Open-Path Fourier Transform Infrared Studies of Large-Scale Laboratory Biomass Fires

A series of nine large-scale, open fires was conducted in the Intermountain Fire Sciences Laboratory (IFSL) controlled-environment combustion facility. The fuels were pure pine needles or sagebrush or mixed fuels simulating forest-floor, ground fires; crown fires; broadcast burns; and slash pile burns. Mid-infrared spectra of the smoke were recorded throughout each fire by open path Fourier transform infrared (FTIR) spectroscopy at 0.12 cm−1 resolution over a 3 m cross-stack pathlength and analyzed to provide pseudocontinuous, simultaneous concentrations of up to 16 compounds. Simultaneous measurements were made of fuel mass loss, stack gas temperature, and total mass flow up the stack. The products detected are classified by the type of process that dominates in producing them. Carbon dioxide is the dominant emission of (and primarily produced by) flaming combustion, from which we also measure nitric oxide, nitrogen dioxide, sulfur dioxide, and most of the water vapor from combustion and fuel moisture. Carbon monoxide is the dominant emission formed primarily by smoldering combustion from which we also measure carbon dioxide, methane, ammonia, and ethane. A significant fraction of the total emissions is unoxidized pyrolysis products; examples are methanol, formaldehyde, acetic and formic acid, ethene (ethylene), ethyne (acetylene), and hydrogen cyanide. Relatively few previous data exist for many of these compounds and they are likely to have an important but as yet poorly understood role in plume chemistry. Large differences in emissions occur from different fire and fuel types, and the observed temporal behavior of the emissions is found to depend strongly on the fuel bed and product type

Trace Gas Emissions from Laboratory Biomass Fires Measured by Open-Path Fourier Transform Infrared Spectroscopy: Fires in Grass and Surface Fuels

The trace gas emissions from six biomass fires, including three grass fires, were measured using a Fourier transform infrared (FTIR) spectrometer coupled to an open-path, multipass cell (OP-FTIR). The quantified emissions consisted of carbon dioxide, nitric oxide, water vapor, carbon monoxide, methane, ammonia, ethylene, acetylene, isobutene, methanol, acetic acid, formic acid, formaldehyde, and hydroxyacetaldehyde. By including grass fires in this study we have now measured smoke composition from fires in each major vegetation class. The emission ratios of the oxygenated compounds, formaldehyde, methanol, and acetic acid, were 1–2% of CO in the grass fires, similar to our other laboratory and field measurements but significantly higher than in some other studies. These oxygenated compounds are important, as they affect O3 and HOx chemistry in both biomass fire plumes and the free troposphere. The OP-FTIR data and the simultaneously collected canister data indicated that the dominant C4 emission was isobutene (C4H8) and not 1-butene. The rate constant for the reaction of isobutene with the OH radical is 60% larger than that of 1-butene. We estimate that 67±9% of the fuel nitrogen was volatilized with the major nitrogen emissions, ammonia, and nitric oxide, accounting for 22±8%

Trace Gas Emissions from the Production and Use of Domestic Biofuels in Zambia Measured by Open-Path Fourier Transform Infrared Spectroscopy

[1] Domestic biomass fuels (biofuels) were recently estimated to be the second largest source of carbon emissions from global biomass burning. Wood and charcoal provide approximately 90% and 10% of domestic energy in tropical Africa. In September 2000, we used open-path Fourier transform infrared (OP-FTIR) spectroscopy to quantify 18 of the most abundant trace gases emitted by wood and charcoal cooking fires and an earthen charcoal-making kiln in Zambia. These are the first in situ measurements of an extensive suite of trace gases emitted by tropical biofuel burning. We report emission ratios (ER) and emission factors (EF) for (in order of abundance) carbon dioxide (CO2), carbon monoxide (CO), methane (CH4), acetic acid (CH3COOH), methanol (CH3OH), formaldehyde (HCHO), ethene (C2H4), ammonia (NH3), acetylene (C2H2), nitric oxide (NO), ethane (C2H6), phenol (C6H5OH), propene (C3H6), formic acid (HCOOH), nitrogen dioxide (NO2), hydroxyacetaldehyde (HOCH2CHO), and furan (C4H4O). Compared to previous work, our emissions of organic acids and NH3 are 3–6.5 times larger. Another significant finding is that reactive oxygenated organic compounds account for 70–80% of the total nonmethane organic compounds (NMOC). For most compounds, the combined emissions from charcoal production and charcoal burning are larger than the emissions from wood fires by factors of 3–10 per unit mass of fuel burned and ∼2 per unit energy released. We estimate that Zambian savanna fires produce more annual CO2, HCOOH, and NOx than Zambian biofuel use by factors of 2.5, 1.7, and 5, respectively. However, biofuels contribute larger annual emissions of CH4, CH3OH, C2H2, CH3COOH, HCHO, and NH3 by factors of 5.1, 3.9, 2.7, 2.4, 2.2, and 2.0, respectively. Annual CO and C2H4 emissions are approximately equal from both sources. Coupling our data with recent estimates of global biofuel consumption implies that global biomass burning emissions for several compounds are significantly larger than previously reported. Biofuel emissions are produced year-round, disperse differently than savanna fire emissions, and could strongly impact the tropical troposphere

Emissions from Smoldering Combustion of Biomass Measured by Open-Path Fourier Transform Infrared Spectroscopy

Biomass samples from a diverse range of ecosystems were burned in the Intermountain Fire Sciences Laboratory open combustion facility. Midinfrared spectra of the nascent emissions were acquired at several heights above the fires with a Fourier transform infrared spectrometer (FTIR) coupled to an open multipass cell. In this report, the results from smoldering combustion during 24 fires are presented including production of carbon dioxide, carbon monoxide, methane, ethene, ethyne, propene, formaldehyde, 2-hydroxyethanal, methanol, phenol, acetic acid, formic acid, ammonia, hydrogen cyanide, and carbonyl sulfide. These were the dominant products observed, and many have significant influence on atmospheric chemistry at the local, regional, and global scale. Included in these results are the first optical, in situ measurements of smoke composition from fires in grasses, hardwoods, and organic soils. About one half of the detected organic emissions arose from fuel pyrolysis which produces white smoke rich in oxygenated organic compounds. These compounds deserve more attention in the assessment of fire impacts on the atmosphere. The compound 2-hydroxyethanal is a significant component of the smoke, and it is reported here for the first time as a product of fires. Most of the observed alkane and ammonia production accompanied visible glowing combustion. NH3 is normally the major nitrogen-containing emission detected from smoldering combustion of biomass, but from some smoldering organic soils, HCN was dominant. Tar condensed on cool surfaces below the fires accounting for ∼1% of the biomass burned, but it was enriched in N by a factor of 6–7 over the parent material, and its possible role in postfire nutrient cycling should be further investigated

Measurements of Excess O3, CO2, CO, CH4, C2H4, C2H2, HCN, NO, NH3, HCOOH, CH3COOH, HCHO, and CH3OH in 1997 Alaskan Biomass Burning Plumes by Airborne Fourier Transform Infrared Spectroscopy (AFTIR)

We used an airborne Fourier transform infrared spectrometer (AFTIR), coupled to a flow-through, air-sampling cell, on a King Air B-90 to make in situ trace gas measurements in isolated smoke plumes from four, large, boreal zone wildfires in interior Alaska during June 1997. AFTIR spectra acquired near the source of the smoke plumes yielded excess mixing ratios for 13 of the most common trace gases: water, carbon dioxide, carbon monoxide, methane, nitric oxide, formaldehyde, acetic acid, formic acid, methanol, ethylene, acetylene, ammonia and hydrogen cyanide. Emission ratios to carbon monoxide for formaldehyde, acetic acid, and methanol were 2.2±0.4%, 1.3±0.4%, and 1.4±0.1%, respectively. For each oxygenated organic compound, a single linear equation fits our emission factors from Alaska, North Carolina, and laboratory fires as a function of modified combustion efficiency (MCE). A linear equation for predicting the NH3/NOx emission ratio as a function of MCE fits our Alaskan AFTIR results and those from many other studies. AFTIR spectra collected in downwind smoke that had aged 2.2±1 hours in the upper, early plume yielded ΔO3/ΔCO ratios of 7.9±2.4% resulting from O3 production rates of ∼50 ppbv h−1. The ΔNH3/ΔCO ratio in another plume decreased to 1/e of its initial value in ∼2.5 hours. A set of average emission ratios and emission factors for fires in Alaskan boreal forests is derived. We estimate that the 1997 Alaskan fires emitted 46±11 Tg of CO2

Trace Gas Measurements in Nascent, Aged, and Cloud-Processed Smoke from African Savanna Fires by Airborne Fourier Transform Infrared Spectroscopy (AFTIR)

[1] We measured stable and reactive trace gases with an airborne Fourier transform infrared spectrometer (AFTIR) on the University of Washington Convair-580 research aircraft in August/September 2000 during the SAFARI 2000 dry season campaign in Southern Africa. The measurements included vertical profiles of CO2, CO, H2O, and CH4 up to 5.5 km on six occasions above instrumented ground sites and below the TERRA satellite and ER-2 high-flying research aircraft. We also measured the trace gas emissions from 10 African savanna fires. Five of these fires featured extensive ground-based fuel characterization, and two were in the humid savanna ecosystem that accounts for most African biomass burning. The major constituents that we detected in nascent smoke were (in order of excess molar abundance) H2O, CO2, CO, CH4, NO2, NO, C2H4, CH3COOH, HCHO, CH3OH, HCN, NH3, HCOOH, and C2H2. These are the first quantitative measurements of the initial emissions of oxygenated volatile organic compounds (OVOC), NH3, and HCN from African savanna fires. On average, we measured 5.3 g/kg of OVOC and 3.6 g/kg of hydrocarbons (including CH4) in the initial emissions from the fires. Thus, the OVOC will have profound, largely unexplored effects on tropical tropospheric chemistry. The HCN emission factor was only weakly dependent on fire type; the average value (0.53 g/kg) is about 20 times that of a previous recommendation. HCN may be useful as a tracer for savanna fires. ΔO3/ΔCO and ΔCH3COOH/ΔCO increased to as much as 9% in \u3c1 h of photochemical processing downwind of fires. Direct measurements showed that cloud processing of smoke greatly reduced CH3OH, NH3, CH3COOH, SO2, and NO2 levels, but significantly increased HCHO and NO

Trace Gas and Particle Emissions from Fires in Large Diameter and Belowground Biomass Fuels

[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 EFRSC for both particles with diameter \u3c2.5 μm (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 EFRSC 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

Complex Effects Arising in Smoke Plume Simulations due to Inclusion of Direct Emissions of Oxygenated Organic Species from Biomass Combustion

Oxygenated volatile organic species (oxygenates), including HCOOH, H2CO, CH3OH, HOCH2CHO (hydroxyacetaldehyde), CH3COOH, and C6H5OH, have recently been identified by Fourier transform infrared measurements as a significant component of the direct emissions from biomass combustion. These oxygenates have not generally been included in the hydrocarbon-based initial emission profiles used in previous photochemical simulations of biomass combustion smoke plumes. We explore the effects of oxygenates on this photochemistry by using an established initial emission hydrocarbon profile and comparing simulation results obtained both with and without addition of the above six oxygenates. Simulations are started at noon and carried out for 30 hours in an expanding Lagrangian plume. After an initial transient period during which [NOx] falls rapidly, conditions within the oxygenated smoke plume are found to be strongly NOx-sensitive, and the simulated final species profile is thus strongly dependent upon the Δ[NO]/Δ[CO] initial emission profile. Oxygenate addition results in very significant and complex effects on net O3 production, as well as on the relative amounts of long-lived HOx and NOx reservoir species (H2O2, organic hydroperoxides, HNO3, and peroxyacetyl nitrate (PAN)) that are mixed into the surrounding atmosphere. Oxygenates may either increase or decrease net O3 production (depending upon the initial Δ[NO]/Δ[CO]). However, they always increase H2O2 and organic hydroperoxide production as a result of increased rates of radical + radical reactions. These effects spring largely from accelerated removal of NOx from the smoke plume due to increased radical concentrations resulting both from photolysis of oxygenates (mainly CH2O) and from their relatively high reactivity. Predicted concentrations of H2O2, Δ[O3]/Δ[CO], Δ[NH3]/Δ[CO], and Δ[HCOOH]/Δ[CO] are compared with some available measured values

Comprehensive Laboratory Measurements of Biomass-Burning Emissions: 1. Emissions from Indonesian, African, and Other Fuels

[1] Trace gas and particle emissions were measured from 47 laboratory fires burning 16 regionally to globally significant fuel types. Instrumentation included the following: open-path Fourier transform infrared spectroscopy; proton transfer reaction mass spectrometry; filter sampling with subsequent analysis of particles with diameter \u3c2.5 μm for organic and elemental carbon and other elements; and canister sampling with subsequent analysis by gas chromatography (GC)/flame ionization detector, GC/electron capture detector, and GC/mass spectrometry. The emissions of 26 compounds are reported by fuel type. The results include the first detailed measurements of the emissions from Indonesian fuels. Carbon dioxide, CO, CH4, NH3, HCN, methanol, and acetic acid were the seven most abundant emissions (in order) from burning Indonesian peat. Acetol (hydroxyacetone) was a major, previously unobserved emission from burning rice straw (21–34 g/kg). The emission factors for our simulated African fires are consistent with field data for African fires for compounds measured in both the laboratory and the field. However, the higher concentrations and more extensive instrumentation in this work allowed quantification of at least 10 species not previously quantified for African field fires (in order of abundance): acetaldehyde, phenol, acetol, glycolaldehyde, methylvinylether, furan, acetone, acetonitrile, propenenitrile, and propanenitrile. Most of these new compounds are oxygenated organic compounds, which further reinforces the importance of these reactive compounds as initial emissions from global biomass burning. A few high-combustion-efficiency fires emitted very high levels of elemental (black) carbon, suggesting that biomass burning may produce more elemental carbon than previously estimated