An improved parameterization scheme for size-resolved particle activation ratio and its application on comparison study of particle hygroscopicity measurements between HTDMA and DMA-CCNC. (1st April 2020)

• Record Type: Journal Article
• Authors: Tao, Jiangchuan; Kuang, Ye; Ma, Nan; Zheng, Yijia; Wiedensohler, A.; Zhao, Chunsheng
• Is Part Of: Atmospheric environment. Volume 226(2020)
• Publication Date: 2020-04-01
• Subjects: Air -- Pollution -- Periodicals; Air -- Pollution -- Meteorological aspects -- Periodicals; 551.51
• DOI: 10.1016/j.atmosenv.2020.117403
• Languages: English
• ISSNs: 1352-2310

Abstract

Abstract: Size-resolved Particle Activation Ratio (SPAR), defined as the size-dependence of CCN activity of aerosol particles, is generally parameterized by a scheme that neglects the contribution of nearly-hydrophobic particles. In this paper, it was found that nearly-hydrophobic particles can contribute up to 20% to the CCN activity for large particles and the estimation of particle hygroscopicity would be significantly biased using the original parameterization scheme. An improved parameterization scheme considering the contribution of nearly-hydrophobic particles was proposed and applied on measurements conducted at a rural site in the North China Plain during summer 2013. For hygroscopic particles in range of 50–70 nm diameter, which might be dominated by organic compounds, their number fraction ( f n ) and midpoint activation diameter ( D a ) fitted with the improved scheme were up to 20% lower than the parameters fitted with the original scheme. Both parameterization schemes of SPAR were further applied in a comparison study of aerosol hygroscopicity measurements between Cloud Condensation Nuclei (CCN) Counter coupled with Differential Mobility Analyzer (DMA-CCNC) and Hygroscopicity Tandem Differential Mobility Analyzer (HTDMA) during the Xianghe Campaign. Applying the improved scheme, the correlations of derived f n for hygroscopic particles between measurements of DMA-CCNC and HTDMA were improved (R increased by up to 0.2 with the uncertainty of the regression to be about 10%). In addition, for particles smaller than 100 nm, the size-dependence of hygroscopicity parameter and the diurnal cycle of f n derived using the improved scheme, based on the DMA-CCNC measurements were more consistent with those derived with the HTDMA measurements. These results highlight the importance of considering nearly-hydrophobic particles in SPAR curves fitting and in the calculation of aerosol hygroscopicity based on DMA-CCNC measurements. Highlights: A new parameterization scheme for SPAR considering the contribution of the nearly-hydrophobic particles is proposed. The fitting parameters using the improved scheme were up to 20% lowered for hygroscopic particles. The derived aerosol hygroscopicity using the improved scheme agrees better with aerosol hygroscopicity derived from HTDMA.