Abstract: Comprehensive observations of fog were conducted during winter 2007 in Nanjing University of Information Science and Technology, including the measurements of visibility, raindrop spectrum, fog, and aerosol spectrums. Salient synoptic-scale features were identified using conventional meteorological observations and NCEP reanalyses. We studied the synoptic situation and macro-micro evolutionary characteristics of six precipitation fog events that occurred in Nanjing during December 2007. The results show that (1) The six events were all mainly controlled by the synoptic system and were in the form of fog compared with light rain. The minimum visibility in these events was more than 250 m. In addition, the precipitation fog mostly occurred under the influence of an easterly airstream, and generally weak precipitation occurred first, when the air was close to saturation. An invasion of cold air from the north and vapor condensation finally caused the formation of precipitation fog. (2) An inversion layer was always present near the surface before most precipitation fogs, and the temperament different between 2m and the surface changed from positive to negative as inversion layer disappeared during fogs. However, the observation of inversions below 900 hPa was difficult. Altocumulus (Ac) and Altostratus (As) or Stratocumulus (Sc) and Fractonimbus (Fn) ccurred in the middle and lower layer before precipitation fogs, while the height of low clouds was 0.3-2.5 km. During these processes, the layer below 600 hPa was nearly saturated, most events occurred with Fn, and the height of low clouds markedly decreased. After the fog, the nearly saturated layer may still have been present. In addition, there was significant wind shear near 900 hPa before precipitation fogs. (3) The number and concentration of larger and smaller fog droplets increased markedly in the early stages of precipitation fog formation. Aitken mode particles are more efficiently scavenged through nucleation by precipitation fogs in Nanjing, and the reduction in Aitken particles is closely related to wind direction and speed. Because of the influence of a stronger north wind, the concentration of aerosol particles decreased significantly.