Characteristics and sources of atmospheric aerosols over the East China Sea

Thirty-three total suspended particle samples (TSP) and seven size-segregated particle samples were collected over the East China Sea during the following periods: November to December, 2006, February to March, 2007, May 2008 and June 2008. Concentrations of particulate water-soluble, inorganic ions were measured to investigate their seasonal variations, size distributions and potential sources. The sum of the concentrations of the total particulate water-soluble inorganic ions in the TSP ranged from 13.5 to 93.5 μg·m^-3, with an average concentration of 33.9 μg·m^-3. The ions contributed to 54%, on average, of the TSP mass concentration. SO₄^2- was the dominant ion, followed by Cl^-, Na⁺, NO₃^- and NH₄⁺ while K⁺, Mg²⁺, Ca²⁺ and PO₄^3- yielded a minor contribution to the TSP mass concentration. Sea-salt ions and secondary ions (nss-SO₄^2-, NO₃^-, NH₄⁺) contributed to 38% and 57%, on average, of the total mass concentration of water- soluble ions respectively. When the ion balance was analyzed, the observed aerosol particles appear to be typically neutralized. A distinctive seasonal variation of ion concentrations was exhibited with higher values in winter and lower in spring and summer. However, the fraction of the sum of all ions to the TSP mass concentration was evidently lower in spring than in winter and summer. As reported in the literature, the dominant mode of Na⁺, Cl^- and Mg²⁺ occurred at 3.3~7.0 μm while the dominant mode of Ca²⁺ shifted to a smaller size at 2.1~4.7 μm. However, SO₄^2-, NH₄⁺, K⁺ overwhelmingly distributed at 0.43~1.10 μm fine particles. It is interesting that most NO₃^- existed in the 0.43~0.65 μm fine particles in winter, and it dominated in the coarse particles at 3.3~4.7 μm in spring and summer. The results of factor analysis indicated that anthropogenic, marine and crustal sources can explain 53.6%, 28.9% and 7.3% of the total variance in the aerosol samples, respectively. The averaged mass ratio of NO₃^- /nss-SO₄^2- was 0.45±0.25, suggesting that the contribution of stationary source emissions was more important than that of vehicle emissions in the atmospheric aerosols over the East China Sea.