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Nighttime Chemistry of Biomass Burning Plumes in Urban Areas: A Dual Mobile Chamber Study
SPIRO JORGA, Kalliopi Florou, Christos Kaltsonoudis, Jack Kodros, Christina Vasilakopoulou, Spyros Pandis, Carnegie Mellon University, University of Patras
Abstract Number: 84
Working Group: Urban Aerosols
Abstract
Wildfires and human-induced biomass burning are sources of gaseous and particulate pollutants in the atmosphere. Although, important changes in the size distributions and the chemical composition of the biomass burning aerosol during daytime chemistry have been observed, the corresponding changes at nighttime or in winter where photochemistry is slow, have received relatively little attention. In this study, we tested the hypothesis that nightime chemistry in biomass burning plumes can be rapid in urban areas using a dual smog chamber system.
Ambient air during cold nightime periods with high concentrations of biomass burning organic aerosol (OA) was introduced in both chambers. Ozone was added in one of them (perturbed chamber) and upon reaction with the existing NOx formed NO3 radicals. The other chamber was used as a reference to monitor the natural evolution of the system. Following the injection of ozone (approx. 150 ppb), rapid secondary organic aerosol formation was observed in all experiments. NO3 radicals were measured in the perturbed chamber. The OA mass concentration increased by 20-70% in just one hour, while an average increase of 50% in the O:C ratio of OA was observed. Nitrate formation was detected with most of it (on average 70%) being organic nitrate. The AMS mass spectrum of the formed OA showed similarities with oxidized OA mass spectra during winter in urban areas and with spectra from biomass burning plumes oxidized under dark conditions with nitrate radicals.