Abstract. Organic aerosols generated from the smoldering combustion of wood
critically impact air quality and health for billions of people worldwide;
yet, the links between the chemical components and the optical or biological
effects of woodsmoke aerosol (WSA) are still poorly understood. In this
work, an untargeted analysis of the molecular composition of smoldering WSA,
generated in a controlled environment from nine types of heartwood fuels
(African mahogany, birch, cherry, maple, pine, poplar, red oak, redwood, and
walnut), identified several hundred compounds using gas chromatography mass
spectrometry (GC-MS) and nano-electrospray high-resolution mass spectrometry
(HRMS) with tandem multistage mass spectrometry (MSn). The effects of
WSA on cell toxicity as well as gene expression dependent on the aryl hydrocarbon receptor (AhR) and estrogen receptor
(ER) were characterized with cellular assays, and
the visible mass absorption coefficients (MACvis) of WSA were measured
with ultraviolet–visible spectroscopy. The WSAs studied in this work have significant
levels of biological and toxicological activity, with exposure levels in
both an outdoor and indoor environment similar to or greater than those of
other toxicants. A correlation between the HRMS molecular composition and
aerosol properties found that phenolic compounds from the oxidative
decomposition of lignin are the main drivers of aerosol effects, while the
cellulose decomposition products play a secondary role; e.g., levoglucosan
is anticorrelated with multiple effects. Polycyclic aromatic hydrocarbons
(PAHs) are not expected to form at the combustion temperature in this work,
nor were they observed above the detection limit; thus, biological and optical
properties of the smoldering WSA are not attributed to PAHs. Syringyl
compounds tend to correlate with cell toxicity, while the more conjugated
molecules (including several compounds assigned to dimers) have higher AhR
activity and MACvis. The negative correlation between cell toxicity and
AhR activity suggests that the toxicity of smoldering WSA to cells is not
mediated by the AhR. Both mass-normalized biological outcomes have a
statistically significant dependence on the degree of combustion of the
wood. In addition, our observations support the fact that the visible light
absorption of WSA is at least partially due to charge transfer effects in
aerosols, as previously suggested. Finally, MACvis has no correlation
with toxicity or receptor signaling, suggesting that key chromophores in
this work are not biologically active on the endpoints tested.