Abstract

Aerosol impacts on cloud-base height were investigated based on the 5 years (2006 to 2010) groundbased observations of aerosol and cloud properties provided by an atmospheric measurement field station in the Baltimore-Washington corridor operated by Howard University. Opposite to the decreasing trend of the aerosol loading, an increasing trend of cloud-base height was found over the five years. During the investigation, the five-year summer time low-base clouds are separated into clean and polluted groups based on the aerosol particulate matter with aerodynamic diameter ≤ 2.5m (PM2.5) value. With the same lifting condensation level (LCL) the cloud-base heights were found lower under the polluted conditions than that under the clean conditions. Moreover, a significant negative relationship between the difference of cloud-base height to LCL and PM2.5 concentration was found based on the five years observations. This study showed that clouds might form at lower altitude under the polluted conditions compared to the clean conditions.