Data from: Chemically distinct particle phase emissions from highly controlled pyrolysis of three wood types

Wood pyrolysis is a distinct process that precedes combustion and
contributes to biomass and biofuel burning gas phase and particle phase
emissions. Pyrolysis is defined as the thermochemical degradation of wood,
the products of which can be released directly or undergo further reaction
during gas-phase combustion. To isolate and study the processes and
emissions of pyrolysis, a custom-made reactor was used to uniformly heat
small blocks of wood in a nitrogen atmosphere. Pieces of maple, Douglas
fir and oak wood (maximum 155 cm3) were pyrolyzed in a
temperature-controlled chamber set to 400, 500, or 600°C. Real time
particle phase emissions were measured with a Soot Particle Aerosol Mass
Spectrometer (SP-AMS) and correlated with simultaneous gas phase emission
measurements of CO. Particle and gas emissions increased rapidly after
inserting a wood sample, remained high for tens of minutes, and then
dropped rapidly leaving behind char. The particulate mass loading profiles
varied with elapsed experiment time, wood type and size, and pyrolysis
chamber temperature. The chemical composition of the emitted particles was
organic (C, H, O), with negligible black carbon or nitrogen. The emitted
particles displayed chemical signatures unique to pyrolysis and notably
different from flaming or smoldering wood combustion. The most abundant
fragment ions in the mass spectrum were CO+ and CHO+, which together made
up 23 % of the total aerosol mass on average, whereas CO2+ accounted for
less than 4 %, in sharp contrast with ambient aerosol where CO2+ is often
a dominant contributor. The mass spectra also showed signatures of
levoglucosan and other anhydrous sugars. The fractional contribution of
m/z 60, traditionally a tracer for anhydrous sugars including
levoglucosan, to total loading (f60) was observed to be between 0.002 and
0.039, similar to previous observations from wild and controlled wood
fires. Atomic ratios of oxygen and hydrogen to carbon, O : C and H : C as
calculated from AMS mass spectra, varied between 0.41–0.81 and 1.06–1.57,
respectively, with individual conditions lying within a continuum of O : C
and H : C for wood’s primary constituents: cellulose, hemicellulose, and
lignin. This work identifies the mass spectral signatures of particle
emissions directly from pyrolysis, including f60 and CO+/CO2+ ratio,
through controlled laboratory experiments in order to help understand the
importance of pyrolysis emissions in the broader context of wild and
controlled wood fires.