石家庄市冬季一次重污染过程分析与反馈效应研究

为深入探究高ρ（PM_2.5）地区重污染过程的发展变化规律，以石家庄市一次重污染过程（2017年1月13-20日）为例，结合空气质量监测数据、PM_2.5组分测试数据、气象观测资料，从重污染发展阶段（简称"P1阶段"）、维持阶段（简称"P2阶段"）和清除阶段（简称"P3阶段"）分析PM_2.5及其化学组分的变化特征、气象条件和高低空天气形势演变特征，并利用WRF-Chem模型定量研究重污染过程气溶胶反馈效应对典型气象要素的影响.结果表明:①此次重污染过程属于逐步累积增长、快速清除型，在P2阶段ρ（PM_2.5）平均值为241.0 μg/m3，最大值为367.5 μg/m3.②P1和P2阶段高低空大气环流配置稳定，大气边界层高度范围为620.6~712.2 m，风速范围为1.3~2.5 m/s，相对湿度范围为60%~80%.③P2阶段SOR（硫氧化率）和NOR（氮氧化率）均为0.3，ρ（SNA）（SNA为SO₄2-、NO₃-和NH₄+的统称）为128.8 μg/m3，占ρ（PM_2.5）的56.2%；OM有机质，ρ（OM）=ρ（POA）+ρ（SOA），其中，POA为一次有机气溶胶，SOA为二次有机气溶胶]是除SNA以外的第二大组分，在P1和P3阶段ρ（POA）大于ρ（SOA），而在P2阶段ρ（SOA）与ρ（POA）相等，均为28.0 μg/m3，表明在重污染过程中二次污染严重；整个污染过程ρ（NO₃-）/ρ（SO₄2-）为1.0，表明石家庄市移动源和固定源对ρ（PM_2.5）贡献相当.④WRF-Chem模型模拟结果表明，太阳辐射量、温度和大气边界层高度受气溶胶反馈效应的影响在P2阶段的下降量分别为75.1 W/m2、2.7℃和109.9 m，比P1阶段分别高33.6%、91.4%和18.6%，比P3阶段分别高147.0%、305.3%和24.1%.研究显示，此次静稳天气下的重污染过程二次污染严重，气溶胶反馈效应整体使得太阳辐射量、温度和大气边界层高度均向不利于污染扩散的趋势发展，造成石家庄市的ρ（PM_2.5）进一步增加. 

Analysis of Heavy Air Pollution Process and Aerosol Feedback Effect in Shijiazhuang City in Winter

In order to explore the development and change of heavy pollution process in Shijiazhuang City with high ρ(PM_2.5), a heavy pollution process from January 13th to 20th, 2017 was studied. Based on the air quality monitoring data, PM_2.5 chemical components and meteorological observation, the variation characteristics of PM_2.5 and its chemical components, corresponding meteorological conditions and the evolution characteristics of weather situation at high and low altitude were comprehensively analyzed in three stages:development (P1 stage), maintenance (P2 stage) and removal (P3 stage). Moreover, the aerosol feedback effect in the heavy pollution process was quantitatively evaluated by the WRF-Chem model. The characteristics of 'cumulative growth and rapid removal' were determined in the heavy pollution process. During the period of P2 stage, the average ρ(PM_2.5) was 241.0 μg/m3, and the maximum of ρ(PM_2.5) was 367.5 μg/m3. During the period of P1 and P2 stage, the atmospheric circulation at high and low altitudes was stable, the atmospheric boundary layer was 620.6-712.2 m, the wind speed was 1.3-2.5 m/s, the relative humidity was 60%-80%. In the P2 stage, the SOR (sulfur oxidation rate) and NOR (nitrogen oxidation rate) were 0.3, ρ(SNA) (SO₄2-, NO₃- and NH₄+ are called SNA) was 128.8 μg/m3 and accounted for 56.2% of ρ(PM_2.5). OM (organic matter, ρ(OM)=ρ(POA)+ρ(SOA), POA was primary organic aerosol and SOA was secondary organic aerosol) was the largest contributor to ρ(PM_2.5) except for SNA. The ρ(POA) was higher than ρ(SOA) in the P1 and P3 stage. While the ρ(SOA) was equal to ρ(POA), both of which were 28.0 μg/m3 in the P2 stage. The secondary pollution was serious during the process of heavy pollution. In addition, the mobile and stationary sources contributed equally to the concentration of particulate matter in Shijiazhuang City according to the result of ρ(NO₃-)/ρ(SO₄-) of 1.0. The WRF-Chem simulation showed that the aerosol feedback effect reduced the solar radiation, temperature and planetary boundary layer height by 75.1 W/m2, 2.7℃ and 109.9 m, respectively, in the P2 stage. The decrease of solar radiation, temperature and planetary boundary layer height in the P2 stage were 33.6%, 91.4% and 18.6% higher than those in P1 stage, and were 147.0%, 305.3% and 24.1% higher than those in P3 stage, respectively. The study suggests that the secondary pollution is serious under the static and stable meteorological conditions. And the feedback effect makes the solar radiation, temperature and planetary boundary layer height appear to be unfavorable to the diffusion of pollutants, causing further increase of ρ(PM_2.5) in Shijiazhuang City.