Variations in organic aerosol optical and hygroscopic properties upon heterogeneous OH oxidation
Cappa, CD; Che, DL; Kessler, SH; Kroll, JH; Wilson, KR
| HERO ID | 2469705 |
|---|---|
| In Press | No |
| Year | 2011 |
| Title | Variations in organic aerosol optical and hygroscopic properties upon heterogeneous OH oxidation |
| Authors | Cappa, CD; Che, DL; Kessler, SH; Kroll, JH; Wilson, KR |
| Journal | Journal of Geophysical Research: Atmospheres |
| Volume | 116 |
| Issue | D15 (Aug 6 |
| Abstract | Measurements of the evolution of organic aerosol extinction cross sections (sigma(ext)) and subsaturated hygroscopicity upon heterogeneous OH oxidation are reported for two model compounds, squalane (a C-30 saturated hydrocarbon) and azelaic acid (a C-9 dicarboxylic acid). For both compounds, the sigma(ext) values at 532 nm increase substantially as the particles undergo oxidation, exhibiting a logarithmic increase with OH exposure. The increase in sigma(ext) correlates with both an increase in the particle oxygen to carbon (O:C) atomic ratio and density and a decrease in mean molecular weight. The measurements have been used to calculate the variation with oxidation of the mean polarizability, alpha, of the molecules comprising the particles. The absolute alpha values for the two systems are shown to be related through the variation in the particle chemical composition, specifically the relative abundances of C, O, and H atoms and the mean molecular weight. Unlike sigma(ext), it was found that the evolution of the particle hygroscopicity upon oxidation is quite different for the two model systems considered. Hygroscopicity was quantified by measuring gamma(ext), which is a single-parameter representation of hygroscopicity that describes the increase in extinction upon exposure of the particles to a high-relative humidity environment (here, 75% and 85% RH). For unoxidized squalane, gamma(ext) was zero and only increased slowly as the particles were oxidized by OH radicals. In contrast, gamma(ext) for azelaic acid increased rapidly upon exposure to OH, eventually reaching a plateau at high OH exposures. In general, gamma(ext) appears to vary sigmoidally with O:C, reaching a plateau at high O:C. |
| Doi | 10.1029/2011JD015918 |
| Wosid | WOS:000293656700001 |
| Is Certified Translation | No |
| Dupe Override | No |
| Is Public | Yes |
| Keyword | Atmospheric pollution models; Extinction; Organic aerosols in atmosphere; Oxidation; Humidity; Oxygen; Aerosols; Saturated hydrocarbons; Chemical composition; Particulates; 2011) |
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