Physicochemical and toxicological properties of wood smoke particulate matter as a function of wood species and combustion condition

Abstract

Wood burning is a major source of ambient particulate matter (PM) and has been epidemiologically linked to adverse pulmonary health effects, however the impact of fuel and burning conditions on PM properties has not been investigated systematically. Here, we employed our recently developed integrated methodology to characterize the physicochemical and biological properties of emitted PM as a function of three common hardwoods (oak, cherry, mesquite) and three representative combustion conditions (flaming, smoldering, incomplete). Differences in PM and off-gas emissions (aerosol number/mass concentrations; carbon monoxide; volatile organic compounds) as well as inorganic elemental composition and organic carbon functional content of PM_0.1 were noted between wood types and combustion conditions, although the combustion scenario exerted a stronger influence on the emission profile. More importantly, flaming combustion PM_0.1 from all hardwoods significantly stimulated the promoter activity of Sterile Alpha Motif (SAM) pointed domain containing ETS (E-twenty-six) Transcription Factor (SPDEF) in human embryonic kidney 293 (HEK-293 T) cells, a biomarker for mucin gene expression associated with mucus production in pulmonary diseases. However, no bioactivity was observed for smoldering and incomplete combustion, which was likely driven by differences in the organic composition of PM_0.1. Detailed chemical speciation of organic components of wood smoke is warranted to identify the individual compounds that drive specific biological responses.

Keywords: Chemical composition; Combustion conditions; Hardwoods; Mucus production; Particulate matter.

Fig. 1.

Real-time monitoring of particle number concentration and size distribution of emitted nanoparticles during the combustion of oak (A, D), cherry (B, E), and mesquite (C, F) woods under flaming conditions using a Scanning Mobility Particle Sizer Spectrometer (SMPS) covering particle mobility diameter between 5 – 300 nm. Panels A-C display the total emitted nanoparticle number concentration (PNC) as a function of time (or temperature), whereas panels D-F display the nanoparticle number-size distributions captured at the timepoint of peak nanoparticle emission, for the respective woods.

Fig. 2.

Organic functional group characterization of sampled wood smoke PM_0.1 particles generated from (A) oak wood flaming combustion, (B) cherry wood flaming combustion, (C) mesquite wood flaming combustion, (D) oak wood smoldering combustion, and (E) oak wood incomplete combustion. Pie charts show the relative abundances of the protons (% by mol of total non-exchangeable functional organic hydrogen) associated with the respective functional groups characterized by 1-D ¹H-NMR spectroscopy. The following functional groups of non-exchangeable organic hydrogen were quantified: (i) saturated aliphatic hydrogen [H-R]; (ii) allylic hydrogen [H-C-C=]; (iii) saturated oxygenated hydrogen, including α-hydrogen to hydroxyl, ether and ester group [H-C-O]; (iv) acetalic and vinylic hydrogen ([O-CH-O]+[H-C=]); (v) aryl hydrogen [H-Ar]; and (vi) carbonyl hydrogen [H-C=O].

Fig. 3.. SPDEF promoter activities of wood smoke PM_0.1.

Wood smoke PM_0.1 size fraction and its dissolved component obtained by filtration of the PM_0.1 aqueous extract were tested at 10, 100 and 1000 ng/mL concentrations for SPDEF promoter luciferase activity in HEK-293 cells for (A) oak wood flaming combustion, (B) cherry wood flaming combustion, (C) mesquite wood flaming combustion, (D) oak wood smoldering combustion, and (E) oak wood incomplete combustion. SPDEF promoter construct in PGL3 basic vector was transfected into HEK-293 cells one day prior to treatment with PM_0.1 or vehicle control from blank PM substrates (PFU) or left untreated (NT). SPDEF promotor activity in the cell lysates was measured by luminometer. For each figure, the mean +/− SEM is graphed, with significant differences at *p<0.05, **p<0.01, and ***p<0.001 from NT control.