• 关键词：PM_2.5  霾  冷锋  降水  清除  武汉

• 基金项目：国家重点研发计划（No.2017YFC0212604）；湖北省自然科学基金（No.2016CFB347）；国家自然科学基金（No.41675136）；湖北省气象局科技发展基金（No.2017Y01）

• 岳岩裕
• 武汉中心气象台, 武汉 430074

• 周悦
• 武汉区域气候中心, 武汉 430074

• 王晓玲
• 武汉中心气象台, 武汉 430074

• 祝波
• 湖北省环境监测中心站, 武汉 430072

• 摘要：基于2013-2016年93次冷锋影响过程，研究了冷锋和降水对武汉市PM_2.5浓度增加和降低的影响机制，并对浓度下降幅度开展了定量分析.结果表明：受冷锋影响PM_2.5浓度变化表现为"两类五型"，其中，PM_2.5浓度下降占比为62%，平均下降幅度为41 μg·m^-3，主要发生在中等强度冷锋过程中，下降幅度最大时24 h变温、24 h变压和极大风速的区间分别为-4~-2℃、8~12 hPa和>8 m·s^-1；而PM_2.5浓度上升主要出现在弱冷锋影响下，上升幅度最大的相应区间分别为-2~0℃、<6 hPa和<4 m·s^-1.直接下降型风速最大，直接上升型冷锋强度偏弱，先升后降型PM_2.5浓度平均值最高.71%的冷锋过程伴有降水.对于重污染过程，污染持续时间最长的天气型为低压倒槽，PM_2.5浓度值最大的天气型为均压场.同时，清除方式中冷空气和降水共同作用占44.4%，单纯冷空气影响占37.0%，仅冷空气作用时的清除速度最快，下降速度为71.1 μg·m^-3·d^-1，但结束时的浓度最高；配合降水时清除效果明显，结束浓度一般在46 μg·m^-3左右，但清除速率较小.

• Abstract：In this paper, 93 cold front processes were selected from 2013 to 2016. Meanwhile, we analyzed the air pollution characteristics under the influence of cold front and precipitation with the aid of PM_2.5 datasets from the Hubei province environmental monitoring center station in Wuhan. The influence mechanism of cold front and precipitation on the variation of PM_2.5 concentrations were studied quantitatively. The results showed that the variations of PM_2.5 concentrations could be divided into 2 categories with 5 types under the effect of cold front. The decline-category accounted for 62%, with PM_2.5 concentration decreased by 41 μg·m^-3, which mainly occurred in the processes of medium-strength cold front. The biggest decrease of PM_2.5 concentrations would appear in the conditions of temperature in 24 h variability from -4 to -2℃, or air pressure in 24 h variability from 8 to 12 hPa, or the extreme wind speed above 8 m·s^-1 during the cold front process. While, the ascending-category mainly occurred in the processes of weak-strength cold front. The biggest increase of PM_2.5 concentrations would appear in the conditions of temperature in 24 h variability from -2 to 0℃, or air pressure in 24 h variability below 6 hPa, or the extreme wind speed below 4 m·s^-1 during the cold front process. There was the biggest wind speed in direct-descending type, weaker intensity of cold front in direct-ascending type, and highest PM_2.5 concentrations in ascending-descending type. There were 71% of cold front processes accompanied by precipitation. During heavy pollution processes, the weather type causing the longest pollution duration is the low pressure inverted trough, and causing the highest concentration is the uniform pressure field. For the pollution-cleaning processes, cold air with precipitation accounted for 44.4%, while only cold air accounted for 37.0%. Pollution-cleaning process with only cold air had the fastest cleaning speed of 71.1 μg·m^-3·d^-1, with the highest PM_2.5 concentration at the end of process. However, the cleaning effect was obvious when cold air is combined with precipitation, the average concentration was 46 μg·m^-3 at the end of process, but the cleaning speed was slow.

• Key words：PM_2.5  haze  cold front  precipitation  elimination effect  Wuhan

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