Atmos. Chem. Phys. Discuss., 13, 20885-20922, 2013
© Author(s) 2013. This work is distributed
under the Creative Commons Attribution 3.0 License.
Review Status
This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
Aerosol hygroscopicity derived from size-segregated chemical composition and its parameterization in the North China Plain
H. J. Liu1, C. S. Zhao1, B. Nekat2, N. Ma1, A. Wiedensohler2, D. van Pinxteren2, G. Spindler2, K. Müller2, and H. Herrmann2
1Department of Atmospheric and Oceanic Sciences, School of Physics, Peking University, Beijing 100871, China
2Leibniz-Institute for Tropospheric Research, TROPOS, 04318 Leipzig, Germany

Abstract. Hygroscopic growth of aerosol particles is of significant importance in quantifying the aerosol radiative effect in the atmosphere. In this study, hygroscopic properties of ambient particles are investigated based on particle chemical composition at a suburban site in the North China Plain during the HaChi campaign (Haze in China) in summer 2009. The size-segregated aerosol particulate mass concentration as well as the particle components such as inorganic ions, organic carbon and water-soluble organic carbon (WSOC) is identified from aerosol particle samples collected with a 10-stage impactor. An iterative algorithm is developed to evaluate the hygroscopicity parameter κ from the measured particle chemical compositions. During the HaChi summer campaign, almost half of the mass concentration of particles between 150 nm and 1 μm is contributed by inorganic species. Organic matter (OM) is abundant in ultrafine particles, and 77% of the particulate mass with diameter (Dp) around 30 nm is composed of OM. A large fraction of coarse particle mass is undetermined and is assumed to be insoluble mineral dust and liquid water. The campaign average size distribution of κ values shows three distinct modes: the less hygroscopic mode (Dp < 150 nm) with κ slightly above 0.2, the highly hygroscopic mode (150 nm<Dp < 1 μm) with κ larger than 0.3 and the nearly hydrophobic mode (Dp > 1 μm) with κ about 0.1. The peak of the κ curve appears around 450 nm with a maximum value of 0.35. The derived κ values are consistent with results measured with a High Humidity Tandem Differential Mobility Analyzer within the size range of 50 nm to 250 nm. Inorganics are the predominant species contributing to particle hygroscopicity, especially for particles between 150 nm and 1 μm. For example, NH4NO3, H2SO4, NH4HSO4 and (NH4)2SO4 account for nearly 90% of κ for particles around 900 nm. For ultrafine particles, WSOC plays a critical role in particle hygroscopicity due to the predominant mass fraction of OM in ultrafine particles. 52% of κ is contributed by WSOC for particles around 30 nm. Aerosol particles are more hygroscopic during daytime, which can result from the diurnal evolution of planetary boundary layer, photochemical aging process during daytime and enhanced elemental carbon emission at night. κ is highly correlated with mass fractions of SO42−, NO3 and NH4+ for all sampled particles as well as with the mass fraction of WSOC for particles less than 100 nm. A parameterization scheme of κ is developed using mass fractions of SO42−, NO3, NH4+ and WSOC due to their high correlations with κ, and κ calculated from parameterization agrees well with κ derived from the particle chemical composition. Further analysis shows that the parameterization scheme is applicable to other aerosol studies in China.

Citation: Liu, H. J., Zhao, C. S., Nekat, B., Ma, N., Wiedensohler, A., van Pinxteren, D., Spindler, G., Müller, K., and Herrmann, H.: Aerosol hygroscopicity derived from size-segregated chemical composition and its parameterization in the North China Plain, Atmos. Chem. Phys. Discuss., 13, 20885-20922, doi:10.5194/acpd-13-20885-2013, 2013.
Search ACPD
Discussion Paper
    Final Revised Paper