![]() Recondensation of species initially evaporated from the particles may have contributed to the subsequent slow rise in OA. Decreasing OA accompanied by increased scattering/particle coating in initial aging may be due to a combination of particle coagulation and evaporation processes. The fraction of thickly coated rBC particles increased up to ~85% over the 4 h aging period. In the California plume, however, ΔOA/ΔCO 2 decreased sharply for the first hour and then increased slowly with a net decrease of ~20% over 4 h. The increase in light scattering was similar to that observed in an earlier study of a biomass burning plume in Mexico where significant secondary formation of OA closely tracked the increase in scattering. The excess aerosol light scattering in the plume (normalized to excess CO 2) increased by a factor of 2.50 ± 0.74 over 4 h. NO x was converted to PAN and particle nitrate with PAN production being about two times greater than production of observable nitrate in the first ~4 h following emission. Some of the gas phase NH 3 loss may have been due to condensation on, or formation of, particles below the AMS detection range. The observed ammonium increase was a factor of 3.90 ± 2.93 in about 4 h, but accounted for just ~36% of the gaseous ammonia lost on a molar basis. ![]() Ammonium, nitrate, and sulfate all increased over the course of 4 h. Based on the rapid decay of C 2H 4 we infer an in-plume average OH concentration of 5.27 (☐.97) × 10 6 molec cm −3, consistent with previous studies showing elevated OH concentrations in biomass burning plumes. Excess acetic and formic acid (normalized to excess CO) increased by factors of 1.73 ± 0.43 and 7.34 ± 3.03 (respectively) over the same time since emission. The molar ratio of excess O 3 to excess CO in the plume (ΔO 3/ΔCO) increased from −5.13 (☑.13) × 10 −3 to 10.2 (☒.16) × 10 −2 in ~4.5 h following smoke emission. Our measurements included: CO 2 CO NO x NH 3 non-methane organic compounds organic aerosol (OA) inorganic aerosol (nitrate, ammonium, sulfate, and chloride) aerosol light scattering refractory black carbon (rBC) and ambient temperature, relative humidity, barometric pressure, and three-dimensional wind velocity. ![]() The measurements were carried out onboard a Twin Otter aircraft outfitted with an airborne Fourier transform infrared spectrometer (AFTIR), aerosol mass spectrometer (AMS), single particle soot photometer (SP2), nephelometer, LiCor CO 2 analyzer, a chemiluminescence ozone instrument, and a wing-mounted meteorological probe. We also measured physical and chemical changes that occurred in the isolated downwind plume in the first ~4 h after emission. We measured a suite of gases and aerosols emitted from an 81 hectare prescribed fire in chaparral fuels on the central coast of California, US on 17 November 2009. Accurately representing the production and evolution of these emissions is an important goal for atmospheric chemical transport models. Biomass burning (BB) is a major global source of trace gases and particles. ![]()
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