Relating particle hygroscopicity and CCN activity to chemical composition during the HCCT-2010 field campaign

作者：Zhijun Wu, Laurent Poulain, Silvia Henning, K. Dieckmann, W. Birmili, Maik Merkel, Dominik van Pinxteren, Gerald Spindler, K. Müller, Frank Stratmann, Hartmut Herrmann, Alfred Wiedensohler · 发表于：Atmospheric chemistry and physics · 年份：2013 · DOI：10.5194/acp-13-7983-2013 · 被引用次数：178 · 研究领域：Atmospheric chemistry and aerosols、Atmospheric aerosols and clouds、Air Quality and Health Impacts

Abstract. Particle hygroscopic growth at 90% RH (relative humidity), cloud condensation nuclei (CCN) activity, and size-resolved chemical composition were concurrently measured in the Thüringer Wald mid-level mountain range in central Germany in the fall of 2010. The median hygroscopicity parameter values, κ, of 50, 75, 100, 150, 200, and 250 nm particles derived from hygroscopicity measurements are respectively 0.14, 0.14, 0.17, 0.21, 0.24, and 0.28 during the sampling period. The closure between HTDMA (Hygroscopicity Tandem Differential Mobility Analyzers)-measured (κHTDMA) and chemical composition-derived (κchem) hygroscopicity parameters was performed based on the Zdanovskii–Stokes–Robinson (ZSR) mixing rule. Using size-averaged chemical composition, the κ values are substantially overpredicted (30 and 40% for 150 and 100 nm particles). Introducing size-resolved chemical composition substantially improved closure. We found that the evaporation of NH4NO3, which may happen in a HTDMA system, could lead to a discrepancy in predicted and measured particle hygroscopic growth. The hygroscopic parameter of the organic fraction, κorg, is positively correlated with the O : C ratio (κorg = 0.19 × (O : C) − 0.03). Such correlation is helpful to define the κorg value in the closure study. κ derived from CCN measurement was around 30% (varied with particle diameters) higher than that determined from particle hygroscopic growth measurements (here, hydrophilic mode is considered only). ...