A preliminary analysis of chemical characteristics of atmospheric pollutants and their deposition budget on the Fu-shan Forest in Taiwan

This paper presents the chemical characteristics of atmospheric pollutants measured at the Fu-Shan forest (620 m MSL) during two two-weeks field experiments held in the summer and winter of 1993. Chemical compositions of these atmospheric pollutants in solid, gaseous and liquid phases were analyzed. The deposition budget of S and N compounds through dry and wet deposition pathways were particularly assessed. As a result, aerosol mass spectra were found to be bimodal, having the 50% cut size < 1.0 μm and around 3.2 μm for fine and coarse modes, respectively. In summer, fine and coarse modes were primarily composed of ammonium sulfate and nitrate, respectively. But, in winter the coarse mode was dominated by sea salts due to the influence of northeast monsoon flows. Our average HNO₂ (∼ 0.10 ppb) was appreciably higher than those observed in clean troposphere, whereas HNO₃ was at a comparable level. Meanwhile, ammonia gas and particulate ammonium were at a lower concentration level compared with those generally observed on the continental grounds. The SO₂ (< 1 ppb) was comparable with those frequently observed in the free troposphere, while SO₄^2- was close to the lowest level typically obtained in urban areas. In addition, NO₃^- which is thought to be associated with local pollution was limited. Therefore, we believe that excessive SO₄^2-, to a larger extent, was transported to the site via long-range transport, particularly in winter. With regard to the deposition budget, wet deposition pathway (> 90%) was the most effective mechanism for delivering atmospheric S and N compounds to the Fu-Shan forest during the periods of our field experiments.