PNNL

Abstract

Fuels commonly managed by prescribed burning were collected from five Department of Defense (DoD) bases in the southeast and southwest U.S. and burned under controlled conditions at the USFS Firelab in Missoula, MT. The smoke emissions were measured with a large suite of state-of-the-art instrumentation. A key instrument used in the measurement of the gas-phase species in smoke was an open-path Fourier transform infrared (OP FTIR) spectrometer. The OP FTIR detected and quantified 19 gas-phase species in these fires - CO2, CO, H2O, NO2, NO, HONO, NH3, HCl, SO2, CH4, CH3OH, HCHO, HCOOH, C2H2, C2H4, CH3COOH, HCN, C3H6 and C4H4O. Of particular interest, gas-phase nitrous acid (HONO) was detected in the smoke from all fires. The HONO emission factor ranged from 0.15 to 0.60 g kg 1 and was higher for the southeast fuels. Similarly, the fire-integrated molar emission ratios (relative to NOx) ranged from approximately 0.03 to 0.20, with higher values observed for the southeast fuels. HONO is an important precursor in the production of OH, the primary oxidizing species in the atmosphere but there exists little previous data documenting HONO emissions from either wild or prescribed fires. The detected non-methane organic compound (NMOC) emissions were dominated by oxygenated volatile organic compounds (OVOCs) with total identified molar OVOC emissions ranging from 39 to 79% of the total identified molar non-methane organic compounds (NMOC). Emitted NMOC can undergo further oxidation and photolysis in the case of OVOC and thus involved in secondary aerosol formation. Elevated amounts of gas-phase HCl and SO2 were also detected in the smoke, with the amounts varying depending on location and vegetation type. Emission factors for HCl were typically much higher for the southwest fuels, particularly those found in the chaparral biome in the coastal regions of California.