Chemical composition of PM2.5 and its impact on visibility in Guangzhou, Southern China

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 PM2.5 and reconstruct the IMPROVE Algorithm to investigate the impact of aerosol components on visibility. Annual average PM2.5 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 (SO42–), and nitrate (NO3–) among the dominant components, accounting for 40.3%, 16.3%, and 8.0% of the PM2.5 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 m2 g–1 and 2.63 ± 0.66 m2 g–1 at urban site and 2.22 ± 0.31 m2 g–1 and 2.76 ± 0.84 m2 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 m2 g–1 and 1.15 ± 0.11 m2 g–1 at the urban site and 1.18 ± 0.09 m2 g–1 and 1.10 ± 0.09 m2 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, SO42– and NO3– 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.