Ozone photochemistry and free radical budgets in the Los Angeles basin: A comparison of ground-based observations in 2021 and 2010

Michael Robinson,
ANYL 3rd year, Brown group

"Radical precursors and termination products are important factors to understanding sensitivities of ozone (O3) production to nitrogen oxides (NO + NO2 = NOx) and volatile organic compounds (VOCs). During the summer of 2021, an extensive set of photochemical measurements were conducted at a ground site on the Caltech campus in Pasadena, CA to evaluate emissions and photochemistry in the Los Angeles (LA) basin. Here we present the calibration and measurement of important radical precursors and compare them to observations from the CalNex 2010 field intensive. Major radical sources include formaldehyde (HCHO) and other aldehydes, nitrous acid (HONO), nitryl chloride (ClNO2), ozonolysis of alkenes, and O(1D) + H2O. In addition to radical precursors, radical termination products were measured, including peroxy acetyl nitrates (PAN), nitric acid (HNO3), organic nitrates and organic peroxides. The comparison of radical precursors and termination products illustrates shifts in photochemical regime resulting from NOx and VOC emissions changes over the past ten years in the LA basin, as well as other influences such as temperature, seasonality and day of week."