Impact of size distributions of major chemical components in fine particles on light extinction in urban Guangzhou

Abstract

To evaluate the impact of fine particulate matter (PM2.5) size distribution on aerosol chemical and optical properties, dominant chemical components including water-soluble inorganic ions (WSII), organic carbon (OC) and elemental carbon (EC) in PM1 and PM2.5, aerosol scattering coefficient (bsp), and aerosol absorption coefficient (bap) were collected synchronously at an urban site in Guangzhou, south China during a typical summer month in 2009 and a winter month in 2010. PM1 (sizes smaller than 1μm) constituted 77% and 63% of PM2.5 in summer and winter, respectively. From the reconstructed mass concentrations, the sum of SO42−, NO3− and NH4+ (SNA) distributed more in PM1 than in PM1–2.5 (PM2.5 minus PM1) in summer and the opposite was found in winter, while carbonaceous aerosols distributed more in PM1 in both summer and winter. With the aggravation of PM2.5 pollution, the mass fraction of PM1/PM2.5 increased for (NH4)2SO4 (AS), NH4NO3 (AN) and EC but decreased for organic matter (OM) in summer, and the opposite was found in winter. Bsp of PM1 and PM1–2.5 was estimated from the mass extinction efficiencies (MSEs) of the dominant chemical components, which showed good correlations (R2=0.99) with measured ones and those estimated using the IMPROVE formula. The fractional contributions of dominant chemical components to extinction coefficient (bext) were consistent with their respective mass size distributions, indicating the importance of chemically-resolved aerosol size distributions on aerosol optical properties and haze formation.