Aerosol Physical Properties and Emission Factors from Open Biomass Burning and Cookstove Emissions.

摘要

Biomass burning (BB) releases trace gases and significant amount of aerosols into the atmosphere. The sizing optical properties of aerosols from biomass smoke influence the scattering and absorption of incoming solar radiation, environmental air quality, visibility, as well as significant effects on human health and climate. Recent laboratory experiments (Fire Laboratory at Missoula Experiment, FLAME IV) focused on the effects of fuel type, stove type, and modified combustion efficiency (MCE) in real-time measurements of cookstove emissions. This thesis presents the results from examination of these same properties in laboratory experiments with the open combustion of biomass. Measurement of the particle light scattering and absorption coefficients were made using a photoacoustic extinctiometer (PAX, DMT, Inc., Model 870nm), while a fast mobility particle sizer (FMPS, TSI, Inc., Model 3091) was used for measuring the size distribution at 1-sec resolution over particle diameters from 5.6 to 560 nm. The mixing ratios of CO and CO2, which quantify the MCE, were measured simultaneously by an open-path Fourier transform infrared spectrometer (OP-FTIR). Emission ratios, fire-integrated emission factors for gas-phase CO2, CO, CH4, and HCHO, and particle number emission factors (PNEF) for different fuels were estimated. The average emission factors were 1459 +/- 121, 110 +/- 71, 4.7 +/- 2.6, 3.4 +/- 0.9 grams per kg of dry fuel for CO2, CO, CH4, and HCHO, respectively. These results agreed with average emission factors determined from other studies as magnitudes and trends observed here were consistent with previous work that found that gas-species depend on MCE. Estimated PNEF ranges between 2.48 x 1015 particles/kg and 5.04 x 1016 particles/kg. PNEF produced during open burning of fuel samples produced higher values of 1.94 x 1016 particles/kg to 5.04 x 1016 particles/kg compared to PNEFs from cookstoves with PNEF = 3.50 x 1015 -- 6.34 x 1015 particles/kg. Trends show PNEF to be a strong function of the particle size range; however, a systematic dependence was not observed for total PNEF as a function of MCE. Comparison between open burning and cookstove established that improvements in combustion efficiency influenced the range of sizes of particles emitted. Advanced cookstoves maximize the MCE by reducing the smoldering combustion, thereby reducing the PNEF. At the same time, a large number concentration of highly absorbing particles with smaller geometric mean diameter in size range ∼ Dp less than 30 nm were emitted in advanced cookstoves resulting in lower single scattering albedo (SSA).