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Methane emissions were measured at nine U.S. landfill sites using chamber and/or tracer flux techniques. These flux measurement methodologies were compared at two sites, and excellent agreement (

The mean isotopic composition of CH4 emitted from six New England (United States) landfills was 13C and D enriched (−48.1 to −50.4‰ and −273 to −281‰) relative to anoxic zone landfill CH4 (mean values of −55.9 to −56.2‰ and −296 to −300‰) owing to the oxidation of methane as it was transported from the landfill to the atmosphere through the soil cap. The fraction of methane oxidized f0 during its passage through the soil cap was calculated from the degree of 13C enrichment in emitted CH4 relative to anoxic zone CH4 in conjunction with values determined for the preference of soil methane oxidizing bacteria for 12CH4 over 13CH4 (α = 1.022 ± 0.008). Mean values for methane oxidation in six landfills were from 24 to 35% of the total flux through the soil during the warm season, depending upon how the data were grouped. Our results bracket recent estimates of methane oxidation of about 30% in the warm summer period produced using a model with the input terms of soil temperature, moisture, depth, and oxygen concentration. Because of variations in the response of methane oxidation to temperature at these New England sites, our study is consistent with the modeling results of Czepiel et al. [1996b] that the best estimate for the annual value for methane oxidation in the landfills considered is about 10%.

The current atmospheric mixing ratio of nitrous oxide (N2O), a chemically significant trace gas, is increasing at a rate of 0.25−0.31% yr-1, apparently well correlated with human activity. Better quantification of all N2O sources is required in efforts to stabilize this rate of increase. N2O emissions from the composting of wastewater sludge and livestock wastes were measured during 1993 and 1994 using enclosure methods. Static chambers were placed on the surface of the compost piles, and N2O mixing ratios within the chamber headspace were measured over time from which fluxes were calculated. The flux measurements resulted in mass-based emission factors of 0.7 g of N2O (dry kg)-1 and 0.5 g of N2O (dry kg)-1 for the sludge compost and the livestock waste compost, respectively. The derived emission factors were used in conjunction with recent waste generation and disposal statistics to estimate potential global N2O emissions from the treatment of organic wastes. Livestock waste treatment appears to hold the...

Nitrous oxide (N 2 0) emissions from primary and secondary wastewater treatment processes were measured during spring and summer 1993 in Durham, NH. The most significant emissions occurred during secondary aeration. Dissolved N 2 0 generated as a result of denitrification during primary settling was stripped from the liquid during mechanical aeration. Emission factors derived from our field measurements included per capita emissions of 3.2 g of N 2 0 person -1 yr -1 and flow based emissions of 1.6 x 10 -6 of N 2 0 (L of wastewater) -1 .