Parameterization Of CCN Number Concentration In High Altitude Areas Of Southern China And Impacts Of CCN On Droplet Spectra Of Rain And Fog

Quantifying regional CCN concentration is important for reliable estimations of aerosol indirect effects. Based on observational data of the number concentrations of total aerosol (NCN) and cloud condensation nuclei (NCCN), particle number size distribution (PNSD) and, size-resolved activation ratio (SRAR) obtained on Mt. Huang in southeast China from September 19 to October 11,2012, seven parameterization schemes are used to calculate NCCN employing CCN spectra, bulk activation ratio, cut-off diameter and SRAR. The calculations and the observations are compared and analyzed at four supersaturations (S) from 0.109% to 0.67%. By comparing the CCN parameterizations in Wuqing and Mt. Huang, the strengths and limitations of different CCN parameterization schemes are analyzed and evaluated, with the aim of throwing light upon the factors influencing parameterization methods for different backgrounds. The primary goal of this paper is to provide insight into CCN activation properties and NCCN characteristics on Mt. Huang, trying to find the best parameterization schemes for NCCN, and facilitating the estimation and modeling of NCCN in relatively clean and humid southeast China. In addition, the number concentration of aerosols in Weining, Guizhou province are inferred using the CCN parameterizations obtained on Mt. Huang and CCN data obtained in Weining. The impacts of atmospheric pollutants on CCN and the droplet spectra of rain and fog are also analyzed. Results show that:1) the parameterization using the average cut-off diameter Dm, which is derived from the various measured PNSD and NCCN, provides the best estimate of NCCN, with coefficient of determination, R2=0.70-0.90 and NCCN,cal/NCCN,obs=0.92-1.11, followed by the method of combining an average size-resolved activation curve with the PNSD, with R2=0.71-0.91 and NCCN,cal/NCCN,obs=0.92-1.02; average Dso together with the PNSD also provides a rational scheme for NCCN prediction, with NCCN,cal/NCCN,obs=0.86-0.94 and R2=0.70-0.89;the method of parameterizing CCN spectra, though straightforward, has limits under polluted conditions. Reasonable NCCN estimate could only be obtained at high S (R2≥0.85 at S=0.39% and 0.67%). For the method employing the bulk activation ratio ARB(S), NCCN are substantially overestimated by using total mode-based ARB(S) (NCCN,cal/NCCN,obs= 0.94-1.39, R2=0.17-0.67), while applying ammonium sulfate-based ARB(S) yields improved CCN predictions (NCCN,cal/NCCN,obs=0.91-1.11,R2=0.70-0.91).2) the CCN concentration in Weining display significant daily variations, with three peaks appear at about 12:00,16:00 and 20:00, which is relate to human activities, turbulent exchange and meteorological conditions; by fitting the CCN spectra using the expression N=CSk, the fitting parameter C=14288 cm-3, k=0.8, indicating that the CCN spectra can be classified as a typical continental type; the precipitation characteristics of stratiform cloud provide critical synoptic situations, and high CCN concentration is an important microphysical condition for narrow droplet spectra of rain and fog.