The impacts of dust storms with different transport pathways on aerosol chemical compositions and optical hygroscopicity of fine particles in the Yangtze River Delta

Aerosol physicochemical properties during two dust storms (DS1: March 30-31, and DS2: May 7-8) are measured in 2021 in Nanjing, aiming to investigate the impacts of dust storms on aerosol chemical compositions and optical hygroscopicity in the Yangtze River Delta (YRD). During DS1, the dust air masses are transported in the lower atmosphere and pass through the inlands and sea areas before reaching the YRD region. During DS2, the dust air masses are transported in the upper atmosphere and pass through the inlands only. Both of them are accompanied by an increase in black carbon (BC) mass fraction and a decrease in nitrate mass fraction in fine particles (PM2.5, particles with diameters less than 2.5 μm) near the surface. However, the impacts on the mass fractions of organics or sulfate are adverse between DS1 and DS2. During dust-influence periods the enlarged mass ratio of sulfate to nitrate (greater than 4) promote aerosol deliquescence although dust aerosols can significantly suppress aerosol optical hygroscopicity. To improve model simulations of aerosol optical hygroscopicity, it is necessary to use a segment parameterization to describe aerosol light scattering enhancement factor during dust-influence periods. The closure study of optical hygroscopicity parameters with two different methods reveals the impact of aerosol mixing state on the estimation of optical hygroscopicity parameter. The results highlight the impact of dust storms on aerosol chemical compositions and optical hygroscopicity are different for DS events with different transport pathways.