Numerical simulation and sensitive factors analyse for dry deposition of SO₂ and NO₂ in Bohai Rim area of China

Nested air quality prediction modeling system (NAQPMS), had been coupled with the Wesely large leaf resistance dry deposition model from USA. The influencing factors of dry deposition and dry deposition flux of SO₂ and NO₂ in Bohai Rim area were simulated and analyzed. The main sensitive factors of dry deposition included atmospheric stabilities, solar radiation, seasons and surface pattern. The dry deposition velocity decreased with the increasing atmospheric stabilities and it rose more with intensive solar Radiation. The dry deposition velocity of SO₂ had the minimum value in early autumn and the maximum value in winter. The dry deposition velocity of NO₂ had the similar values during spring, summer, early autumn and late autumn, and reached its minimum value in winter. The dry deposition velocity of SO₂ was maximum on the water surface while minimum in desert area. To dry deposition velocity of NO₂ was lower on the water surface, while it remained higher on the farmlands. Because of the cumulative effect of different sensitive factors, the dry deposition flux of SO₂ in the most of the research area remained between 0.05~0.25 μg/(m²·s) whereas the dry deposition flux of NO₂ was between 0.05~0.30 μg/(m²·s). The higher value were noted in the south of Hebei, north west of Shandong and middle of Liaoning province. For the four season the dry deposition flux was ranked as: autumn>spring>winter> summer. The dry deposition flux was larger in daytime than at night, it included some dry deposition flux of SO₂ on the sea surface of Bohai region. In order of the effects of dry deposition, emission and transport, the concentration of SO₂ in Bohai Rim was between (5~20)×10^-6, NO₂ between (20~60)×10^-6. The maximum values of all the factors were observed in south of Hebei, north west of Shandong and the middle of Liaoning. The concentration was higher in summer in some area, while lower in most of the area, it remained higher during spring, autumn and winter.