To fully understand the physical and chemical influencing mechanisms of the frequent low visibility (VIS) events at urban Chongqing in recent years, this study explores the crucial causes for low VIS in Chongqing mainly from the perspectives of chemical light extinction combined with aerosol hygroscopic growth by using the simultaneous meteorological data and PM_2.5 chemical compositions from 2015 to 2021. Results show that the VIS<10 km cases were mainly observed in autumn and winter, with over half number of the days. Nitrate gradually dominated over sulfate and organics to be the predominant secondary inorganic component of PM_2.5 in both seasons, and nitrate possessed the largest contribution to the total light extinction. Along with the visibility deterioration and the increase of relative humidity (RH), the light extinction contribution due to nitrate and its corresponding hygroscopic growth enhanced significantly. Accompanied with the marked decrease in PM_2.5 concentrations since 2018, nitrate on average occupied a higher mass fraction and light extinction contribution at the same visibility level in comparison to previous years, specifically under high RH conditions. The above highlights that the continuous control of nitrate and relevant precursors will be beneficial for the effective improvement of low visibility in autumn and winter at urban Chongqing, given the precondition of generally low anthropogenic emission levels in the future.