Abstract
Abstract. Gas–particle partitioning of water-soluble organic compounds plays a significant role in influencing the formation, transport, and lifetime of organic aerosols in the atmosphere, but is poorly characterized. In this work, gas- and particle-phase concentrations of isoprene oxidation products (C5-alkene triols and 2-methylterols), levoglucosan, and sugar polyols were measured simultaneously at a suburban site of the western Yangtze River Delta in east China. All target polyols were primarily distributed into the particle phase (85.9 %–99.8 %). Given the uncertainties in measurements and vapor pressure predictions, a dependence of particle-phase fractions on vapor pressures cannot be determined. To explore the impact of aerosol liquid water on gas–particle partitioning of polyol tracers, three partitioning schemes (Cases 1–3) were proposed based on equilibriums of gas vs. organic and aqueous phases in aerosols. If particulate organic matter (OM) is presumed as the only absorbing phase (Case 1), the measurement-based absorptive partitioning coefficients (Kp,OMm) of isoprene oxidation products and levoglucosan were more than 10 times greater than predicted values (Kp,OMt). The agreement between Kp,OMm and Kp,OMt was substantially improved when solubility in a separate aqueous phase was included, whenever water-soluble and water-insoluble OM partitioned into separate (Case 2) or single (Case 3) liquid phases, suggesting that the partitioning of polyol tracers into the aqueous phase in aerosols should not be ignored. The measurement-based effective Henry's law coefficients (KH,em) of polyol tracers were orders of magnitude higher than their predicted values in pure water (KH,wt). Due to the moderate correlations between log(KH,em/KH,wt) and molality of sulfate ions, the gap between KH,em and KH,wt of polyol tracers could not be fully parameterized by the equation defining “salting-in” effects and might be ascribed to mechanisms of reactive uptake, aqueous phase reaction, “like-dissolves-like” principle, etc. These study results also partly reveal the discrepancy between observation and modeling of organic aerosols.
Highlights
The water-soluble organic carbon (WSOC) in ambient aerosols can account for 20 %–80 % of particulate organic matter (OM) based on carbon mass (Saxena and Hildemann, 1996; Kondo et al, 2007)
The top quartz filter (Qf) in the filter pack was loaded with PM2.5, gaseous organic compounds adsorbed on the backup quartz filter (Qb) were determined to evaluate sampling ar
Individual parts of the two types of composites were analyzed for seven samples, and target compounds were only detected in the top PUF
Summary
The water-soluble organic carbon (WSOC) in ambient aerosols can account for 20 %–80 % of particulate organic matter (OM) based on carbon mass (Saxena and Hildemann, 1996; Kondo et al, 2007). WSOC plays an important role in changing radiative and cloud-nucleating properties of atmospheric particles. Particulate WSOC is a complex mixture of polar organic compounds containing oxygenated functional groups C. Qin et al.: Gas–particle partitioning of polyol tracers at a suburban site in Nanjing, east China boxyl, and carbonyl groups), among which a list of organic compounds with multiple hydroxyl (polyols) groups have been identified using gas chromatography–mass spectrometry (GC–MS) and linked with specific emission sources. C5-alkene triols and 2-methyltetrols are isoprene oxidation products (Claeys et al, 2004; Wang et al, 2005; Surratt et al, 2006), levoglucosan is a typical pyrolysis product of cellulose (Simoneit et al, 1999), and primary saccharides (e.g., fructose and glucose) and saccharide polyols (e.g., arabitol and mannitol) are commonly associated with soil microbiota and fungal spores, respectively (Simoneit et al, 2004; Bauer et al, 2008)
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