R. A. Rasmussen

Greenhouse gases and other airborne pollutants from household stoves in China: a database for emission factors

Abstract Emissions from household stoves, especially those using solid fuels, can contribute significantly to greenhouse gas (GHG) inventories and have adverse health impacts. Few data are available on emissions from the numerous types of cookstoves used in developing countries. We have systematically measured emissions from 56 fuel/stove combinations in India and China, a large fraction of the combinations in use world-wide. A database was generated containing emission factors of direct and indirect GHGs and other airborne pollutants such as CO2, CO, CH4, TNMHC, N2O, SO2, NOx, TSP, etc. In this paper, we report on the 28 fuel/stove combinations tested in China. Since fuel and stove parameters were measured simultaneously along with the emissions, the database allows construction of complete carbon balances and analyses of the trade-off of emissions per unit fuel mass and emissions per delivered energy. Results from the analyses show that the total emissions per unit delivered energy were substantially greater from burning the solid fuels than from burning the liquid or gaseous fuels, due to lower thermal and combustion efficiencies for solid-fuel/stove combinations. For a given biomass fuel type, increasing overall stove efficiency tends to increase emissions of products of incomplete combustion. Biomass fuels are typically burned with substantial production of non-CO2 GHGs with greater radiative forcing, indicating that biomass fuels have the potential to produce net global warming commitments even when grown renewably.

The Global Distribution of Methane in the Troposphere

Methane has been measured in air samples collected at approximately weekly intervals at 23 globally distributed sites in the NOAA/GMCC cooperative flask sampling network. Sites range in latitude from 90° S to 76° N, and at most of these we report 2 years of data beginning in early 1983. All measurements have been made by gas chromatography with a flame ionization detector at the NOAA/GMCC laboratory in Boulder, Colorado. All air samples have been referenced to a single secondary standard of methane-in-air, ensuring a high degree of internal consistency in the data. The precision of measurements is estimated from replicate determinations on each sample as 0.2%. The latitudinal distribution of methane and the seasonal variation of this distribution in the marine boundary layer has been defined in great detail, including a remarkable uniformity in background levels of methane in the Southern Hemisphere. We report for the first time the observation of a complete seasonal cycle of methane at the South Pole. A significant vertical gradient is observed between a sea level and a high altitude site in Hawaii. Globally averaged background concentrations in the marine boundary layer have been calculated for the 2 year-period May 1983–April 1985 inclusive, from which we find an average increase of 12.8 ppb per year, or 0.78% per year when referenced to the globally averaged concentration (1625 ppb) at the mid-point of this period. We present evidence that there has been a slowing down in the methane growth rate.

The global sources of nitrous oxide

We use atmospheric and ice core data on the concentrations of nitrous oxide to estimate that the present global anthropogenic emissions are 7±1 tg/yr. If the atmospheric lifetime of N2O is a hundred years or more, this estimate is virtually independent of the actual lifetime. The natural sources are estimated to be about 15 tg/yr. We also find that nitrous oxide started increasing rapidly only during the last century. The trends over the last decade are extremely variable; over 3-year periods the trends have ranged from 0.5 ± 0.2 parts per billion by volume (ppbv/yr) to 1.2 ± 0.1 ppbv/yr. The average rate of increase is about 0.80 ± 0.02 ppbv/yr or 0.27 ± 0.01 %/yr (1977–1988). There is an indication that N2O may be increasing faster in recent years than during the middle 1970s by about 0.2 ± 0.1 ppbv/yr. It is likely that several small anthropogenic sources may be causing the present trends, all emitting between 0.1 and 1.5 Tg/yr.

Smoke and fire characteristics for cerrado and deforestation burns in Brazil: BASE‐B Experiment

Fires of the tropical forests and savannas are a major source of particulate matter and trace gases affecting the atmosphere globally. A paucity of quantitative information exists for these ecosystems with respect to fuel biomass, smoke emissions, and fire behavior conditions affecting the release of emissions. Five test fires were performed during August and September 1990 in the cerrado (savannalike region) in central Brazil (three fires) and tropical moist forest (two fires) in the eastern Amazon. This paper details the gases released, the ratios of the gases to each other and to particulate matter, fuel loads and the fraction consumed (combustion factors), and the fire behavior associated with biomass consumption. Models are presented for evaluating emission factors for CH4, CO2, CO, H2, and particles less than 2.5 μm diameter (PM2.5) as a function of combustion efficiency. The ratio of carbon released as CO2 (combustion efficiency) for the cerrado fires averaged 0.94 and for the deforestation fires it decreased from 0.88 for the flaming phase to <0.80 during the smoldering phase of combustion. For tropical ecosystems, emissions of most products of incomplete combustion are projected to be lower than previous estimates for savanna ecosystems and somewhat higher for fires used for deforestation purposes.

Global average concentration and trend for hydroxyl radicals deduced from ALE/GAGE trichloroethane (methyl chloroform) data for 1978–1990

Atmospheric measurements at several surface stations made between 1978 and 1990 of the anthropogenic chemical compound 1,1,1-trichloroethane (methyl chloroform, CH3CCl3) show it increasing at a global average rate of 4.4 ± 0.2% per year (1σ) over this time period. The measured trends combined with industrial emission estimates are used in an optimal estimation inversion scheme to deduce a globally averaged CH3CCl3 tropospheric (and total atmospheric) lifetime of 5.7 (+0.7, −0.6) years (1σ) and a weighted global average tropospheric hydroxyl radical (OH) concentration of (8.7 ± 1.0) × 105 radical cm−3 (1σ). Inclusion of a small loss rate to the ocean for CH3CCl3 of 1/85 year−1 does not affect the stated lifetime but lowers the stated OH concentration to (8.1 ± 0.9) × 105 radical cm−3 (1σ). The rate of change of the weighted global average OH concentration over this time period is determined to be 1.0 ± 0.8% per year (1σ) which has major implications for the oxidation capacity of the atmosphere and more specifically for methane (CH4), which like CH3CCl3 is destroyed primarily by OH radicals. Because the weighting strongly favors the tropical lower troposphere, this deduced positive OH trend is qualitatively consistent with hypothesized changes in tropical tropospheric OH and ozone concentrations driven by tropical urbanization, biomass burning, land use changes, and long-term warming. We caution, however, that our deduced rate of change in OH assumes that current industry estimates of anthropogenic emissions and our absolute calibration of CH3CCl3 are accurate. The CH3CCl3 measurements at our tropical South Pacific station (Samoa) show remarkable sensitivity to the El Nino-Southern Oscillation (ENSO), which we attribute to modulation of cross-equatorial transport during the northern hemisphere winter by the interannually varying upper tropospheric zonal winds in the equatorial Pacific. Thus measurements of this chemical compound have led to the discovery of a previously unappreciated aspect of tropical atmospheric tracer transport.

Biomass Burning Airborne and Spaceborne Experiment in the Amazonas (BASE‐A)

In the Biomass Burning Airborne and Spaceborne Experiment in the Amazonas (BASE-A), conducted in September 1989, trace gas and particulate matter emissions were measured from biomass burning due to deforestation and grassland fires in South America. This information is required for a better understanding of the environmental impacts of biomass burning in the tropics and to improve algorithms for remote sensing of biomass burning from satellite platforms. The field experiment utilized the twin-engine Embraer Bandeirante EMB-1Ol instrumented aircraft of the Brazilian Institute for Space Research (INPE). Concentrations of ozone, CO2, CO, CH4, and particulate matter were measured from the aircraft. Fires were observed from satellite imagery, and the smoke optical thickness, particle size, and profiles of the extinction coefficient were measured using sunphotometers in the aircraft and from the ground. Four smoke plumes were sampled, three vertical profiles were measured, and extensive ground measurements were conducted of smoke optical characteristics for different smoke types. The collected data were analyzed for determining the emission ratios and combustion efficiency (the efficiency of a fire to convert the total burned carbon to carbon dioxide) and were compared with the results from fires in North America. Combustion efficiency was found to be higher in the tropics (97% for the cerrado and 90% for the deforestation fires) with emission factors similar to those of North American fires, for a given combustion efficiency. A strong relation was found between the spatial distribution of fires (up to 9000 per day in one state) and ozone concentration (up to 80 ppbv) and between biomass burning and concentrations of trace gases, particulate matter, and ozone. These relations strongly suggest a correlation between biomass burning in the tropics and ozone formation. An optical model of the smoke aerosol was derived and applied to radiance measurements. The smoke single scattering albedo was computed from the graphitic carbon concentration (assuming external mode mixture) as 0.90 ± 0.01. The particles effective radii were 0.1 to 0.2 μm, except for 1-day aged smoke with values up to 0.4 μm. Radiance measurements indicate that the width of the particle size distribution may be smaller in the tropics than for North American fires. The measured optical properties of smoke and the high correlation between emitted trace gases and particles form a basis for remote sensing of radiatively important trace gases and particulate matter from biomass burning using AVHRR imagery.

Atmospheric Trends in Methylchloroform and the Global Average for the Hydroxyl Radical

Frequent atmospheric measurements of the anthropogenic compound methylchloroform that were made between 1978 and 1985 indicate that this species is continuing to increase significantly around the world. Reaction with the major atmospheric oxidant, the hydroxyl radical (OH), is the principal sink for this species. The observed mean trends for methylchloroform are 4.8, 5.4, 6.4, and 6.9 percent per year at Aldrigole (Ireland) and Cape Meares (Oregon), Ragged Point (Barbados), Point Matatula (American Samoa), and Cape Grim (Tasmania), respectively, from July 1978 to June 1985. These measured trends, combined with knowledge of industrial emissions, were used in an optimal estimation inversion scheme to deduce a globally averaged methylchloroform atmospheric lifetime of 6.3 (+ 1.2, -0.9) years (1σ uncertainty) and a globally averaged tropospheric hydroxyl radical concentration of (7.7 � 1.4) x 105 radicals per cubic centimeter (1σ uncertainty). These 7 years of gas chromatographic measurements, which comprise about 60,000 individual calibrated real-time air analyses, provide the most accurate estimates yet of the trends and lifetime of methylchloroform and of the global average for tropospheric hydroxyl radical levels. Accurate determination of hydroxyl radical levels is crucial to understanding global atmospheric chemical cycles and trends in the levels of trace gases such as methane.

A review and synthesis of monoterpene speciation from forests in the United States

Abstract The monoterpene composition (emission and tissue internal concentration) of major forest tree species in the United States is discussed. Of the 14 most commonly occurring compounds ( α -pinene, β -pinene, Δ 3 -carene, d -limonene, camphene, myrcene, α -terpinene, β -phellandrene, sabinene, ρ -cymene, ocimene, α -thujene, terpinolene, and γ -terpinene), the first six are usually found to be most abundant. Expected regional variability based on the monoterpene composition fingerprints and corresponding tree species distribution and abundance is examined. In the southeast, α -pinene and β -pinene seem to dominate monoterpene emissions, while in the northern forests emissions are distributed more evenly among the six major compounds. In some parts of western forests, β -pinene and Δ 3 -carene can be more abundant than α -pinene. Among the other eight compounds, β -phellandrene and sabinene occasionally are significant percentages of expected local monoterpene emissions. Ocimene and ρ -cymene are estimated to be more common in regions dominated by deciduous broadleaf forests, although total emission rates are generally lower for these forests relative to those dominated by conifers. These percentages are compared with monoterpene composition measured in ambient air at various sites. Estimated monoterpene emission composition based on local forest species composition agrees fairly well with ambient measurements for the six major compounds. The past assumption that α -pinene composes approximately 50% of total monoterpene emissions appears reasonable for many areas, except for possibly the northern coniferous forests and some areas in the west dominated by true firs, spruce, and western pines (lodgepole and ponderosa pines). The oxygenated monoterpenes such as camphor, bornyl acetate, and cineole often compose high percentages of the monoterpenes within plant tissues, but are much less abundant in emission samples. Even after adjusting for lower vapor pressures of these compounds, emission rates relative to the hydrocarbon monoterpenes are often lower than would be expected from their internal concentrations. More study is warranted on monoterpene emission rates and composition, especially from the spruces, true firs, hemlocks, cedars, and some deciduous species such as the maples. Non-invasive canopy level and whole ecosystem flux studies are also needed to establish uncertainty estimates for monoterpene emission models.

Global sources, lifetimes and mass balances of carbonyl sulfide (OCS) and carbon disulfide (CS2) in the earth's atmosphere

Abstract Emissions of carbonyl sulfide (OCS) and carbon disulfide (CS2) from natural and anthropogenic sources have been estimated consistent with the observed latitudinal and vertical distributions of these trace gases. Anthropogenic emissions appear to be a small part (⩽ 25 %) of the yearly emissions of OCS and CS2. Oceans and soils are the largest sources, representing about 50 % of the yearly emissions of OCS. Biomass burning is perhaps the largest anthropogenic source, while coal-fired power plants and automobiles contribute small amounts. Chemical uses may be the largest anthropogenic source of CS2. The results suggest that the lifetime of OCS is about 2 years and of CS2 about 12 days.

Causes of increasing atmospheric methane - Depletion of hydroxyl radicals and the rise of emissions

Abstract The observed rapid rise of atmospheric methane at rates of about 1.3% per year may be caused by the increase of emissions effected by anthropogenic activities and by a possible decline in the global concentrations of hydroxyl radicals (OH) which remove methane from the atmosphere. Moreover, the measurements of methane in air bubbles buried deep in polar ice suggest that the concentrations of methane several hundred years ago may have been only about 45% of present levels. We extrapolated the present emissions of methane from human activities (250 Tg y−1) backwards in time proportional to the estimated change of human population. Our calculations show that much of the increase of methane over the past 200 years is probably due to the increase of emissions (70%) and a lesser amount is due to a possible depletion of OH (30%). Projections indicate that in another 20 years the average tropospheric concentrations of methane may reach 1900–1950 ppbv or about 25% greater than present (1980) levels. Our findings, based on two complementary approaches, support the idea that the present abundance of hydroxyl radicals may be about 20% less than several hundred years ago.