Exploring\nthe Effect of Environmental Conditions on\nDecay Kinetics of Aerosol Unsaturated Fatty Acids: New Insights Gained\nfrom Long-Term Ambient Measurements

Unsaturated fatty acids (uFAs) are\nimportant constituents of atmospheric\norganic aerosols, undergoing rapid degradation in the atmosphere that\nsignificantly influences aerosol’s physical and chemical properties.\nThis study quantified the effective pseudo-first order decay rates\nof three abundant uFAs-oleic, elaidic, and linoleic acids under real\natmospheric conditions using continuous bihourly measurement at a\nsuburban site in Hong Kong over a 9-month period from November 2020\nto August 2021. The impact of key environmental parameters, including\nozone, initial uFA concentration, relative humidity, and temperature,\non the decay rates was rigorously examined. Distinct kinetic behaviors\nwere observed across different temperature ranges (TR<sub>1</sub>:\n5–13 °C; TR<sub>2</sub>: 13–22 °C; TR<sub>3</sub>: 22–26 °C; TR<sub>4</sub>: 26–30 °C).\nArrhenius plots of the decay rates revealed contrasting effective\nactivation energies under TR<sub>2</sub> and TR<sub>4</sub>, likely\ndue to different phase states of aerosols and reaction mechanisms\nunder varying environmental conditions. This study extends previous\nlaboratory research by incorporating a wider range of ambient conditions,\nuncovering the complex interactions between environmental factors\nand the decay kinetics of uFAs. The findings provide critical insights\nfor accurately modeling the fate of ambient organic aerosols and understanding\nthe intricate impacts of atmospheric conditions on aerosol chemistry.