American Association for Aerosol Research - Abstract Submission

AAAR 39th Annual Conference
October 18 - October 22, 2021

Virtual Conference

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Photolysis of Atmospherically Relevant Monoterpene-derived Organic Nitrates

YUCHEN WANG, Masayuki Takeuchi, Tianchang Xu, Siyuan Wang, Nga Lee Ng, Georgia Institute of Technology

     Abstract Number: 178
     Working Group: Aerosol Chemistry

Abstract
Organic nitrates (ONs) have been detected in atmospheric environments as potential NOx reservoirs and they can impact the spatial distribution of reactive nitrogen species and subsequently ozone formation. While photolysis of ONs can result in the release of NO2 back to atmosphere, the rates and mechanisms of photolysis of atmospherically relevant ONs have not been well constrained especially for monoterpene-derived ONs (MT-ONs). In this work, we investigated the photolysis of three synthetic ONs derived from α-pinene, β-pinene and limonene through chamber experiments. The measured photolysis rate constants for these three MT-ONs are in the range of 0.45 – 1.81 10-5 s-1 with corresponding photolysis lifetimes ranging from 15.4 – 62.2 hours. With consideration of the difference in solar and chamber light spectra and the absorption cross section of these synthetic MT-ONs measured by ultraviolet–visible spectrophotometry, the ambient photolysis lifetimes for these MT-ONs decreased to 2.0 – 16.2 hours. Photolysis mechanisms are proposed based on major photolysis products identified by high-resolution time-of-flight chemical-ionization mass spectrometer (HR-ToF-CIMS). We found that the NOx produced via photolysis of MT-ONs can participate in further reactions to produce new ON species with a higher oxidation state. Finally, with our proposed photolysis mechanisms and ambient photolysis rates, we employed a 0D-model to simulate photolysis of α-pinene-derived ON under ambient conditions and found that 90% of α-pinene-derived ON can be converted to NOx and HNO3 within 12 hours of irradiation time and ozone was formed correspondingly. These findings show that photolysis is a major atmospheric sink for MT-ONs and highlight their important role in NOx recycling and ozone formation.