Abstract
Abstract. This study investigates aerosol hygroscopicity, mixing state, and cloud condensation nucleation as part of the Atmosphere–Aerosol–Boundary Layer–Cloud Interaction Joint Experiment performed in the summer of 2016 at Xingtai (XT), a suburban site located in the center of the North China Plain (NCP). In general, the probability density function (PDF) of the hygroscopicity parameter (κ) for 40–200 nm particles had a unimodal distribution, and mean κ-PDF patterns for different sizes were similar, suggesting that the particles were highly aged and internally mixed because of strong photochemical reactions. The κ calculated from the hygroscopic growth factor in the daytime and at night suggests that photochemical reactions largely enhanced the aerosol hygroscopicity. This effect became weaker as the particle size increased. In addition, the aerosol hygroscopicity was much larger at XT than at other sites in the NCP. This is because new particle formation takes place much more frequently in the central NCP, which is heavily polluted from industrial activities, than elsewhere in the region. The evolution of the planetary boundary layer played a dominant role in dictating aerosol mass concentration. Particle size was the most important factor influencing the ability of aerosols to activate, whereas the effect of chemical composition was secondary, especially when supersaturation was high. Using a fixed value of κ=0.31 to calculate the cloud condensation nuclei number concentration in this region suffices.
Highlights
Aerosols, defined as the mixture of solid and liquid particles suspended in air, are ubiquitous in the atmosphere because of direct emissions from biogenic and anthropogenic sources and the secondary transformation from gas precursors
Phenomena suggest that new particle formation (NPF) events frequently occurred at XT during the field experiment
The probability density function (PDF) of the hygroscopicity parameter κ (κ-PDF) for 40–200 nm particles was a unimodal distribution, which is different from distributions at other sites in China
Summary
Aerosols, defined as the mixture of solid and liquid particles suspended in air, are ubiquitous in the atmosphere because of direct emissions from biogenic and anthropogenic sources and the secondary transformation from gas precursors. Previous studies have addressed three main aerosol properties influencing the CCN activation, namely, particle size, chemical composition, and mixing state Their relative importance is different under different environmental conditions (e.g., Dusek et al, 2006; Ervens et al, 2007; Cubison et al, 2008; Deng et al, 2011; Zhang et al, 2014; Schmale et al, 2018). Deng et al (2011) have shown that the aerosol number size distribution is critical in the prediction of NCCN while Zhang et al (2014, 2017) have highlighted the importance of chemical composition in determining particle activation properties These studies were carried out using data from the northern part of the NCP.
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