In October 2003, thirteen major wildfires in southern California burned more than 300,000 hectares of mainly chaparral biome. High-precision 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, and methyl halide mixing ratios, as well as with particle number concentrations (10–300 nm and 500–2500 nm aerodynamic diameter). Aerosol time-of-flight mass spectrometry of individual aerosol particles (50–2500 nm range) showed that 70–85% had typical biomass burning signatures (levoglucosan coupled with potassium). Only 5–18% of particles in the 50–300 nm range had vehicle signatures. Molar trace gas enhancement ratios (ERs) versus ethane and CO₂ were calculated and showed a narrow age distribution, consistent with the short distance from the wildfires. ERs for N₂O and CH₃CCl₃ versus CO₂ were determined, but correlations were poor. No significant CH₂Cl₂ or CHCl₃ emissions were detected. CO₂ emissions from the nearby Cedar fire were estimated both with a simple Lagrangian atmospheric transport model and a burned area approach and extrapolated to 11 Tg CO₂ for the total burned area in southern California. Total CO₂, CH₄, C₂-hydrocarbons, benzene, toluene, methyl chloride, methyl iodide, and PM_2.5 emissions were ∼0.2–3.5% of yearly global extratropical forest fire emissions and more than 28% of CH₄, C₆H₆, and PM_2.5 2003 San Diego and South Coast Air Basins anthropogenic emissions. Particle distributions and single particle chemistry are discussed. PM_2.5 considerably exceeded the EPA short-term exposure limit.