Chemical Characteristics Of Wet Deposition At Mt. Tai

With the development of economy, acid rain occurred frequently in the northern part of China. Shandong province has become the focus of attention because of the emitting of large amount of pollutants. As a branch project of the National "973" Project, wet deposition chemistry was conducted at Mount Tai region. Mount Tai is located in the eastern edge of Eurasia and the Midwest of East Asia with the altitude of 1545m. The Taishan Mount-top site stands between the planetary boundary layer and the free troposphere where atmospheric turbulence is very notable. These conditions were of great benefit to dispersion and transmission of pollutants. Therefore, the samples collected at the Mount-top were more representative of regional source of pollution. The other sampling site is the Mount-foot site, 128.6 a.s.1., which locates at the suburb of Tai'an city. Comparison of these two sites was very important for the study on the spatial characteristic of air pollution and wet deposition chemistry at Mount Tai region.111 precipitation samples were collected from Jan 2005 to Dec 2006, pH, EC, cations and anions (F^-, Cl^-, HCO₃^-,SO₄^2-, NO₃^-, NH₄⁺, K⁺, Na⁺, Ca²⁺, Mg²⁺), organic acids and heavy metals (Al, Mn, Fe, Ni, Cu, Zn, As, Cd, Pb, Cr) were determined and we got the primary wet deposition chemistry characteristics of Mount Taishan region.Wet deposition of Mount Tai showed strong acidity. The annual volume-weighted pH value of rainwater sampled from Mount-top site was 4.55, and Mount-foot site was 4.42, which is stronger than Mount-top. SO₄^2- , NO₃^- NH₄⁺ and Ca²⁺ are main anions and cations, respectively. The annual volume-weighted concentrations of SO₄^2- , NO₃^- , NH₄⁺ and Ca²⁺ in wet deposition were SO₄^2- 148.3 / 209.9μeq/l, NO₃^- 38.1 / 49.9μeq/l, NH₄⁺101.3 / 139.8μeq/l, Ca²⁺ 69.5 / 100.4 μeq/l, and about 80% in total ion concentrations. The concentrations of formate and acetic acid were higher than oxalic acid, formate 8.2 / 10.7μeq/l, acetic acid 5.6 / 7.6μeq/l at Mount top and Mount foot sites respectively. The percentage of Zn is 53.9%-58.5, indicating Zn was most abundant heavy metal at both sites and following are Fe, Al and Mn.The concentrations of most elements such as NH₄⁺ , SO₄^2- Zn and Fe in the samples of 2006 are much higher than those of 2005, indicating that precipitation amount is a significant factor which can infiuence the precipitation characteristic, on the other hand, air pollution are getting worse at Mountain Tai region. The concentrations of NH₄⁺, Ca²⁺ NO₃^- SO₄^2- , Zn and Fe were influenced greatly than other elements indicating that the most abundant components of wet deposition have great variations than other components.At the same time, we also discussed seasonal variations of main ions, heavy metals and organic acids. It showed that the seasonal variations of main ions and heavy metals are different between two sites: the concentrations of all of the target elements in Mount-top site samples are higher in spring than other seasons, mainly because of the sand storm influence. On the other hand, spring and autumn were seriously polluted time when ions' concentrations were higher than summer and winter.Comparison of two sites indicating that, air pollutants that near the surface of the earth affected the concentrations of most cations and anions, especially SO₄^2- , NO₃^-, NH₄⁺ and Ca²⁺ , that is why these ions' concentrations at Mount foot were higher than Mount top. But Zn and Fe concentrations were opposite to the ions, may be certain pollutants that were transported from far places were significant factor that can influence the characteristics of heavy metals in wet deposition of Mount Tai.Statistic analysis showed that SO₄^2-, NO₃^-, NH₄⁺ and Ca²⁺ in wet deposition had high correlation which existed as the following configuration: (NH₄)₂SO₄, NH₄HSO₄, NH₄NO₃ and Ca(NO₃)₂ before wet deposition formed. As and Cd, Ni and Zn, Al and Fe also had high correlation. At both sites, formate and acetic acid have similar sources, mainly come from plant emittion. Correlation analysis between two sites showed that two site did not correlated with each other. However, high correlation existed if only the rain events that happened nearly the same time of two sites and have similar air mass origin were taken into account.In a word, wet deposition at the Mount Taishan were seriously polluted by anthropogenic activities, acid precipitation occurred frequently. Ionic composition and the kinds of heavy metals were similar between two sites. But there was difference between seasonal variations of these two sites and relationship of the two sites was influenced greatly by the wet deposition happened time and the direction of air mass.