Wei Min Hao

Comprehensive laboratory measurements of biomass‐burning emissions: 1. Emissions from Indonesian, African, and other fuels

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 <2.5 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, CH 4 , NH 3 , 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.

Emissions of trace gases and aerosols during the open combustion of biomass in the laboratory

[1] We characterized the gas- and speciated aerosol-phase emissions from the open combustion of 33 different plant species during a series of 255 controlled laboratory burns during the Fire Laboratory at Missoula Experiments (FLAME). The plant species we tested were chosen to improve the existing database for U.S. domestic fuels: laboratory-based emission factors have not previously been reported for many commonly burned species that are frequently consumed by fires near populated regions and protected scenic areas. The plants we tested included the chaparral species chamise, manzanita, and ceanothus, and species common to the southeastern United States (common reed, hickory, kudzu, needlegrass rush, rhododendron, cord grass, sawgrass, titi, and wax myrtle). Fire-integrated emission factors for gas-phase CO2, CO, CH4 ,C 2–4 hydrocarbons, NH3 ,S O2, NO, NO2, HNO3, and particle-phase organic carbon (OC), elemental carbon (EC), SO4� ,N O3 ,C l � ,N a + ,K + , and NH4 generally varied with both fuel type and with the fire-integrated modified combustion efficiency (MCE), a measure of the relative importance of flaming- and smoldering-phase combustion to the total emissions during the burn. Chaparral fuels tended to emit less particulate OC per unit mass of dry fuel than did other fuel types, whereas southeastern species had some of the largest observed emission factors for total fine particulate matter. Our measurements spanned a larger range of MCE than prior studies, and thus help to improve estimates of the variation of emissions with combustion conditions for individual fuels.

Emissions of formaldehyde, acetic acid, methanol, and other trace gases from biomass fires in North Carolina measured by airborne Fourier transform infrared spectroscopy

Biomass burning is an important source of many trace gases in the global troposphere. We have constructed an airborne trace gas measurement system consisting of a Fourier transform infrared spectrometer (FTIR) coupled to a “flow-through” multipass cell (AFTIR) and installed it on a U.S. Department of Agriculture Forest Service King Air B-90. The first measurements with the new system were conducted in North Carolina during April 1997 on large, isolated biomass fire plumes. Simultaneous measurements included Global Positioning System (GPS); airborne sonde; particle light scattering, CO, and CO2; and integrated filter and canister samples. AFTIR spectra acquired within a few kilometers of the fires yielded excess mixing ratios for 10 of the most common trace gases in the smoke: water, carbon dioxide, carbon monoxide, methane, formaldehyde, acetic acid, formic acid, methanol, ethylene, and ammonia. Emission ratios to carbon monoxide for formaldehyde, acetic acid, and methanol were each 2.5±1%. This is in excellent agreement with (and confirms the relevance of) our results from laboratory fires. However, these ratios are significantly higher than the emission ratios reported for these compounds in some previous studies of “fresh” smoke. We present a simple photochemical model calculation that suggests that oxygenated organic compounds should be included in the assessment of ozone formation in smoke plumes. Our measured emission factors indicate that biomass fires could account for a significant portion of the oxygenated organic compounds and HOx present in the tropical troposphere during the dry season. Our fire measurements, along with recent measurements of oxygenated biogenic emissions and oxygenated organic compounds in the free troposphere, indicate that these rarely measured compounds play a major, but poorly understood, role in the HOx, NOx, and O3 chemistry of the troposphere.

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 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 <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 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. INDEX TERMS: 0345 Atmospheric Composition and Structure: Pollution—urban and regional (0305); 0368 Atmospheric Composition and Structure: Troposphere—constituent transport and chemistry; 0394 Atmospheric Composition and Structure: Instruments and techniques; 0365 Atmospheric Composition and Structure: Troposphere—composition and chemistry; KEYWORDS: biomass burning, smoldering combustion, oxygenated organic compounds, ammonia, methanol, smoke Citation: Bertschi, I., R. J. Yokelson, D. E. Ward, R. E. Babbitt, R. A. Susott, J. G. Goode, and W. M. Hao, Trace gas and particle emissions from fires in large diameter and belowground biomass fuels, J. Geophys. Res., 108(D13), 8472, doi:10.1029/2002JD002100, 2003.

Aerosol optical depth (AOD) and Angstrom exponent of aerosols observed by the Chinese Sun Hazemeter Network from August 2004 to September 2005

500, and 650 nm were analyzed for the period of August 2004 to September 2005. The smallest mean AOD (0.15) was found in the Tibetan Plateau where a showed the largest range in value (0.06‐0.9). The remote northeast corner of China was the next cleanest region with AODs ranging from 0.19 to 0.21 and with the largest a (1.16‐1.79), indicating the presence of fine aerosol particles. The forested sites exhibited moderate values of AOD (0.19‐0.51) and a (0.97‐1.47). A surprising finding was that the AOD measured at a few desert sites in northern China were relatively low, ranging from 0.24 to 0.36, and that a ranged from 0.42 to 0.99, presumably because of several dustblowing episodes during the observation period. The AOD observed over agricultural areas ranges from 0.38 to 0.90; a ranges from 0.55 to 1.11. These values do not differ much from those observed at the inland urban and suburban sites where AOD ranges from 0.50 to 0.69 and a ranges from 0.90 to 1.48. Given the geographic heterogeneity and the rapid increase in urbanization in China, much longer and more extensive observations are required.

Emissions of CO2, CO, and hydrocarbons from fires in diverse African savanna ecosystems

Emissions of CO2, CO, and hydrocarbons from 13 savanna fires (∼7 ha) were investigated in Zambia and South Africa in August and September 1992. The experiments were conducted at two moist woodland savanna sites, a moist grassland savanna site, and a semiarid woodland savanna site in Zambia, and nine semiarid woodland savanna sites in South Africa. The hydrocarbons measured were CH4, C2–C6 alkanes, alkenes, and alkynes, and aromatic compounds. The linear relationship between the emission factor of CH4 and the combustion efficiency is similar regardless of the phase of combustion (flaming or smoldering), the climatic zone, the herbaceous species, or the amount of aboveground biomass. Concentrations of emitted nonmethane hydrocarbons are linearly correlated with those of CH4. The emission ratio of a trace gas to CH4 is constant for either phase of combustion in these ecosystems. Biomass burning in African savannas is a significant source of CO, ethyne, propene, and benzene in the atmosphere. The amount of CO, ethene, ethane, ethyne, propene, propane, and benzene emitted per year from these fires is about 20–95% of the amount released from global industrial activities.

Emissions from the laboratory combustion of wildland fuels : Particle morphology and size

[1] The morphology of particles emitted by wildland fires contributes to their physical and chemical properties but is rarely determined. As part of a study at the USFS Fire Sciences Laboratory (FSL) investigating properties of particulate matter emitted by fires, we studied the size, morphology, and microstructure of particles emitted from the combustion of eight different wildland fuels (i.e., sagebrush, poplar wood, ponderosa pine wood, ponderosa pine needles, white pine needles, tundra cores, and two grasses) by scanning electron microscopy. Six of these fuels were dry, while two fuels, namely the tundra cores and one of the grasses, had high fuel moisture content. The particle images were analyzed for their density and textural fractal dimensions, their monomer and agglomerate number size distributions, and three different shape descriptors, namely aspect ratio, root form factor, and roundness. The particles were also probed with energy dispersive X-ray spectroscopy confirming their carbonaceous nature. The density fractal dimension of the agglomerates was determined using two different techniques, one taking into account the three-dimensional nature of the particles, yielding values between 1.67 and 1.83, the other taking into account only the two-dimensional orientation, yielding values between 1.68 and 1.74. The textural fractal dimension that describes the roughness of the boundary of the two-dimensional projection of the particle was between 1.10 and 1.19. The maximum length of agglomerates was proportional to a power a of their diameter and the proportionality constant and the three shape descriptors were parameterized as function of the exponent a.

Methane production from global biomass burning

Emissions of methane from various sources of biomass burning are determined quantitatively for tropical, temperate, and boreal regions. About 85% of the total CH{sub 4} is emitted in the tropical area, which is mainly the result of shifting cultivation, fuelwood use, and deforestation. Methane emissions from biomass burning may have increased by at least 9% during the last decade because of increases in tropical deforestation and the use of fuelwood. Changes in land use practices and population growth in the tropics are possible causes of the increase of atmospheric CH{sub 4} concentration. 31 refs., 1 fig., 4 tabs.

Fire and smoke observed from the Earth Observing System MODIS instrument—products, validation, and operational use

The Moderate Resolution Imaging Spectroradiometer (MODIS) sensor, launched on the National Aeronautics and Space Administration Terra satellite at the end of 1999, was designed with 36 spectral channels for a wide array of land, ocean, and atmospheric investigations. MODIS has a unique ability to observe fires, smoke, and burn scars globally. Its main fire detection channels saturate at high brightness temperatures: 500 K at 4 µm and 400 K at 11 µm, which can only be attained in rare circumstances at the 1 km fire detection spatial resolution. Thus, unlike other polar orbiting satellite sensors with similar thermal and spatial resolutions, but much lower saturation temperatures (e.g. Advanced Very High Resolution Radiometer and Along Track Scanning Radiometer), MODIS can distinguish between low intensity ground surface fires and high intensity crown forest fires. Smoke column concentration over land is for the first time being derived from the MODIS solar channels, extending from 0.41 µm to 2.1 µm. The smoke product has been provisionally validated both globally and regionally over southern Africa and central and south America. Burn scars are observed from MODIS even in the presence of smoke, using the 1.2 to 2.1 µm channels. MODIS burned area information is used to estimate pyrogenic emissions. A wide range of these fire and related products and validation are demonstrated for the wild fires that occurred in northwestern USA in Summer 2000. The MODIS rapid response system and direct broadcast capability is being developed to enable users to obtain and generate data in near real-time. It is expected that health and land management organizations will use these systems for monitoring the occurrence of fires and the dispersion of smoke within two to six hours after data acquisition.