In October 2003, thirteen major wildfires in southern California burned more than 300,000 hectares of mainly chaparral biome, strongly impacting an urban area populated by ~20 million people. In situ trace gas and particle measurements of the wildfire plumes in La Jolla, California, showed a high degree of correlation among carbon dioxide (CO2), methane (CH4), nonmethane hydrocarbons (NMHCs), and methyl halide mixing ratios, as well as with particle number concentrations. The chemical compositions of individual particles with aerodynamic diameters of 50-300 nm and 200-2500 nm showed that 70-85% had typical biomass burning signatures with levoglucosan and potassium. Only 5-18% of particles in the 50-300 nm range had vehicle signatures, and C6H6/C7H8 and C6H6/C2H2 ratios confirmed the minor influence of urban pollution.
With the help of trace gas correlations with CO2, a Lagrangian atmospheric transport ”puff” model and a burned area approach, the emissions of the greenhouse gases CO2 and CH4, NMHCs (C2-hydrocarbons, benzene, and toluene), methyl halides (CH3Cl and CH3I), and PM2.5 particulate matter were estimated to have been at least 0.2-3.5% of global annual emissions from extratropical forest fires. CO2 and CH4 emissions over these few days corresponded to 0.2-0.4% of total U.S. emissions in 2003, and 3-7% of total California emissions in 2002. CH4, C6H6, and PM2.5 emissions corresponded to at least 28-36% of total yearly emissions from the San Diego and South Coast Air Basins. PM2.5 considerably exceeded the EPA short-term exposure limit, reaching severely unhealthy levels.
If future winter precipitation in the western U.S. shifts from snow to rain and local climate becomes dryer as predicated by climate models, more pronounced wildfire activity and increased emissions of trace gases and particles with local and global impacts are likely to occur.
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Article: Trace gas and particulate emissions from the 2003 southern California wildfires. J. Mühle, T.J. Lueker, Y. Su, B.R. Miller, K.A. Prather and R.F. Weiss (2007), Journal of Geophysical Research, 112: D03307 (doi:10.1029/2006JD007350).