临汾市地形气象特征及大气自净能力分析

Analysis of Topographic and Meteorological Characteristics and Atmospheric Self-purification Ability of Linfen

利用临汾市的空气质量和气象观测数据,结合气象预报模型WRF分析其地形和气象特征,讨论地形和气象对空气质量和大气自净能力的影响.研究发现,临汾市地形轮廓大体呈"凹"字型分布,四周环山,受地形影响,边界层以内大气流场易出现辐合,特别是在重污染过程中,这种辐合流场造成大气污染物在局部地区堆积.临汾市2017年采暖季的平均通风系数约为2016年同期的2倍,扩散条件总体有利,是其污染程度较低的重要原因,且重污染过程累积期及稳定期的通风系数约为清洁时段及污染消散期的80%和30%.临汾市春季(4月、5月)风速最大、相对湿度最低、混合层高度最高,大气自净能力最好.临汾市大气对污染物的扩散能力弱且利于颗粒物的吸湿增长和二次粒子生成,加剧了大气污染.

Using the air quality and meteorological data of Linfen and combining with the meteorological forecast model WRF to analyze the topography and meteorological characteristics of Linfen, the effects of topography and meteorology on air quality and atmospheric self-purification are discussed. The study found that the terrain outline of Linfen is generally "concave" type distribution and surrounded by mountains, affected by the terrain, the large airflow field under the boundary layer is prone to convergence, especially in the process of heavy pollution, this convergence field caused the accumulation of atmospheric pollutants in local areas. In the heating season of 2017, the average ventilation coefficient of Linfen is about twice as much as that of the same period of 2016. Generally, the diffusion condition is favorable,which is an important reason for the low pollution in 2017. In addition, the ventilation coefficient in the accumulation period and the stable period of heavy pollution process is about 80% and 30% of that in the cleaning period and the pollution dissipation period. Compared with other cities in Shanxi Province, Linfen has the smallest annual average wind speed, higher relative humidity than the average level, and the lowest mixing layer height. The atmosphere has a weak ability to diffuse pollutants and is conducive to the moisture absorption growth of particles and the generation of secondary particles, which aggravates air pollution. Overall, the atmospheric self-purification capacity of Linfen is the lowest in Shanxi Province.