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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 ratios of sulfate to nitrate (greater than 4) promote the occurrence of deliquescent behavior of ambient aerosols 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 scattering Ångström exponent on the estimation of optical hygroscopicity parameter. The results highlight that the impact of dust storms on aerosol chemical compositions and optical hygroscopicity are different for DS events with different transport pathways. Plain Language Summary: Dust storm (DS) is one of the severest natural disasters. Studying the change of aerosol properties during DS is important to understand the role of dust in the earth‐atmosphere system. This study chooses two DS events (DS1 and DS2) in March and May 2021 to investigate the impacts of DS on aerosol chemical compositions and optical hygroscopicity in the YRD region. It is found that DS1 transporting in the lower atmosphere makes a larger increase of coarse‐mode particles near the surface than DS2 transporting in the upper atmosphere. The weak impact of DS2 on the surface aerosols leads to a small change in aerosol chemical compositions of fine particles near the surface. The enlarged mass ratio of sulfate to nitrate (greater than 4) during dust periods can promote ambient aerosol deliquescence, which is important to quantify aerosol optical properties. To provide a reference for improving the model simulation of aerosol optical hygroscopicity, different parameterization schemes are derived to fit the change of aerosol light scattering enhancement factor with RH during dust and no‐dust periods. The closure study of aerosol optical hygroscopicity parameters suggests that aerosol scattering Ångström exponent plays an important role in the overestimation of optical hygroscopicity parameters. Key Points: The dust storms influencing the YRD region have different transport pathways and impacting atmospheric layersThe enlarged mass ratio of sulfate to nitrate in fine particles makes the deliquescence phenomenon appear more in dust‐influence periodsAerosol scattering Ångström exponent is an important factor to estimate optical hygroscopicity parameters [ABSTRACT FROM AUTHOR]

The evolution of the planetary boundary layer (PBL) and the effect of aerosols on the PBL in Beijing and Nanjing were compared based on measurements made during two long-term field campaigns. Monthly PBL height (PBLH) trends in Nanjing and Beijing were similar, opposite to those of the mass concentration of particles with diameters less than 2.5 μm (PM 2.5). This phenomenon was more obvious in Nanjing than in Beijing. The negative correlation between PBLH and PM 2.5 mass concentration was weaker in Nanjing than in Beijing. The PBLH varied during the day. Heavy aerosol pollution made this variation weak in autumn and winter in Beijing. Further results suggest that out of all the seasons, summertime PM 2.5 had the greatest influence on the evolution of the PBL. The PBLH was more sensitive to the variation in PM 2.5 mass concentration in Nanjing than in Beijing. Aerosol type (scattering or absorbing) had a weak effect on the evolution of the PBLH in Nanjing, but absorbing aerosols played a dominant role in Beijing. Our results highlight the cross-regional difference in aerosol-PBL interactions. • The evolution of planetary boundary layer heights (PBLHs) in Nanjing and Beijing differ. • The PBLH is more sensitive to the variation in PM 2.5 mass concentration in Nanjing than in Beijing. • Aerosol type makes a difference in aerosol-PBL interactions in Nanjing and Beijing. [ABSTRACT FROM AUTHOR]