Technical Note: Pyrolysis principles explain time-resolved organic aerosol release from biomass burning

Abstract

Abstract. Emission of organic aerosol (OA) from wood combustion is not well constrained; understanding the governing factors of OA emissions would aid in explaining the reported variability. Pyrolysis of the wood during combustion is the process that produces and releases OA precursors. We performed controlled pyrolysis experiments at representative combustion conditions. The conditions changed were the temperature, wood length, wood moisture content, and wood type. The mass loss of the wood, the particle concentrations, and light gas concentrations were measured continuously. The experiments were repeatable as shown by a single experiment, performed nine times, in which the real-time particle concentration varied by a maximum of 20 %. Higher temperatures increased the mass loss rate and the released concentration of gases and particles. Large wood size had a lower yield of particles than the small size because of higher mass transfer resistance. Reactions outside the wood became important between 500 and 600 °C. Elevated moisture content reduced product formation because heat received was shared between pyrolysis reactions and moisture evaporation. The thermophysical properties, especially the thermal diffusivity, of wood controlled the difference in the mass loss rate and emission among seven wood types. This work demonstrates that OA emission from wood pyrolysis is a deterministic process that depends on transport phenomena.

Chemical characterization of prescribed burn emissions from a mixed forest in Northern Michigan

“…88 Hardwoods, a highdensity wood, are expected to burn longer and slower, leaving behind more unreacted wood mass compared to pine, a lowdensity softwood, when burned at the same pyrolysis temperature. 22,90,91 This is consistent with the increased presence of PAHs in the individual biomass burning particles measured during Plume 5 (Table 1). In addition, the higher peak intensities for nitrate (m/z -46 (NO 2 -) and -62 (NO 3 -)) in the Plume 5 biomass burning particles compared to Plume 1 is 89 that results from the combustion of eugenol.…”

“…Molecular ion peaks corresponding to the PAHs 88 High-density hardwoods are expected to burn longer and slower, leaving behind more unreacted wood mass compared to pine, a low-density sowood, when burned at the same pyrolysis temperature. 22,90,91 This is consistent with the increased presence of PAHs in the individual biomass burning particles measured during plume 5 (Table 1). In addition, the higher peak intensities for nitrate (m/ z −46 (NO 2…”

“…4a), with OA/rBC ratios of 25-37 (Table S2 †). The OA/rBC ratios were higher than previous laboratory studies of lodgepole pine (15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28). 67 Black carbon production is associated with aming combustion.…”

“…The prominence of PAH markers in the latter plume periods may be associated with the incomplete combustion of higher-density woods. 22,90,91 Previous field measurements in the western and southeastern United States had higher emission ratios of particulate OA and rBC than what was emitted in this northern Michigan prescribed burn. However, the first two plots burned in this study occurred at low to moderate severity, which may have contributed to the lower rBC emission ratios.…”

“…1 PM 2.5 and gases emitted from res vary widely by region, fuel type, density, and burning conditions. [19][20][21][22] Gas and particle emissions from prescribed burns in the western 20,23,24 and southeastern 15,17,20,25 regions of the United States have been characterized by comparing fuel types (i.e. chaparral, montane, pine trees) and burn conditions (smoldering or aming combustion).…”