Showing papers by "Robert J. Yokelson published in 2012"

Evolution of trace gases and particles emitted by a chaparral fire in California

Abstract: Biomass burning (BB) is a major global source of trace gases and particles. Accurately representing the pro- duction and evolution of these emissions is an important goal for atmospheric chemical transport models. We measured a suite of gases and aerosols emitted from an 81 hectare pre- scribed fire in chaparral fuels on the central coast of Cali- fornia, US on 17 November 2009. We also measured physi- cal and chemical changes that occurred in the isolated down- wind plume in the first 4 h after emission. The measure- ments were carried out onboard a Twin Otter aircraft outfit- ted with an airborne Fourier transform infrared spectrome- ter (AFTIR), aerosol mass spectrometer (AMS), single par- ticle soot photometer (SP2), nephelometer, LiCor CO2 an- alyzer, a chemiluminescence ozone instrument, and a wing- mounted meteorological probe. Our measurements included: CO2; CO; NOx; NH3; non-methane organic compounds; or- ganic aerosol (OA); inorganic aerosol (nitrate, ammonium, sulfate, and chloride); aerosol light scattering; refractory black carbon (rBC); and ambient temperature, relative hu- midity, barometric pressure, and three-dimensional wind ve- locity. The molar ratio of excess O3 to excess CO in the plume (1O3/1CO) increased from 5.13 (±1.13)◊ 10 3 to 10.2 (±2.16)◊ 10 2 in 4.5 h following smoke emis- sion. Excess acetic and formic acid (normalized to excess CO) increased by factors of 1.73± 0.43 and 7.34± 3.03 (re- spectively) over the same time since emission. Based on the rapid decay of C2H4 we infer an in-plume average OH concentration of 5.27 (±0.97)◊ 10 6 molec cm 3 , consistent with previous studies showing elevated OH concentrations in biomass burning plumes. Ammonium, nitrate, and sulfate all increased over the course of 4 h. The observed ammo- nium 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. Some of the gas phase NH3 loss may have been due to condensation on, or formation of, particles be- low the AMS detection range. NOx 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. The excess aerosol light scattering in the plume (normalized to excess CO2) increased by a fac- tor of 2.50± 0.74 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 forma- tion of OA closely tracked the increase in scattering. In the California plume, however, 1OA/1CO2 decreased sharply for the first hour and then increased slowly with a net de- crease of 20 % over 4 h. The fraction of thickly coated rBC particles increased up to 85 % over the 4 h aging period. Decreasing OA accompanied by increased scattering/particle coating in initial aging may be due to a combination of par- ticle coagulation and evaporation processes. Recondensation of species initially evaporated from the particles may have contributed to the subsequent slow rise in OA. We compare our results to observations from other plume aging studies

Measurements of reactive trace gases and variable O3 formation rates in some South Carolina biomass burning plumes [Discussions]

Abstract: In October–November 2011 we measured trace gas emission factors from seven prescribed fires in South Carolina (SC), US, using two Fourier transform infrared spectrometer (FTIR) systems and whole air sampling (WAS) into canisters followed by gas-chromatographic analysis. A total of 97 trace gas species were quantified from both airborne and ground-based sampling platforms, making this one of the most detailed field studies of fire emissions to date. The measurements include the first emission factors for a suite of monoterpenes produced by heating vegetative fuels during field fires. Due to rapid plume dilution, it was only possible to acquire high-quality downwind data for two other trace gas species (formaldehyde and methanol) during two of the fires. In all four of these cases, significant increases in formaldehyde and methanol were observed in <2 h. This is likely the first direct observation of post-emission methanol production in biomass burning plumes. Post-emission production of methanol does not always happen in young biomass burning plumes, and its occurrence in this study could have involved terpene precursors to a significant extent.

Corrigendum to "Airborne and ground-based measurements of the trace gases and particles emitted by prescribed fires in the United States" published in Atmos. Chem. Phys., 11, 12197–12216, 2011

Abstract: Unfortunately there was a typo in the proofs that we failed to notice and as a result Eq (2) was shown incorrectly We apologize for any inconvenience this may have caused The correct definition of modified combustion efficiency (MCE) was used for all our calculations and results; including everything shown in our tables and figures The correct definition is: MCE = 1CO2/(1CO2+1CO) Finally, we note that Eq (2) was shown correctly in the discussion version of the paper and in all the cited references