Byard W. Mosher

Quantifying the effect of oxidation on landfill methane emissions

Field, laboratory, and computer modeling methods were utilized to quantitatively assess the capability of aerobic microorganisms to oxidize landfill-derived methane (CH4) in cover soils. The investigated municipal landfill, located in Nashua, New Hampshire, was operating without gas controls of any type at the time of sample collection. Soil samples from locations of CH4 flux to the atmosphere were returned to the laboratory and subjected to incubation experiments to quantify the response of oxidation in these soils to temperature, soil moisture, in situ CH4 mixing ratio, soil depth, and oxygen. The mathematical representations of the observed oxidation reponses were combined with measured and predicted soil characteristics in a computer model to predict the rate of CH4 oxidation in the soils at the locations of the measured fluxes described by Czepiel et al. [this issue]. The estimated whole landfill oxidation rate at the time of the flux measurements in October 1994 was 20%. Local air temperature and precipitation data were then used in conjunction with an existing soil climate model to estimate an annual whole landfill oxidation rate in 1994 of 10%.

Landfill methane emissions measured by enclosure and atmospheric tracer methods

Methane (CH4) emissions were measured from the Nashua, New Hampshire municipal landfill using static enclosure and atmospheric tracer methods. The spatial variability of emissions was also examined using geostatistical methods. One hundred and thirty nine enclosure measurements were performed on a regular grid pattern over the emitting surface of the landfill resulting in an estimate of whole landfill emissions of 15,800 L CH4 min−1. Omnidirectional variograms displayed spatial correlation among CH4 fluxes below a separation distance of 7 m. Eleven tracer tests, using sulfur hexafluoride (SF6) as a tracer gas, resulted in a mean emissions estimate of 17,750 L CH4 min−1. The favorable agreement between the emission estimates was further refined using the observed relationship between atmospheric pressure and CH4 flux. This resulted in a pressure-corrected tracer flux estimate of whole landfill emissions of 16,740 L CH4 min−1.

The influence of atmospheric pressure on landfill methane emissions.

Landfills are the largest source of anthropogenic methane (CH4) emissions to the atmosphere in the United States. However, few measurements of whole landfill CH4 emissions have been reported. Here, we present the results of a multi-season study of whole landfill CH4 emissions using atmospheric tracer methods at the Nashua, New Hampshire Municipal landfill in the northeastern United States. The measurement data include 12 individual emission tests, each test consisting of 5-8 plume measurements. Measured emissions were negatively correlated with surface atmospheric pressure and ranged from 7.3 to 26.5 m3 CH4 min(-1). A simple regression model of our results was used to calculate an annual emission rate of 8.4 x 10(6) m3 CH4 year(-1). These data, along with CH4 oxidation estimates based on emitted landfill gas isotopic characteristics and gas collection data, were used to estimate annual CH4 generation at this landfill. A reported gas collection rate of 7.1 x 10(6) m3 CH4 year(-1) and an estimated annual rate of CH4 oxidation by cover soils of 1.2 x 10(6) m3 CH4 year(-1) resulted in a calculated annual CH4 generation rate of 16.7 x 10(6) m3 CH4 year(-1). These results underscore the necessity of understanding a landfills dynamic environment before assessing long-term emissions potential.

Development of atmospheric tracer methods to measure methane emissions from natural gas facilities and urban areas.

Environ. Sci. Techno/. 1995, 29, 1468-1 479 Introduction Tracer -Methods To Measure Downloaded by UNIV OF CALIFORNIA IRVINE on August 26, 2015 | http://pubs.acs.org Publication Date: June 1, 1995 | doi: 10.1021/es00006a007 Gas Faciliies and U h n Areas BRIAN K. LAMB,*,’ J. BARRY MCMANUS,* JOANNE H. SHORTER,* CHARLES E . KOLB,* BYARD MOSHER,

Chemical constituents in the air and snow at Dye 3, Greenland—I. Seasonal variations

R O B E R T C . HARRISS,§ EUGENE ALLWINE,’ DENISE BLAHA,

Seasonal aerosol chemistry at Dye 3, Greenland

T O U C H E H O W A R D , ” A L E X GUENTHER,l ROBERT A. LOTT,A ROBERT SIVERSON,’ HAL WESTBERG,’ AND PAT ZIMMERMAN- Laboratory for Atmospheric Research, Department of Civil & Environmental Engineering, Washington State University, Pullman, WA 99164-2910, Center for Chemical and Environmental Physics, Aerodyne Research, Inc., Billerica, Massachusetts 01821, Institute for the Study of Earth, Oceans and Space, University of New Hampshire, Durham, New Hampshire 03824, Indaco Air Quality Services, Inc., Pullman, Washington 99163, National Center for Atmospheric Research, Boulder, Colorado 80303, and Gas Research Institute, Chicago, Illinois 60631 -3562 A new, integrated methodologyto locate and measure methane emissions from natural gas systems has been developed. Atmospheric methane sources are identified by elevated ambient CH4 concentrations measured with a mobile laser-based methane analyzer. The total methane emission rate from a source is obtained by simulating the source with a sulfur hexafluoride (SFS) tracer gas release and by measuring methane and tracer concentrations along downwind sampling paths using mobile, real-time analyzers. Combustion sources of methane are dis- tinguished from noncombustion sources by concur- rent ambient carbon dioxide measurements. Three variations on the tracer ratio method are described for application to (1) small underground vaults, (2) above- ground natural gas facilities, and (3) diffuse methane emissions from an entire town. Results from controlled releases and from replicate tests demonstrate thatthe tracer ratio approach can yield total emission rates to within approximately &15%. The estimated accuracy of emission estimates for urban areas with a variety of diffuse emissions is &50%. Methane (CH4) has been a contributor to the increasing burden of greenhouse gases in the earth’s atmosphere for more than a century (1). Faced with significant risks identified in scenarios of increasing greenhouse gas con- centrations, many countries are developing plans to reduce emissions. However, uncertainties in specific source emission rates for CH4 and other non-COz greenhouse gases currently limit the quantitative risk-benefit analysis needed to answer key policy questions related to the socioeconomic impacts of large-scale mitigation actions (2, 3 ) . Initial attempts to estimate CH4 losses to the atmosphere from natural gas production and use assumed that emis- sions could be approximated by industry reports of “unac- counted for” gas (e.g., ref 4). Unaccounted for gas, defined as the difference between the amount of natural gas metered into a system and the amount of gas metered out of a system, does not account for gas losses from wells to the processing plant, gas used as fuel in facilities, theft of gas, meter inaccuracies, and differences in accounting procedures between companies (4,5). Thus, the unaccounted for gas estimates cannot unambiguously be considered an upper or lower bound on emissions (5). Extrapolation of engi- neering estimates or data obtained from component by component sniffing methods also leads to large uncertain- ties in estimated emissions. In the United Kingdom, the British Gas Company estimates CH4 emissions from gas distribution system components to be less than 1% of throughput, while others estimate losses as high as 11% of gas throughput (6). A recent estimate of CH4 leakage from the natural gas system in the former Soviet Union, which was characterized as “tentative and highly conditional” suggested a range of total losses from 3.3% to 7% of gas production ( 7 ) . The U.S. Environmental Protection Agency (EPA) and the Gas Research Institute (GRI) have recently sponsored an integrated field measurement and analysis program to better define methane emissions from the U.S. natural gas system. Drawing on initial measurements using some of the techniques reported here as weil as engineering estimates, GRI has developed a preliminary estimate of methane emissions from the gas industry that equals approximately 1.5 i 0.5% of annual throughput (8). In the case of CH4 emissions due to the use of natural gas, there is an added motivation for correctly prescribing the methane source strength. Since natural gas typically produces 32-45% less COz per unit of thermal output compared to coal and 30% less compared to fuel oil, switching from coal and fuel oil to natural gas has the potential to reduce carbon dioxide emissions and reduce global warming (5). However, CH4 is a more potent greenhouse gas than CO2 on a molecule for molecule basis (9- 1 I). As a result, increasing the usage of natural gas may * To whom correspondence should be addressed: e-mail address: blamb@wsu.edu. + Washington State University. Aerodyne Research, Inc. 5 University of New Hampshire. I’ Indaco Air Quality Services, Inc. National Center for Atmospheric Research. A Gas Research Institute. 1468 ENVIRONMENTAL SCIENCE &TECHNOLOGY / VOL. 29, NO. 6, 1995 0013-936)(/95/0929-1468

Chemical constituents in the air and snow at Dye 3, Greenland—II. Analysis of episodes in April 1989

09.00/0 @ 1995 American Chemical Society

Methane emission measurements in urban areas in eastern Germany

Chemical constituent concentrations in air and snow from the Dye 3 Gas and Aerosol Sampling Program show distinct seasonal patterns. These patterns are different from those observed at sea-level sites throughout the Arctic. Airborne SO42− and several trace metals ofcrustal and anthropogenic origin show strong peaks in the spring, mostly in April. Some species also have secondary maxima in the fall. The spring peaks are attributed to transport over the Pole from Eurasian sources, as well as transport from eastern North America and western Europe. The fall peaks are attributed primarily to transport from North America, and less frequent transport from Europe. Airborne 7Be and 210Pb show strong peaks in both spring and fall, suggesting that vertical atmospheric mixing is favored during these two seasons. Several other airborne constituents peak at other times. For example, Na peaks in winter due to transport of seaspray from storms in ice-free oceanic areas, while MSA peaks in summer due to biogenic production in the oceans nearby. Many trace gases such as freons and other chlorine-containing species show roughly uniform concentrations throughout the year. CO and CH4 show weak peaks in February–March. Concentrations of chemical constituents in fresh snow at Dye 3 also show distinct seasonal patterns. SO42− and several trace metals show springtime maxima, consistent with the aerosol data. Na shows a winter maximum and MSA shows a summer maximum in the snow, also consistent with the aerosols. 7Be and 210Pb in the snow do not show any strong variation with season. Similarly, soot and total carbon in snow do not show strong variation. When used with dry deposition models, these air and snow concentration data suggest that dry deposition of submicron aerosol species has relatively minor influence on constituent levels in the snowpack at Dye 3 compared to wet deposition inputs (including scavenging by fog); crustal aerosol, on the other hand, may have a more significant input by dry deposition. Overall, the results suggest that gross seasonal patterns of some aerosol species are constistent in the air and in fresh snow, although individual episodes in the air are not always reflected in the snow. The differences in data reported here compared with data sets for sea-level arctic sites demonstrate the need for sampling programs on the Ice Sheet in order to properly interpret Greenland glacial record data.

Sources of pollution aerosol at dye 3, Greenland

Aerosol trace element concentrations spanning an eleven month period at Dye 3, Greenland are presented. Sea salt input into the lower atmosphere of the ice sheet occurs predominantly in the winter months of December-February. These aerosols are the product of vigorous Arctic winter storms. Long range transport of crustal material from lower latitude arid regions to the Greenland Ice Sheet takes place predominantly during the spring. The onset of Arctic sunrise and associated weakening of the surface and upper level inversion over the ice sheet appear to be important factors resulting in higher crustal aerosol concentrations in the lower levels of the Greenland atmosphere during the month of April. A strong pulse of crustal aerosol (260 ng Al scm−1) was observed at Dye 3 on 14–15 April 1989. Meteorological evidence suggests that strong winds and deep convective activity injected dust high into the atmosphere over the Sahara desert region. This airmass then appears to have passed northwand over western Europe where it mixed with anthropogenic aerosols and arrived in the Dye 3 region some 4–6 d hence. Elevated concentrations of anthropogenic aerosol species were also observed at the surface during the months of April and May. Long range transport of these aerosols appears to be important during the Arctic winter and spring, while enhanced downward mixing due to a weakening inversion results in elevated concentrations at the surface during April and May. An increase in scavenging due to persistent Arctic stratus and the northward migration of the Polar Front in the spring results in very low anthropogenic aerosol concentrations during the summer months. Particulate aerosol iodine and bromine concentrations also peak during the month of April at Dye 3. It has been suggested that this spring particulate halogen peak, which is observed throughout the Arctic, may be the result of photochemical aerosol production from biogenic organo-halogen species. Regional meteorological phenomena as well as seasonal variations in source strength and long range transport appear to be important factors influencing aerosol concentrations in the surface atmosphere of the Greenland Ice Sheet.

Mitigation of methane emissions at landfill sites in New England, USA

Detailed examination of a two-week period in April 1989 during the Dye 3 Gas and Aerosol Sampling Program shows that episodes of relatively high concentration of certain chemical constituents occur at this time of year. Airborne concentrations of crustal metals such as Al and Ca can exceed 100 ng m−3, while concentrations of SO42− can exceed 1000 ng m−3. Elevated concentrations of MSA, 7Be and 210Pb are also noted. Consideration of synoptic maps and backward air mass trajectories suggests that the episodes are due to transport from a variety of source regions, including Eurasia (transport over the Pole), North America and western Europe. In addition to elevated airborne concentrations, levels of these constituents in surface snow are high during April. However, it is difficult to develop quantitative relationships between concentrations in air and in snow due to the difficulty in measuring airborne concentrations at cloud-level; variations in scavenging by clouds may also be significant. It is concluded that the springtime maxima in airborne concentrations resulting from long-range transport from a variety of source regions are responsible for strong identifiable signals in ice cores and snowpits from this region.