Chemical composition of fog water in Nanjing area of China and its related fog microphysics

Fog samples were collected at Pancheng in the Nanjing area of China during December 2006 and December 2007. Fog droplet spectra, surface meteorological elements and visibility were also measured during the same period. The data from PM10, SO2 and NO2 measurements were obtained from the air quality monitoring networks of Nanjing. The total ionic concentration (TIC) and electrical conductivity (EC) in fog samples, and the local pollutant emissions were one or two orders of magnitude higher than those found in Europe or South America for instance. Pollutants were expected to be mainly from local sources, including factories, plants, freeways, soil sources, house construction, and biomass burning. Advection also contributed to pollution levels in radiation–advection fogs. The scavenging of NH3 and coarse particles by fog droplets was the main cause for the high mean pH value of 5.9. In-phase temporal evolution of TIC, [SO42−], [NO3−], SO2, NO2, PM10 and S/LWC (S: the surface area of fog droplets per unit volume of air; LWC: liquid water content) was found to be due to the interaction of air pollutants and fog droplets, change of air mass due to advection, and so on. S/LWC seemed to be a better indicator for describing the relationship between TIC and microphysics with respect to LWC. A formula between TIC and S/LWC was derived and the related parameters were discussed. Depositions of chemical species in fog cases were estimated and the result showed that deposition was efficient.