Abstract
Abstract. Secondary organic aerosols (SOAs) affect human health and climate change prediction; however, the factors (e.g., temperature, acidity of pre-existing particles, and oxidants) influencing their formation are not sufficiently resolved. Using a compact chamber, the temperature and acidity dependence of SOA yields and chemical components in SOA from α-pinene ozonolysis were systematically investigated under 278, 288, and 298 K temperatures using neutral ((NH4)2SO4) and acidic (H2SO4+((NH4)2SO4)) seed aerosols. SOA components with m/z less than 400 were analyzed using negative electrospray ionization liquid-chromatography time-of-flight mass spectrometry. Based on the slightly negative temperature dependence of the SOA yields, the enthalpies of vaporization under neutral and acidic seed conditions were estimated to be 25 and 44 kJ mol−1, respectively. In addition, SOA yields increased with an increase in the acidity of seed particles (solid/near-solid state) at low SOA mass loadings, when compared with the seed particle amounts. Acidity dependence analysis of the chemical formula, molecular mass, and O:C ratio of the detected compounds indicated the enhanced formation of multiple oligomers in the wide molecular mass range with a wide range of O:C ratios under acidic seed conditions. The peak abundances of some chemical compounds increased with an increase in the acidity of seed particles (e.g., m/z 197, 311, 313, 339, 355, and 383), while decreases in the peak abundances of some chemical compounds were observed (e.g., m/z 171, 185, 215, 343, and 357). The acidity dependence could be explained by acid-catalyzed heterogeneous reactions or acid-catalyzed decomposition of hydroperoxides. In addition, organosulfate (OS) formation was observed under acidic seed conditions. Six out of the 11 detected OSs were potentially formed via the aldehyde + HSO4- pathway.
Highlights
Secondary organic aerosol (SOA) in the atmosphere is a complex set of organic compounds which are formed through oxidation of precursor volatile organic compounds (VOCs) of either biogenic or anthropogenic origins, or both (Hallquist et al, 2009)
Because aldehydes should dominate the products from α-pinene ozonolysis in the presence of an OH scavenger (Gaona-Colmán et al, 2017) and pinonaldehyde has been detected in previous αpinene ozonolysis studies with an OH scavenger (Jackson et al, 2017), we propose that the aldehyde pathway could be one of the dominant OS formation pathways in this study
Using the compact chamber system, SOA formation from αpinene ozonolysis was studied with diethyl ether as an OH radical scavenger at temperatures of 278, 288, and 298 K, with acidic and neutral seed aerosol particles
Summary
Secondary organic aerosol (SOA) in the atmosphere is a complex set of organic compounds which are formed through oxidation of precursor volatile organic compounds (VOCs) of either biogenic (e.g., monoterpene and isoprene) or anthropogenic (e.g., alkanes and aromatics) origins, or both (Hallquist et al, 2009). While enhancements of SOA yields from α-pinene ozonolysis reactions under acidic seed aerosol conditions compared with neutral seed conditions have been generally observed in previous studies (Czoschke et al, 2003; Gao et al, 2004; Iinuma et al, 2004, 2005; Czoschke and Jang, 2006; Jang et al, 2006; Northcross and Jang, 2007), the degree of enhancement varied probably because of the different experimental settings among the studies. OS compounds and their possible formation mechanisms have been targeted during the analysis
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