Bridging the gap between air quality and precipitation chemistry

Data sets recently have become available providing simultaneous, regional scale observations of ambient air quality and precipitation chemistry. The data cover parts of the greater northeastern United States. With certain key assumptions, the observations of ambient SO_x and NO_x concentrations can be linked with precipitation concentrations through Junge's concept of rainout efficiency, assumed to be qualitatively equivalent to the washout ratio. A preliminary comparison between data taken from the Sulfate Regional Experiment (SURE) and the parallel precipitation studies using Junge's approach reveals certain useful consequences. Apparent dramatic differences in SO_x and NO_x scavenging are found. Ratios between sulfate in the aerosol and in precipitation compared with trace elements suggest the importance of particulate scavenging processes. Such results show promise for simplified analysis of these data as approaches to differentiating mechanisms involved in cloud-precipitation chemistry.