HR: 0800h
AN: A51C-0587 [Abstracts]
TI: Cl2, Br2, and I2 Measurements in the Tropical Marine Boundary Layer in Cape Verde, Africa
AU: * Lawler, M J
EM: mlawler@uci.edu
AF: University of California, Irvine, Earth System Science Department
1212 Croul Hall, Irvine, CA 92697,
AU: Finley, B D
EM: bfinley@uci.edu
AF: University of California, Irvine, Earth System Science Department
1212 Croul Hall, Irvine, CA 92697,
AU: Saltzman, E S
EM: esaltzma@uci.edu
AF: University of California, Irvine, Earth System Science Department
1212 Croul Hall, Irvine, CA 92697,
AB:
The dihalogens Cl2, Br2, and I2 were measured in marine boundary layer air at a windward tropical
coastal site in Cape Verde, off West Africa, as part of the RHaMBLe halogen campaign (May-June 2007). These
halogen species are thought to be released via heterogeneous processes on aerosols and photolyze quickly
during the daytime to generate highly reactive halogen atoms. These radicals can catalytically destroy ozone and
oxidize organic molecules. The measurements were made with an atmospheric pressure ionization triple-
quadrupole mass spectrometer by negative atom detection following collisional dissociation of the parent
molecular ion (e.g. Cl2- to Cl-). Each species exhibited a consistent and unique diel cycle. Cl2 had
nighttime maxima of ~3-20 ppt, based on preliminary calibrations, and was below the detection limit during the
day. I2 showed a semi-diurnal cycle, peaking most strongly at night (up to ~1 ppt) and also around solar noon
(up to ~0.5 ppt). Br2 also peaked near solar noon but was still detectable at other times of day for almost the
entire campaign. The midday Br2 peaks, based on our current calibrations, were usually a few ppt but
reached levels upwards of 20 ppt. Such levels in the daytime are incompatible with observed ozone
concentrations, which did not show dramatic depletion. These observations suggest a particularly strong local
source or some positive analytical artifact.
DE: 0322 Constituent sources and sinks
DE: 0345 Pollution: urban and regional (0305, 0478, 4251)
DE: 0365 Troposphere: composition and chemistry
DE: 0368 Troposphere: constituent transport and chemistry
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting