Impacts of biomass-burning on aerosol properties of a severe haze event over Shanghai

Anthropogenic aerosols have significant impacts on the environment and human health in the Yangtze River Delta region, one of the most densely populated regions in the world. A biomass-burning plume swept across this area (Shanghai) in May 2009, leading to changes in the physical and optical properties of aerosols, which were investigated using ground-based remote sensing and in situ measurements via comparisons with dust pollution and background conditions. Experiments show that the biomass-burning plume led to an increase in the average aerosol optical depth (AOD) at 500 nm from 0.73 to 1.00 (37% higher), an absorption Angstrom exponent (AAE) of 1.48, and an increase in the Angstrom exponent (α) up to 1.53. Furthermore, local dust aerosols derived from road dust and/or construction dust also led to higher values of AOD (2.68) and AAE (2.16), and a daily average value of α of 1.05. For the biomass-burning plume, the aerosol particles exhibited significant variations in short-wavelength spectra. The single scattering albedo at 670 nm decreased remarkably under the influence of the biomass-burning plume, indicating the significant absorptive ability of the biomass-burning pollution and higher ratio of absorption aerosols within the plume. Under the effects of the biomass-burning, the volume concentration of fine-mode aerosols increased significantly and the PM-fine/PM-coarse volume concentration ratio reached 12.33. This relatively large change in fine-mode particles indicates that biomass-burning has a greater impact on fine-mode aerosols than on coarse-mode aerosols.