Trace gas emissions from laboratory biomass fires measured by open-path Fourier transform infrared spectroscopy: Fires in grass and surface fuels

The trace gas emissions from six biomass fires, including three grass fires , were measured using a Fourier transform infrared (FTIR) spectrometer coup led to an open-path, multipass cell (OP-FTIR). The quantified emissions con sisted of carbon dioxide, nitric oxide, water vapor, carbon monoxide, metha ne, ammonia, ethylene, acetylene, isobutene, methanol, acetic acid, formic acid, formaldehyde, and hydroxyacetaldehyde. By including grass fires in th is study we have now measured smoke composition from fires in each major ve getation class. The emission ratios of the oxygenated compounds, formaldehy de, methanol, and acetic acid, were 1-2% of CO in the grass fires, similar to our other laboratory and field measurements but significantly higher tha n in some other studies. These oxygenated compounds are important, as they affect O-3 and HOx chemistry in both biomass fire plumes and the free tropo sphere. The OP-FTIR data and the simultaneously collected canister data ind icated that the dominant C-4 emission was isobutene (C4H8) and not 1-butene . The rate constant for the reaction of isobutene with the OH radical is 60 % larger than that of 1-butene. We estimate that 67 +/- 9% of the fuel nitr ogen was volatilized with the major nitrogen emissions, ammonia, and nitric oxide, accounting for 22 +/- 8%.