Effect of Torrefaction on Aerosol Emissions at Combustion Temperatures Relevant for Domestic Burning and Power Generation

Torrefied biomass is a promising carbon-neutral alternative to coal. However, the effect of torrefaction on aerosol production in biomass combustion is understudied. Here, we compared the emissions and physicochemical properties of aerosols produced by the combustion of raw pine, torrefied pine, and bituminous coal. At the highest combustion temperature of 1000 degrees C, aerosol emission from coal was 5.2 +/- 0.4 mg/MJ, while emissions from raw and torrefied pine were negligible (<10-2 mg/ MJ). The coal-combustion aerosol was dominated by inorganics (85%), with a small organic fraction (15%), a composition typical of condensable particulate matter observed in power generation applications. At the lowest combustion temperature of 400 degrees C, aerosol emissions from raw pine (25.3 +/- 4 mg/MJ) and torrefied pine (5.6 +/- 0.8 mg/MJ) were dominated by organics. The organic molecules probed using electrospray ionization mass spectrometry were dominated by CHO and CHNO groups for both raw and torrefied pine. Torrefied pine emissions featured less aromatics (17% vs 22%), which can be attributed to the reduction in volatile matter content associated with torrefaction. Overall, our findings support the adoption of torrefied pine for domestic burning and power generation because of the added benefit of reducing aerosol emissions in addition to being carbon-neutral.