The Ion Chemistry And Seasonal Variation Of TSP Aerosol Over The East China Coastal Seas

The water-soluble ions (WSI) are important constituent of the atmospheric aerosol and play roles in a number of important atmospheric processes through their direct and indirect radiative force which could influence the Earth's radiation budget and consequently the climate variations. The East Asia troposphere is characterized by high aerosol loadings from both natural and anthropogenic sources, these aerosols could have a significant impact on the atmospheric chemistry and ecosystem over the remote ocean once reaching the Pacific Ocean through long-range transport. In this present dissertation we choose the Yellow Sea and the East China Sea as the study areas, which act as the major tunnels through which the East Asia aerosols could be transported to the Pacific Ocean. The marine aerosol samples were collected over the offshore of Shandong Peninsular, the North Yellow Sea (NYS) and the East China Sea (ECS) during spring and autumn 2007, spring and autumn 2007 and autumn 2007, respectively. The seasonal and regional variations as well as the sources of major WSI are studied, the main conclusions are drawn as follows:(1) The concentration of the major WSI follow the order of nss-SO₄^2- > NO₃^- > NH₄⁺ > nss-Ca2+ > Na⁺ > nss-K+ > Mg2+ in the total suspended particulates (TSP) during the spring cruise over the offshore of Shandong Peninsular, while during the autumn cruise follow the order of nss-SO₄^2- > NO₃^- > NH₄⁺ > nss-Ca2+ > nss-K+ > Na⁺ > Mg2+. The secondary ions (nss-SO₄^2-, NO₃^-, NH₄⁺) occupy the major part during these two cruises, with a concentration of 37.76±11.91 (1 SD) and 39.73±15.96μg·m^-3, respectively, contributing over 80% of the total determined WSI mass concentrations; while the rest of the ions (Na⁺, nss-K+, nss-Ca2+) share relatively similar mass ratios, the Mg2+ contribute the lowest mass ratio of 1.2%. The mass ratios of the WSI indicate that the chemical composition of TSP over the offshore of Shandong Peninsular is strongly influenced by anthropogenic emissions. Methanesulfonic acid (MSA) has a significant seasonal variations, with a mean concentration of 0.041±0.022μg·m^-3 in spring and 0.012±0.0031μg·m^-3 in autumn, respectively.(2) The concentration of the major WSI follow the order of nss-SO₄^2- > NH₄⁺ > NO₃^- > nss-Ca2+ > Na⁺ > nss-K+ > Mg2+ and nss-SO₄^2- > NH₄⁺ > NO₃^- > Na⁺ > nss-Ca2+ > nss-K+ > Mg2+ in the TSP during spring and autumn cruises over the NYS, respectively, similar to over the offshore of Shandong Peninsular. However, the concentration of NO₃^- is lower than NH₄⁺ over the NYS. The mass ratio of nss-SO₄^2- significantly increase to around 50% during the two cruises over the NYS, higher than over the offshore of Shandong Peninsular; meanwhile, the mass ratios of NO₃^- and NH₄⁺ over the NYS are lower than over the offshore of Shandong Peninsular. The mass ratio variations of secondary ions indicate that as the distance between the sampling area and the continent increased, the mass ratio of NO₃^- tend to decrease due to its faster deposition rate relative to nss-SO₄^2-. The concentration of MSA during the spring and the autumn cruises are 0.073±0.034μg·m^-3 and 0.011±0.0044μg·m^-3, respectively, the significant seasonal variation is due to the higher concentration of dimethylsulfide (DMS) in surface seawater during the spring, resulting in higher atmospheric MSA concentration.(3) The concentration of the major WSI follow the order of nss-SO₄^2- > Na⁺ > NH₄⁺ > NO₃^- > Mg2+ > nss-Ca2+ > nss-K+ during the autumn cruise over the ECS, the sea salt ions increase significantly due to the high wind speed, with concentration of Na⁺ higher than NH₄⁺ and NO₃^-, Mg2+ higher than nss-Ca2+ and nss-K+. The mass ratio of NO₃^- is comparable with the NYS cruises, indicating the similar deposition processes during the long-range transport over these two sampling areas. The concentration of MSA is 0.0081±0.0047μg·m^-3, comparable with over the NYS in autumn.(4) Correlation analysis between the WSI concentrations and the meteorological data indicate that the sea salt component are strongly influenced by wind speed; the significant positive relationships between the secondary ions and the temperature/relative humidity (RH) indicates that the secondary ions tend to form better at a relatively higher temperature and RH; correlation between temperature and the crustal ions indicates a continental source of mineral aerosols. Simple relationships between ion pairs are found through cross-correlation analysis, correlations between the secondary ions indicates the three share similar sources, mainly from the anthropogenic transport; strong relationships are found between Na⁺ and Mg2+, the linear regression result shows that both are from bulk seawater; the enrichment factor of K+ shows that it mainly comes from crustal source.(5) Biogenic contribution is calculated based on the empirical nss-SO₄^2-/MSA ratio over the remote ocean. Over the offshore of Shandong Peninsular, the biogenic contributions during spring and autumn are 4.5% and 1.5%, respectively; while over the NYS the biogenic contributions during spring and autumn are 11.0% and 2.0%, respectively; the biogenic contribution over the ECS during autumn is 2.0%. Biogenic contributions are higher during spring than autumn over the sampling areas; the higher primary productivity during spring contributes to higher DMS in surface seawater, which consequently contributes to the higher atmospheric MSA concentration and higher biogenic contribution. Generally, the atmospheric nss-SO₄^2- over the sampling areas mainly comes from anthropogenic sources, however, it is worth noting that the biogenic contribution is significant, especially when the marine biological activity is higher during spring bloom.