Aerosol chemical properties and related pollutants measured in Dongsha Island in the northern South China Sea during 7-SEAS/Dongsha Experiment

Aerosol observations were conducted at Dongsha Island in two batches from 19 to 23 March and 10 to 19 April 2010. Dongsha Island is located in a remote area over the northern South China Sea (SCS), distantly surrounded by southern China, Taiwan, the Philippines, and the Indochinese Peninsula. During the study period, the average PM₁₀ and PM_2.5 mass concentrations were 26.5±19.4 and 12.6±6.0μgm^-3, respectively. In particular, a daily PM₁₀ concentration of 94.1μgm^-3 caused by a yellow-dust event originating from the Asian Continent was recorded on 21 March. Other than this event, the PM_2.5 and PM_10-2.5 daily levels were 7.1±1.2 and 12.6±5.0μgm^-3, respectively, on days without pollution from anthropogenic sources in the surrounding areas. Water-soluble ions (WSIs) were the predominant components that accounted for 58.7%±10.5% and 51.1%±7.2% of the PM₁₀ and PM_2.5 mass. The second most abundant component was carbonaceous content, which accounted for 9.5%±4.7% and 17.5%±5.3% of PM₁₀ and PM_2.5, respectively. SO42- was the most abundant PM_2.5 WSI, whereas the Na⁺ and Cl^- pair was the most abundant PM_10-2.5 WSI. Based on the U.S. IMPROVE protocol, the resolved carbonaceous fractions were mainly distributed in PM_2.5 and influenced by coal combustion, mobile vehicles, and biomass burning. Most of the resolved WSIs in particles were in the liquid phase due to the humid environment around the northern SCS.