Trace gas and particle emissions from fires in large diameter and belowground biomass fuels

Abstract

[1] We adopt a working definition of residual smoldering combustion (RSC) as biomass combustion that produces emissions that are not lofted by strong fire-induced convection. RSC emissions can be produced for up to several weeks after the passage of a flame front and they are mostly unaffected by flames. Fuels prone to RSC include downed logs, duff, and organic soils. Limited observations in the tropics and the boreal forest suggest that RSC is a globally significant source of emissions to the troposphere. This source was previously uncharacterized. We measured the first emission factors (EF) for RSC in a series of laboratory fires and in a wooded savanna in Zambia, Africa. We report EF RSC for both particles with diameter <2.5 mm (PM2.5) and the major trace gases as measured by open-path Fourier transform infrared (OP-FTIR) spectroscopy. The major trace gases include carbon dioxide, carbon monoxide, methane, ethane, ethene, acetylene, propene, formaldehyde, methanol, acetic acid, formic acid, glycolaldehyde, phenol, furan, ammonia, and hydrogen cyanide. We show that a model used to predict trace gas EF for fires in a wide variety of aboveground fine fuels fails to predict EF for RSC. For many compounds, our EF for RSC-prone fuels from the boreal forest and wooded savanna are very different from the EF for the same compounds measured in fire convection columns above these ecosystems. We couple our newly measured EF RSC with estimates of fuel consumption by RSC to refine emission estimates for fires in the boreal forest and wooded savanna. We find some large changes in estimates of biomass fire emissions with the inclusion of RSC. For instance, the wooded savanna methane EF increases by a factor of 2.5 even when RSC accounts for only 10% of fuel consumption. This shows that many more measurements of fuel consumption and EF for RSC are needed to improve estimates of biomass burning emissions.

Spatial and temporal variability in the ratio of trace gases emitted from biomass burning

“…The CH 4 EF more than doubled for boreal fires when RSC was included. Besides boreal areas, Bertschi et al (2003) also measured EFs in African miombo; a flaming-smoldering ratio of 90-10 was taken, and AFTIR measurements from a study of were used to represent the flaming part. A change in these flaming-smoldering ratio's will impact the overall EF substantially, so the assumptions made by different authors are therefore important to consider .…”

“…For tropical forest and boreal fires smoldering combustion is more important. Bertschi et al (2003), for example, assumed that the smoldering and flaming phases combusted equal amounts of biomass in boreal areas, and residual smoldering combustion (RSC) measurements of pure smoldering were combined with airborne measurements of Goode et al (2000) to calculate an overall EF. The CH 4 EF more than doubled for boreal fires when RSC was included.…”

“…Interest in this topic grew when studies suggested that for several trace gases and aerosol species, biomass burning emissions could rival fossil fuel emissions (Seiler and Crutzen, 1980;Crutzen and Andreae, 1990), and that these vegetation fires could affect large parts of the world due to longrange transport processes (Andreae, 1983;Fishman et al, 1990;Gloudemans et al, 2006). During the last two decades biomass burning has received considerable interest, leading for example to the realization that vegetation fires impact 8 out of 14 identified radiative forcing terms (Bowman et al, 2009), contribute to interannual variability (IAV) in growth rates of many trace gases (Langenfelds et al, 2002), and influence human health and plant productivity downwind of fires through enhanced ozone and aerosol concentrations (e.g. Sitch et al, 2007).…”

Airborne and ground-based measurements of the trace gases and particles emitted by prescribed fires in the United States

“…Biomass burning is the largest source of primary, fine carbonaceous particles and a significant source of trace gases in the global atmosphere (Bond et al, 2004;Crutzen and Andreae, 1990) and impacts both the chemical composition as well as the radiative balance of the atmosphere. The majority of biomass burning occurs unregulated in the tropics (Crutzen and Andreae, 1990).…”

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

“…Discuss., https://doi.org/10.5194/acp-2017-1083 Manuscript under review for journal Atmos. Chem absorbed by plants with low boiling point (e.g., Tisoprene  307 K), macromolecular bonds can be broken (i.e., low-temperature pyrolysis), gasification reactions converting carbon in the solid char to CO and CO2 can occur and the flames efficiently oxidize the volatile gases to species such as H2O, CO2, and NOx (Bertschi et al, 2003;Longo et al, 2009). The release of isoprene and other BVOCs is dependent on the different phases of biomass combustion, and diverse vegetation communities affect the amount and diversity of volatile organic compounds released (Ciccioli et al, 2014).…”