Chemical and dynamical controls on rapid secondary organic aerosol accumulation over a large lake in eastern China

Abstract. Lake-induced meteorological conditions can influence the formation and spatial distribution of secondary organic aerosol (SOA) by modulating precursor mixing, chemical processing, and aerosol transport. Yet how these processes act together to drive rapid SOA accumulation remains insufficiently understood. Here we conducted comprehensive measurements of aerosol composition at Taihu Lake in the Yangtze River Delta during the summer of 2023. Throughout the campaign, organic aerosol (OA) dominated submicron particulate matter (PM₁) mass, accounting for 56 % of the total PM₁ (compared to 41 % at a nearby suburban station), with secondary components comprising 84 % of the total OA at Taihu Lake. During a prominent pollution episode (August 10–12), OA reached 73.7 μg m^-3 (78 % of PM₁), and the SOA fraction rose to 90 %. This rapid SOA accumulation was driven by a unique physicochemical synergy at the lake-land interface. The convergence of anthropogenic and biogenic emissions supplied a highly reactive precursor pool, while enhanced atmospheric oxidation capacity promoted rapid oxidation and aerosol aging, leading to efficient SOA formation. As revealed by modeling analyses, the lake–land thermal contrast further drove a pronounced lake–land breeze circulation, inducing localized subsidence over the lake that efficiently transported SOA formed aloft down to the surface, thereby favoring its rapid accumulation. These findings suggest that lake environments can provide favorable chemical and meteorological conditions for efficient SOA production, highlighting the need to consider large inland lakes in assessments of regional aerosol chemistry and air quality.