Impact of Physicochemical and Hygroscopic Properties of Urban Aerosols on CCN Activity in Seoul, Korea

Aerosol hygroscopicity is considered to be important as it is closely associated with cloud condensation nuclei (CCN) activity and thereby crucial to the aerosol indirect effect on climate change. Aerosol hygroscopicity is considered to be determined by the physicochemical properties of aerosols and can be changed by chemical processes involving aerosol species. Although many attempts have been made to compile observational data for understanding the hygroscopic behaviors of aerosols, our understanding is still lacking, especially for the urban aerosols that are influenced by multiple anthropogenic sources. As a part of a comprehensive measurement campaign, KORea-United States Air Quality study (KORUS-AQ), we measured aerosol properties in Seoul during spring/summer in 2016 with an extensive suite of instruments. Our aim is to enhance our understanding of the physicochemical properties of urban aerosols in Seoul and their links to the size-resolved aerosol hygroscopicity as well as CCN activity.

The measurement was conducted at Olympic Park, one of the supersites of the KORUS-AQ campaign, located at the eastern part of Seoul where local sources from a highly urbanized areas and transported sources are intermingled. During the campaign, the information of size-resolved hygroscopicity as well as the mixing state of aerosol were obtained from hygroscopic tandem differential mobility analyzer (HTDMA). Size-resolved chemical composition data was measured by an aerosol mass spectrometer (HR-ToF-AMS). For detailed analysis, size-resolved organic factors using m/z tracer method were calculated. Additionally, data from other instruments including SMPS, CPC, CCNC, and MAAP were used to analyze the physicochemical properties of aerosols.

In short, the average κvalues for four dry diameters (30, 50, 100 and 150 nm) ranged from 0.11 to 0.24 with distinct diurnal patterns. The ‘κ-closure’ using GF-derivedκfrom HTDMA and AMS-based κ showed good correspondence, implying that aerosol hygroscopicity is closely related to aerosol chemical composition. Particularly, analyses with size-resolved chemical composition data give meaningful implications for size-resolved κ and mixing state of aerosols that cannot be explained only with bulk chemical composition data. More detailed results will be discussed at the conference.