively at Raciborz and Zloty Potok. They were relatively high, which showed clear prevalence of the organic carbonaceous species over EC. The finding also indicates the SOA formation (Plaza et al., 2011; Satsangi et al., 2012). At both stations, there were no clear seasonal changes in the OC/EC ratios (Table 4). However, the maximum OC/EC ratios were found in the non-heating season.
The OC/EC ratio can be used to gain some insight into the emission and transformation characteristics of the carbonaceous aerosol (Yang et al., 2011). The contributions of the primary and secondary organic carbon (POC and SOC, respectively) to OC have been difficult to quantify. The lack of a direct chemical analysis method to identify these components has led the researchers to employ several indirect methods (Strader et al., 1999). In this study, the SOC and POC levels were calculated according to the methodology proposed by Castro et al. (1999): POC = EC·(OC/EC)pri (1) SOC = OC – POC (2) where (OC/EC)pri is the ratio of primary OC to EC, assumed to be relatively constant for a specific location, season and local meteorology (Castro et al., 1999). To estimate (OC/EC)pri, the least-squares regression was performed for 10% of the samples with the lowest 24-h OC/EC ratio (Strader et al., 1999) (Fig. 2). The regression curve slope
represents the ratio of the primary OC to EC (OC/EC)pri. The 24-h SOC concentrations varied within broad limits
(Fig. 3). Their values were 0.00–52.45 µg m–3 and 0.00–17.06 µg m–3 for Racibórz and Złoty Potok, respectively. Over the whole measurement period, the mean SOC concentrations were 4.29 µg m–3 (Racibórz) and 3.24 µg m–3 (Złoty Potok), which accounted for 33.54% and 36.06% of the mean PM2.5-bound OC mass at both locations, respectively. The mean ambient concentration of SOC was slightly higher in Racibórz, because of the location of the station close to the urban area and this could contribute in higher concentrations of PM2.5 and its chemical constituents. The station in Złoty Potok lies at a distance of about 20 kilometers to the south-east of Częstochowa and about 25 kilometers to the north from Zawiercie. The direct surroundings of the station are the meadows and fields of crops. Therefore the concentrations of PM2.5 and its chemical components were quite lower.
The mean SOC percentage in the PM2.5 mass was comparable for both locations ~12%). No clear seasonal dependence was observed (Table 4). Moreover the SOC content in the PM2.5 mass from both measurement stations was nearly twice as low as the POC content (Table 4; Fig. 3). The mean POC percentage in PM2.5 was 27.62% and 21.00% (Racibórz) and 25.40% and 17.66% (Złoty Potok) in the heating and non-heating seasons, respectively. The higher POC percentage in the PM2.5 mass in the heating season suggests that biomass burning was an important OC source, because it often generates fairly substantial amounts of organic matter of primary origin (Pio et al., 2007; Plaza et al., 2011). Local heating systems, particularly in small towns and villages, are often based on the combustion of low quality coal, wood, dung and domestic waste, which leads to the increase of the amount of carbonaceous particles of primary origin (Braniš et al., 2007). On the other hand, abundant vegetation is present in rural areas. It releases significant amounts of primary organic matter, such as biological matter (e.g., fungal spores, vegetation detritus, and plant waxes), especially in the warm season (Yang et al., 2011).
Blaszczak et al., Aerosol and Air Quality Research, 16: 2333–2348, 2016 2340
(a)
(b)
Fig. 2. The ratio of the primary OC to EC (OC/EC)pri, calculated for Racibórz (a) and Złoty Potok (b).
Ionic Compounds. SI Contribution Taking into consideration the entire measurement period,
the mean ionic concentrations in PM2.5 were in the following order (Table 2): - SO4
2– > NO3– > NH4
+ > Na+ > Cl– > K+ > Ca2+ > Mg2+ (Złoty Potok); - SO4
2– > NO3– > NH4
+ > Cl– > Na+ > K+ > Ca2+ > Mg2+ (Racibórz).
The common mass share of above mentioned ions equalled 20.35% (Złoty Potok) and 33.56% (Racibórz) of PM2.5. Secondary ions (SI; SO4
2–, NO3– and NH4
+) dominated in the PM2.5 ionic composition from both measurement stations. Higher SI concentrations were observed at both stations in the heating season (Table 3), which was probably caused by the enhanced intensity of the local emission sources (emission of gaseous precursors of SI) and atmospheric conditions that were unfavourable to the spreading and
favourable to the formation of secondary inorganic compounds (Rogula Kozłowska et al., 2014; Błaszczak et al., 2016). The SI concentrations revealed also spatial variability, with higher levels recorded in Racibórz, because of the localization of the station on the outskirts of the town, where mean SI concentrations were 14.167 µg m–3 (26.76% of PM2.5) (heating season) and 4.270 µg m–3 (30.32% of PM2.5). In Złoty Potok, the mean SI concentrations were 5.845 µg m–3 (18.50% of the PM2.5 mass) in the heating season and 2.795 µg m–3 (17.09% of the PM2.5 mass) in the non-heating one.
The mean seasonal percentage of nss-SO42– (non-sea salt
sulphates), NO3– and NH4
+ in the SI sum and total PM2.5 mass is shown in Table 5. Interestingly, the SO4
2– concentration was almost identical with the nss-SO4
2– concentration (Fig. 4). As both stations were located inland, the sea salt influence on PM2.5 could be ignored (Deshmukh et al., 2010). The occurrence of Na+ and Cl– in fine PM at different locations in Southern Poland should be solely linked to the emission
Blaszczak et al., Aerosol and Air Quality Research, 16: 2333–2348, 2016 2341
(a)
(b)
Fig. 3. Time series of the POC and SOC contributions to PM2.5 in Racibórz (a) and Złoty Potok (b).
from the coal combustion and biomass burning (Rogula-Kozłowska and Klejnowski, 2013; Rogula-Kozłowska et al., 2012, 2013). The situation in Racibórz and Złoty Potok was probably the same as higher Na+ and Cl– concentrations were observed in the heating season along with high contents of carbonaceous compounds (particularly OC) in the PM2.5 mass.
At both stations, the SI percentage in the PM2.5 was visibly higher than the SOC share (Tables 4 and 5). The considered stations did not only differ in the total SI content in the PM2.5 but also in the share of each secondary ion in the SI and PM2.5 masses. The mean nss-SO4
2– percentage in SI was higher in Złoty Potok (48.59% and 64.60% in the heating and non-heating seasons, respectively). In Racibórz,
Blaszczak et al., Aerosol and Air Quality Research, 16: 2333–2348, 2016 2342
the mean seasonal nss-SO42– percentage in SI was 34.89%
(heating period) and 56.19% (non-heating period). The values for NO3
– in SI were higher (44.16% and 32.97%) in
Racibórz than in Złoty Potok (34.97% and 24.93%) (Table 5). The content of NH4
+ in SI was twice as low as the contents of SO4
2– and NO3– and was comparable at both stations.
Table 5. Mass contributions of each secondary ion (nss-SO42–, NH4
+, NO3–) to their sum (SI) and PM2.5, SI percentage in
PM2.5, selected molar ratios, and assessed (NH4)2SO4 and NH4NO3 concentrations in Racibórz and Złoty Potok.
Ratio Unit Racibórz Złoty Potok
Heating season Non-heating season Heating season Non-heating seasonnss-SO4
2–/SIa % 34.89 ± 9.85 56.19 ± 8.99 48.59 ± 8.07 64.60 ± 7.16 NO3
–/SI % 44.16 ± 12.21 32.97 ± 10.07 34.97 ± 7.77 24.93 ± 7.32 NH4
+/SI % 20.95 ± 8.32 10.84 ± 2.99 16.44 ± 4.84 10.46 ± 4.00 nss-SO4
2–/ PM2.5 % 9.26 ± 4.39 17.00 ± 5.23 9.02 ± 3.01 11.00 ± 2.59 NO3
–/PM2.5 % 11.90 ± 5.76 10.09 ± 4.42 6.43 ± 2.19 4.31 ± 1.73 NH4
+/PM2.5 % 5.59 ± 2.94 3.23 ± 1.13 3.05 ± 1.21 1.78 ± 0.70 SI//PM2.5 % 26.76 ± 9.27 30.32 ± 7.51 18.50 ± 5.11 17.09 ± 3.57
SO42–/NH4
+ - 0.88 ± 1.01 2.22 ± 1.20 1.26 ± 0.56 2.67 ± 1.13 ∑cations /∑anions - 0.73 ± 0.29 0.44 ± 0.08 0.60 ± 0.11 0.56 ± 0.15
(NH4)2SO4 µg m–3 8.83 ± 10.56 8.69 ± 4.38 3.31 ± 2.01 1.09 ± 0.61 NH4NO3 µg m–3 7.77 ± 6.57 0.60 ± 0.01 2.64 ± 3.78 0.07 ± 0.40
a nss-SO42– - non-sea salt sulphate; [nss-SO4
2–] = [SO42–] – 0.246·[Na+] (Sillanpää et al., 2006).
(a)
(b)
Fig. 4. SO42– vs. nss-SO4
2– in Racibórz (a) and Złoty Potok (b).
Blaszczak et al., Aerosol and Air Quality Research, 16: 2333–2348, 2016 2343
The SI percentage in the PM2.5 did not demonstrate significant seasonal differences (Table 5). However, contributions of individual inorganic ions to PM2.5 and SI revealed different seasonal variations, which agreed well with the literature data (Rogula-Kozłowska et al., 2014; Zhang et al., 2014). At both stations, the nss-SO4
2– percentage in the SI and PM2.5 masses was higher in the non-heating season, which was related to the increased intensity of the photochemical transformations (Mirante et al., 2014). In the heating season, the observed higher values for NO3
–/SI, NH4
+/SI, NO3–/PM2.5 and NH4
+/PM2.5 were due to low temperatures and stable meteorological conditions that were favourable to the reactions of the nitric acid transformations (mainly in the gaseous phase) into nitrates (Deshmukh et al., 2010; Mirante et al., 2014).
Generally, over the entire measurement period, the SO42–
contents in the air significantly exceeded the NH4+ contents
(Fig. 5). The mean nss-SO42–/NH4
+ values in Racibórz were 0.88 ± 1.01 (heating season) and 2.22 ± 1.20 (non-heating season). In Złoty Potok, the values were 1.26 ± 0.56 and 2.67 ± 1.13, respectively (Table 5). It may be said that (NH4)2SO4 was the main component of SIA at both locations in the non-heating season. The remaining SO4
2- ions in the PM2.5
samples could have come from soluble salts (such as CaSO4,
Na2SO4) or from H2SO4. The occurrence of H2SO4 and HNO3 in PM2.5 at both
locations (particularly in the non-heating season) was confirmed, to some extent, with analysing the ratios of the total cations Σcations [µeq m–3] (µeq m–3 - micromole of a given ion in 1 m3 of ambient air, e.g., 2 µeq m–3 of Na+ means 2 µmol of Na+ in 1 m3 of ambient air) to the total anions Σanions [µeq m–3] in PM2.5. Regardless of the measurement season, Σcations/Σanions seasonal values were less than 1 at both locations (Table 5). This means that anions extracted from PM2.5 could have come also from compounds with other elements than those determined in the cation forms in the water extracts. As the sum of the crustal and trace elements usually makes a small percentage of the PM2.5 mass (Sillanpää et al., 2006; Zhao et al., 2015), it seems probable that some part of SO4
2– and NO3– in PM2.5 could have formed compounds
with hydrogen (undetermined in the extracts) before the extraction. The highest daily values of Σcations/Σanions ratio was observed in Racibórz in the heating season of 2011 (Fig. 6). The high Σcations/Σanions value was accompanied by very high concentrations of NH4
+, K+ and Na+. This situation could have been caused by the occurrence/inflow of a specific alkaline aerosol. At that time, the correlation of Σcations vs. Σanions was linear. However, its character was different from
Fig. 5. Temporal trend of the daily values of the nss-SO4
2–/NH4+ concentration ratio in Racibórz and Złoty Potok.
Blaszczak et al., Aerosol and Air Quality Research, 16: 2333–2348, 2016 2344
the remaining measurement period (Fig. 7). In Złoty Potok, concentrations of all the ions increased in the similar way and proportionately to the PM2.5 concentrations in the heating season.
If it is assumed that all NH4+ ions form (NH4)2SO4 in the
periods when the SO42–/NH4
+ ratio is greater than 1, (NH4)2SO4 concentration in the air can be easily calculated with the stoichiometric calculations (Rogula-Kozłowska, 2016). It may also be assumed that the content of NH4
+ reacting with SO4
2– is sufficient to completely neutralize SO4
2– and the remaining NH4+ ions make NH4NO3 in the
periods when the SO42–/NH4
+ ratio is less than 1 whereas the Σcations/Σanions ratio is higher than the ratio in the remaining periods. Those assumptions helped to calculate the 24-h and mean concentrations of (NH4)2SO4 and NH4NO3 (Table 5; Fig. 8).
In the heating season, the mean concentrations of (NH4)2SO4 and NH4NO3 were similar at both locations (Racibórz: 8.83 and 7.77 µg m–3, respectively; Złoty Potok:
3.31 and 2.64 µg m–3, respectively) (Table 5). For both locations, the sum of the ambient (NH4)2SO4 and NH4NO3
concentrations slightly exceeded the SI concentration, which resulted from the highly simplified assumptions for the assessment of the ambient (NH4)2SO4 and NH4NO3 concentrations. In the non-heating season, only trace amounts of NH4NO3 were found in the sum of the two discussed secondary components of PM2.5. In the warm seasons, the sum of the (NH4)2SO4 and NH4NO3 concentrations did not cover even the half of the SI concentrations. CONCLUSIONS
Observed PM2.5 concentrations at both regional background sites in Southern Poland are much higher than values from other stations of this type in Europe. This is most strongly pronounced during the heating season when the PM2.5 concentration in Racibórz was above twice greater than in the most polluted European regional background stations
Fig. 6. Temporal trend of the daily values of Σcations/Σanions ratio and daily concentrations of NH4
+, K+ and Na+ [µg m–3] in Racibórz and Złoty Potok.
Blaszczak et al., Aerosol and Air Quality Research, 16: 2333–2348, 2016 2345
(a)
(b)
Fig. 7. Σcations [µeq m–3] vs. Σanions [µeq m–3] in Racibórz (a) and Złoty Potok (b).
located in Ispra (IT) and Melpitz (DE). These results show the necessity of separate treatment of heating and non-heating seasons during analyses of air pollution. Moreover, at both considered Polish stations, the air quality standards for PM2.5 had not been met, which may lead to adverse effects on human health.
The concentrations of PM2.5 and PM2.5-bound major components revealed clear seasonality, with the maxima in the heating season caused by the changes in the emission profile and unfavourable meteorological conditions. Regardless of the season, the PM2.5 chemical composition was generally dominated by the carbonaceous matter, especially organic carbon, which concentration was at least twice higher than values observed in other background stations in Europe. The assessment of the SOC and POC concentrations revealed a much higher contribution of POC to the PM2.5 mass at both stations. The mean SOC percentage in the PM2.5 mass was similar at both locations.
No clear seasonal dependence was observed. At both locations, the ionic content of PM2.5 was dominated
by SI (SO42–, NO3
– NH4+), which generally followed the
mass abundance pattern of SO42– > NO3
– > NH4+. The total
SI percentage in the PM2.5 was similar in heating and non-heating seasons. On the other hand, the contributions of individual inorganic ions to PM2.5 and SI revealed different seasonal variations.
The rough assessments of the seasonal and daily mean concentrations of (NH4)2SO4 and NH4NO3 indicated general correlations concerning both regional background stations in Poland. In the cold heating seasons, both NH4NO3 and (NH4)2SO4 were equal components of PM2.5. In the warm non-heating seasons, NH4NO3 could not be practically found in PM2.5. The specificity of both considered stations could have resulted from the higher SO2 level in the air than at other background locations in Europe, which was observed in summer. Even though the level was even higher
Blaszczak et al., Aerosol and Air Quality Research, 16: 2333–2348, 2016 2346
Fig. 8. Temporal trend of daily concentrations [µg m–3] of (NH4)2SO4 and NH4NO3 in Racibórz and Złoty Potoka).
in the heating season, the emission of ammonia, which neutralizes sulphuric acid in the air, was also higher.
The PM2.5 found at regional background sites in this area was different from the PM2.5 found at similar sites in various parts of Europe. The obtained results suggest that the main reasons for these differences were: utilization structure of fossil fuels in Poland and the periodically occurring combination of meteorological conditions particularly unfavourable to the pollutant spread. Even though the results of the present study should not be generalized, the findings show that higher aerosol pollution may not necessarily be restricted to larger cities. It is also common in small villages. Due to the rising prices of oil, electricity and natural gas, people have returned to more traditional and cheaper fuels as low-quality coal, dust coal or waste wood. Consequently, traditional heating in villages may strongly contribute to the local air pollution to a great extent and may pose serious health problems.
ACKNOWLEDGMENTS
The study was prepared as a part of the research project no. 2011/03/N/ST10/05542 financed by the National Science Centre. The Racibórz results come from the project no.
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Received for review, September 10, 2015 Revised, January 11, 2016 Accepted, March 5, 2016