Characterization and parameterization of aerosol cloud condensation nuclei activation under different pollution conditions.

H C Che,Y W Zhang,X J Shen,Y Q Wang,Q L Ma,T T Wang,Y M Zhang,J Y Sun,L Zhang,X Y Zhang

doi:10.1038/srep24497

Abstract

To better understand the cloud condensation nuclei (CCN) activation capacity of aerosol particles in different pollution conditions, a long-term field experiment was carried out at a regional GAW (Global Atmosphere Watch) station in the Yangtze River Delta area of China. The homogeneity of aerosol particles was the highest in clean weather, with the highest active fraction of all the weather types. For pollution with the same visibility, the residual aerosol particles in higher relative humidity weather conditions were more externally mixed and heterogeneous, with a lower hygroscopic capacity. The hygroscopic capacity (κ) of organic aerosols can be classified into 0.1 and 0.2 in different weather types. The particles at ~150 nm were easily activated in haze weather conditions. For CCN predictions, the bulk chemical composition method was closer to observations at low supersaturations (≤0.1%), whereas when the supersaturation was ≥0.2%, the size-resolved chemical composition method was more accurate. As for the mixing state of the aerosol particles, in haze, heavy haze, and severe haze weather conditions CCN predictions based on the internal mixing assumption were robust, whereas for other weather conditions, predictions based on the external mixing assumption were more accurate.

Highlights

Hygroscopicity parameter (κ) to link the Cloud condensation nuclei (CCN) activity and hygroscopic ability of aerosol particles, and is widely used in CCN predictions[16,20]
The aerosol chemical composition shows unique characteristics between the haze- and fog-polluted environments[28], and the mixing state may be different to the clean areas; measurements of aerosol CCN activation and CCN concentration predictions are especially needed for the high polluted conditions
The total aerosol chemical composition mass concentration measured by the aerosol mass spectrometer (AMS) increased by nearly four times in the polluted episode compared with clean conditions

Summary

Introduction

Hygroscopicity parameter (κ) to link the CCN activity and hygroscopic ability of aerosol particles, and is widely used in CCN predictions[16,20]. Numerous studies have parameterized CCN concentration using aerosol-determined κ11,13,21–23. The aerosol pollution-induced haze and fog episodes have become increasingly worse in recent years[25,26]. The aerosol chemical composition shows unique characteristics between the haze- and fog-polluted environments[28], and the mixing state may be different to the clean areas; measurements of aerosol CCN activation and CCN concentration predictions are especially needed for the high polluted conditions. In this paper we present long-term in situ aerosol CCN activation measurements, including all four seasons, from January to October 2013, at a regional GAW (Global Atmospheric Watch) station in the YRD. Parameterization of time dependent CCN predictions using different approaches with aerosol size, chemical composition and mixing states under different pollution conditions are presented and discussed

Methods

Results

Conclusion