Abstract Number: 145 Working Group: Biomass Combustion: Emissions, Chemistry, Air Quality, Climate, and Human Health
Abstract Wood pyrolysis contributes to biomass and biofuel burning emissions while being a distinct phase from flaming combustion. To isolate and study the processes and emissions of pyrolysis, a custom-made reactor was used to uniformly heat small blocks of wood under nitrogen. Small (max 154 cm3) pieces of maple, Douglas fir, and oak wood were pyrolyzed in a temperature-controlled chamber at 400, 500, or 600 C. The mass of wood lost during pyrolysis was measured in situ gravimetrically, gas phase CO was measured, and aerosol emissions were measured with an Aerodyne aerosol mass spectrometer (AMS) and a TSI Engine Exhaust Particle Sizer (EEPS). Gas and particle emissions increased rapidly after inserting a wood sample, remained high for tens of minutes, and then dramatically dropped off, leaving char behind. The particulate mass and chemical compositions (i.e., mass spectra) varied with experiment time, wood type, and chamber temperature. The emitted particles consisted primarily of low O:C organic matter, as measured by the AMS. Unlike flaming wood combustion, the oxygen poor pyrolysis organic emissions were dominated by small, singly oxygenated fragments including CO+ and CHO+, which together made up approximately 30-45% of the total aerosol mass, whereas CO2+ accounted for less than 3%. Typical biomass burning marker ions, such as C2H4O2+ at m/z 60, were significantly (~2X) more abundant than published literature for flaming combustion. Large unsaturated hydrocarbons were emitted with increasing abundance near the end of an experiment. These observations are reflective of the complex chemical processes occurring as each wood piece heats from the surface to core and thermally decomposes, and will be compared and contrasted with previous flaming combustion results. These results will help inform models of pyrolysis.