Seasonal Variations of Terrestrial OC Sources in Aerosols over the East China Sea: The Influence of Long-Range Air Mass Transport.

Aerosols represent an important source of terrestrial organic carbon (OC) from the East Asian continent to the China marginal seas, thus their provenance and transport play important roles in the global carbon cycle. Fifty samples of total suspended particle were collected seasonally from the nearshore Huaniao Island (HNI) in East China Sea (ECS) from April 2018 to January 2019; and they were analyzed for total organic carbon (TOC) content and stable carbon isotope (δ¹³C), as well as terrestrial bio-markers including n-alkanes (C₂₀-C₃₃), n-alkanols (C₂₀-C₃₂) and n-fatty acids (n-FAs, C₂₀-C₃₀), to distinguish the seasonal variabilities of terrestrial OC sources and reveal the influence of the long-range air mass transport on these sources. The TOC-δ¹³C values (range from −27.3‰ to −24.3‰) and molecular distributions of terrestrial biomarkers both suggested that terrestrial OC contributions to aerosols had significant seasonal variations. The source indices of terrestrial biomarkers (e.g., Fossil% = 82.8% for n-alkanes) revealed that the fossil fuel OC contributions, including coal burning and vehicular emission, were higher in winter, mainly because of the long-range air mass transport from the north of the East Asian continent. The terrestrial plant OC contributions were higher in summer (e.g., Wax% = 32.4% for n-alkanes), likely due to local vegetation sources from HNI and East Asian continental air masses. Cluster analysis of air mass backward-trajectories clearly showed that transport pathway plays an important role in determining the organic constituents of aerosols in China marginal seas. A comparison of these terrestrial OC contributions from different air mass origins suggested that fossil fuel OC showed less variations among various air mass origins from northern China in winter, while terrestrial plant OC sources from northern and southern China in summer contributed more than that from the air masses transported through the ECS. These results provided a basis for future quantification of terrestrial OC from different origins in marine aerosols, by combining biomarker index and carbon isotopes. [ABSTRACT FROM AUTHOR]