中文摘要：

利用边界层探空资料、地面气象要素及污染物资料，研究了2012年6月中上旬淮河下游一次连续多日大范围雾-霾天气的雾-霾转换过程及成因.结果表明：近地面静小风为雾-霾长时间维持提供良好动力条件，边界层中低层维持的近中性层结或逆温层结创造良好热力条件，秸秆燃烧提供凝结核条件；雾和霾过程中风速下降伴随着能见度降低，风速增大则伴随着能见度升高.中度以上霾的形成和发展都伴随着空气比湿增大，霾向雾转换过程中比湿下降.比湿越大雾-霾持续时间越长，雾前比湿越高雾中最低能见度越低.能见度与 SO2浓度呈正相关（ Pearson相关系数为0.42）、与PM2.5和PM10浓度呈反相关（Pearson相关系数分别为-0.49和-0.56）；雾-霾过程中上风向SO2、NO2浓度高于下风向2倍左右，下风向NO和PM10浓度高于上风向1.5倍左右，出现污染物转化.

英文摘要：

Based on the soundings of temperature, surface meteorological parameters, air pollutants concentration, the multi-day widespread fog-haze processes and the transformation between fog and haze during June 2012 at the downstream of the Huai River were investigated. Surface layer breeze provided nice dynamic conditions for the longtime maintain fog-haze; the neutrosphere or the inversion layer near the surface supplied a thermodynamic conditions; the large-scale crop residue burning provided enough condensation nucleus. During the haze-fog process, the visibility reduced with the wind speed decrease, and lifted with the wind speed increase. The formation and development of moderate and severe haze were accompanied with increasing specific humidity, while the haze-fog conversion processes were accompanied with decreasing specific humidity. The higher the specific humidity, the longer the fog-haze duration. The higher the specific humidity before the fog, the lower the minimum visibility during the fog. Visibility was positively correlated with the concentration of SO2 （Pearson correlation coefficients is 0.42）, but was inversely correlated with PM2.5 and PM10 concentrations （Pearson correlation coefficients are-0.49and-0.56, respectively）. During the fog-haze processes, the upwind SO2, NO2 concentrations were higher than about 2times those of downwind. However, the downwind NO and PM10 concentrations were about 1.5 times higher than those of the upwind. Pollutants conversions occurred during the fog-haze processes.