Atmos. Chem. Phys. Discuss., 12, 1493-1516, 2012
www.atmos-chem-phys-discuss.net/12/1493/2012/
doi:10.5194/acpd-12-1493-2012
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This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
Impact of aerosol composition on cloud condensation nuclei activity
Q. Zhang1, J. Meng1, J. Quan1,2, Y. Gao1, D. Zhao1, P. Chen1, and H. He1
1Beijing Weather Modification Office, Beijing, China
2Institude of Urban Meteorology, CMA, Beijing, China

Abstract. The impact of aerosol composition on cloud condensation nuclei (CCN) activity was analyzed in this study based on field experiments carried out at downtown Tianjin, China, in September 2010. In the experiments, the CCN measurements were performed at supersaturation (SS) of 0.1%, 0.2% and 0.4% using a thermal-gradient diffusion chamber (DMT CCNC), whereas the aerosol size distribution and composition were simultaneously measured with a TSI SMPS and an Aerodyne Aerosol Mass Spectrometer (AMS), respectively. The results show that the influence of aerosol composition on CCN activity is notable under low SS (0.1%), and their influence decreased with increasing SS. For example, under SS of 0.1%, the CCN activity increases from 4.5 ± 2.6% to 12.8 ± 6.1% when organics fraction decrease from 30–40% to 10–20%. The rate of increase reaches up to 184%. While under SS of 0.4%, the CCN activity increases only from 35.7 ± 19.0% to 46.5 ± 12.3%, correspondingly. The calculated NCCN based on the size-resolved activation ratio and aerosol number size distribution correlates well with observed NCCN at high SS (0.4%), but this correlation decreases with the falling of SS. The slopes of linear fitted lines between calculated and observed NCCN are 0.708, 0.947, and 0.995 at SS of 0.1%, 0.2% and 0.4%, respectively. Moreover, the standard deviation (SD) of calculated NCCN increases with the decreasing of SS. A case study of CCN closure analyses indicates that the calculated error of NCCN can reach up to 34% at SS of 0.1% if aerosol composition is not included, and the calculated error decreases with the raising of SS. It decreases to 9% at SS of 0.2%, and further decreases to 4% at SS of 0.4%.

Citation: Zhang, Q., Meng, J., Quan, J., Gao, Y., Zhao, D., Chen, P., and He, H.: Impact of aerosol composition on cloud condensation nuclei activity, Atmos. Chem. Phys. Discuss., 12, 1493-1516, doi:10.5194/acpd-12-1493-2012, 2012.
 
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