Abstract: During the time period of 7-9 December 2013, two deep dense fog events occurred in Nanjing. By using the observational data acquired from a field experiment conducted during this time period, this study investigated the contributions of different suspended aerosols with various sizes to the formation of fog droplets as well as the impacts of the ions in condensation nucleus on the chemical properties of the fog water. The observational data used in the present study consist of the concentrations of the water-soluble ions in three-stage fog droplets, the particle-size aerosols, number distributions of aerosol particles, distributions of the fog droplets, and meteorological factors etc. The micro-physicochemical properties of the three stages fog water (4-16 μm for stage 3, 16-22 μm for stage 2, larger than 22 μm for stage 1) as well as the particle-size aerosols were compared and discussed. The result demonstrates that under the condition of the deep dense fog (visibility≈ 50 m), a stable temperature inversion layer tended to form due to the weakening of the radiation. As a result, the contaminated aerosols would accumulate and transit to fog droplets. Moreover, it was found that the aerosols in 0.5-1 μm contributed the most to the increase in the number of the fog droplets in stage 3. There existed higher concentrations of NO₃^- and SO₄^2- in the particle-size aerosols and that of Ca²⁺ was the highest among the cations. In addition, among the fog droplets in these three stages, both of the anions and cations possessed the highest concentrations in the droplets in stage 3. In contrast, the difference in the anion and cation concentrations between stage 1 and stage 2 was negligible. The results also show that the anion and cation in drop size fog water mostly were originated from the suspended aerosols and the chemical reactions. It was also found that the concentration of Ca²⁺ was the highest among all the cations in stage 1 and NH₄⁺ was the highest in both stage 2 and stage 3. For the anions, NO₃^- and SO₄^2- had the highest concentration with little difference. At last, it was observed that the fog was acidic (pH=2.7-6.9), and the fog drops with smaller size had relatively stronger acidity.