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Recent measurements suggest that the terrestrial plant community may be an important source of methane with global contributions between 62 and 236 Tg CH4 y(-1). If true, terrestrial plants could rival wetlands as being the largest global source of methane forcing us to rethink the methane budget. While further measurements are needed to confirm the methane release rates from this source and their dependencies, in this work we use the preliminary measurements to assess the potential impact of the methane release from this source globally. Using novel techniques we extrapolate the initially reported chamber measurements to the global scale and calculate the global methane emissions from the terrestrial plant community to be in the range 20 to 69 Tg CH4 y(-1). The spread in emissions is largely due to the sensitivity of the global flux to the prescribed temperature dependence of the plant emission rate, which is largely unknown. The spread of calculated emissions is in good agreement with the upper limit imposed on the source during the late pre-industrial period, which we estimate to range from 25 to 54 Tg CH4 y(-1) during the years 0 to 1700 A.D. using the published atmospheric delta13CH4 record. In addition, if we assume that plant emissions have been constant at the mean value of 45 Tg CH4 y(-1), we find that the methane release from wildfires and biomass burning during the pre-industrial span 0-1000 A.D. must be near 12 Tg CH4 y(-1), which would be in better agreement with previous estimates of the pyrogenic source during this time than a methane budget missing the plant source. We conclude that methane release from the terrestrial plant community as presently understood does not require major innovations to the global methane budget.

Collectively, man-made emissions of a few greenhouse gases may cause about the same amount of global warming as increasing carbon dioxide. Among the most potent of these non-CO2 greenhouse gases are the perfluorocarbons that have extraordinarily long atmospheric lifetimes of 10,000 to more than 50,000 yr. We report atmospheric concentrations over two decades, between 1978 and 1997, of the three most abundant perfluorocarbons--CF4, C2F6, and C3F8--and delineate the sources that account for the present abundances and trends. We show that C2F6 and C3F8 are present at only 2.9 and 0.2 pptv, respectively. CF4 is the most abundant perfluorocarbon at 74 pptv (in 1997) of which about 40 pptv are from natural emissions, 33 pptv from aluminum manufacturing, and 1 pptv from the semiconductor industry. The increasing trend of CF4 has slowed in recent years due to the major reductions in the emission rate per ton of aluminum produced. The effect of the falling emission factor is partially offset by increased production and increasing use by the semiconductor industry.

Emission contributions from cookstoves to indoor, regional, and global air pollution largely depend on stove and fuel types. This paper presents a database on emission factors of speciated non-methane hydrocarbons (NMHCs) for 16 fuel/stove combinations burning 2 types of crop residue, wood, 4 types of coal, kerosene, and 3 types of gaseous fuels. The emission factors are presented both on a fuel mass basis (compound mass per fuel mass) and on a cooking task basis (compound mass per unit energy delivered to the pot). These fuel/stove combinations cover a large spectrum of the cookstoves used in both urban and rural households in China. Up to 54 hydrocarbons were identified, some of which are reactive precursors of photochemical smog. Based on published maximum incremental reactivity (MIR) values for NMHCs, we estimated stove-specific and fuel-specific ozone forming potentials (OFPs). The results indicate that raw coal powder, wood, and crop residues have higher OFP values than the other types of fuels tested. Strikingly, burning the coal briquette and honeycomb coal briquette produced OFP values more than 2 orders of magnitude lower than burning unprocessed (raw) coal, even in the same vented metal stove, for every 1 MJ delivered to the pot.

In the wake of the Kyoto and Montreal Protocols, there is a need to verify whether policies to reduce emissions are working. We present data showing that emissions of ozone-depleting compounds, such as the chlorofluorocarbons and methyl chloroform, are decreasing from some regions of the United States but emissions of the greenhouse gases do not appear to be declining.

The authors report globally averaged concentrations of atmospheric methane for every month of the past 8 years based on measurements taken at six locations ranging in latitude from within the Arctic Circle to the South Pole. This record shows that methane concentration increased at an average rate of 16.6 {plus minus} 0.4 ppbv/yr or {approximately} 1.02 {plus minus} 0.02%/yr over 8 years. This trend has not been constant according to their record but has varied between 12 {plus minus} 2 and 23 {plus minus} 2 ppbv/yr over 2-year periods after seasonal variations are removed. The causes of these interannual variations are not known. They also show that the total mass of methane in the earth's atmosphere undergoes seasonal variations, with highest levels during late fall and early winters of the northern hemisphere and lowest levels in the summers. After the main features of the record are taken into account, residual random fluctuations remain, which have a variability of only 3 ppbv or 0.2% of the mean concentrations. The variation of the trends at different times during the past decade accounts for the differences of trends reported in various studies. Uncertainties in the estimates are reported as 90% confidence limits.

Methane emissions from rice fields in China are found to be 4-10 times higher than emission rates from rice fields in the United States and Europe. Average emission rates during the growing season were {approximately}60 mg m{sup {minus}2} h{sup {minus}1} from rice fields at TuZu in the Sczhuan Province of China. These results show that rice fields are a major source of methane to the atmosphere.

I Air pollutart concentrations have been measured in residences in the Himalayas of Nepal where biomass fuels are used for cooking and heating. Levels of- total sus- pended parl icles are in the tange 3-42 mg/m3. with res- pirable suspended particles in the range 1 14 mg/m'in the houses sampled. High concentrations of several trace elements have also been measured. Limited data for gaseous species show appreciable levels of carbon mon- oxide, carbon dioxide, methane, artd several non-methare hydrocarbons. A questionnaire concerning energy use administered in each household suggests that high per capita use of biomass fuels is responsible for the excessive pollutant concentrations. Application of a one-compart- ment mass balaace model to these houses shows only rough agreement between calculated and measured values, due to uncertainties in model input parameters as well as difficulties in estimating average pollutant concentrations throughout each house. High outdoor concentrations of potassium and methyl chloride, previously shown to be iracers of biomass combustion, indicate that the indoor biomass combustion also degrades the outdoor environ- ment. Values of crustal enrichrnent factors for trace ele- ments in the air and snow of the region suggest that the polluted air is generally confined to the populated villages, with more pristine air at higher elevations.

The results of an experiment to determine the ratio of fine aerosol to methyl chloride in residential wood burning are presented. Accurate measurements of this ratio are necessary for receptor models that use methyl chloride as a unique tracer of woodsmoke and for chemical mass balance (CMB) models that include methyl chloride in the wood-burning source composition matrix. It is demonstrated how the values of the fine particle to methyl chloride ratios for various types of wood and burn conditions may be used in a stratified sampling scheme to determine a composite value of the ratio, which is found to be about 0.68 +/- 0.13 (..mu..g/m/sup 3/)/parts per trillion (volume) in Portland, OR. The ratio is used in a CMB calculation to estimate the wood-burning contribution to fine particulate concentrations in a residential neighborhood. Ratios of several hydrocarbon gases to CO/sub 2/ in residential wood burning are also presented for use in models that may attempt source reconcilation of hydrocarbon species. 20 references, 1 figure, 6 tables.

The global emissions of methylchloroform (CH/sub 3/CCl/sub 3/), in addition to increasing steadily over the years, have also undergone substantial cyclic fluctuations (+/- approx. 20% peak to peak). When these cycles are taken into account, the atmospheric observations of the rate of increase of CH/sub 3/CCl/sub 3/ and the changes in the interhemispheric ratio of CH/sub 3/CCl/sub 3/ concentrations come into close agreement with theoretically expected values.