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 °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 °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.