Abstract
Abstract. Precise quantification of the cloud condensation nuclei (CCN) number concentration is crucial for understanding aerosol indirect effects and characterizing these effects in models. An evaluation of various methods for CCN parameterization was carried out in this paper based on in situ measurements of aerosol activation properties within HaChi (Haze in China) project. Comparisons were made by closure studies between methods using CCN spectra, bulk activation ratios, cut-off diameters and size-resolved activation ratios. The estimation of CCN number concentrations by the method using aerosol size-resolved activation ratios, either averaged over a day or with diurnal variation, was found to be most satisfying and straightforward. This could be well expected since size-resolved activation ratios include information regarding the effects of size-resolved chemical compositions and mixing states on aerosol activation properties. The method using the averages of critical diameters, which were inferred from measured CCN number concentrations and particle number size distributions, also provided a good prediction of the CCN number concentration. Based on comparisons of all these methods in this paper, it was recommended that the CCN number concentration be predicted using particle number size distributions with inferred critical diameters or size-resolved activation ratios.
Highlights
A key factor to characterise aeroSsocliiendnirceectseffects, i.e. the positions and mixing states on aerosol activation properties. impacts of aerosols as CCN on climate
The size-resolved aerosol activation ratios (A(Dp,S) = NCCN,s(Dp,S)/NCN,s(Dp)) were inverted from size-selected CCN number concentrations and particle number size distribution (PNSD) using a modified algorithm based on Hagen and Alofs (1983)
The bulk CCN number concentrations were the integration of the CCN number size distribution, and referred to as measured CCN number concentration in the following content
Summary
Measurements of PNSD and aerosol activation properties were conducted at Wuqing Meteorological Station from 5 November to 30 December 2011. Number size distributions and activation properties of aerosols dried to less than 30 % relative humidity were measured by an aerodynamic particle sizer (APS Model 3320, TSI, USA), a scanning mobility particle sizer (SMPS, Model 3936, TSI, USA) and a continuousflow CCN counter (CCNC, Model CCN-200, DMT, USA) (Roberts and Nenes, 2005; Lance et al, 2006). The size-resolved aerosol activation ratios (A(Dp,S) = NCCN,s(Dp,S)/NCN,s(Dp)) were inverted from size-selected CCN number concentrations and PNSD using a modified algorithm based on Hagen and Alofs (1983). The other column of the CCNC was used to measure total CCN number concentrations at supersaturations of 0.07, 0.10, 0.20, 0.40 and 0.80 %, of which direct measurements could lead to considerable underestimations under polluted. The bulk CCN number concentrations were the integration of the CCN number size distribution, and referred to as measured CCN number concentration in the following content
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