Abstract
Abstract. Measurements of cloud condensation nuclei (CCN), condensation nuclei (CN) and aerosol chemical composition were performed simultaneously at an urban site in Shanghai from 6 to 9 November 2010. The variations of CCN number concentration (NCCN) and aerosol activity (activated aerosol fraction, NCCN/NCN) were examined during a fog–haze co-occurring event. Anthropogenic pollutants emitted from vehicles and unfavorable meteorological conditions such as low planetary boundary layer (PBL) height exerted a great influence on PM2.5 and black carbon (BC) loadings. NCCN at 0.2% supersaturation (SS) mostly fell in the range of 994 to 6268 cm−3, and the corresponding NCCN/NCN varied between 0.09 and 0.57. NCCN and NCCN/NCN usually were usually higher in the hazy case due to increased aerosol concentration in the accumulation mode (100–500 nm), and lower in the foggy–hazy and clear cases. The BC mass concentration posed a strong positive effect on NCCN in the foggy–hazy and hazy cases, whereas it poorly correlated with NCCN in the clear case. NCCN/NCN was weakly related with BC in both foggy–hazy and hazy cases. 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 NCCN at 0.2% SS was very successful compared with the observed NCCN in clear case (R2=0.96) and foggy–hazy/hazy cases (R2=0.91). In addition, their corresponding ratios of predicted to observed NCCNwere on average 0.95 and 0.92, respectively. More organic matter is possibly responsible for this closure difference between foggy–hazy/hazy and clear cases. These results reveal that the particulate pollutant burden exerts a significant impact on NCCN, especially NCCN/NCN promotes effectively during the polluted periods.
Highlights
Cloud condensation nuclei (CCN), which constitutes an important fraction of atmospheric aerosol, can influence the microphysical and radiative properties and lifetime of cloud indirectly and impact the hydrological cycle (IPCC, 2013)
A continuous 4-day data set obtained at an urban site in Shanghai over a fog–haze event from 6 to 9 November 2012 was analyzed for cloud condensation nuclei (CCN) and aerosol
Meteorological conditions such as wind speed, wind direction and temperature exerted a great influence on PM2.5 and black carbon (BC) loadings
Summary
Cloud condensation nuclei (CCN), which constitutes an important fraction of atmospheric aerosol, can influence the microphysical and radiative properties and lifetime of cloud indirectly and impact the hydrological cycle (IPCC, 2013). Elevated CCN loadings (NCCN) tend to reduce cloud droplet size and suppress precipitation in shallow and short-lived clouds (Lohmann and Feichter, 2005), in addition to which they can promote great convective overturning and enhance precipitation in deep convective clouds (Rosenfeld et al, 2008). Numerous aerosol properties, including particle size distribution, chemical composition and mixing state, are closely linked with the ability of particles to take up water vapor, i.e., the ability to act as CCN The current assessment of aerosol indirect effects induced by increasing anthropogenic aerosols remains poorly understood, and this brings a big uncertainty in fully picturing climate change (Andreae et al, 2005; IPCC, 2013)
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