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 above sea level (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 the MS site, with an average fraction of ∼43 % being ∼7-fold that at the MF site. As the prevalent BSOA tracer, the isoprene-derived SOA tracers (BSOAI) stayed at a comparable level at the MF site (183±81ngm-3) and MS site (197±127ngm-3) yet exhibited an inverse diurnal pattern between the two sites. And the BSOAI fraction in OM aloft moderately decreased during the daytime and correlated positively with the 2-methyltetrol/2-methylglyceric acid ratio but negatively with NOx transported from ground level, indicating that anthropogenic NOx significantly affected the daytime BSOA formation aloft by inhibiting the HO2⚫-pathway products. Additionally, the further formation of sulfate in a lifting air mass significantly enhanced aerosol water content aloft, which suppressed the reactive uptake of isoprene epoxydiol and ultimately diminished the BSOAI yields during the daytime. These findings provide more insight into the intricate anthropogenic–biogenic interactions affecting BSOA formation in the upper boundary layer.