Abstract
A one-year field experiment was conducted in 2013 at an urban and suburban site in Guangzhou, Southern China to study the chemical compositions of PM_(2.5) and reconstruct the IMPROVE Algorithm to investigate the impact of aerosol components on visibility. Annual average PM_(2.5) mass concentration was 61.3 ± 27.6 and 54.2 ± 29.7 μg m^(-3) at the urban and suburban site, with organic matter (OM), sulfate (SO_4^(2-)), and nitrate (NO_3^-) among the dominant components, accounting for 40.3%, 16.3%, and 8.0% of the PM_(2.5) mass concentration respectively. Based on the modified IMPROVE Algorithm, the localized Mass Scattering Efficiencies (MSE) for sulfate and nitrate was obtained, with values of 2.16 ± 0.34 m^2 g^(-1) and 2.63 ± 0.66 m^2 g^(-1) at urban site and 2.22 ± 0.31 m^2 g^(-1) and 2.76 ± 0.84 m^2 g^(-1) at suburban site. Hygroscopic growth factors (Gf) for OM and EC were also taken into consideration with average values of 1.28 ± 0.13 m^2 g^(-1) and 1.15 ± 0.11 m^2 g^(-1) at the urban site and 1.18 ± 0.09 m^2 g^(-1) and 1.10 ± 0.09 m^2 g^(-1) at the suburban site. The estimated total light extinction coefficient was 294.7 ± 106.9 and 255.8 ± 119.0 Mm^(-1) at the urban and suburban site, with OM, SO_4^(2-) and NO_3^- contributing 41.7%, 16.5% and 11.5% at the urban site, and 42.1%, 21.3% and 9.1% at the suburban site. Secondary water-soluble ions and OM as a whole was becoming increasingly vital under polluted conditions, with nitrate in particular being more important under heavily polluted conditions in Guangzhou.
Highlights
Atmospheric aerosols impair visibility, negatively affect human health, and directly and indirectly impact regional and global climate (Chung and Seinfeld, 2005; Liu et al, 2011; Chen et al, 2013; Huang et al, 2014)
A one-year field experiment was conducted in 2013 at an urban and suburban site in Guangzhou, Southern China to study the chemical compositions of PM2.5 and reconstruct the IMPROVE Algorithm to investigate the impact of aerosol components on visibility
Visibility is inversely proportional to the light extinction coefficient (Koschmieder, 1924), with particles contributing about 90% of the total column light extinction, and playing the critical role in visibility degradation
Summary
Atmospheric aerosols impair visibility, negatively affect human health, and directly and indirectly impact regional and global climate (Chung and Seinfeld, 2005; Liu et al, 2011; Chen et al, 2013; Huang et al, 2014). The IMPROVE Algorithms are empirical formulas developed from using long-term observations at remote sites (e.g., parks, mountains, and wilderness areas) in the U.S, meaning that direct application to other locations can introduce errors on the order of –5.0%~+37% due to the different physical, chemical, mixing, and optical properties of PM2.5 at different locations (Bian, 2011; Jung et al, 2009a, b; Cao et al, 2012). This work fixed a fraction of these two parts of OC to the total OC, and used the water curves for hygroscopic OC derived from the curves for sulfate and nitrate For these reasons, we take the hygroscopic properties of OC and EC into consideration when we reconstruct the PM2.5 light extinction coefficient using long-term measurements
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