Particulate matter and black carbon optical properties and emission factors from prescribed fires in the southeastern United States

Abstract

Aerosol optical properties of biomass burning emissions are critical parameters determining how these emissions impact the Earth's climate. Despite their importance, field measurements of aerosol optical properties from fires remain scarce. Aerosol emissions from prescribed fires of forested and grass plots in the southeastern United States were measured and compared to emissions from laboratory simulations. Fine particulate matter (PM 2.5 ), black carbon (BC), and aerosol light scattering and absorption were characterized for all fires. Refractory BC emission factors (EFs) measured at ground level (~2 m) were 0.76 ± 0.15 g/kg, comparable to the 0.93 ± 0.32 g/kg measured aloft (~100-600 m). However, PM EFs measured by aircraft were only 18% (5.4 ± 2.0 g/kg) of those measured on the ground (28.8 ± 9.8 g/kg). Such large differences in PM EFs for the same fire have not been previously reported and may plausibly be due to the differing particle measurement methodologies being applied but also likely related to partitioning of organic compounds to the gas phase as the plume dilutes aloft. Higher PM EFs on the ground may also be related to a higher contribution from smoldering combustion. The absorption Ångström exponents (α a ) for the high intensity South Carolina fires were 3.92 ± 0.6, which was larger than prescribed forest fire in Florida (2.84) and the grass fire in Florida (2.71), implying a larger absorption contribution from brown carbon from higher-intensity fires. Aerosol optical properties from laboratory simulations did not represent field measurements.

Ground‐Based Field Measurements of PM2.5 Emission Factors From Flaming and Smoldering Combustion in Eucalypt Forests

“…We observed a consistency in PM 2.5 EFs within forest fuels under similar combustion phases. The median value for flaming combustion of 16.9‐g/kg fuel (Figure ) is in the range of previously reported values for flaming combustion of forest fuels (11–29 g/kg; Alves et al, ; Aurell & Gullett, ; Aurell et al, ; Balachandran et al, ; Burling et al, ; Holder et al, ; McMeeking et al, ; Robertson et al, ; Urbanski et al, ; Yokelson et al, ). Figure further highlights the consistency in PM 2.5 EFs between measurements at prescribed burns in SE Australia and published data from fires or prescribed burns in temperate forests, including both field and laboratory measurements.…”

“…This could be attributed to differences in sampling methods, for example, near‐source versus plume measurements. The higher plume dilution in airborne measurements due to clean background air becoming entrained into the smoke plume would cause a shift in semivolatile species into the gas‐phase, which may account for the difference between EFs (Holder et al, ; May et al, ). In low dilution smoke plumes with higher concentrations of organic aerosols, such as those measured on the ground, semivolatile species would predominantly occur in the particle phase (May et al, ).…”

“…Many studies have looked at particle emissions from the combustion of various fuels under controlled laboratory conditions (Aurell et al, ; Bertschi et al, ; Chen et al, ; Christian et al, ; Freeborn et al, ; Hays et al, ; Holder et al, ; Hosseini et al, ; McMeeking et al, ; Yokelson et al, ); however, ground‐based field measurements of PM are few (Aurell et al, ; Holder et al, ; Robertson et al, ; Urbanski et al, ). Very little is also known on particle emissions from RSC of coarse woody debris (CWD), for example, logs larger than 50 mm in diameter.…”

Air-Quality Challenges of Prescribed Fire in the Complex Terrain and Wildland Urban Interface Surrounding Bend, Oregon

“…It is important to recognize that the method of observing particulate matter via light scattering is subject to uncertainty as mass scattering efficiency may be affected by chemical composition of biomass, the fraction of light absorbing black and brown carbon, and size distribution of particles [29][30][31]. Particles are made up of different constituents and come in many shapes and sizes.…”

Recognizing Women Leaders in Fire Science: Revisited

“…Her notable works include assessing the chemical composition and sources of particulate matter [388,389]. Her recent works include assessing particulate matter and black carbon emissions from prescribed fires [390], and assessing the impacts of California wildfires on near-road air quality [391].…”