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- Title
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.
- Authors
Mingfu Cai; Haobo Tan; Chan, Chak K.; Yiming Qin; Hanbing Xu; Fei Li; Schurman, Misha I.; Liu Li; Jun Zhao
- Abstract
A hygroscopicity-tandem differential mobility analyzer (H-TDMA), a scanning mobility CCN analyzer (SMCA), and an aerodyne high resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) were used to respectively measure the hygroscopicity, condensation nuclei activation, and chemical composition of aerosol particles at the Panyu site in the Pearl River Region during wintertime 2014. The distribution of the size-resolved cloud condensation nuclei (CCN) at four supersaturations (SS = 0.1 %, 0.2 %, 0.4 %, and 0.7 %) and the aerosol particle size distribution were obtained by the SMCA. The hygroscopicity parameter κ (κCCN, κH-TDMA, and κAMS) was respectively calculated based upon the SMCA, H-TMDA, and AMS measurements. The results showed that the κH-TDMA value was slightly smaller than the κCCN one at all diameters and for particles larger than 100 nm the κAMS value was significantly smaller than the others (κCCN, and κH-TDMA), which could be attributed to the underestimated hygroscopicity of the organics (κorg). The activation ratio (AR) calculated from the growth factor - probability density function (Gf-PDF) without surface tension correction was found to be lower than that from the H-TDMA measurement, due most likely to the uncorrected surface tension (σs/a) that did not consider the surfactant effects of the organic compounds. We demonstrated that better agreement between the calculated and measured AR could be obtained by adjusting σs/a. Various schemes were proposed to predict the CCN number concentration (NCCN) based on H-TDMA and AMS measurements. In general, the predicted NCCN agreed reasonably well with the corresponding measured ones using different schemes. For H-TDMA measurements, the NCCN value predicted from the real time AR measurements was slightly smaller (~6.8 %) than that from the activation diameter (D50) method due to the assumed internal mixing in the D50 prediction. The NCCN values predicted from bulk PM1 were higher (~11.5 %) than those from size-resolved composition measured by the AMS because a significant fraction of PM1 was composed of inorganic matter. The NCCN calculated from AMS measurement were under-predicted at 0.1 % and 0.2 % supersaturations, which could be due to underestimate of κorg and overestimate of σs/a. For SS = 0.4 % and 0.7 %, slight over-predicted NCCN was found because of the internal mixing assumption. Our results highlight the need for accurately evaluating the effects of organics on both the hygroscopic parameter κ and the surface tension σ in order to accurately predict CCN activity.
- Subjects
CLOUD condensation nuclei; ATMOSPHERIC aerosols; DELTAS; MASS spectrometry; SUPERSATURATION
- Publication
Atmospheric Chemistry & Physics Discussions, 2018, p1
- ISSN
1680-7367
- Publication type
Article
- DOI
10.5194/acp-2018-339