苏州市一次重霾污染天气过程的数值模拟

本文对苏州地区2015年12月13—15日发生的一次典型的重霾污染天气过程进行了数值模拟,分析了颗粒物及其组分的时空变化特征及其气象影响因子,以期为该区域空气污染治理和预防提供科学依据。结果表明:(1)利用WRF-Chem模式对此次重霾污染天气过程的污染气体成分进行数值模拟后发现,小时平均的PM_(2.5)、PM_(10)、CO、SO_2、NO_2模拟值与实测值的相关系数较高,达到0.68以上,通过了P0.01的显著性检验,且日变化过程对应也较好。(2)通过分析此次污染过程的天气背景,发现污染形成期高空环流比较平直,中层为均匀的弱高压控制,地面受弱高压脊控制,这种形势容易导致颗粒物的堆积。后期地面等压线密集时,风速大,有利于污染物的输送与扩散。(3)通过分析此次污染过程期间气象要素的变化发现,有逆温、风速小、相对湿度大等不利的气象条件是导致此次污染过程发生的重要原因之一。(4)HYSPLIT轨迹分析显示,此次重霾过程主要受北方大范围灰霾颗粒物南下影响,北方污染气团逐步南推,14至15日本地大气扩散条件差、污染物累积,最终导致本地污染加重,从而发生重霾事件。(5)火点图的分布进一步验证了此次重霾污染过程是由外来污染气团输入所导致。

Numerical simulation on a heavy haze pollution weather process in Suzhou City

With the constant acceleration of urbanization in Suzhou and the rapid growth of particulate pollutions, the health of the residents have been seriously affected. In order to provide a scientific basis for air pollution controlling and prevention in this area, this paper conducts a numerical simulation for a typical heavy haze pollution event which occurred in Suzhou region during the period from 13 to 15 Dec. in 2015, to analyze the temporal and spatial variation characteristics of the particulates and their components and their meteorological impact factors. The results showed: (1) After analysis on the numerical simulation results of the pollutant gas components in the heavy haze pollution weather process from WRF-Chem model, it was found that there was a highpositive correlation between the simulated values and the observed values of hourly average PM_2.5, PM₁₀, CO, SO₂ with the correlation coefficients higher than 0.68 (they passed the significance test of P<0.01). The correspondence of their diurnal variations was also good. (2) The analysis of the weather backgrounds during this polluting process indicated that high-altitude circulation during pollution formation period is relatively straight, the middle layer is controlled by uniform weak high-pressure, and the ground is controlled by weak high-pressure ridges. this situation was conducive to the accumulation of particulates. When the ground isobars were dense later, the wind speed became great, which was conducive to the transportation and diffusion of pollutants. (3) The investigation of meteorological factors changes in the process displayed that the adverse weather conditions such as small wind speed, temperature inversion and high relative humidity were one of the important causes of the pollution process. (4) The trajectory calculation results from HYSPLIT revealed that the pollution process was mainly affected by the large scale southward movement of haze weather from the north China. The north pollution air mass pushed southward gradually. The local diffusion condition was poor during the period from 14 to 15 Dec. in 2015 and the local pollutants were accumulated. All of these above factors led to the aggravation of pollution and the occurrence of the heavy haze weather process in Suzhou. (5) The distribution of fire points further verified that this heavy haze pollution process was resulted from the input of extraneous pollution air mass.