Diurnal Variations in Primary and Secondary Organic Aerosols in an Eastern China Coastal City: The Impact of Land-Sea Breezes

Abstract

The land-sea breeze circulation significantly impacts the atmospheric transport of organic aerosols in coastal regions.However, the links between atmospheric organic compounds and land-sea breezes remain poorly understood. In this study, organic marker compounds for biomass burning, primary biological aerosols, biogenic and anthropogenic secondary organic aerosols (SOA) in fine particles (PM2.5) from a coastal city in East China were analysed using gas chromatography–mass spectrometry. Land-sea breeze circulations were identified to explore their potential influence of organic molecular compositions. The results indicate that biogenic and anthropogenic secondary aerosol formations,pollen and plant debris were the main sources during early autumn, especially during the daytime. While the contributions of biomass burning and coal combustion increased significantly in early spring, especially during nocturnal hours. During land-sea breeze periods, all detected organic makers decreased except α/β-pinene SOA makers in early autumn; whereas, all the organic markers increased except α/β-pinene SOA makers, pollen and plant debris makers in early spring. Furthermore, the reaction pathway and aging of biogenic SOA were also related to land-sea breezes. During the land-sea breeze periods, the ratios of 2-methylglyceric acid to 2-methyltetrols increased during early autumn, indicating that more isoprene-derived SOA generated from the high-NO x  (nitrogen oxides) pathway when the land-sea breezes occurred; while the ratios decreased in early spring, implying that more isoprene-derived SOA generated from the low-NO x  pathway. Changes in the ratio of monoterpene SOA makers demonstrate that monoterpene SOA was relatively aged during sea breeze periods, while it was fresher when the land breeze occurred. In addition, night/day ratios of molecular marker compounds increased significantly when land-sea breezes occurred in both early spring and early autumn. Our resultsprovide new insights into the shift in the chemical composition of organic aerosols over coastal areas where are influenced by land-sea breezes.

Keywords: land-sea breezes, diurnal variations, biomass burning, primary biological aerosols, SOA