Exploring the Effect of Environmental Conditions on Decay Kinetics of Aerosol Unsaturated Fatty Acids: New Insights Gained from Long-Term Ambient Measurements.

Unsaturated fatty acids (uFAs) are important constituents of atmospheric organic aerosols, undergoing rapid degradation in the atmosphere that significantly influences aerosol's physical and chemical properties. This study quantified the effective pseudo-first order decay rates of three abundant uFAs-oleic, elaidic, and linoleic acids under real atmospheric conditions using continuous bihourly measurement at a suburban site in Hong Kong over a 9-month period from November 2020 to August 2021. The impact of key environmental parameters, including ozone, initial uFA concentration, relative humidity, and temperature, on the decay rates was rigorously examined. Distinct kinetic behaviors were observed across different temperature ranges (TR: 5-13 °C; TR: 13-22 °C; TR: 22-26 °C; TR: 26-30 °C). Arrhenius plots of the decay rates revealed contrasting effective activation energies under TR and TR, likely due to different phase states of aerosols and reaction mechanisms under varying environmental conditions. This study extends previous laboratory research by incorporating a wider range of ambient conditions, uncovering the complex interactions between environmental factors and the decay kinetics of uFAs. The findings provide critical insights for accurately modeling the fate of ambient organic aerosols and understanding the intricate impacts of atmospheric conditions on aerosol chemistry.