Variations of Cloud Condensation Nuclei (CCN) and aerosol activity during fog-haze episode: a case study from Shanghai

C. Leng, D. Zhang, Q. Zhang, C. Xu, T. Cheng, R. Zhang, J. Tao, J. Chen, S. Zha, Y. Zhang, X. Li, L. Kong
2014 Atmospheric Chemistry and Physics Discussions  
Measurements of Cloud condensation nuclei (CCN), condensation nuclei (CN) and aerosol chemical composition were performed simultaneously at an urban site of Shanghai from 6 to 9 November 2010. The variations of CCN number concentration (N<sub>CCN</sub>) and aerosol activity (activated aerosol fraction, N<sub>CCN</sub>/N<sub>CN</sub>) were examined during a fog-haze co-occurring event. Anthropogenic pollutants emitted from vehicles and unfavorable meteorological conditions such as low planetary
more » ... h as low planetary boundary layer (PBL) height exerted a great influence on CN and black carbon (BC) loadings. N<sub>CCN</sub> at 0.2% supersaturation (SS) mostly fell in the range of 994 to 6268 cm<sup>&minus;3</sup>, and the corresponding N<sub>CCN</sub>/N<sub>CN</sub> varied between 0.09 and 0.57. N<sub>CCN</sub> and N<sub>CCN</sub>/N<sub>CN</sub> usually were higher in hazy days due to increased aerosol concentration in the accumulation mode (100–500 nm), and lower in foggy-hazy and clear days. BC mass concentration posed a strong positive effect on N<sub>CCN</sub> in foggy-hazy and hazy days, whereas it poorly correlated with N<sub>CCN</sub> in clear days. N<sub>CCN</sub>/N<sub>CN</sub> was weakly related with BC both in foggy-hazy/hazy and clear days. By using a simplified particle hygroscopicity (κ), the calculated critical dry size (CDS) of activated aerosol did not exceed 130 nm at 0.2% SS in spite of diverse aerosol chemical compositions. The predicted N<sub>CCN</sub> at 0.2% SS was very successful compared with the observed N<sub>CCN</sub> in clear days (<i>R</i><sup>2</sup>=0.96) and foggy-hazy/hazy days (<i>R</i><sup>2</sup>=0.91). In addition, their corresponding ratios of predicted to observed N<sub>CCN</sub> were on average 0.95 and 0.92, respectively. More organic matter is possibly responsible for this closure difference between foggy-hazy/hazy and clear days. These results reveal that the particulate pollutant burden exerts a significant impact on N<sub>CCN</sub>, especially N<sub>CCN</sub>/N<sub>CN</sub> promotes effectively during the polluted periods.
doi:10.5194/acpd-14-16997-2014 fatcat:tjaljtcmvzgkjn5fpmdjo5wbkq