OH-Radical Oxidation of Surface-Active cis-Pinonic Acid at the Air–Water Interface
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- 作者：Shinichi Enami ; Yosuke Sakamoto
- 刊名：Journal of Physical Chemistry A
- 出版年：2016
- 出版时间：May 26, 2016
- 年：2016
- 卷：120
- 期：20
- 页码：3578-3587
- 全文大小：647K
- 年卷期：0
- ISSN：1520-5215
文摘
Gaseous biogenic volatile organic compounds (BVOCs) are immediately oxidized by gaseous oxidants to form BVOC-acids that rapidly condense onto aqueous aerosol phase and thus contribute to the growth of atmospheric particles. Because BVOC-acids are highly hydrophobic and hence surface-active in nature, it seems critical to study the oxidation by gaseous hydroxyl radical (·OH(g)) at the air–water interface. Here we report on the fast (≤10 μs) oxidation of aqueous cis-pinonic acid (C10H16O3, CPA, cis-pinonate anion’s m/z = 183), a representative BVOC-acid, by ·OH(g) at the air–water interface for the first time. We find that cis-pinonate anion is more enriched at the air–water interface by ∼4 and ∼14 times than n-octanoate anion at 10 and 100 μM, respectively, as revealed by an interface-specific mass spectrometry of the equimolar mixture of microjets. Exposure of aqueous CPA microjets to ·OH(g) pulses from the 266 nm laser photolysis of O3(g)/O2(g)/H2O(g)/N2(g) mixtures yields pinonic peroxyl radicals (m/z = 214) that lead to the functionalization products carbonyls (m/z = 197), alcohols (m/z = 199), and pinonic hydroperoxides (m/z = 215) in addition to smaller-mass products including carbonyls (m/z = 155 and 157). We confirmed the formation of the corresponding alcohols, aldehydes, and hydroperoxides in experiments performed in D2O solvent. The analysis of total mass balance implies a significant amount (>70%) of products would be emitted into the gas-phase during the heterogeneous ·OH-oxidations. Our results suggest ·OH-oxidations of amphiphilic BVOC-acids at the air–water interface may play a far more significant role in photochemical aging process of aqueous aerosols than previously assumed.