Effects of Anthropogenic Pollutants on Biogenic Secondary Organic Aerosol Formation in the Atmosphere of Mt. Hua, China

Abstract. Anthropogenic effects on biogenic secondary organic aerosol (BSOA) formation in the upper boundary layer are still not fully understood. Here, A synchronized 4-hourly monitoring of three typical BSOA tracers from isoprene, monoterpenes, β-caryophyllene and other particulate pollutants was conducted at the mountain foot (MF, 400 m a.s.l.) and mountainside (MS, 1120 m a.s.l.) of Mt. Hua, China, to investigate the chemical evolution of BSOA in air mass lifting. Our findings revealed that BSOA was the predominant source of organic matter (OM) at MS site, with an average fraction of ~43 % being ~7-fold of that at MF site. As the prevalent BSOA tracer, isoprene-derived SOA tracers (BSOA_I) maintained comparable level at MF site (182.5±81 ng/m³) and MS site (197.3±127 ng/m³), yet exhibited an inverse diurnal pattern between both sites. And the BSOA_I fraction in OM aloft moderately decreased during the daytime, and correlated positively with 2-methyltetrols/2-methylglyceric acid ratio but negatively with NOx transported from ground level, indicating that anthropogenic NOx would significantly affect the daytime BSOA formation aloft by inhibiting the HO₂·-pathway products. Additionally, the further formation of sulfate in lifting air mass would significantly enhance aerosol water content aloft, which suppressed the reactive uptake of isoprene epoxydiol and ultimately diminished the BSOA_I yields during the daytime. These findings provide more insight into the intricate anthropogenic–biogenic interactions affecting BSOA formation in the upper boundary layer atmosphere.