Aerosol hygroscopicity derived from size-segregated chemical composition and its parameterization in the North China Plain

Abstract

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) are identified from aerosol particle samples collected with a ten-stage impactor. An iterative algorithm is developed to evaluate the hygroscopicity parameter κ from the measured chemical composition of particles. 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) of 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's average size distribution of κ values shows three distinct modes: a less hygroscopic mode (Dp < 150 nm) with κ slightly above 0.2, a highly hygroscopic mode (150 nm < Dp < 1 μm) with κ greater than 0.3 and a nearly hydrophobic mode (Dp > 1 μm) with κ of 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 50–250 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 of 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. WSOC for particles of around 30 nm contribute 52% of κ. Aerosol hygroscopicity is related to synoptic transport patterns. When southerly wind dominates, particles are more hygroscopic; when northerly wind dominates, particles are less hygroscopic. Aerosol hygroscopicity also has a diurnal variation, which can be explained by the diurnal evolution of planetary boundary layer, photochemical aging processes during daytime and enhanced black 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 of less than 100 nm. A parameterization scheme for κ is developed using mass fractions of SO42−, NO3−, NH4+ and WSOC due to their high correlations with κ, and κ calculated from the parameterization agrees well with κ derived from the particle's chemical composition. Further analysis shows that the parameterization scheme is applicable to other aerosol studies in China.

A study of aerosol liquid water content based on hygroscopicity measurements at high relative humidity in the North China Plain

“…This shows an existent but not remarkable correlation between the ALWC and the number concentration. Although some aerosols in the coarse mode are water soluble and have certain impacts on the ALWC, nearly hydrophobic aerosols, such as dust particles, contribute a large number fraction to the coarse mode (Hussein et al, 2004;Liu et al, 2008Liu et al, , 2014. The R 2 for the accumulation mode is significantly higher than those for the other three modes (Fig.…”

“…All chemical components the BLPI filter sample analysis yielded are considered in this model except for the organic species. Liu et al (2014) shows that the overall particle hygroscopicity is mostly contributed by inorganic compounds in the NCP and the water-soluble organic compounds play a critical role only for ultrafine particles smaller than 100 nm. The thermodynamics of the crustal species including Ca 2+ , K + and Mg 2+ have been added to the model's treatment components along with NH + 4 , Na + , SO 2− 4 , NO − 3 , Cl − and H 2 O, but organic species are not taken into account.…”

“…Based on its computational rigour and performance on computational speed, ISORROPIA II appears to be an extremely desirable choice for large-scale atmospheric transport and air quality models (Fountoukis and Nenes, 2007). The ISORROPIA II model can simulate the ALWC with the input of aerosol chemical composition measured by BLPI sampling (Liu et al, 2014).…”

“…The lower and upper bounds for each stage are shown in Table 1. For detailed information about the particle size ranges and mean diameters for the individual impactor stages see Liu et al (2014). By preweighing and then weighing and analysing the films afterwards in the laboratory, the stage-segregated aerosol chemistry information was determined.…”

Analysis of extinction properties as a function of relative humidity using a <i>κ</i>-EC-Mie model in Nanjing

“…κ can be calculated according to many methods (Liu et al, 2014;Miao et al, 2015;Petters and Kreidenweis, 2007). In this study, κ was calculated with the ZSR rule (Petters and Kreidenweis, 2007) Gysel et al (2007), and his method is as accurate as the ADDEM model (Topping et al, 2005).…”