Emissions of formaldehyde, acetic acid, methanol, and other trace gases from biomass fires in North Carolina measured by airborne Fourier transform infrared spectroscopy

Biomass burning is an important source of many trace gases in the global tr oposphere. We have constructed an airborne trace gas measurement system con sisting of a Fourier transform infrared spectrometer (FTIR) coupled to a "f low-through" multipass cell (AFTIR) and installed it on a U. S. Department of Agriculture Forest Service King Air B-90. The first measurements with th e new system were conducted in North Carolina during April 1997 on large, i solated biomass fire plumes. Simultaneous measurements included Global Posi tioning System (GPS); airborne sonde; particle light scattering, CO, and CO 2; and integrated filter and canister samples. AFTIR spectra acquired withi n a few kilometers of the fires yielded excess mixing ratios for 10 of the most common trace gases in the smoke: water, carbon dioxide, carbon monoxid e, methane, formaldehyde, acetic acid, formic acid, methanol, ethylene, and ammonia. Emission ratios to carbon monoxide for formaldehyde, acetic acid, and methanol were each 2.5 +/- 1%. This is in excellent agreement with (an d confirms the relevance of) our results from laboratory fires. However, th ese ratios are significantly higher than the emission ratios reported for t hese compounds in some previous studies of "fresh" smoke. We present a simp le photochemical model calculation that suggests that oxygenated organic co mpounds should be included in the assessment of ozone formation in smoke pl umes. Our measured emission factors indicate that biomass fires could accou nt for a significant portion of the oxygenated organic compounds and HOx pr esent in the tropical troposphere during the dry season. Our fire measureme nts, along with recent measurements of oxygenated biogenic emissions and ox ygenated organic compounds in the free troposphere, indicate that these rar ely measured compounds play a major, but poorly understood, role in the HOx , NOx, and O-3 chemistry of the troposphere.