Analysis of cloud condensation nuclei properties at a polluted site in southeastern China during the AMF-China Campaign

Abstract

[1] Cloud condensation nuclei (CCN) measurements are essential to understanding cloud processes but CCN measurements are scarce. This study analyzes CCN measurements acquired at Shouxian, a polluted site in southeastern China, from August 1–October 31, 2008 during the deployment of the U.S. Department of Energy’s (DOE) Atmospheric Radiation Measurement (ARM) Mobile Facility (AMF). The ranges of daily mean condensation nuclei concentrations (NCN) were approximately 3100–12000, 2300–7400, and 4260–15500 cm −3 in August, September, and October, respectively; the corresponding ranges of CCN concentrations (NCCN) at 0.49% supersaturation were about 1960–5670, 1770–3530, and 1500–5700 cm −3 . The average ratio of NCCN/NCN was 0.04, 0.12, 0.35, 0.53, 0.65, 0.69 and 0.72 for supersaturation values of 0.08%, 0.20%, 0.34%, 0.49%, 0.78%, 1.07% and 1.37%, respectively. NCN and NCCN peaked in the early morning and late afternoon, when human activities were most intense. CCN were more abundant in air masses influenced by anthropogenic pollution from densely populated areas. NCCN was proportional to NCN, but NCCN/NCN decreased with increasing NCN. There was a good correlation between NCCN (at 0.49% supersaturation) and aerosol optical depth (AOD) (500 nm), that is especially strong for fine‐mode aerosols (Angstrom exponent (a) > 0.8). This relationship can be fitted with a power law function. The changes of NCCN with various factors are explained. A dust event was identified showing a significant increase in NCN and a dramatic decrease in the NCCN/NCN ratio, implying that dust particles do not increase NCCN much, despite mixing with other anthropogenic aerosols.