Photochemical Aging of Light-Absorbing Secondary Organic Aerosol Material
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- 作者：Neha Sareen ; Samar G. Moussa ; V. Faye McNeill
- 刊名：The Journal of Physical Chemistry A
- 出版年：2013
- 出版时间：April 11, 2013
- 年：2013
- 卷：117
- 期：14
- 页码：2987-2996
- 全文大小：410K
- 年卷期：v.117,no.14(April 11, 2013)
- ISSN：1520-5215
文摘
Dark reactions of methylglyoxal with NH4+ in aqueous aerosols yield light-absorbing and surface-active products that can influence the physical properties of the particles. Little is known about how the product mixture and its optical properties will change due to photolysis as well as oxidative aging by O3 and OH in the atmosphere. Here, we report the results of kinetics and product studies of the photochemical aging of aerosols formed by atomizing aqueous solutions of methylglyoxal and ammonium sulfate. Experiments were performed using aerosol flow tube reactors coupled with an aerosol chemical ionization mass spectrometer (Aerosol鈥揅IMS) for monitoring gas- and particle-phase compositions. Particles were also impacted onto quartz windows in order to assess changes in their UV鈥搗isible absorption upon oxidation. Photooxidation of the aerosols leads to the formation of small, volatile organic acids including formic acid, acetic acid, and glyoxylic acid. The atmospheric lifetime of these species during the daytime is predicted to be on the order of minutes, with photolysis being an important mechanism of degradation. The lifetime with respect to O3 oxidation was observed to be on the order of hours. O3 oxidation also leads to a net increase in light absorption by the particles due to the formation of additional carbonyl compounds. Our results are consistent with field observations of high brown carbon absorption in the early morning.