Optical properties closure and sources of size-resolved aerosol in Nanjing around summer harvest period

Abstract

Abstract Aerosol size distribution, chemical components and their mixing state are key factors impacting the optical properties of aerosols. The researches on optical properties closure and sources for size-segregated aerosols are still scattered. A sampling campaign covering a summer harvest period was conducted in Nanjing, considering the influence of open biomass burning (BB) on optical properties of size-resolved aerosol. Two parallel FA-3 samplers were employed to collect nine size-segregated particles (0.43–10\xa0μm), with water-soluble ions, carbonaceous components and elements analyzed. Aerosol light absorption (bap) and scattering (bsp) coefficients were synchronously online monitored. Results indicated that sulfate, nitrate and ammonium (SNA), crustal materials (CM) and organic matter (OM) were the main contributors of aerosol mass, totally accounting for 61.3%–81.4%. On hazy days, PM1.1 occupied 82.3% of the total estimated bsp by Mie model, with SNA and OM accounting for 40.9% and 16.2%, respectively. PM1.1 contributed 61.7% of the total estimated bap with EC accounting for 41.6%. Positive matrix factorization modeling indicated that vehicle emission contributed most (13.1%–52.9%) to bap especially for particles with diameter smaller than 0.43\xa0μm. On hazy days, BB was the main source for bsp, contributing to 24.7% (for particle within 1.1–2.1\xa0μm)-38.2% (0.65–1.1\xa0μm), then followed by secondary inorganic aerosol, contributing to 16.3% (1.1–2.1\xa0μm)-18.8% (0.65–1.1\xa0μm). For the summer harvest period, the open BB impacts obviously on bsp rather than bap, promoting the haze formation. The temporal variations of aerosol externally mixed ratio and significant negative correlations between the mixed ratio and OC/EC also verified that fresh BB emissions deteriorated the visibility. This study highlights the different roles of aerosol chemical components and emission sources impacting optical properties for size-resolved aerosols, which is helpful to give more accurate visibility improvement strategies.