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. Secondary organic aerosols (SOAs) affect human health andclimate change prediction; however, the factors (e.g., temperature, acidityof pre-existing particles, and oxidants) influencing their formation are notsufficiently resolved. Using a compact chamber, the temperature and aciditydependence of SOA yields and chemical components in SOA from α-pinene ozonolysis were systematically investigated under 278, 288, and298 K temperatures using neutral ((NH4)2SO4) and acidic(H2SO4+((NH4)2SO4)) seed aerosols. SOA componentswith m/z less than 400 were analyzed using negative electrospray ionizationliquid-chromatography time-of-flight mass spectrometry. Based on theslightly negative temperature dependence of the SOA yields, the enthalpiesof vaporization under neutral and acidic seed conditions were estimated tobe 25 and 44 kJ mol−1, respectively. In addition, SOA yields increasedwith 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:Cratio of the detected compounds indicated the enhanced formation of multipleoligomers in the wide molecular mass range with a wide range of O:C ratiosunder acidic seed conditions. The peak abundances of some chemical compoundsincreased 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 somechemical compounds were observed (e.g., m/z 171, 185, 215, 343, and 357). Theacidity dependence could be explained by acid-catalyzed heterogeneousreactions or acid-catalyzed decomposition of hydroperoxides. In addition,organosulfate (OS) formation was observed under acidic seed conditions. Sixout of the 11 detected OSs were potentially formed via the aldehyde +HSO4- pathway.

atmospheric chemistry and physics

Temperature and acidity dependence of secondary organic aerosol formation from &amp;lt;i&amp;gt;α&amp;lt;/i&amp;gt;-pinene ozonolysis with a compact chamber system