Observations and implications of molecular chlorine and bromine in the marine troposphere

This paper will describe preliminary results from a collaborative research program, conducted under the auspices of the Department of Energy`s Atmospheric Chemistry Program, to improve current understanding of the role of chlorine and bromine in marine tropospheric chemistry. The overall program includes laboratory, field and modeling components. This presentation will emphasize recent field observations of CL{sub 2}, and Br{sub 2} which have for the first time been identified in a specific manner in the marine boundary layer. Results from laboratory and modeling studies will be utilized to interpret the field observations. Field measurements were performed in late summer of 1995 over the North Atlantic Ocean. The measurements were made from a Gulfstream G-1 research aircraft equipped with an extensive array of air monitoring and meteorological instruments. The chlorine and bromine observations utilized a tandem mass spectrometer operated in a continuous monitoring mode with atmospheric pressure chemical ionization. This mode of operation allowed very specific monitoring of the gaseous halogens, with detection limits of 15 ppt for chlorine and 6 ppt for bromine. Calibrations were performed both before and during the monitoring flights using certified permeation sources of CL{sub 2} and Br{sub 2}. In-flight zeroing of the instrument made use ofmore » an annular denuder.« less