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

Indoor secondary organic aerosols (SOAs) generated from reactive organic gases (ROGs) reacting with O 3 have a substantial impact on indoor PM 2.5 levels. China's recent decrease in atmospheric PM 2.5 and increase in atmospheric O 3 have resulted in correspondingly lower levels of indoor PM 2.5 and higher levels of indoor O 3 , which will further affect indoor SOA concentration. Thus, the aims of this study were to evaluate indoor SOA concentrations and their contribution to indoor PM 2.5 and analyze the impact of the air exchange rate, window-opening status, proportion of indoor organic particles, and O 3 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 O 3 , along with indoor and outdoor PM 2.5 concentrations. We found a maximum indoor SOA concentration of 35.23 μg/m³, contributing over 50% to indoor PM 2.5 , 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 O 3 concentration being an important influencing factor. Compared to the measured benchmark scenario, when the O 3 concentration reached 156 ppb, the average indoor SOA concentration increased approximately 20-fold while its contribution to indoor PM 2.5 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. • We evaluated the indoor SOA concentration and its contribution to indoor PM 2.5 • In over 80% of samples, indoor SOA was <1 μg/m³, contributing <10% to indoor PM 2.5 • Terpenoid compounds were identified as crucial precursors for indoor SOA generation. • Indoor O 3 concentration had the most substantial impact on indoor SOA generation. • Shanghai had the lowest, while Shenzhen had the highest average SOA concentration. [ABSTRACT FROM AUTHOR]