河谷城市大气环境容量的研究

科学核算大气环境容量，对于合理确定污染物总量控制指标，进而实施大气污染管控措施、治理区域大气污染问题有重要意义.以河谷城市兰州市中心城区为研究区域，利用WRF模式模拟了研究区域的边界层高度及混合层平均风速，并根据地形条件，从污染气象角度给出了扩散单元面积，利用A值法（A为地理区域性总量控制系数）计算兰州市中心城区SO₂、NO_x及VOCs的大气环境容量；同时，将兰州市中心城区2016年SO₂和NO_x的排放总量与SO₂和NO_x的环境容量进行对比，结合区域环境质量监测资料说明大气环境容量设置的合理性.结果表明:①兰州市中心城区的A值具有季节性变化特征，其在春、夏两季较大，在秋、冬两季较小，春、夏两季A值较大的主要原因是边界层高度及边界层内的平均风速较大，而冬季则相反.②兰州市中心城区SO₂、NO_x和VOCs的大气环境容量分别为4.05×104、1.81×104和5.44×104 t/a.③2016年SO₂的实际年排放量（1.62×104 t）未超过大气环境容量限值（4.05×104 t），尚有余量（2.43×104 t），这与兰州市2016年4个环境空气质量监测点ρ（SO₂）年均值均达到GB 3095-2012《环境空气质量标准》二级标准的现状一致；NO_x的实际年排放量（3.16×104 t）已超过大气环境容量限值（1.81×104 t），无环境容量（-1.35×104 t），这与兰州市2016年4个环境空气质量监测点ρ（NO_x）年均值均超过GB 3095-2012二级标准值的现状一致.研究显示，采用A值法计算的兰州市大气环境容量符合区域污染扩散特征. 

Atmospheric Environmental Capacity in River Valley Terrain

In order to determine the total volume control quotas of pollutants rationally and further to control regional air pollution, scientific calculation air environmental capacity has a high impact. In this paper, the total amount of SO₂, NO_x and VOCs are calculated based on the A-value method (A is total volume control coefficient of geographical region). Firstly, the height of atmospheric boundary layer and average wind speed in the mix layer were simulated by the WRF model in the study region. Then, diffusive units were distributed by GIS considering geographical factor. Finally, to verify the rationality of the results, the capacity of SO₂ and NO_x were compared with the emissions of SO₂ and NO_x. The results indicated that:(1) A value shows seasonal variation, the lower values occur in autumn and winter, and higher values were observed in spring and summer, which is in accordance with meteorological conditions. (2) The capacity of SO₂, NO_x and VOCs in the center of Lanzhou City was 4.05×104, 1.81×104 and 5.44×104 t/a, respectively. (3) The SO₂ emissions was 1.62×104 t in 2016, which was less than the SO₂ capacity (4.05×104 t), and there were 2.43×104 t left, so the SO₂ concentration monitored by four air monitoring stations met the Grade Ⅱ of Ambient Air Quality Standards (GB 3095-2012). The NO_x emissions were 3.16×104 t in 2016, which was higher than the NO_x capacity (1.81×104 t), and the NO_x concentration monitored by four air monitoring stations exceeded the Grade Ⅱ of GB 3095-2012. The results show that the environment capacity of air pollutants estimated by the A-value is rational and in coincidence with the characteristics of pollutant diffusion.