Evolution of gases and particles from a savanna fire in South Africa

Abstract

[1] Airborne measurements of particles and gases from a 1000-ha savanna fire in South Africa are presented. These measurements represent the most extensive data set reported on the aging of biomass smoke. The measurements include total concentrations of particles (CN), particle sizes, particulate organic carbon and black carbon, light-scattering coefficients, downwelling UV fluxes, and mixing ratios for 42 trace gases and 7 particulate species. The ratios of excess nitrate, ozone, and gaseous acetic acid to excess CO increased significantly as the smoke aged over $40-45 min, indicating that these species were formed by photochemistry in the plume. For 17 other species, the excess mixing ratio normalized by the excess mixing ratio of CO decreased significantly with smoke age. The relative rates of decrease for a number of chemical species imply that the average OH concentration in the plume was $1.7 Â 10 7 molecules cm À3 . Excess CN, normalized by excess CO, decreased rapidly during the first $5 min of aging, probably due to coagulation, and then increased, probably due to gas-to-particle conversion. The CO-normalized concentrations of particles <1.5 mm in diameter decreased, and particles >1.5 mm diameter increased, with smoke age. The spectral depletion of solar radiation by the smoke is depicted. The downwelling UV flux near the vertical center of the plume was about two-thirds of that near the top of the plume.

Biomass burning emissions disturbances on the isoprene oxidation in a tropical forest

“…The photochemical environment in young biomass burning plumes differs 370 from the clean conditions, especially near the surface. Hobbs et al (2003) found OH concentrations of about 1  10 7 molecules cm -3 for a fresh plume from savanna fire in South Africa, value higher than those found in our estimation. In CL, the estimated OH in AP showed a reduction of 15% relative to BG (0.5  10 6 molecules cm -3 ) environment, in opposition to increased pattern in FP (1.2  10 6 molecules cm -3 ).…”

Aged boreal biomass-burning aerosol size distributions from BORTAS 2011

“…In addition, the primary organic aerosol (POA) emitted by the fires may evaporate during the dilution of the plume (Huffman et al, 2009;May et al, 2013). Finally, new particle formation in smoke plumes has been observed in smog chamber studies as well as in the field Hobbs et al, 2003;Rissler et al, 2006).…”

“…Quantifying the natural variations in biomass-burning aerosols is therefore necessary for accurate predictions. Previous studies of field and lab experiments show biomass-burning size distributions vary according to plume age, combustion phase, and fuel type (Adler et al, 2011;Capes et al, 2008;Hobbs et al, 2003;Hosseini et al, 2010;Janhäll et al, 2010;Okoshi et al, 2014). A review of observed size-distribution data by Janhäll et al (2010) shows the differences in modal width and median diameter as a function of fuel type (forest, savannah, grass), modified combustion efficiency, and plume age (fresh versus aged).…”

“…Carbon monoxide (τ co ∼ months; Staudt et al, 2001) and acetonitrile (τ ace ∼ 6 months; Holzinger et al, 2005) were used in conjunction as gaseous tracers due to their high mixing ratios in biomass-burning plumes relative to the background and long atmospheric lifetimes relative to the estimated plume transport times. The background CO levels were 80-120 ppbv (parts per billion by volume) with an overall average of 100 ppbv.…”

Emissions from forest fires near Mexico City

“…The AFTIR, MPS-3, and WAS were used to acquire "grab" samples in the smoke plumes. More than a few kilometers downwind from the source, smoke samples are usually already "photochemically aged" and better for probing post-emission chemistry than estimating initial emissions (Goode et al, 2000;Hobbs et al, 2003). To determine excess concentrations in the smoke-plume grabsamples, paired background grab-samples were acquired just outside the plume.…”