Seasonal and vertical variations in aerosol distribution over Shijiazhuang, China

To obtain a representative sampling of aerosol vertical profiles, we performed an extensive airborne characterization of aerosols under different environmental conditions over Shijiazhuang, China. Surface aerosol concentration and aerosol vertical distribution were analyzed using a set of 104 vertical profiles of aerosol number concentration and size distribution ranging from 0.1 to 3 μm observed by PCASP-100X. A four modal lognormal size distribution with 10-based logarithm was applied to fit measured aerosol size distributions at different altitudes of three seasons (spring, summer and autumn). It was found that the surface aerosol number concentration had a negative correlation with wind speed. In addition to wet removal of aerosols owing to precipitation in summer, vertical transport of aerosols from the surface to high levels is strongly influenced by convective instability, which contributes to the seasonality of aerosol vertical profiles. The aerosol vertical profiles under a wide range of synoptic conditions can be categorized as “ED” (exhibiting an exponential declining tendency with altitude), “SAL” (aerosol layers existing near surface), and “BAL” (aerosol layers at the boundary layer height). The multi-lognormal fitting captures the total aerosol number size distribution at 0.1-3 μm reasonably well. The average scale height of aerosols during spring, summer and autumn is 1.0 km, 1.6 km and 1.0 km, respectively.