西宁市大气环境风险模拟研究

Simulation of atmospheric environmental risks in Xining

利用中尺度气象模式模拟了特殊地形下的气象变化特征,通过CALPUFF模拟了大气环境风险事件的精细化扩散特征。结果表明:西宁市地面风特征与河谷地形走向基本一致,典型风场表现为湟水河谷盛行西北和东南风,北川河谷则多为偏北风。青藏高原昼间强烈的山坡辐射增热和夜间冷却效应致使低空出现逆温层频率高,全年逆温的频率约为36%,最高逆温强度达每百米增温2.0℃以上,不利于污染物在垂直方向的扩散,河谷剖面模拟温度场的结果显示相同高度山坡附近比河谷中心的温度大约高1.5℃。CALPUFF在西宁市大气环境风险模拟结果中能清楚描绘出污染物沿河谷输送与扩散的初始状况和细致分布,同时出现山体对烟团的阻碍效应、烟团因流场在山脊处形变以及山谷风环流影响等非定常扩散现象,扩散轨迹符合复杂地形和气象条件影响的特征和规律,模拟结果对准确预估大气环境风险事件在复杂地形和气象条件下城市中的扩散特征、影响范围和程度具有重要意义。

The meteorological elements under special terrain were simulated by a mecoscale numerical model, and the fine diffusion characteristics for an atmospheric environment risk event were simulated by the CALPUFF mod- el. The results show that surface wind direction is parallel to the valley direction. The west-north and east-south wind and north wind prevail in Huangshui river valley and in Beichuan fiver valley, respectively. Strongly hillside daytime radiative heating and night cooling effect in Qinghai-Tibet plateau lead to inversion layer frequently with high intensity, and the frequency of inversion temperature reaches 36%, while the maximum intensity increases 2. 0 ~C every the 100 m height, which is not favorable to diffuse pollutants in vertical direction. By simulation, tem- perature in same height hillside is about 1.5 ~C higher than in the center of valley. CALPUFF plume trajectory model can be applied to the simulation of atmospheric environmental risk events, and the simulation results clearly depict the initial condition and detailed distribution about pollutant transport and diffusion along the valley. Under the complex terrain and weather conditions, some diffusion phenomena will appear such as puff is hindered by the mountain, puff diffusion locus accords to the characteristic and regulation from stream affection and puff diffusion is influenced by circulation of valley wind, which have important significance to estimate the diffusion, influencing range and extent for atmospheric environmental risks in the city.