Tracing the Formation of Secondary Aerosols Influenced by Solar Radiation and Relative Humidity in Suburban Environment

Secondary particulate matter exerts adverse effects on air quality and human health. The production or reaction rate of secondary aerosols in polluted environments remains uncertain and is complicated by diverse emissions and meteorological conditions. By concurrently measuring the mass spectra of compounds in both particulate (using an aerosol mass spectrometer) and gas phases (using proton-transfer-reaction mass spectrometry) in suburban Beijing, we linked the secondary organic aerosol (OA) and volatile organic compounds (VOCs) to photochemical age (t(age)) and obtained their reaction or production rates. Factorization analysis of the mass spectra of OA and the 108 VOC species resolved three oxygenated OAs (OOA) and three secondary VOC factors at different oxidation levels. Primary organic aerosols and VOCs from traffic sources were determined to be important sources for secondary aerosol formation. At high pollution levels under the conditions of weaker solar radiation and higher relative humidity, moderately oxygenated OA (O/C = 0.61) and secondary inorganics were coproduced in combination with rapid consumption of all VOCs. At lower pollution levels, the intense solar radiation caused substantial and rapid production of OOA (O/C = 0.81) and intermediate VOCs (both in a high oxidation state) at a rate of 15.0% h(-1) and 14.0% h(-1), respectively. These results highlight the feedback effects between radiation and moisture in terms of altering the formation mechanism of secondary aerosols. In particular, highly oxygenated secondary airborne products under strong radiation should be considered in regard to their environmental impact.

Automated summary

Secondary particulate matter has adverse effects on air quality and human health. The production or reaction rate of secondary aerosols is influenced by diverse emissions and meteorological conditions. This study found that primary organic aerosols and volatile organic compounds from traffic sources are important contributors to secondary aerosol formation. The feedback effects between radiation and moisture alter the formation mechanism of secondary aerosols.