Abstract <p>Atmospheric aerosols have a significant impact on air quality, climate, and human health. The comparison of gaseous impurity and ionic composition monitoring data in the surface atmosphere over Antwerp and Beijing showed that the hygroscopicity level of dense haze particles over Beijing in winter is determined by the depth of heterogeneous reactions of sulfate and nitrate formation. The paper discusses the dynamics and mechanisms of these nonphotochemical processes, as well as the features of their coupling in a haze-polluted atmosphere. Their rapid occurrence in particles in combination with the uptake of water vapor from the air causes abnormally high mass concentrations of aerosol and their variability during the haze period over Beijing. The results are necessary for forecasting the occurrence of dense hazes, as well as for constructing models of transport of gas and aerosol microimpurities in the atmosphere.</p>