Chemical Characteristics of Marine Fine Aerosols over Sea and at Offshore Islands during Three Cruise Sampling Campaigns in the Taiwan Strait– Sea Salts and Anthropogenic Particles
Abstract. Marine fine aerosols were simultaneously collected over sea and at offshore islands during three cruise sampling campaigns to investigate the spatial distribution of atmospheric fine particles (PM2.5) and the influences of sea salts and anthropogenic particles on the chemical characteristics of PM2.5 in the Taiwan Strait. Field sampling results indicated that PM2.5 concentrations over sea were generally higher than those at the offshore islands, while the PM2.5 concentrations in the daytime were commonly higher than those at nighttime. Moreover, the concentrations of PM2.5 were generally higher than those of coarse particles (PM2.5–10) with an exception of the winter cruise in 2014. Moreover, sea salts accounted for 6.5–11.1 % and 11.0–13.5 % of PM2.5 at the offshore islands and over sea, respectively. The contributions of non-sea salt-water soluble ions (nss-WSI) to PM2.5 at the offshore islands were obviously higher than those over sea, while the contributions of ss-WSI for PM2.5 at the offshore islands were much lower than those over sea during the cruise sampling campaigns. Anthropogenic metallic elements including Zn, Mn, Pb, Cr, and Ni had higher concentrations over sea than those at the offshore islands, suggesting that PM2.5 was not only influenced by marine aerosols but also by anthropogenic particles originated from human activities such as industrial processing, fuel burning, and vehicular and shipping exhausts. Higher mass ratios of Ni/Al and Ni/Fe over sea than those at the offshore islands suggested that shipping emissions had higher influences on marine fine particles than crustal dusts in open sea while compared to those at the offshore islands. The carbonaceous contents of PM2.5 indicated that the concentrations of organic carbons (OC) were generally higher than those of elemental carbons (EC). The higher mass ratios of organic and elemental carbons (OC/EC) were observed at the central and north Taiwan Strait, and follow by the offshore islands and the south Taiwan Strait. Overall, sea salts and anthropogenic particles had significant influences on the chemical composition of PM2.5 over sea and at the offshore islands.