Physical and chemical characteristics of winter fogs in Nanjing

To study the macro and micro-physical structure and the physicalchemical processing of Nanjing dense fogs in winter, and reveal the relationship between the airpollution and characteristics of fogwater, three comprehensive field observations are conducted during 2006, 2007 and 2008 winters in Nanjing University of Information Science & Technology (NUIST). Observations include macro and microstructure of fog, characteristics of fog water, particle spectrum and chemical composition of atmospheric aerosols, radiation and heat components and turbulence, as well as the conventional meteorological observational elements and environmental monitoring items. The continual observation is carried out during the fog episode. 37 fog-water samples and 27 cases, which are divided into three types of fogs (the radiation fog, advectionradiation fog and evaporation fog), are obtained. Macro and micro-structure of different types of fogs are analysed in detail and physical processes in the development of dense fog are studied. The findings are as follows. Most of fogs in winter of Nanjing are the warm fog among them the advectionradiation fog had the thickest layers with its top at 851 m on average; the radiation fog was in the second place with its top at 486 m on average, and the evaporation fog had the lowest layers with the top at 428 m on average. For the fog microphysical parameters, the advectionradiation fog had also the largest values, which could reach 1 g/m3, followed are the radiation fog and, the evaporation fog, the smallest. From the analysis of the continuous changes of fog microphysical parameters, there was a burst reinforcement in the mature stage for either the advectionradiation fogs or the radiation fogs. The fogwater analysis shows that, the ions concentrations of the fogwater are very high with the acid fog being about 43% of the total number of samples which belongs to the sulfate type and is related to air pollutants (SO2, NO2 and particulate matter).