Size-Segregated Characteristics of Organic Carbon (OC) and Elemental Carbon (EC) in Marine Aerosol in the Northeastern South China Sea

Abstract

Organic carbon (OC) and elemental carbon (EC) size-segregated characteristics were analyzed at the junction of sea and land (JSL) and the marine aerosol during the navigation along the northeastern South China Sea (NSCS), including the shallow ocean (NSCS-SO) and the remote ocean (NSCS-RO), from 3 to 20 March 2016. More than 90% of the OC and EC were concentrated in fine particles, and the OC and EC mean concentrations were 10.1 ± 0.63 and 3.44 ± 0.82, 2.67 ± 1.27 and 0.72 ± 0.36, and 1.41 ± 0.50 and 0.40 ± 0.28 μg m−3 in PM3.0 at the JSL, NSCS-SO, and NSCS-RO, respectively. Approximately 75–83% of OC and 84–98% of EC were found in PM1.5. Three sampling sites showed similar OC mass size distributions that had a dominant peak in the 0.49–0.95 μm size range. The mass mean diameters (MMDs) of OC were 0.65 ± 0.15 and 0.59 ± 0.16 μm at the NSCS-SO and NSCS-RO, respectively, followed by 0.53 ± 0.25 μm in fine particles at the JSL. Similar characteristics were found for EC MMDs. Each particle-size bin had OC concentrations that were higher than the EC values of all three sites, and the OC/EC mass ratios were generally more than 2.0. The mean secondary organic carbon (SOC) concentrations in PM1.5 were as follows: JSL (5.42 ± 1.35 μg m−3) > NSCS-SO (1.08 ± 1.02 μg m−3) > NSCS-RO (0.38 ± 0.25 μg m−3), indicating that the contribution of secondary carbonaceous aerosols to organic carbon is relatively low in the remote ocean region.