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As has been the case in North America and western Europe, the emissions have substantially reduced in the North China Plain (NCP) in recent years. Differential rates of reduction in and concentrations result in the frequent occurrence of particulate matter pollution dominated by nitrate () over the NCP. In this study, we observed a polluted episode with the particulate nitrate mass fraction in nonrefractory PM (NR-PM) being up to 44 % during wintertime in Beijing. Based on this typical -dominated haze event, the linkage between aerosol water uptake and enhancement, further impacting on visibility degradation, has been investigated based on field observations and theoretical calculations. During haze development, as ambient relative humidity (RH) increased from  % to 70 %, the aerosol particle liquid water increased from  µgm-3 at the beginning to  µgm-3 in the fully developed haze period. The aerosol liquid water further increased the aerosol surface area and volume, enhancing the condensational loss of over particles. From the beginning to the fully developed haze, the condensational loss of increased by a factor of 20 when only considering aerosol surface area and volume of dry particles, while increasing by a factor of 25 when considering extra surface area and volume due to water uptake. Furthermore, aerosol liquid water favored the thermodynamic equilibrium of in the particle phase under the supersaturated and in the atmosphere. All the above results demonstrated that is enhanced by aerosol water uptake with elevated ambient RH during haze …