Nitrate-mediated Photooxidation of Green Leaf Volatiles under Cloud/Fog-like vs. Aerosol-like Conditions
Yuting Lyu, Ruihan Ma, Tianye Zhou, Taekyu Joo, Shun Yeung, Cheuk Yi Wong, Yifang Gu, Yiming Qin, THEODORA NAH, City University of Hong Kong
Abstract Number: 79
Working Group: Aerosol Chemistry
Abstract
Inorganic nitrate and sulfate are prominent components of atmospheric aqueous phases such as fog/cloud droplets and aqueous aerosols. Inorganic nitrate photolysis in atmospheric phases produce a variety of oxidants, which participate in chemical reactions with organic compounds to produce aqueous secondary organic aerosols (aqSOA). Green leaf volatiles (GLVs) are biogenic oxygenated hydrocarbons that can partition into atmospheric aqueous phases and be oxidized by oxidants to form aqSOA. There are several intrinsic differences between fog/cloud droplets and aqueous aerosols, including differences in their concentrations of constituents and ionic strengths, but it is unclear how these differences affect reaction kinetics and aqSOA formation. We report results from our laboratory investigations of the nitrate-mediated photooxidation of four GLVs (cis-3-hexen-1-ol, trans-2-hexen-1-ol, trans-2-penten-1-ol, and 2-methyl-3-buten-2-ol) at different pH, ionic strengths, and sulfate concentrations under conditions mimicking fog/cloud droplets vs. aqueous aerosols. Higher reactions rates were measured under fog/cloud-like conditions. Ionic strength, pH, and sulfate differences had little effect on the reaction rates of the GLVs under fog/cloud-like conditions. In contrast, ionic strength, pH, and sulfate had significant effects on the reaction rates of the GLVs under aerosol-like conditions. Additionally, the reaction rates of the GLVs increased substantially when high concentrations of sulfate were present, thus suggesting that reactive oxidants formed from sulfate photolysis contributed to the increased reaction rates. We also compared the products and the mass yields of aqSOA formed under these different conditions. Our results highlight how intrinsic differences (in this case, concentrations of constituents and ionic strength) between fog/cloud droplets and aqueous aerosols can contribute to differences in pH-dependent aqueous chemistry of organic compounds in atmospheric organic phases, with implications for the composition and mass concentration of aqSOA formed.