Seasonal variability in anthropogenic halocarbon emissions

Area of Science:

• Atmospheric Chemistry
• Environmental Science
• Air Quality Monitoring

Background:

• Anthropogenic halocarbons are potent greenhouse gases and ozone-depleting substances.
• Understanding current emission sources and trends is crucial for effective environmental policy.
• Previous studies have not fully captured the seasonal variability of halocarbon emissions.

Purpose of the Study:

• To quantify ambient concentrations and estimate anthropogenic emissions of eight halocarbons in California's South Coast air basin.
• To investigate seasonal differences in halocarbon emissions.
• To compare South Coast air basin per capita emissions with national estimates.

Main Methods:

• In situ gas chromatography was used to measure halocarbon concentrations during summer and fall 2005.
• Halocarbon emissions were estimated using regressions with carbon monoxide mixing ratios and emission inventories.
• Per capita emissions were calculated and compared to national data.

Main Results:

• Ongoing emissions of methylchloroform and CFC-11 were observed; CFC-113 emissions had ceased.
• Estimated per capita emissions for methylchloroform and chloroform were 6.6 and 19 g/(person.year), respectively.
• Summer emissions of methylchloroform and chloroform were 4.5 and 2.5 times higher than fall emissions, respectively.

Conclusions:

• South Coast air basin per capita emissions for several halocarbons are lower than national estimates.
• Seasonal emission variations, potentially from landfills and water chlorination, are significant and unaddressed in current inventories.
• The omission of seasonal variability may lead to inaccuracies in post-2000 methylchloroform emission estimates and hydroxyl radical calculations.