Fog and Precipitation Chemistry in Nanjing, China

Fog and rain water samples were collected at Pancheng in Nanjing area, China during two consecutive winters from 2006 to 2007. Chemical characterizations of these samples are analyzed and summarized. In general, the average ion concentrations and electrical conductivity (EC) are much higher, while acidities are lower in fog water with respective to those in rain water; EC and most ion concentrations in fog water in 2007 are found lower compared with those in 2006, but the situations are inverse in rain water from 2006 to 2007. These phenomena are caused by the formation differences between fog and rain droplets, mostly influenced by local pollution and advection processes, respectively. Fog samples were collected using a self-fabricated active fog collector. With the help of a fan, air containing fog droplets was drawn through a chamber, and the droplets were collected by impaction on Teflon strands. The fog water was stored in polyethylene bottles. Rain water was collected with a special collector and was also stored in polyethylene bottles. Immediately after collection, both fog and rain samples were kept in a refrigerator. In the laboratory, pH and electric conductivity (EC) of fog and rain water were conducted with a digital pH meter and a conductivity meter. Dionex (Sunnyvale, CA, USA) model 2000 ion chromatographic systems were used for anion and cation analysis, respectively. In addition, some other observations were carried out in this experiment. Boundary layer structure, fog microphysics and routine surface meteorological elements were detected with a tethersonde system (DigiCORA Ⅲ, Vaisala), a droplet spectrometer (model FM-100, DMT) and automatic weather station (EnviroStation™, ICT International Pty Ltd) .