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. A hygroscopic tandem differential mobility analyzer (HTDMA), ascanning mobility cloud condensation nuclei (CCN) analyzer (SMCA), and an Aerodyne high-resolutiontime-of-flight aerosol mass spectrometer (HR-ToF-AMS) were used to,respectively, measure the hygroscopicity, condensation nuclei activation, andchemical composition of aerosol particles at the Panyu site in the PearlRiver Delta region during wintertime 2014. The distribution of the size-resolvedCCN at four supersaturations (SSs of 0.1  %,0.2 %, 0.4 %, and 0.7 %) and the aerosol particle size distributionwere obtained by the SMCA. The hygroscopicity parameter κ ( κCCN , κHTDMA , and κAMS ) was,respectively, calculated based upon the SMCA, HTDMA, and AMS measurements. The resultsshowed that the κHTDMA value was slightly smaller than the κCCN one at all diameters and for particles larger than100 nm, and the κAMS value was significantly smaller than the others( κCCN and κHTDMA ), which could be attributed tothe underestimated hygroscopicity of the organics ( κorg ). Theactivation ratio (AR) calculated from the growth factor – probabilitydensity function (Gf-PDF) without surface tension correction was found to belower than that from the CCN measurements, due most likely to theuncorrected surface tension ( σs∕a ) that did not consider thesurfactant effects of the organic compounds. We demonstrated that betteragreement between the calculated and measured ARs could be obtained byadjusting σs∕a . Various schemes were proposed to predict theCCN number concentration ( NCCN ) based on the HTDMA and AMSmeasurements. In general, the predicted NCCN agreed reasonably wellwith the corresponding measured ones using different schemes. For the HTDMAmeasurements, the NCCN value predicted from the real-time ARmeasurements was slightly smaller ( ∼6.8  %) than that fromthe activation diameter ( D50 ) method due to the assumed internal mixingin the D50 prediction. The NCCN values predicted from bulkchemical composition of PM 1 were higher ( ∼11.5  %) thanthose from size-resolved composition measured by the AMS because asignificant fraction of PM 1 was composed of inorganic matter. The NCCN values calculated from AMS measurement were underpredicted at0.1 % and 0.2 % supersaturations, which could be due to underestimation of κorg and overestimation of σs∕a . For SS values of 0.4 %and 0.7 %, slight overpredicted NCCN values were found because ofthe internal mixing assumption. Our results highlight the need foraccurately evaluating the effects of organics on both the hygroscopicparameter κ and the surface tension σ in order to accuratelypredict CCN activity.

atmospheric chemistry and physics

The size-resolved cloud condensation nuclei (CCN) activity and its prediction based on aerosol hygroscopicity and composition in the Pearl Delta River (PRD) region during wintertime 2014