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

Abstract

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 (N CN) were approximately 3100-12000, 2300-7400, and 4260-15500 cm -3 in August, September, and October, respectively; the corresponding ranges of CCN concentrations (N CCN) at 0.49% supersaturation were about 1960-5670, 1770-3530, and 1500-5700 cm -3. The average ratio of N CCN /N CN 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. N CN and N CCN 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. N CCN was proportional to N CN, but N CCN /N CN decreased with increasing N CN. There was a good correlation between N CCN (at 0.49% supersaturation) and aerosol optical depth (AOD) (500 nm), that is especially strong for fine-mode aerosols (Angstrom exponent () > 0.8). This relationship can be fitted with a power law function. The changes of N CCN with various factors are explained. A dust event was identified showing a significant increase in N CN and a dramatic decrease in the N CCN /N CN ratio, implying that dust particles do not increase N CCN much, despite mixing with other anthropogenic aerosols. Copyright 2011 by the American Geophysical Union.