2019年—2020年秋、冬季淮南市灰霾过程拉曼-米气溶胶雷达观测研究

拉曼-米气溶胶激光雷达因无需假设雷达比，而在准确测量气溶胶消光系数方面较传统米散射雷达更具优势。在合肥市的外场探空比对实验结果表明，2.5 km以下拉曼-米激光雷达反演的消光系数更为准确，相差可达0.04 km-1，且获取的水汽混合比廓线与探空数据一致性良好。利用该技术获得了2019年—2020年秋、冬季期间淮南市的气溶胶消光系数廓线和边界层高度等数据，进而对空气质量污染期间的污染类型（本地污染排放、传输型污染、传输型污染叠加本地污染累积）和颗粒物的时空演变特征进行了统计分析。结果显示该市在此期间受到20次细颗粒传输和8次沙尘传输影响。其中沙尘传输主要来自西北方向，由高空沉降至近地面（厚度达2 km以上），平均大气边界层高度达1.23 km以上。在典型细颗粒传输过程中，边界层高度基本维持在1.1~1.2 km左右，近地面风向以西北风为主，少量东南风主导。在细颗粒传输叠加本地累积的复合污染过程中，边界层高度略低（平均高度在1.0 km左右），近地面风向以偏北风为主，污染气团自低空出现后，其下沿高度持续降低并最终与近地面污染耦合。在细颗粒导致的重污染过程中，近地面水汽混合比及相对湿度数据与PM_2.5的浓度变化趋势一致性良好，说明颗粒物的吸湿性增长和气态污染物二次转化过程可能助推了PM_2.5的生成，加重污染形势。对边界层的统计结果表明，其高度变化对污染气团的沉降和近地面污染累积有十分明显的正相关性。秋冬季期间，该市的小时边界层高度大部分分布在1.6 km以下，平均为1.0 km左右，小时空气质量达重度污染期间，边界层高度普遍不足0.6 km。从气团后向轨迹模拟结果来看，该市空气质量为中度及以上污染期间的气流主要来自偏北方向，少量来自东南沿线，因而污染期间需要加强市区偏北方向污染源的管控，防止叠加影响。

Study on the Haze Process in Huainan City From October 2019 to March 2020 Observed by Raman-Mie Aerosol Lidar

The Raman-Mie Aerosol Lidar (RMAL) has advantages over traditional Mie scattering Lidar in accurately measuring aerosol extinction coefficient without assuming radar ratios. The results of the outfield sounding comparison experiment in Hefei indicated that the extinction coefficient retrieved by RMAL below 2.5 km is more accurate than the traditional Mie scattering Lidar with a difference of up to 0.04 km-1, obtained water vapor mixing ratio profiles were consistent well with the sounding. This study presented the long-time observational results of aerosol extinction coefficient and height of atmospheric boundary layer (ABL) data over Huainan City during the autumn and winter from 2019 to 2020 using this technology for the first time. The pollution types (local pollution discharge, transmission pollution, transmission pollution and local pollution accumulation) and spatial-temporal changes of aerosol during the air quality pollution period were analyzed and discussed. The results showed that Huainan City is affected by 20 fine particle air pollution and 8 times dust air pollution during this period. The transportation of dust mainly came from the northwest, and it generally sunk from high altitude to the ground, with a thickness of more than 2 km. The average height of ABL was more than 1.23 km. In the typical fine particle transportation process, the height of the ABL was maintained at about 1.1~1.2 km, and the ground wind direction was mainly northwest, with a small amount of southeast. In the coincidence pollution process of fine particle transmission and local accumulation, the height of ABL was slightly lower (the average height is about 1.0 km), the near-surface wind direction is dominated by northerly winds. The lower edge height of the polluted air masses continued to decrease from low altitude and eventually coupled with near-ground pollution. In the process of heavy pollution caused by fine particles, the evolution trend of surface water vapor mixing ratio, relative humidity and PM_2.5 concentration were in good agreement. This showed that increasing moisture absorption of particulate matter and secondary transformation of gaseous pollutants might promote the second generation process of PM_2.5. In particular, the trend of atmospheric boundary layer height was closely related to the settlement of polluted air masses and the accumulation of surface pollution. During the attention period, most of the city’s hourly height of ABL was distributed below 1.6 km, with an average of around 1.0 km. When the hourly air quality reached severe pollution, the height of the boundary layer was generally less than 0.6 km. According to the simulation results of the backward trajectory of the air mass, the polluted air mass mainly came from the northerly direction, with a small amount came from the southeast, during the air pollution period of the city with moderate or above pollution. Therefore, it is necessary to strengthen the management and control of pollution sources in the north of the urban area to prevent superimposed effects.