宝鸡市冬季一次持续性重污染过程特征分析

污染气象成因和污染物区域传输作用对本地污染影响较大，研究不同地区污染气象成因和污染物区域传输作用对本地污染的治理有重要意义.利用污染物浓度监测和气象要素观测资料，采用统计学分析方法、特征雷达图和HYSPLIT-4后向轨迹模型分析宝鸡市2018年12月29日—2019年1月8日一次持续性重污染过程的气象成因和污染特征.结果表明:①此次重度污染持续时间长、强度大，污染过程中有6 d空气质量指数(AQI)达到重度及以上污染(AQI>200)，ρ(PM_2.5)平均值达205.4 μg/m3，有2 d达到严重污染(AQI>300).②气象条件对污染物浓度的影响显著，高低空环流形势形成稳定层结，容易造成污染物累积.东南大风将污染气团远距离输送到宝鸡市，西北静小风使得污染物在本地聚集加重污染.③重污染维持阶段，ρ(PM_2.5)/ρ(PM₁₀)在0.9左右，说明此次污染过程PM_2.5占比较大，污染物的二次转化作用明显；ρ(NO₂)/ρ(SO₂)为6.2，表征移动源贡献率高于固定源；ρ(CO)/ρ(SO₂)呈先增后减的变化特征，表明静稳天气持续，本地源排放对重污染的贡献逐渐凸显.④特征雷达图结果表明，此次重污染过程的污染类型由发展阶段的污染特征不明显和燃煤型污染特征，逐渐转化为偏二次污染类型，重污染过程结束后污染类型以偏扬尘型为主.研究显示，气象条件和传输扩散对宝鸡市重污染影响显著，宝鸡市重污染应急需优先管控移动源，汾渭平原应加强区域联动，共同治理环境污染问题. 

Characteristics and Mechanism of a Heavy Haze Episode in Baoji City

Meteorological and the regional transmission have a great impact on local pollution.It is of great significance to study the meteorological and the regional transmission of pollutants in different areas. The Baoji City experienced a severe haze event from December 29th, 2018 to January 8th, 2019. Here, we investigated the pollution characteristics and formation mechanism of this haze event with emphasizing the concentration variations of polluting components, the synoptic pattern, and the sources of the air pollutants. The analysis was conducted by combining the concentrations of pollutant, meteorological data, characteristic radar chart, and the HYSPLIT-4 model. Our analysis showed that the pollution event had 6 days of air quality above the level of heavy pollution (AQI>200), 2 days with a serious pollution level (AQI>300). The average concentration of PM_2.5 during the haze event was 205.4 μg/m3. Furthermore, meteorology had significant effects on the pollution event. Steady circumfluence and warm advection before the ridge warmed the middle atmosphere and hence inhibited the pollutants diffusing horizontally quickly. Then, the southeast gale transported the polluted air mass to the Baoji City and the static wind in the northwest caused pollutants to accumulate locally. The PM_2.5 and PM₁₀ concentration ratio during the heavy pollution maintenance stage was around 0.9, indicating that the pollution was dominated by fine particles. The NO₂ and SO₂ concentration ratio was 6.2, indicating that the contribution rate of mobile source was higher than that of fixed source. The CO and SO₂ concentration ratio first increased and then decreased. The steady and stable weather continues, and the contribution of local source emissions to heavy pollution is gradually prominent. Finally, through the characteristic radar map analysis, the haze pollution event in Baoji City started from coal-burning pollution characteristics, and then gradually transformed into secondary pollution types. After the heavy pollution process, the pollution type was dominated by dust. The results show that meteorological conditions and the regional transmission have a significant impact on heavy pollution in Baoji City. Baoji City should prioritize the control of mobile sources. Fenwei Plain strengthened regional cooperation to jointly tackle environmental pollution.