Light-absorbing Carbonaceous Aerosol Emissions from Biomass Burning under Wildfire and Prescribed-fire Conditions
CHASE GLENN, Omar El Hajj, Anita Anosike, Kruthika Kumar, Robert Penland, Joseph O'Brien, Rawad Saleh,
University of Georgia Abstract Number: 208
Working Group: Carbonaceous Aerosol
AbstractThe Georgia Wildland-fire Simulation Experiment (G-WISE) involved burning forest-floor fuel beds constructed from surface fuels with proportions representative of 3 ecoregions in Georgia. The burns were performed under moist (prescribed fires) and dry (drought-induced wildfires) conditions. Here, we present the relative elemental carbon (EC) and organic carbon (OC) emissions, as well as brown carbon (BrC) light-absorption properties for 3 fuel bed scenarios: (i) surface fuels burned under wildfire conditions (W), (ii) identical surface fuels burned under prescribed conditions (Rx), and (iii) surface fuels with duff, burned under wildfire conditions (W-DUFF).
The EC/OC ratio for W was approximately 2.5 times higher than Rx, signifying the effect of fuel moisture content on burn conditions and consequently carbonaceous aerosol emissions. W-DUFF emissions were OC dominated with negligible EC, indicating the impact of duff on wildfire smoke composition.
We retrieved the BrC imaginary part of the refractive index at 550 nm (k
550) and wavelength dependence (w) using optical closure. The process involved Mie calculations, photoacoustic spectrometer light-absorption measurements (422 nm, 532 nm, 785 nm), size distribution measurements, and black carbon absorption estimated from optical calculations using EC/OC measurements. The results were as follows: W (k
550 = 0.015 and w = 1.3), Rx (k
550 = 0.006 and w = 2.7), and W-DUFF (k
550 = 0.001 and w = 5.3), indicating BrC optical properties have strong dependence on burn conditions.
We collected filter samples and retrieved k
550 and w of the methanol-extracts from UV-Vis absorption measurements. The results for the methanol-soluble BrC (MSBrC) were as follows: W (k
550 = 0.001 and w = 7.1), Rx (k
550 = 0.002 and w = 6.2), and W-DUFF (k
550 = 0.001 and w = 6.5). These findings indicate that MSBrC approximates weakly-absorbing BrC aerosol (W-DUFF), but underestimates BrC light absorption for moderately-absorbing BrC aerosol (W and Rx).