Abstract. Atmospheric submicron aerosols have a great effect on air quality and human health, while their formation and evolution processes are still not fully understood. Herein, the crucial role of atmospheric oxidation capacity, as characterized by OH exposure dose in the formation and evolution of secondary submicron aerosols, was systematically investigated based on a highly time-resolved chemical characterization of PM1 in a southern suburb of Beijing in summertime from 25th July to 21st August 2019. The averaged concentration of PM1 was 19.3 ± 11.3 μg m−3, and nearly half (48.3 %) of the mass was organic aerosols (OA) during the observation period. The equivalent photochemical age (ta) estimated from the ratios of toluene to benzene was applied to characterize the OH exposure dose of the air mass. The relationships of NR–PM1 species, OA factors (i.e., one hydrocarbon-like (HOA) and three oxygenated (LO-OOA, SV-OOA and MO-OOA) organic aerosol factors) and elemental compositions (e.g., H / C, O / C, N / C, S / C, OM / OC, and OSc) to ta were analyzed in detail. It was found that higher PM1 concentration accompanied longer ta, with an average increase rate of 0.8 μg m−3 per hour. Meanwhile, the formation of SO42− and MO-OOA were most sensitive to the increase in ta, and their contributions to PM1 were enhanced from 19 % to 27 % and from 27 % to 48 %, respectively, as ta increased from 9.4 h to 19.6 h. In addition, OSc and the ratios of O / C and OM / OC increased with the increase in ta. These results indicated that photochemical aging is a key factor leading to the evolution of OA and the increase of PM1 in summertime.
Measurement report: Effects of photochemical aging on the formation and evolution of summertime secondary aerosol in Beijing