Evaluation of indoor secondary organic aerosol concentrations and contributions in Chinese residences: Insights from field testing

Abstract

Indoor secondary organic aerosols (SOAs) generated from reactive organic gases (ROGs) reacting with O3 have a substantial impact on indoor PM2.5 levels. China's recent decrease in atmospheric PM2.5 and increase in atmospheric O3 have resulted in correspondingly lower levels of indoor PM2.5 and higher levels of indoor O3, which will further affect indoor SOA concentration. Thus, the aims of this study were to evaluate indoor SOA concentrations and their contribution to indoor PM2.5 and analyze the impact of the air exchange rate, window-opening status, proportion of indoor organic particles, and O3 concentrations on indoor SOA generation. To this end, measurements were conducted in Beijing, Shanghai, and Shenzhen, China by synchronously collecting samples of indoor ROGs and O3, along with indoor and outdoor PM2.5 concentrations. We found a maximum indoor SOA concentration of 35.23 μg/m3, contributing over 50% to indoor PM2.5, although most samples had an average concentration of 1.65 ± 4.89 μg/m3. Shanghai had the lowest average SOA concentration and contribution, whereas Shenzhen had the highest. Terpenoid compounds were identified as crucial precursors for indoor SOA generation, with the indoor O3 concentration being an important influencing factor. Compared to the measured benchmark scenario, when the O3 concentration reached 156 ppb, the average indoor SOA concentration increased approximately 20-fold while its contribution to indoor PM2.5 increased by approximately 7-fold. Our results provide a meticulous look at indoor SOA pollution and its determinants, the knowledge of which is pivotal for the implementation of effective strategies to mitigate indoor SOA pollution.