HR: 0800h
AN: A51C-0583 [Abstracts]
TI: Measurements of Cl2, Br2, I2, and BrCl in Polluted Coastal Air
AU: * Finley, B D
EM: bfinley@uci.edu
AF: University of CA, Irvine, 1212 Croul Hall, Irvine, CA 92697, United States
AU: Lawler, M J
EM: mlawler@uci.edu
AF: University of CA, Irvine, 1212 Croul Hall, Irvine, CA 92697, United States
AU: Saltzman, E S
EM: esaltzma@uci.edu
AF: University of CA, Irvine, 1212 Croul Hall, Irvine, CA 92697, United States
AB:
Halogen atoms have the potential to produce and destroy ozone in polluted air, but there are few field studies of
reactive halogens and their precursors in coastal urban environments. Here we present API/MS/MS
measurements of dihalogen mixing ratios in Malibu, CA during October, 2006, as part of a field campaign to
determine the impact of halogens on urban ozone photochemistry and air quality.
During this study, Cl2 mixing ratios ranged from <1.2-11 ppt with a geometric mean of 1.1±1.5.
Cl2 was observed both day and night with no dependence on wind direction. Br2 levels ranged from
<0.3-11 ppt with a geometric mean of 0.3±0.6. Br2 was frequently observed at night and the highest
levels were detected in off-shore winds, suggesting a possible continental or anthropogenic source. BrCl was
observed above detection limit for the first time in marine air, at levels ranging from 0.5-2.2 ppt, with a geometric
mean of 0.2±0.8.
I2 ranged from <0.3-1.4 ppt with a mean of 0.2±0.4. The highest I2 mixing ratios were
observed in westerly winds that recently passed over local kelp beds. I2 exhibited a consistent diurnal
cycle with typical daytime levels 0.2-0.4 ppt higher than nighttime levels.
A photochemical box model was used to infer the impact of dihalogen chemistry on ozone under the moderately
polluted conditions encountered during this study. The results suggest that chlorine oxidation of hydrocarbons
may be responsible for up to 5% of the observed O3 levels. At the observed Br2 levels, destruction of
ozone by bromine radicals is minor, lowering O3 levels by only 1-2%. Iodine radicals generated from
photolysis of I2 contribute to O3 destruction, partially off-setting the O3 produced from chlorine
radicals. The efficiency of ozone destruction by Br and I atoms in polluted air is reduced in polluted air compared
to clean air, due to halogen-NOx interactions that short-circuit catalytic O3 destruction cycles.
DE: 0300 ATMOSPHERIC COMPOSITION AND STRUCTURE
DE: 0345 Pollution: urban and regional (0305, 0478, 4251)
DE: 0365 Troposphere: composition and chemistry
DE: 0394 Instruments and techniques
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting