Evaluation of Adsorption Effects on Measurements of Ammonia, Acetic Acid, and Methanol

[1] We examined how adsorption and desorption of gases from inlets and a cell could affect the accuracy of closed-cell FTIR measurements of carbon dioxide (CO2), carbon monoxide (CO), methane (CH4), nitric oxide (NO), nitrogen dioxide (NO2), methanol (CH3OH), acetic acid (CH3COOH), and ammonia (NH3). When standards were delivered to the cell through a stainless steel inlet, temporarily reduced transmission was observed for CH3OH and NH3. However, a halocarbon wax coated inlet (normally used on the system) had excellent transmission (comparable to room temperature Teflon) for both CH3OH and NH3, even at temperatures as low as 5°C. Thus the wax is valuable for coating sampling system components that cannot be fashioned from Teflon. The instrument had a delayed response (∼10–40 s) for NH3 only, which was attributed to passivation of the Pyrex multipass cell. To determine sampling artifacts that could arise from the complex sample matrix presented by smoke, the closed-cell FTIR system was intercompared with an open-path FTIR system (which is immune to sampling artifacts) in well-mixed smoke. A similar cell passivation delay for NH3 was the only artifact found in this test. Overall, the results suggest that ∼10 s is sufficient to detect \u3e80% of an NH3/CO ratio sampled by our fast-flow, closed-cell system. Longer sampling times or consecutive samples return better results. In field campaigns the closed-cell system sampling times were normally 10 to \u3e100 s so NH3 was probably underestimated by 5–15%

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

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

Emissions of Trace Gases and Particles From Savanna Fires in Southern Africa

Airborne measurements made on initial smoke from 10 savanna fires in southern Africa provide quantitative data on emissions of 50 gaseous and particulate species, including carbon dioxide, carbon monoxide, sulfur dioxide, nitrogen oxides, methane, ammonia, dimethyl sulfide, nonmethane organic compounds, halocarbons, gaseous organic acids, aerosol ionic components, carbonaceous aerosols, and condensation nuclei (CN). Measurements of several of the gaseous species by gas chromatography and Fourier transform infrared spectroscopy are compared. Emission ratios and emission factors are given for eight species that have not been reported previously for biomass burning of savanna in southern Africa (namely, dimethyl sulfide, methyl nitrate, five hydrocarbons, and particles with diameters from 0.1 to 3 μm). The emission factor that we measured for ammonia is lower by a factor of 4, and the emission factors for formaldehyde, hydrogen cyanide, and CN are greater by factors of about 3, 20, and 3–15, respectively, than previously reported values. The new emission factors are used to estimate annual emissions of these species from savanna fires in Africa and worldwide