Characterization of Carbonaceous Aerosols Emitted from Outdoor Wood Boilers

Abstract

This study examines the chemical properties of carbonaceous aerosols emitted from different outdoor wood-fired boiler (OWB) technologies including two cord wood heaters, a pellet heater, and a multistage gasifier/combustor. The effect of fuel type [red oak wood (Quercus rubra), white pine wood (Pinus strobes), and red oak with supplementary refuse] on aerosol composition was examined using a classic boiler unit. Aerosol particle emissions were captured using established filter-based sampling methodology and subsequently analyzed using thermal-optical analysis and gas chromatography–mass spectrometry (GC-MS) techniques. GC-MS was coupled with a novel reduced-volume solvent extraction technique for semivolatile organic compound (SVOC) analysis. GC-MS identified 9% w/w of the aerosol mass emitted from the OWBs on average. The OWB aerosols comprised 1–5% w/w levoglucosan, an important molecular marker of cellulose pyrolysis. Organic acid and methoxyphenol SVOC classes showed the highest average concentrations in the OWB aerosol. Polycyclic aromatic hydrocarbons (PAHs) accounted for between 0.1 and 4% w/w of the aerosol mass; PAH emissions from pine wood combustion in the classic OWB were notably high. Each of the original 16 EPA priority PAHs was detected in the OWB PM emissions. Wood combustion in the OWB released significantly more PAH per unit mass of fuel burned than either domestic fireplace or woodstove appliances; although, changes in PAH enrichment (μg/kg aerosol) among domestic wood combustion aerosols was less certain. Of the OWBs tested, the pellet heater showed the lowest SVOC emissions on a mass of fuel burned basis. However, OWB technology did not always significantly influence the SVOC composition of the particle emissions