Source signatures of carbon monoxide and organic functional groups

in Asian Pacific Regional Aerosol Characterization Experiment

(ACE-Asia) submicron aerosol types

S. F. Maria,1 L. M. Russell,2 B. J. Turpin,3 R. J. Porcja,3 T. L. Campos,4 R. J. Weber,5

and B. J. Huebert6

Received 21 April 2003; revised 30 July 2003; accepted 27 August 2003; published 21 November 2003.

[1] Atmospheric submicron particles were collected on Teflon filters downstream of athree-stage concentrator aboard the National Center for Atmospheric Research C-130aircraft near Japan during the Asian Pacific Regional Aerosol Characterization Experiment(ACE-Asia). Particle-phase organic carbon (OC) was quantified using Fourier transforminfrared (FTIR) transmission spectroscopy. Silicate, carbonate, alkane, alkene, aromatic,alcohol, carbonyl, amine, and organosulfate functional groups were identified andseparated with a four-solvent rinsing procedure. X-ray fluorescence identified elementalcomposition. Total OC constructed from FTIR measurements agreed with simultaneousthermal-optical OC measurements with a slope of 0.91 and an R2 value of 0.93. OC variedfrom 0.4 to 14.2 mg m!3, and organic mass varied from 0.6 to 19.6 mg m!3, representingon average 36% of the identified submicron aerosol mass. Measured carbon monoxide(CO) to OC slopes illustrate 10 groups of air from regions described by an Asianemissions inventory. The CO/OC slope is used to compare sources and their influence onorganic composition. Fifty-two percent of ACE-Asia samples have CO/OC slopesindicative of biomass combustion. Unitless CO/OC slopes above 15 are associated withincreased fractions of alcohol groups, unsaturated C-H groups, and inorganic nitrate.Increased carbonyl carbon fractions in air originating over northern Asia are consistentwith secondary OC formation. Case studies in the boundary layer demonstrate that aerosolcompositions downwind of large Asian aerosol sources show clear regional compositionsignatures. INDEX TERMS: 0305 Atmospheric Composition and Structure: Aerosols and particles (0345,4801); 0322 Atmospheric Composition and Structure: Constituent sources and sinks; 0345 AtmosphericComposition and Structure: Pollution—urban and regional (0305); 0394 Atmospheric Composition andStructure: Instruments and techniques; KEYWORDS: organic aerosols, organic carbon, carbon monoxide

Citation: Maria, S. F., L. M. Russell, B. J. Turpin, R. J. Porcja, T. L. Campos, R. J. Weber, and B. J. Huebert, Source signatures ofcarbon monoxide and organic functional groups in Asian Pacific Regional Aerosol Characterization Experiment (ACE-Asia)submicron aerosol types, J. Geophys. Res., 108(D23), 8637, doi:10.1029/2003JD003703, 2003.

1. Introduction

[2] Asia is one of the largest aerosol source regions onEarth, and plumes of Asian aerosol have been observedcrossing the Pacific to reach the West Coast of the UnitedStates [Husar et al., 2001; Jaffe et al., 1999]. The aerosol

downwind of the Asian continent is a complex mixture ofanthropogenic and natural sources that has been measuredin several campaigns but that is still poorly understood[Kinne and Pueschel, 2001; Parungo et al., 1994]. Organiccompounds in particles may enhance or inhibit the ability ofan aerosol particle to absorb water and form a cloud droplet[Jacobson et al., 2000; Saxena et al., 1995], and in thisrespect can affect the probability that the Asian plume willbe removed by wet deposition before it reaches the WestCoast of the United States.[3] Understanding the behavior and atmospheric effects

of the Asian plume requires knowledge of the amount oforganic mass present in the aerosol and the solubilityproperties of the aerosol components. However, completecharacterization of the organic aerosol fraction is extremelydifficult because the organic fraction covers a wide range ofchemical and thermodynamic properties. For this reason,organic speciation studies often identify only 10–20% ofthe organic compounds present, while thermal methods

JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 108, NO. D23, 8637, doi:10.1029/2003JD003703, 2003

1Department of Chemical Engineering, Princeton University, Princeton,New Jersey, USA.

2Scripps Institution of Oceanography, University of California at SanDiego, La Jolla, California, USA.

3Department of Environmental Science, Rutgers University, NewBrunswick, New Jersey, USA.

4National Center for Atmospheric Research, Boulder, Colorado, USA.5School of Earth and Atmospheric Sciences, Georgia Institute of

Technology, Atlanta, Georgia, USA.6Department of Oceanography, University of Hawaii, Honolulu,

Hawaii, USA.

Copyright 2003 by the American Geophysical Union.0148-0227/03/2003JD003703$09.00

ACE 5 - 1

that can identify all of the carbon present give no informa-tion about its chemical and physical properties [Turpin etal., 2000]. Organic compounds are usually the secondmost abundant component of fine aerosols after sulfates[Heintzenberg, 1989], and are therefore a large componentof the atmospheric aerosol that has not been completelycharacterized. Our understanding of Asian aerosols inparticular, and atmospheric aerosols in general, is currentlylimited by the lack of information about the compositionand hygroscopicity of this fraction.[4] Several studies have used thermal-optical measure-

ments of the organic carbon (OC) to elemental carbon (EC)slope as an indicator of aerosol source types and as ameans offinding evidence of secondary organic aerosol formation[Kadowaki, 1990; Kim et al., 2000; Lim and Turpin, 2002].These analyses utilize the notion that particulate EC isproduced only in combustion processes as a primary pollut-ant while particulate OC is both emitted from sources andproduced by atmospheric reactions from gaseous precursors.However, differences between OC-EC analysis methods canlead to factor of two differences in reported EC [Lim et al.,2003]. CO, like EC, is generated predominantly by primarycombustion sources [de Laat et al., 2001]. In fact, EC and COare often found to co-vary [Chen et al., 2002; Lim and Turpin,2002]. The CO/OC slope, like the EC/OC slope, is thereforean indicator of organic aerosol source types and secondaryorganic aerosol formation. Sulfate, ammonium, and nitrateare associated with many of these same combustion sources,so that the CO/OC slope is also a source indicator forinorganic species. Dust from sources that are likely to bespatially and temporally uncorrelated with CO sources is notexpected to show a trend with the CO/OC slope.[5] This work presents quantitative measurements of

submicron aerosol organic and inorganic composition. OCand organic mass (OM) concentrations are calculated fromFourier transform infrared (FTIR) functional group mea-surements, and the FTIR-derived OC is compared to OCmeasured with a thermal-optical method. An air massclassification scheme based on back trajectories is used toseparate the Asian Pacific Regional Aerosol Characteriza-tion Experiment (ACE-Asia) data into groups with similarCO/OC ratios and organic functional group composition.The CO/OC slope is used along with the OM/OC ratio,functional group information, and an emissions inventory toexamine the atmospheric processes influencing the submi-cron particulate matter in the ACE-Asia region.

2. Experimental and Analysis Procedure2.1. Particle Concentration and Collection

[6] During ACE-Asia in April and May of 2001, submi-cron aerosol samples were collected near Japan fromthe NCAR C-130 aircraft. Sample air was brought intothe C-130 at 180 l min!1 through a solid diffuser inletfollowed by a 1.06 mm cutoff impactor and three virtualimpactors in series. The virtual impactors concentrated theaerosol into a 2 l min!1 submicron sample stream prior tocollection on two Teflon filters in series (64 cm s!1 facevelocity). Except for the differences noted here, thesampling method is identical to that of Maria et al. [2002].[7] Mass flow controllers on all flow streams (Teledyne-

Hastings HFC-202 and HFC-203) were electronically ad-

justed in real time to provide constant volumetric flowrates as the inlet temperature and pressure changed, anda relative humidity probe (Vaisala Humitter-50U) immedi-ately upstream of the impactor monitored the relativehumidity of the sample stream. In the filter holders, oneTeflon gasket was used upstream of the sample filter duringresearch flights 1–6. For research flights 7–19, two gasketswere used, one immediately upstream of the sample filterand the other immediately downstream of the backup filterthat was used as a blank. Sampling with a single gasketupstream of the sample filter resulted in an aerosol depositthat was nearly uniform across the entire 31 mm diameterfilter. The use of two gaskets confined the sample deposit tothe filter’s center 10 mm diameter circular area, andincreased the amount of sample within the FTIR analysisarea by a factor of 2.75. This difference was corrected inthe reported concentrations, all of which are at standardtemperature and pressure (298!K and 1 atm).[8] The mass-average concentration factor, defined as the

submicron mass concentration in the filter flow divided bythat in the ambient air, varied from 10 to 16 during ACE-Asia. A concentration factor was calculated for each filtersample using a laboratory-measured size-dependent concen-tration curve [Maria et al., 2002] and ambient size distri-butions measured using an optical particle counter (OPC)(S. Howell et al., manuscript in preparation, 2003). Uncer-tainties in the solid diffuser inlet efficiency and OPC sizedistributions add "7% to the error of all calculated mass-average concentration factors.[9] During ACE-Asia, 172 filter samples and 172 down-

stream blanks (backup Teflon filters) were collected duringresearch flights in the marine boundary layer and in freetropospheric air masses of Asian origin. Of the 172 samples,69 were collected in high-altitude free tropospheric air, 75were collected within the marine boundary layer, and 28were collected during vertical profiles. The one-gasketsampling method was used for the first 42 samples, andthe two-gasket method for all others. Sample collectiontimes ranged in length from 9 to 100 min, and allowed forthe characterization of Asian aerosol downwind of urban,desert, and volcanic sources. Throughout the project, nodetectable peaks were observed on downstream blankfilters, consistent with previous studies that found loworganic artifacts on Teflon filters [Turpin et al., 1994].Downstream blanks were placed behind the sample filtersto determine the detection limits for each quantified func-tional group.[10] After sampling, filters were placed in polystyrene

petri dishes (Pall Corporation) sealed with Teflon tape andstored in a freezer until analysis. Powder-free vinyl glovesand Teflon-coated tweezers were used when handling filters.

2.2. Solvent-Rinsed FTIR Spectroscopy

[11] Field samples were analyzed for functional groupcomposition and solubility behavior at the Environmentaland Occupational Health Sciences Institute at RutgersUniversity using the method described by Maria et al.[2002]. The identified functional groups, along with theircorresponding absorption frequencies and detection limits,are shown in Table 1. Functional group identification wasexpanded from previous work to include alkene and aro-matic C-H groups as well as alcohol, amine, organosulfur,

ACE 5 - 2 MARIA ET AL.: SOURCE SIGNATURES IN ACE-ASIA SUBMICRON AEROSOL

nitrate and carbonate groups, as illustrated in Figure 1. Allof these groups were positively identified in ACE-Asiasample spectra using absorption frequencies determinedfrom previously published aerosol FTIR spectra [Allen etal., 1994; Blando et al., 1998], laboratory-generated stan-dards, and spectral libraries. Particles-into-liquid-sampler(PILS) ion chromatography measurements [Weber et al.,2001] are reported in this paper for characterization ofsulfate, ammonium, and nitrate.

[12] Absorbance peaks were identified both by locationand by solubility behavior as shown in Table 1. For example,the 1437 cm!1 peak was separated into ammoniumand carbonate absorbances on the basis of rinsing fraction(Table 1), resulting in an improved linear correlation be-tween the integrated areas of the 1437 and 3238 cm!1

ammonium peaks (R2 = 0.8 using only the hexane,dichloromethane, acetone, and water fractions of the1437 cm!1 peak; R2 = 0.6 using the entire 1437 cm!1

Table 1. Peaks Used in FTIR Quantification of Aerosol Functional Groups

Functional Group Absorption Frequencies, cm!1QuantifiedPeaks, cm!1

Absorptivityabs!1a

Detection Limit,mg cm!2 Rinsing Stage,b

SO42! sulfate ions 612-5, 1103–35 618 0.41 0.37 h, d, a, w

HSO4! bisulfate ions 580–90, 867, 1029, 1180 618 0.41 0.37 h, d, a, w

SiO44! silicate ions 772–812, 1035 1035 0.011 0.03 h, d, a, w, r

NH4+ ammonium ions 1410–35, 3030–52, 3170–3200 1437 0.14 0.056 d, a, w

CO32! carbonate ions 860–80, 1410–90 1437 0.11 0.08 r

NO3! nitrate ions 815–40, 1350–80 1345 0.019 0.35 h, d, a

H2O liquid water 1623, 3350–3450 not used w, rC-H aliphatic carbon 1452–5, 2800–3000 2850–2920 1.06c 0.57 h, d, a, w, rC = C-H alkene carbon 2900–3100 2980–3005 0.30c 0.64 h, d, a, rC = C-H aromatic carbon 3000–3100 3065 0.17c 0.47 h, d, a, rC = O carbonyl carbon 1640–1850 1720 0.061c 0.11 h, d, a, w, rC-OH alcohols 3100–3500 3297 0.063c 0.08 h, d, aC-O-S organosulfates 876 0.031c 0.02 h, d, aC-NH2 amines 1630 1621 0.19c 0.26 h, d, a

aHere, abs (absorptivity) is the peak area (in absorbance units) per micromole of functional group. The calibration of absorptivity is instrument-specific.bHere, h, hexane; d, dichloromethane; a, acetone; w, water; and r, residual.cAll organic absorptivities were determined from n-nonadecane, 1-docosanol, camphor, anthracene, perinaphthenone, citric acid, adipic acid, oxalic acid,

EDTA, alanine, and methane sulfonic acid standards.

Figure 1. (a) FTIR spectra of a typical ACE-Asia sample, collected south of Korea at 150 m from 02:06to 02:34 on 27 April 2001 (research flight 15). The original sample is shown (bold solid line) with spectraafter rinsing with hexane (thick dotted line), DCM (thin solid line), acetone (thin dashed line), and water(thin dot-dashed line). The 1150–1300 cm!1 Teflon and 2300–2380 cm!1 CO2 interference regionshave been removed from the raw data (gray areas). In Figure 1a, vertical lines indicate the functionalgroup absorbance regions of (from right to left) sulfate (618 cm!1), organosulfur (876 cm!1), silicate(1035 cm!1), nitrate (1345 cm!1), ammonium (1437 cm!1), amine (1621 cm!1), carbonyl (1720 cm!1),alkane (2850–2920 cm!1), alkene (2980 cm!1), aromatic (3065 cm!1), and alcohol (3297 cm!1).Carbonate is the residual peak at 1437 cm!1. All functional groups except for organosulfur were abovedetection limit in this sample. Enlargements show details of (b) the 2600–3400 cm!1 region, (c) the1500–1850 cm!1 region, and (d) the 1300–1500 cm!1 region.

MARIA ET AL.: SOURCE SIGNATURES IN ACE-ASIA SUBMICRON AEROSOL ACE 5 - 3

sample peak). Similarly, organosulfur was identified usingthe fractions of the 876 cm!1 peak that were removed inorganic solvents, distinguishing it from bisulfate which isremoved in water [Blando et al., 1998]. Alcohol, alkane,and aromatic groups removed in water could not be identifiedbecause of the large interference from ammonium, which isremoved in the water rinse.[13] An absorbance peak at 1620 cm!1 was observed in

39% of the ACE-Asia samples. Absorbances at 1620 cm!1

can be caused by organonitrate, aromatic, amide, and amineorganic functional groups, as well as by aerosol water[Nakanishi and Solomon, 1977]. The lack of correspondingpeaks at 1280 cm!1 (organonitrate), 1500 cm!1 (aromatic),and 1650–1690 cm!1 (amide) eliminates all possibleorganic functionalities except for amine. Aerosol water isremoved with water-soluble aerosol components in thewater rinse or is left behind in the residual fraction, so allsolvent-removed fractions of the 1620 cm!1 absorbance arequantified as organic amines.[14] The absorbance calibrations of anthracene, docosa-

nol, methane sulfonic acid, ammonium nitrate, calciumcarbonate, ethylenediaminetetraacetic acid, alanine, andsodium silicate varied linearly with the number of molesof bonds and mass loading as shown in Figure 2. Thesestandards, in addition to the calibration of Maria et al.[2002], provide a basis for quantifying the mole and massquantities detected by FTIR in ambient aerosol samples. Foreach standard a linear fit above the detection limit had acorrelation above R2 = 0.88, and the slope of each fit is

reported as the functional group absorbance per micromoleof bonds in Table 1. Detection limits for each species wereset to a visually-determined minimum identifiable peak size,taking into consideration signal noise from downstreamblanks.

2.3. X-Ray Fluorescence (XRF) Analysis

[15] After FTIR analysis, XRF was performed on thesame filters to quantify all elements heavier than sodium,including iron, silicon, sulfur, calcium, chlorine, and vana-dium (Chester LabNet, Tigard, Oregon). XRF detectionlimits for most elements are on the order of 1–10 ngcm!2, a notable exception being Na (which has a detectionlimit of 150 ng cm!2, too high to be quantified in thesesamples). XRF detection limits reflect the signal-to-noiseratio for each element, and reported errors include thedetection limit plus a 5% calibration uncertainty as wellas spectral overlap uncertainties when a secondary line fromone element overlaps the primary line from another element.XRF errors do not reflect uncertainties in field blanks,which were less than 4% of the corresponding samplevalues.

2.4. CO Measurement

[16] The NCAR CO instrument operates on the principleof vacuum UV resonance fluorescence (Aero-Laser 5002),as published by Gerbig et al. [1999]. It has a detection limitof 3 ppbv with an accuracy of 5 ppbv + 2% for a 1-secondsampling rate.

2.5. Organic Mass Estimates

[17] OC and OM were estimated according to the follow-ing formulas:

OC # 0:5$ moles alkane C-H% & $ 12 g mole!1! "# $

' moles alkene C-H% & $ 12 g mole!1! "# $

' moles aromatic C-H% & $ 12 g mole!1! "# $

' moles C # O% & $ 12 g mole!1! "# $

' moles C-OH% & $ 12 g mole!1! "# $

' moles C-NH2% & $ 12 g mole!1! "# $

' moles C-O-S% & $ 12 g mole!1! "# $

(1)

OM # 0:5$ moles alkane C-H% & $ 14 g mole!1! "# $

' moles alkene C-H% & $ 13 g mole!1! "# $

' moles aromatic C-H% & $ 13 g mole!1! "# $

' moles C # O% & $ 28 g mole!1! "# $

' moles C-OH% & $ 29 g mole!1! "# $

' moles C-NH2% & $ 28 g mole!1! "# $

' moles C-O-S% & $ 54 g mole!1! "# $

(2)

[18] As defined, OC includes carbon mass only and OMincludes carbon, hydrogen, oxygen, nitrogen, and sulfur.This definition is equivalent to a carbon mass to organiccompound mass conversion factor of 1.1 for alkene andaromatic groups, 1.2 for alkane groups, 2.3 for carbonyland amine groups, 2.4 for alcohol groups, and 4.5 fororganosulfur groups. These conversion factors more thanspan the range given by Turpin and Lim [2001], whosuggested that 1.6 ± 0.2 is a reasonable factor for an urbanaerosol and 2.1 ± 0.2 is more appropriate for an aged (non-urban) aerosol. Different combinations of FTIR-identified

Figure 2. FTIR response for laboratory-generated aerosolof species in varying sample amounts. Circles are CO3

!

(1437 cm!1) from calcium carbonate aerosol, squares areNO3

2! (1345 cm!1) from ammonium nitrate aerosol,upward pointing triangles are C-H (aromatic: 3065 cm!1)from anthracene aerosol, diamonds are C-H (alkene:2980 cm!1) from 1-decene aerosol, downward pointingtriangles are C-OH (3297 cm!1) from 1-docosanol aerosol,sideways hourglasses are C-N (amine: 1621 cm!1) fromEDTA aerosol, vertical hourglasses are C-S (876 cm!1)from methane sulfonic acid aerosol, plus signs are SiO4

4!

(1035 cm!1) from sodium silicate aerosol, and crosses areC-N (amine: 1621 cm!1) from alanine aerosol. Linesindicate best fit linear correlations to the data.

ACE 5 - 4 MARIA ET AL.: SOURCE SIGNATURES IN ACE-ASIA SUBMICRON AEROSOL

functional groups produce OM/OC ratios that are reason-able both for urban and non-urban conditions. FTIR char-acterization of OM is the first technique to utilize nearly100% of the atmospheric OC in its calculation. Othermethods have depended on extrapolation from chromatog-raphy measurements that typically identify less than 20% ofthe total OC [Schauer et al., 1999; Turpin and Lim, 2001;White and Roberts, 1977]. The estimated errors in ourreported OM/OC ratios are on average 24% [Russell, 2003].[19] Equations (1) and (2) are similar to equations pro-

posed by Maria et al. [2002], expanding those expressionsto include groups other than alkane and carbonyl. Toillustrate the importance of this extension, consider anorganic aerosol composed of 50% nonadecane, 25% anthra-cene, and 25% oxalic acid by mass. For this example,assuming that enough sample is collected such that allfunctional groups are above detection limits, the currentequations would overestimate OC by 3% and OM by 2%while the equations of Maria et al. [2002] would underes-timate OC by 29% and OM by 32%.

3. Results and Discussion3.1. OC Comparison

[20] Measurements of OC, EC and carbonate carbon(CC) were performed on ACE-Asia C-130 samples (T.Bertram et al., manuscript in preparation, 2003) using aSunset Labs Model 3 TOT carbon analyzer [Schauer et al.,2003]. The ACE-Asia TOT sampling system on the C-130was a PC-BOSS [Lewtas et al., 2001] that incorporated adenuder upstream of a quartz filter to minimize positivesampling artifacts and a carbon-impregnated glass fiberfilter downstream to correct for negative artifacts. In theanalysis OC is operationally defined as carbon that vola-tilizes upon heating to 870!C in the absence of oxygen,plus any OC that charred and then oxidized after oxygenaddition.[21] The correlation between TOT OC and FTIR OC

is strong, with a coefficient of determination (R2) of0.93 (Figure 3a) for simultaneous samples shorter than20 minutes in length. Samples were considered simulta-

neous if differences in sampling start and stop times for thetwo collection systems did not exceed 10% of the totalsample time. The slope of the correlation (0.91) and the zerointercept imply that both the FTIR and TOT methodsmeasured very similar groups of species as OC. A pairedt-test shows no significant difference between the two datasets (p = 0.78). The TOT OC/EC distinction is accurate formany organic compounds, with average measurements ofless than 3% EC for sucrose and 1% EC for EDTA [Birch,1998]. In the more complex ACE-Asia samples, the OC/ECsplit determined by TOT has larger uncertainties. The lessthan 10% difference between the TOT and FTIR measure-ments might be caused by a combination of uncorrectedpositive artifacts in the TOT collection system (due topossible denuder inefficiency), deviations from assumptionsinherent to the correction for pyrolysis of OC to EC[Subramanian et al., 2002], and uncorrected negative arti-facts in the FTIR collection system. Such artifacts wouldincrease in magnitude with increased sampling time andincreased ambient temperature variations.

3.2. CO-OC Relationship

[22] CO is produced in Asia through incomplete com-bustion processes, and is often associated with the emissionof particulate EC. General circulation models have pre-dicted a relatively long atmospheric lifetime of CO (10–360 days [Holloway et al., 2000] as compared to an OClifetime of 3.4 days [Cooke et al., 2002]), resulting in a CO/OC ratio that increases with distance from the emissionsource. Formation of secondary organic aerosol decreasesthe CO/OC ratio. The CO/OC ratio varies widely betweensources, and despite atmospheric processing is suitable forthe identification of dominant source types. On the C-130during ACE-Asia, the CO/OC ratio was more accuratelymeasured than the OC/EC ratio.[23] CO concentration as a function of OC concentration

is shown in Figure 4 for all ACE-Asia samples. Byaveraging the smallest 5% of CO measurements, a back-ground CO concentration of "100 ppbv can be inferredfrom the ACE-Asia data both above and within the bound-ary layer. This value is comparable to the average CO

Figure 3. FTIR OC concentrations compared to TOT OC measurements, with the 1:1 line shown as adotted line. Solid circles indicate samples that were collected simultaneously. Open circles represent allother samples collected. The best fit lines (solid) are shown for (a) samples less than 20 minutes in length(slope = 0.91, R2 = 0.93) and (b) all simultaneous samples (slope = 0.90, R2 = 0.82).

MARIA ET AL.: SOURCE SIGNATURES IN ACE-ASIA SUBMICRON AEROSOL ACE 5 - 5

concentration of 92 ppbv for aged marine air downwind ofAsia during the spring of 1994 [Talbot et al., 1997]. Theunitless CO/OC slope for ACE-Asia samples is calculatedusing the following formula:

x # CO! 49( )=OC (3)

where x is the CO/OC slope, CO and OC are in mgC m!3,and the 49 mgC m!3 offset represents the background COconcentration. In Figures 4a and 4b, location-specific andsource-specific CO/OC slopes were calculated from directmeasurements of OC and CO.[24] The CO/OC slope is as high as 110 for some ACE-

Asia samples but falls near 6.4 for the majority of the ACE-Asia project. The average measured ACE-Asia CO/OCslope is significantly lower than slopes measured in Japanand the United States, and 56% of ACE-Asia samples haveCO/OC slopes lower than that of the average Asian primaryCO and OC emissions [Streets et al., 2003] (Figure 4a). The

large number of samples with low slopes suggests thatemissions from the transportation sector are not as largeas emissions from biomass burning and coal combustion inthe ACE-Asia region (Figure 4b). A large portion of thetotal coal and biomass combustion in China is residential,and Klimont et al. [2002] estimate that emissions factorsfrom residential combustors are more than 10 times largerthan those from industrial combustors. Asian coal andbiomass combustion may therefore significantly affect theCO/OC ratio in some regions. Figure 4b shows that 52% ofACE-Asia samples have CO/OC slopes within 25% of thevalue for wood and biomass burning sources and 43% haveslopes within 25% of the values for automobiles and dieseltrucks. The remaining 5% of samples have CO/OC slopesthat are between biomass burning and coal sources. Thesepercentages were calculated using only samples with COconcentrations larger than 75 mgC m!3 or OC concentra-tions larger than 1.0 mg m!3, because of uncertainty in theCO/OC slope for samples with lower concentrations.

3.3. Back Trajectory Classification

[25] Source regions were assigned to each aerosol sampleusing isentropic 5-day back trajectories from the HYSPLIT4model [Draxier and Hess, 1998], with the resulting quali-tative groups shown in Figure 5 numbered in order ofincreasing measured CO/OC slopes. An average trajectorywas calculated for each back trajectory group, and the totalemissions [Streets et al., 2003] from the area within 113 km(1 degree) of the average 5-day back trajectory weresummed to calculate a primary CO/OC slope. CO/OCslopes were comparable within 7 out of the 10 backtrajectory groups (R2 = 0.52–0.93) and agreed well withthe primary emissions inventory for 6 out of the 10 backtrajectory groups (see Figure 5).[26] Group 10, unlike the other back trajectory groups,

contains samples collected directly within the plume of amajor city (Qingdao, in the Shandong Province). A sum-mation of the emissions from the area within 113 km ofthe first 6 hours of the back trajectory (instead of the entire5-day back trajectory) agrees well with the measurementsfor group 10, demonstrating the importance of the localsource in this case. The large CO/OC slope (84) for thisgroup reveals that the Qingdao emissions are dominated bylarge sources of CO that do not produce appreciableamounts of OC. Automobiles, which are associated withcities such as Qingdao, are an example of such sources.High-OC sources such as biomass, coal, and natural gascombustion are not significant contributors to the Qingdaoemissions. The inventory of Streets et al. [2003] shows thatthe transportation sector is the largest contributor to COemissions in the Shandong Province.[27] CO/OC slopes 50–55% smaller than predicted by

the emissions inventory were observed in air masses thatoriginated over northern Asia (groups 1–3). For thesegroups, measured CO/OC slopes were "7.4, consistent withbiomass burning sources. CO/OC slopes calculated from theemissions inventory were 14–16. This discrepancy suggestssecondary OC formation in these air masses, becausesecondary formation lowers the CO/OC slope of an aerosolafter emission. Alternatively, the emissions inventory maybe underestimating the amount of biomass burning in theNorth Asian source regions for groups 1–3. Uncertainties in

Figure 4. Carbon monoxide concentrations versus FTIROC concentrations, with ACE-Asia measurements shown asopen circles. In Figure 4a, lines correspond to CO/OC slopesfrom measurements at (1) Atlanta, Georgia [Lim and Turpin,2002], (2) Fort Meade, Maryland [Chen et al., 2002],(3) Nagoya, Japan [Kadowaki, 1990], and (4) Asia [Streets etal., 2003]. In Figure 4b, lines correspond to CO/OC slopesfrom the following emission sources: (1) automobiles [U.S.Environmental Protection Agency (USEPA), 2003; Schaueret al., 2002] (the former is available at http://www.epa.gov/ttn/chief/ap42/index.html), (2) diesel trucks [Lloyd andCackette, 2001], (3) wood burning [USEPA, 2003; Cabadaet al., 2002], (4) biomass burning [Andreae and Merlet,2001], (5) cigarette smoking [Martin et al., 1997; Cabada etal., 2002], (6) natural gas [USEPA, 2003; Cabada et al.,2002], and (7) coal [USEPA, 2003; Cabada et al., 2002].

ACE 5 - 6 MARIA ET AL.: SOURCE SIGNATURES IN ACE-ASIA SUBMICRON AEROSOL

the modeled paths of the back trajectories may also con-tribute to the discrepancy.[28] Tables 2 and 3 show the average fractional ACE-

Asia functional group composition for each back trajectorygroup in order of increasing CO/OC slope. Variations infunctional group composition within each back trajectorygroup are small compared to differences between groups,suggesting that the aerosol source region and its associatedCO/OC slope are good indicators of aerosol composition inthe ACE-Asia region. Aerosol sulfate, ammonium, andnitrate all show positive correlations with the CO/OCslope. Dust species do not show a correlation because dustdoes not have sources or regions that are common to CO.The small OM/OC ratios of all categories are consistentwith organic compounds emitted from urban and industrialsource regions less than 24 hours before sampling.

[29] The composition of group 5, which includes only backtrajectories that spent at least 5 days over the ocean beforesampling, is a reference marine background compositionwith submicron aerosol mass composed of 25% OM, 31%sulfate, 8% ammonium, 5% nitrate and 31% dust elements(Table 2). The OC in group 5 is composed largely of alkanecarbon (65%) with an additional 18% alkene carbon, 8%aromatic carbon, and 3% carbonyl carbon (Table 3). Thisbackground marine air has a CO/OC slope of 9.9 (R2 = 0.33),which is between the CO/OC slopes of biomass burning andwood burning. Marine CO/OC slopes are also within 15% ofthe modeled value for total Asian emissions, consistent withan aerosol that reflects the regional background emissionsrather than being dominated by local sources.[30] Compared to this background, larger carbonyl carbon

fractions of OC (6–9%) were observed in the North Asian

Figure 5. ACE-Asia back trajectories classified into 10 groups based on source region. Each trajectoryplot contains all of the sample trajectories for the group (thin dotted lines), the calculated averagetrajectory for the group (thick dashed line), and the group number (upper right hand corner). To the rightof each trajectory plot are the corresponding CO and OC measurements (black circles), the best fit lineartrends to the data (solid lines) with equations and R2 values, and the calculated emissions from Streets etal. [2003] along the 5-day average back trajectory (thin dashed lines). For group 10, the emissions alongonly the first 6 hours of the back trajectory are also indicated (thick dot-dashed line).

MARIA ET AL.: SOURCE SIGNATURES IN ACE-ASIA SUBMICRON AEROSOL ACE 5 - 7

air masses associated with groups 1–3. With increasing CO/OC slopes, the alkane carbon fraction of submicron OCdecreases from"60% (CO/OC< 13) to"50% (CO/OC>15),with alkene and aromatic carbon fractions correspondinglyincreasing. Alcohol groups are present at elevated concen-trations in groups 7–10 (CO/OC >15), along with elevatednitrate and ammonium fractions of submicron mass. Thesecorrelations suggest that a less saturated OC (alkene andaromatic as opposed to alkane) and elevated levels ofalcohol, ammonium, and nitrate are all associated withcombustion sources in the transportation sector that havelarge CO/OC emission ratios. Consistent with this observa-tion, unsaturated OC comprises more than 40% of thechemically-resolved OC emitted from diesel trucks andnoncatalyst-equipped automobiles but less than 5% of thechemically-resolved OC emitted from Asian biomass burn-ing [Schauer et al., 1999, 2002; Sheesley et al., 2003].Alcohols have not been measured in significant quantitiesin motor vehicle exhaust, making the identity of the high-CO/OC-ratio alcohol source unclear. The measured alcoholgroups may indicate the presence of secondary organicaerosol, or may indicate that alcohols comprise a significantportion of the >95% of OC emitted from motor vehiclesthat cannot be resolved by chromatographic techniques.[31] To illustrate the sample compositions and source

areas associated with each trajectory group, and to analyzedeviations from the general trends, case studies of fourindividual filter samples are described in detail: Hokkaidoemissions over rough seas (group 1), a large Takla Makandust layer (group 3), Shanghai emissions (group 7), and adust and pollution mixture over the Yellow Sea (group 10).

3.4. Case Studies

[32] Rough seas and pollution from Hokkaido wereobserved during a 285m level leg from 3:52 to 4:47 GMTon 20 April 2001 (research flight 11, group 1, Figure 6). TheCO/OC slope of 7.2 for this group is similar to that ofbiomass burning sources. Isentropic back trajectories showthat the air mass had been over the ocean for less than4 hours before sampling, and that the sampled air mass wasat an altitude of less than 150m when it was over land. Thissample contained low concentrations of OC and OM (1.9 ±0.3 and 2.5 ± 0.4 mg m!3, respectively, with an OM/OC

ratio of 1.35). Carbonyl carbon comprised 4% of OC, lowerthan the average of 6% for the ACE-Asia project, makingthis sample an outlier from the other samples in group 1 (seeTable 3). The lower carbonyl fraction for this sample may berelated to the local volcanic influence that was not present forthe other samples of group 1. The average PILS-determinedNH4

+ to SO42! molar ratio for this sample was 1.9 (with a

minimum of 1.4 from 4:12 to 4:15 GMT), smaller than thevalue of 2 in ammonium sulfate. Cl concentrations werelower than average at 0.01 mg m!3, suggesting that most ofthe sea salt was in supermicron particles.[33] During a 450m level leg from 3:50 to 4:30 GMT

on 11 April 2001 (research flight 6, group 3, Figure 7), theC-130 encountered the highest dust levels of the entire fieldproject. The isentropic back trajectory suggests that thesampled aerosol had been over the ocean for 16 hoursbefore sampling, and that the sampled air mass passed overthe Takla Makan desert at 1500m 48 hours prior tosampling. This leg contained 52 ± 0.5 mg m!3 of SiO4

4!,6.2 ± 2.9 mg m!3 of carbonate carbon, 3.5 ± 0.4 mg m!3 ofAl, 2.3 ± 0.3 mg m!3 of Ca, 1.5 ± 0.2 mg m!3 of K, and2.5 ± 0.1 mg m!3 of Fe in the submicron mode, indicatinglarge amounts of mineral dust. These large concentrations ofdust species from the Takla Makan desert are characteristicof all of the samples in group 3, comprising an average of49% of submicron mass. As for group 1, the CO/OC slopeof 7.5 for this group is similar to that of biomass burningsources. OC and OM, 14.2 ± 3.1 and 19.0 ± 3.5 mg m!3

respectively, were near the upper limit of values observedduring ACE-Asia, and the OM/OC ratio was 1.34. ThePILS-determined sulfate to ammonium molar ratio was0.56, consistent with ammonium sulfate. The ratio of Si toAl was 1.7, considerably smaller than the average value of2.9 for PM10 and PM2.5 reported by He et al. [2001],Winchester et al. [1981], and Zhang et al. [1993] but similarto the value of 1.9 reported by Zhang et al. [2003] for PM2.5

in Zhenbeitai on 11 April 2001. Zhenbeitai is a site near amajor dust source region in China that is along the backtrajectory of the air sampled during ACE-Asia. Al is the best

Table 2. Fractional Submicron Compositiona

Group 1b Group 2 Group 3 Group 4 Group 5

OM 0.49 ± 0.07 0.38 ± 0.08 0.31 ± 0.06 0.57 ± 0.05 0.25 ± 0.03Dust 0.22 ± 0.04 0.26 ± 0.05 0.49 ± 0.03 0.25 ± 0.03 0.31 ± 0.05SO4

2!c 0.19 ± 0.03 0.24 ± 0.03 0.12 ± 0.06 0.16 ± 0.01 0.31 ± 0.02NH4

+c 0.05 ± 0.01 0.08 ± 0.03 0.04 ± 0.01 0.01 ± 0.01 0.08 ± 0.02NO3

!c 0.05 ± 0.01 0.05 ± 0.00 0.04 ± 0.01 0.01 ± 0.01 0.05 ± 0.00

Group 6 Group 7 Group 8 Group 9 Group 10

OM 0.48 ± 0.05 0.41 ± 0.05 0.31 ± 0.06 0.25 ± 0.07 0.10 ± 0.05Dust 0.09 ± 0.03 0.27 ± 0.04 0.17 ± 0.03 0.07 ± 0.04 0.20 ± 0.05SO4

2!c 0.30 ± 0.02 0.17 ± 0.02 0.32 ± 0.03 0.48 ± 0.02 0.31 ± 0.04NH4

+c 0.09 ± 0.02 0.09 ± 0.03 0.11 ± 0.02 0.12 ± 0.01 0.12 ± 0.01NO3

!c 0.05 ± 0.01 0.06 ± 0.01 0.10 ± 0.02 0.08 ± 0.01 0.26 ± 0.05

aAverages and standard deviations of the mass fractions of eachsubmicron aerosol component are reported here for each back trajectorygroup.

bGroup numbers are the same as in Figure 5.cThe sulfate, ammonium, and nitrate values used here were taken from

the PILS C-130 data set [Weber et al., 2001].

Table 3. Fractional Organic Compositiona

Group 1b Group 2 Group 3 Group 4 Group 5

Alkane 0.58 ± 0.03 0.60 ± 0.04 0.60 ± 0.03 0.64 ± 0.07 0.65 ± 0.04Alkene 0.15 ± 0.03 0.15 ± 0.03 0.18 ± 0.01 0.12 ± 0.02 0.18 ± 0.02Aromatic 0.08 ± 0.01 0.08 ± 0.01 0.06 ± 0.02 0.09 ± 0.01 0.08 ± 0.01C-OH 0.02 ± 0.01 0.01 ± 0.01 0.02 ± 0.01 0.02 ± 0.01 0.01 ± 0.01C = O 0.08 ± 0.01 0.06 ± 0.02 0.05 ± 0.01 0.02 ± 0.01 0.03 ± 0.02C-NH2 0.08 ± 0.01 0.10 ± 0.02 0.09 ± 0.01 0.12 ± 0.01 0.06 ± 0.01C-O-S 0.00 ± 0.00 0.00 ± 0.00 0.00 ± 0.00 0.00 ± 0.00 0.00 ± 0.00

OM/OC 1.35 ± 0.02 1.36 ± 0.04 1.31 ± 0.02 1.35 ± 0.01 1.27 ± 0.03

Group 6 Group 7 Group 8 Group 9 Group 10

Alkane 0.65 ± 0.03 0.51 ± 0.02 0.56 ± 0.03 0.47 ± 0.04 0.44 ± 0.05Alkene 0.20 ± 0.03 0.28 ± 0.03 0.23 ± 0.04 0.22 ± 0.02 0.24 ± 0.04Aromatic 0.08 ± 0.02 0.09 ± 0.01 0.09 ± 0.03 0.17 ± 0.04 0.07 ± 0.02C-OH 0.01 ± 0.01 0.02 ± 0.01 0.03 ± 0.02 0.05 ± 0.01 0.04 ± 0.01C = O 0.03 ± 0.01 0.04 ± 0.02 0.04 ± 0.01 0.01 ± 0.01 0.05 ± 0.01C-NH2 0.04 ± 0.01 0.05 ± 0.02 0.05 ± 0.01 0.07 ± 0.01 0.16 ± 0.03C-O-S 0.00 ± 0.00 0.00 ± 0.00 0.00 ± 0.00 0.00 ± 0.00 0.00 ± 0.00

OM/OC 1.29 ± 0.02 1.27 ± 0.02 1.29 ± 0.03 1.31 ± 0.02 1.49 ± 0.28

aAverages and standard deviations of the fractions of OM are reportedhere for each back trajectory group.

bGroup numbers are the same as in Figure 5.

ACE 5 - 8 MARIA ET AL.: SOURCE SIGNATURES IN ACE-ASIA SUBMICRON AEROSOL

tracer for clay minerals [Gomes and Gillette, 1993]. Asmaller Si to Al ratio represents an enhancement of the clayfraction of the mineral aerosol in the ACE-Asia samples.[34] During a 250m level leg from 5:22 to 5:50 GMT on

30 April 2001 (research flight 16, group 7, Figure 8),Shanghai emissions were sampled by the C-130. This grouphas an intermediate CO/OC slope of 14.8 that is between theemissions ratios of the transportation sector and woodburning sources. The isentropic back trajectory reveals thatthe Shanghai plume had been over the ocean for "20 hours,

with meteorological observations that indicated precipita-tion during this transit. The sampled air mass was atapproximately 500m over Shanghai, within the well-mixedlowest layer of the atmosphere. This leg containeda condensation nuclei (CN) concentration of 5500 cm!1

and the highest submicron scattering during the project(270 Mm!1), as well as the sixth largest measuredOM concentration (16.3 ± 4.8 mg m!3). The Shanghaiemissions were associated with elevated nitrate concentra-tions (0.4 mg m!3) and an NH4

+ to SO2!4 molar ratio of 0.57,

Figure 6. Vertical profiles of aerosol components on 20 April 2001 (research flight 11) and theirsolubility characteristics. Samples were collected between 34.5! and 42.7!N and 133.2! and 142.4!E. Thesample composition at 285 m is associated with the Hokkaido case study. Sulfate, ammonium, and nitratewere identified with PILS, and all other functional groups were identified with FTIR. PILS data showaverage values and variability during the FTIR sampling times. For FTIR data, from left to right, blackareas represent the residual fraction, dark gray areas represent the fraction removed in hexane, mediumgray areas represent the fraction removed in dichloromethane, light gray areas represent the fractionremoved in acetone, and white areas represent the fraction removed in water. Also shown are totalcondensation nuclei (CN) concentration and potential temperature.

MARIA ET AL.: SOURCE SIGNATURES IN ACE-ASIA SUBMICRON AEROSOL ACE 5 - 9

consistent with ammonium sulfate. Particulate nitrate, am-monium, and sulfate can be formed as automobile emissionproducts [Schauer et al., 2002], and the high CO/OC slopeis consistent with influence from transportation sources. TheOM/OC ratio of 1.24 measured in the Shanghai plume isindicative of organic compounds that have not beenoxidized in the atmosphere. There were no significanttracers of sea-salt or dust sources in the Shanghai plume,with SiO4

4!, Al, Ca, and Cl all being below detection limits.[35] Dust and pollution in the Yellow Sea were sampled

at 490 m from 5:43 to 7:00 GMT on 12 April 2001 (researchflight 7, group 10, Figure 9). Of the group 10 samples, thissample was collected furthest from Qingdao and has nearlya background concentration of CO (103 ppbv, see Figure 5).Back trajectories for this sample show that the air parcel hadbeen near the surface of the Yellow Sea for approximately

28 hours before being sampled by the C-130. This agingunder marine conditions is consistent with the larger ob-served OM to OC ratio of 2.0 for this sample (OC = 1.1 ±0.2 mg m!3, OM = 2.2 ± 0.2 mg m!3). The large alcoholconcentrations characteristic of group 10 were seen in thissample (10% of OC) along with high carbonyl carbonconcentrations (8% of OC). Significant amounts of silicateand carbonate were also observed (4.5 ± 0.1 mg m!3 and0.3 ± 0.1 mg m!3, respectively), indicating some contribu-tion from a dust source. Cl was below detection limit.

3.5. Solubility of Measured Components

[36] Inorganic and organic submicron aerosol composi-tions and solubility characteristics for research flights 6, 7,11, and 16 are shown in Figures 6–9. While the majority ofinorganic ions were either very soluble in water or com-

Figure 7. Vertical profiles of aerosol components on 11 April 2001 (research flight 6) and theirsolubility characteristics. Samples were collected between 33.6! and 36.1!N and 124.3! and 128.5!E. Thesample composition at 450 m is associated with the dust case study. The format is the same as in Figure 6.

ACE 5 - 10 MARIA ET AL.: SOURCE SIGNATURES IN ACE-ASIA SUBMICRON AEROSOL

pletely insoluble, the organic aerosol fraction exhibited amuch wider range of solubility behavior including somepartially soluble compounds.[37] Inorganic species behaved as expected from the

rinsing of standard compounds in the laboratory, withsilicate and carbonate remaining on the filter after all rinseswere performed. An exception to this trend was observedduring flights 11 and 16 when large amounts of the silicatepeaks were removed in hexane, acetone, and water. Lessthan 0.01 ng of some types of silicate, including sheetsilicate, is expected to be removed from each Teflon filterduring rinsing with 3 ml water [Nagy, 1995]. Differences insilicate rinsing behavior can be explained by an enhancedsurface area which may be associated with small silicate-containing particles in some samples [Brantley et al., 1999;

White and Brantley, 1995] or by differences in the physicalform of the measured silicate between samples (for exam-ple, NaO4SiO4 is very soluble in water).[38] Sulfate, ammonium, and nitrate show the same

profile with altitude, as seen in Figures 6, 7, 8, and 9.Silicate and carbonate were also correlated (R2 = 0.77),suggesting similar sources or source regions of each.Elevated levels of both silicate and carbonate from 400 to1000 m during flights 6, 7, and 11 demonstrate that elevateddust levels are often found at the top of the boundary layerin the ACE-Asia sampling region.[39] Despite the variability in solubility characteristics of

the organic aerosol fraction, aromatic and carbonyl groupsmaintained consistent solubility characteristics throughoutthe ACE-Asia project. On average, 68 ± 26% of the

Figure 8. Vertical profiles of aerosol components on 30 April 2001 (research flight 16), and theirsolubility characteristics. Samples were collected between 23.5! and 33.5!N and 124.2! and 131.9!E. Thesample composition at 250 m is associated with the Shanghai plume case study. The format is the same asin Figure 6.

MARIA ET AL.: SOURCE SIGNATURES IN ACE-ASIA SUBMICRON AEROSOL ACE 5 - 11

quantified aromatic C-H groups are found in the residualfraction, the fraction remaining on the filter after all rinses(Figures 6–9). Large organic molecules containing manycarbons per functional group (i.e., low OM/OC) are mostlikely to remain in the residual fraction, suggesting that forthe average ACE-Asia aerosol 68% of aromatic C-H bondsare associated with relatively large and insoluble organicmolecules. Another feature of the data is that a smallfraction of the carbonyl group often remains in the residualfraction. Poorly water-soluble carbonyl groups are present,perhaps associated with the identified residual aromaticcompounds.[40] During the large dust event of 11 April, alkane

groups were removed in water while alkene, alcohol, amine,

and organosulfur groups were removed in hexane. Carbonyl,aromatic, and alkene groups were all below detection limits.Alkanes require a polar functional group to be water soluble.The rinsing behavior suggests that the water soluble alkanegroups are not associated with alcohol groups, but they maybe associated with carbonyl groups which were not concen-trated enough to be measured. The large alcohol signature isunique to flight 6, and may be characteristic of the dustsource because alcohols can be a product of biodegradedvegetal detritus [Alves et al., 2001]. A common source and aninternal mixture of dust and alcohols could explain theremoval of a fraction of silicate in the hexane rinse. TheShanghai plume contained water-soluble alkanes likethe dust layer of 11 April. These Shanghai samples also

Figure 9. Vertical profiles of aerosol components on 12 April 2001 (research flight 7) and theirsolubility characteristics. Samples were collected between 33.1! and 34.9!N and 124.3! and 130.0!E. Thesample composition at 490 m is associated with the Yellow Sea case study. The format is the same as inFigure 6.

ACE 5 - 12 MARIA ET AL.: SOURCE SIGNATURES IN ACE-ASIA SUBMICRON AEROSOL

containedwater-soluble carbonyl groups but lacked aromatic,alcohol, or organosulfur signatures.

4. Conclusions

[41] FTIR and TOT measurements produced OC valuesthat were related with a slope of 0.91 and an R2 value of0.93, suggesting that the two methods quantified verysimilar groups of species as OC. The CO/OC slope corre-lated to aerosol source region, with measured slopes com-paring well with the source characteristics of an emissionsinventory [Streets et al., 2003]. OC composition varied withthe CO/OC slope, with CO/OC slopes above 15 associatedwith increased fractions of alcohol groups, unsaturated C-Hgroups, and inorganic nitrate. These functional groups areall associated with large CO/OC ratio emissions, most likelyfrom the transportation sector.[42] These results demonstrate the ability of a primary

combustion tracer (CO), OM/OC ratios, functional groups,and back trajectories to distinguish among different sourcetypes and to identify secondary organic and inorganicaerosol formation. The types of aerosol categories alsoindicate consistency with emissions inventories. Three ofthe back trajectory groupings (groups 1–3), all containingtrajectories that originated over northern Asia, had lowermeasured CO/OC slopes than predicted. The excess OC andmoderately increased OM/OC ratio may be evidence ofsecondary OC formation, although uncertainties in backtrajectories or emissions inventories cannot be ruled out.[43] Examples of the vertical distribution of chemical

components illustrated that inorganic composition can beunderstood by examining source characteristics. Elevateddust from the Takla Makan desert, elevated nitrate andammonium sulfate downwind of Shanghai, and elevatedsulfate downwind of Hokkaido are all explained by localsources. Dust sources are spatially distinct from CO sourcesand cannot be predicted by the CO/OC slope.[44] CO/OC slopes, OM/OC ratios, and functional group

information together provide a method of classifying atmo-spheric aerosol samples into source-based categories. Thecorrelation between CO/OC slope and organic compositionallows for the approximation of organic aerosol properties,such as hygroscopicity, based on the value of the CO/OCslope. These approximations can be useful for initializingaerosol hygroscopicity models or for achieving aerosolmass closure, because the CO/OC slope is a routine mea-surement that is often available when measurements offurther organic aerosol characteristics are not.

[45] Acknowledgments. This research is a contribution to the Inter-national Global Atmospheric Chemistry (IGAC) Core Project of theInternational Geosphere Biosphere Program (IGBP) and is part of theIGAC Aerosol Characterization Experiments (ACE). Support was providedby NSF grants ATM-0002035 and ATM-0002698 and by NASA grantNAG5-8676. We are grateful to the NCAR Research Aviation Facility fortheir help in the field. We appreciate the help of Tim Bertram in collectingand analyzing the TOT samples and the help of Adam Reff in maintainingthe aerosol generation system used for collection of reference compounds.We are also grateful to the NIEHS Center of Excellence at EOHSI for use ofthe weighing facility and FTIR spectrometer.

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!!!!!!!!!!!!!!!!!!!!!!!T. L. Campos, Atmospheric Chemistry Division, National Center for

Atmospheric Research, 1850 Table Mesa Drive, Boulder, CO 80303, USA.(campos@ncar.ucar.edu)B. J. Huebert, Department of Oceanography, University of Hawaii, 1000

Pope Road, MSB 205, Honolulu, HI 96822, USA. (huebert@hawaii.edu)S. F. Maria, Department of Chemical Engineering, Princeton University,

A317 E-Quad, Princeton, NJ 08544, USA. (smaria@princeton.edu)R. J. Porcja and B. J. Turpin, Department of Environmental Science,

Rutgers University, 14 College Farm Road, New Brunswick, NJ 08901,USA. (porcja@eohsi.rutgers.edu; turpin@aesop.rutgers.edu)L. M. Russell, Scripps Institution of Oceanography, University of

California at San Diego, 9500 Gilman Drive, La Jolla, CA 92093, USA.(lmrussell@ucsd.edu)R. J. Weber, School of Earth and Atmospheric Sciences, Georgia Institute

of Technology, 221 Boddy Dodd Way, Atlanta, GA 30332, USA.(rweber@eas.gatech.edu)

ACE 5 - 14 MARIA ET AL.: SOURCE SIGNATURES IN ACE-ASIA SUBMICRON AEROSOL