Greenhouse gas emissions from municipal solid waste management in Indian mega-cities: a case study of Chennai landfill sites

Municipal solid waste generation rate is over-riding the population growth rate in all mega-cities in India. Greenhouse gas emission inventory from landfills of Chennai has been generated by measuring the site specific emission factors in conjunction with relevant activity data as well as using the IPCC methodologies for CH4 inventory preparation. In Chennai, emission flux ranged from 1.0 to 23.5mg CH4m(-2)h(-1), 6 to 460microg N2Om(-2)h(-1) and 39 to 906mg CO2m(2)h(-1) at Kodungaiyur and 0.9 to 433mg CH4m(-2)h(-1), 2.7 to 1200microg N2Om(-2)h(-1) and 12.3 to 964.4mg CO2m(-2)h(-1) at Perungudi. CH4 emission estimates were found to be about 0.12Gg in Chennai from municipal solid waste management for the year 2000 which is lower than the value computed using IPCC, 1996 [IPCC, 1996. Report of the 12th session of the intergovernmental panel of climate change, Mexico City, 1996] methodologies.     

Effects of copper concentration on methane emission from rice soils

Outdoor pot experiments with various paddy soils representing five soil types were conducted at Nanjing Agricultural University during the 2000 and 2001 rice-growing seasons. Eighteen soils and ten out of the eighteen soils were involved in the 2000 and the 2001 experiment, respectively. Two treatments were designed as mineral fertilization (MF) and mineral fertilizer + wheat straw incorporation (MF + WS) for the 2001 experiment. Seasonal average rate of CH4 emission from different soils ranged from 1.96 to 11.06 mg m(-2) h(-1) in the 2000 experiment, and from 0.89 to 5.92 mg m(-2) h(-1) for the MF treatment in the 2001 experiment, respectively. Incorporation of wheat straw enhanced considerably CH4 emission with an average increment of 7.09 mg m(-2) h(-1). CH4 emissions from the two-year experiment were negatively correlated to soil available and total copper concentration. A further investigation showed that CH4 emission from the MF treatment was positively related to the dissolved organic carbon (DOC) in the soil (r = 0.904, p < 0.001), and that the DOC was negatively correlated to the concentrations of available copper (r = -0.844, p < 0.01) and total copper (r = -0.833, p < 0.01), respectively. Nevertheless, the incorporation of wheat straw did not enhance the soil DOC, and the relationship between CH4 emission and soil DOC was not statistically significant (r = 0.470, p < 0.20). It was concluded that higher concentration of copper in the soils resulted in lower soil DOC and thus reduced CH4 emission when there was no additional organic matter input. Incorporation of wheat straw did not affect soil DOC and available copper concentration but enhanced CH4 emission.     

Effects of earthworm cast and powdered activated carbon on methane removal capacity of landfill cover soils

Landfill gases could be vented through a layer of landfill cover soil that could serve as a biofilter to oxidize methane to carbon dioxide and water. Properly managed landfill cover soil layers may reduce atmospheric CH4 emissions from landfills. In the present study, the effects of earthworm cast and powdered activated carbon (PAC) on the CH4 removal capacity of the landfill cover soil was investigated. For this purpose, column and batch tests were conducted using three different materials: typical landfill cover soil, landfill cover soil amended with earthworm cast, and landfill cover soil amended with PAC. The maximum CH4 removal rate of the columns filled with landfill cover soil amended with earthworm cast was 14.6mol m(-2)d(-1), whereas that of the columns filled with typical landfill cover soil was 7.4mol m(-2)d(-1). This result shows that amendment with earthworm cast could stimulate the CH4-oxidizing capacity of landfill cover soil. The CH4 removal rate of the columns filled with landfill cover soil amended with PAC also showed the same removal rate, but the vertical profile of gas concentrations in the columns and the methanotrophic population measured in the microbial assay suggested that the decrease of CH4 concentration in the columns is mainly due to sorption. Based on the results from this study, amendment of landfill cover soil with earthworm cast and PAC could improve its CH4 removal capacity and thus achieve a major reduction in atmospheric CH4 emission as compared with the same landfill cover soil without any amendment.     

Methane and carbon dioxide emissions from Shan-Chu-Ku landfill site in northern Taiwan

To investigate the methane and carbon dioxide emissions from landfill, samples were taken of material up to 5 years old from Shan-Chu-Ku landfill located in the northern part of Taiwan. Atmospheric concentrations of carbon dioxide, methane and nitrous oxide ranged from 310 to 530, 2.64 to 20.16 and 0.358 to 1.516 ppmv with the measurement of gas-type open-path Fourier transform infra-red (FTIR) spectroscopy during February 1998 to March 2000, respectively. Average methane emission rate was 13.17, 65.27 and 0.99 mgm(-2)h(-1) measured by the gas chromatography chamber method in 1-2, 2-3 and 5 year-old landfill, respectively. Similarly, average carbon dioxide emission rate was 93.70, 314.60 and 48.46 mgm(-2)h(-1), respectively. About 2-3 year-old landfill had the highest methane and carbon dioxide emission rates among the tested areas, while 5 year-old landfill was the least. Methane emission rate at night in most tested locations was higher than that in the daytime. Total amount of methane and carbon dioxide emission from this landfill was around 171 and 828 ton in 1999, respectively.     

Airborne emissions of mercury from municipal solid waste. I: new measurements from six operating landfills in Florida

Mercury-bearing material enters municipal landfills from a wide array of sources, including fluorescent lights, batteries, electrical switches, thermometers, and general waste; however, the fate of mercury (Hg) in landfills has not been widely studied. Using automated flux chambers and downwind atmospheric sampling, we quantified the primary pathways of Hg vapor releases to the atmosphere at six municipal landfill operations in Florida. These pathways included landfill gas (LFG) releases from active vent systems, passive emissions from landfill surface covers, and emissions from daily activities at each working face (WF). We spiked the WF at two sites with known Hg sources; these were readily detected downwind, and were used to test our emission modeling approaches. Gaseous elemental mercury (Hg(O)) was released to the atmosphere at readily detectable rates from all sources measured; rates ranged from approximately 1-10 ng m(-2) hr(-1) over aged landfill cover, from approximately 8-20 mg/hr from LFG flares (LFG included Hg(O) at microg/m3 concentrations), and from approximately 200-400 mg/hr at the WF. These fluxes exceed our earlier published estimates. Attempts to identify specific Hg sources in excavated and sorted waste indicated few readily identifiable sources; because of effective mixing and diffusion of Hg(O), the entire waste mass acts as a source. We estimate that atmospheric Hg releases from municipal landfill operations in the state of Florida are on the order of 10-50 kg/yr, substantially larger than our original estimates, but still a small fraction of current overall anthropogenic losses.     

Seasonal variability in CH4 emissions from a landfill in a cool, semiarid climate

Methane exchange with the atmosphere was measured during three seasons at the Rooney Road landfill in Jefferson County, CO. Substantial spatial and temporal variability in exchange rates were observed. Mean fluxes to the atmosphere were 534, 1290, and 538 mg CH4/m2/day, respectively, in the fall of 1994, winter of 1994-1995, and summer of 1995. Median fluxes were 12.42, 8.62, and 5.65 mg CH4/m2/day, respectively, during those seasons. Forty-three of 177 measurements had small negative fluxes, suggesting methanotrophic activity in the landfill cover soils. Despite probable methanotrophic activity in cover soils, landfills without gas collection systems may emit substantial CH4 to the atmosphere, with large spatial and seasonal variability.     

Non-controlled biogenic emissions to the atmosphere from Lazareto landfill, Tenerife, Canary Islands

GOAL, SCOPE AND BACKGROUND: [corrected] Historically, landfills have been the simplest form of eliminating urban solid waste with the minimum cost. They have been the most usual method for discarding solid waste. However, landfills are considered authentic biochemical reactors that introduce large amounts of contaminants into the environment in the form of gas and leachates. The dynamics of generation and the movement of gas in landfills depend on the input and output parameters, as well as on the structure of the landfill and the kind of waste. The input parameters include water introduced through natural or artificial processes, the characteristics of the urban solid waste, and the input of atmospheric air. The main output parameters for these biochemical reactors include the gases and the leachates that are potentially pollutants for the environment. Control systems are designed and installed to minimize the impact on the environment. However, these systems are not perfect and a significant amount of landfill gas could be released to the atmosphere through the surface in a diffuse form, also known as Non-controlled emission. In this paper, the results of the Non-controlled biogenic gas emissions from the Lazareto landfill in Tenerife, Canary Islands, are presented. The purpose of this study was to evaluate the concentration of CH4 and CO2 in the soil gas of the landfill cover, the CH4 and CO2 efflux from the surface of the landfill and, finally, to compare these parameters with other similar landfills. In this way, a better understanding of the process that controls biogenic gas emissions in landfills is expected. METHODS: A Non-controlled biogenic gas emission survey of 281 sampling sites was carried out during February and March, 2002. The sampling sites were selected in order to obtain a well-distributed sampling grid. Surface landfill CO2 efflux measurements were carried out at each sampling site on the surface landfill together with soil gas collection and ground temperatures at a depth of 30-40 cm.The CH4 efflux was computed from CO2 efflux and from the ratio CH4/CO2 in the soil gas. Soil gas samples were collected at a depth of 30-40 cm using a metallic probe and 20 cc hypodermic syringes, and later stored in evacuated 10 cc vacutainers for laboratory analysis of bulk composition. The gas sample was introduced in a vacutainer filled with deionized water and displacing the water until the vacutainer was filled with the gas sample in order to avoid air contamination from entering. The surface landfill temperature of the landfill was measured at a depth of 40 cm using a digital thermometer type OMEGA 871A. Landfill gases, CO2 and CH4, were analyzed within 24 hours using a double channel VARIAN micro-GC QUAD CP-2002P, with a 10 meter PORAPLOT-Q column, a TCD detector, and He as a carrier gas. The analysis temperature was 40 degrees C and the injection time was 10 msec. Surface landfill CO2 efflux measurements were performed using a portable NDIR spectrophotometer Licor-800 according to the accumulation chamber method (Chiodini et al. 1996). The data treatment, aimed at drawing the flux map and computing the total gas output, was based on the application of stochastic simulation algorithms provided by the GSLIB program (Deutsch and Journel 1998). RESULTS: Diffuse CH4 and CO2 efflux values range from negligible values up to 7,148 and 30,573 g m(-2) d(-1), respectively. The spatial distribution of the concentration and efflux of CO2, CH4 and soil temperature, show three areas of maximum activity in the landfill, suggesting a non-uniform pattern of diffuse degassing. This correlation between high emissions and concentration of CO2, CH4 and soil temperatures suggests that the areas of higher microbial activity and exothermic reactions are releasing CO2 and CH4 to the atmosphere from the landfill. Taking into consideration the spatial distribution of the CO2 and CH4 efflux values as well as the extension of the landfill, the Non-controlled emission of CO2 and CH4 to the atmosphere by the Lazareto's landfill are of 167 +/- 13.3 and 16 +/- 2.5 t d(-1), respectively. DISCUSSION: The patterns of gas flow within the landfill seem to be affected by boundary materials at the sides. The basalt layers have a low permeability and the gas flow in these areas is extensive. In this area, where a basalt layer does not exist, the flow gas diffuses toward the sea and the flux emissions at the landfill surface are lower. This behavior reflects the possible dissolution of gases into water and the deflection of gases towards the surface at the basalt boundary. The proximity to the sea, the installation of a palm tree garden and, as a result, the contribution of water coming from the watering of this garden has reactivated the system. The introduction of sea water into the landfill and the type of boundary could be defining the superficial gas discharges. CONCLUSIONS: Results from this study indicate that the spatial distribution of Non-controlled emission of CO2 and CH4 at the Lazareto's landfill shows a non-uniform pattern of diffuse degassing. The northeast, central and northwest areas of the Lazareto's landfill are the three areas of high emissions and concentration of CO2 and CH4, and high temperatures. The correlation between high emissions and the concentration of CO2, CH4, and the high temperatures suggest that the areas of higher microbial activity and exothermic reactions are releasing more CO2 and CH4 to the atmosphere from the landfill. A high concentration of CO2 is probably due to the presence of methanotrophic bacteria in the soil atmosphere of the landfill. Patterns of gas flow within the landfill seem to be affected by boundary materials (basalt layers) of low permeability, and side boundaries of the flux emissions at the surface are higher. At the sides of seawater and sediment boundaries, flux emissions at the landfill surface are lower. This behavior reflects a possible dissolution of gases into the water and the deflection of gases towards the surface at the basalt boundary. With this study, we can compare the data obtained in this landfill with other landfills and observe the different levels of emission. The proximity to the sea and the installation of the palm tree garden palms and, as a result, the contribution of water coming from the watering of this garden has reactivated the system. Many landfills worldwide located in similar settings could experience similar gas production processes. RECOMMENDATIONS AND PERSPECTIVES: The need for investigating and monitoring sea water and sediment quality in these landfills is advisable. Concentrations and fluxes of contaminants and their impact in the area should be assessed. With this study we can compare the data obtained in these landfills with other landfills and observe the different levels of emission.     

Performance of a semi-industrial scale gasification process for the destruction of polychlorinated biphenyls

A semi-industrial scale test was conducted to thermally treat mixtures of spent oil and askarels at a concentration of 50,000 ppm and 100,000 ppm of polychlorinated biphenyls (PCBs) under a reductive atmosphere. In average, the dry-basis composition of the synthesis gas (syngas) obtained from the gasification process was: hydrogen 46%, CO 34%, CO2 18%, and CH4 0.8%. PCBs, polychlorinated dibenzo-p-dioxins, and polychlorinated dibenzofurans (PCDDs/PCDFs) in the gas stream were analyzed by high-resolution gas chromatography (GC)-mass spectrometry. The coplanar PCBs congeners 77, 105, 118, 156/ 157, and 167 were detected in the syngas at concentrations < 2 x 10(-7) mg/m3 (at 298 K, 1 atm, dry basis, 7% O2). The chlorine released in the destruction of the PCBs was transformed to hydrogen chloride and separated from the gas by an alkaline wet scrubber. The concentration of PCBs in the water leaving the scrubber was below the detection limit of 0.002 mg/L, whereas the destruction and removal efficiency was > 99.9999% for both tests conducted. The concentration of PCDDs/PCDFs in the syngas were 8.1 x 10(-6) ng-toxic equivalent (TEQ)/m3 and 7.1 x 10(-6) ng-TEQ/m3 (at 298 K, 1 atm, dry basis, 7% O2) for the tests at 50,000 ppm and 100,000 ppm PCBs, respectively. The only PCDD/F congener detected in the gas was the octachloro-dibenzo-p-dioxin, which has a toxic equivalent factor of 0.001. The results obtained for other pollutants (e.g., metals and particulate matter) meet the maximum allowed emission limits according to Mexican, U.S., and European regulations for the thermal treatment of hazardous waste (excluding CO, which is a major component of the syngas, and total hydrocarbons, which mainly represent the presence of CH4).     

Effects of environmental factors on N2O emission from and CH4 uptake by the typical grasslands in the Inner Mongolia

The fluxes of N2O emission from and CH4 uptake by the typical semi-arid grasslands in the Inner Mongolia, China were measured in 1998-1999. Three steppes, i.e. the ungrazed Leymus chinensis (LC), the moderately grazed Leymus chinensis (LC) and the ungrazed Stipa grandis (SG), were investigated, at a measurement frequency of once per week in the growing seasons and once per month in the non-growing seasons of the LC steppes. In addition, four diurnal-cycles of the growing seasons of the LC steppes, each in an individual stage of grass growth, were measured. The investigated steppes play a role of source for the atmospheric N2O and sink for the atmospheric CH4, with a N2O emission flux of 0.06-0.21 kg N ha(-1) yr(-1) and a CH4 uptake flux of 1.8-2.3 kg C ha(-1) yr(-1). Soil moisture primarily and positively regulates the spatial and seasonal variability of N2O emission. The usual difference in soil moisture among various semi-arid steppes does not lead to significantly different CH4 uptake intensities. Soil moisture, however, negatively regulates the seasonal variability in CH4 uptake. Soil temperature of the most top layer might be the primary driving factor for CH4 uptake when soil moisture is relatively low. The annual net emission of N2O and CH4 from the ungrazed LC steppe, the moderately grazed LC steppe and the ungrazed SG steppe is at a CO2 equivalent rate of 7.7, 0.8 and -7.5 kg CO2-C ha(-1) yr(-1), respectively, which is at an ignorable level. This implies that the role of the semi-arid grasslands in the atmospheric greenhouse effect in terms of net emission of greenhouse gases (CO2, CH4 and N2O) may exclusively depend upon the net exchange of net ecosystem CO2 exchange.     

Seasonal changes of CO(2), CH(4) and N(2)O fluxes in relation to land-use change in tropical peatlands located in coastal area of South Kalimantan

Tropical peatland could be a source of greenhouse gases emission because it contains large amounts of soil carbon and nitrogen. However these emissions are strongly influenced by soil moisture conditions. Tropical climate is characterized typically by wet and dry seasons. Seasonal changes in the emission of carbon dioxide (CO(2)), methane (CH(4)) and nitrous oxide (N(2)O) were investigated over a year at three sites (secondary forest, paddy field and upland field) in the tropical peatland in South Kalimantan, Indonesia. The amount of these gases emitted from the fields varied widely according to the seasonal pattern of precipitation, especially methane emission rates were positively correlated with precipitation. Converting from secondary forest peatland to paddy field tended to increase annual emissions of CO(2) and CH(4) to the atmosphere (from 1.2 to 1.5 kg CO(2)-C m(-2)y(-1) and from 1.2 to 1.9 g CH(4)-C m(-2)y(-1)), while changing land-use from secondary forest to upland tended to decrease these gases emissions (from 1.2 to 1.0 kg CO(2)-C m(-2)y(-1) and from 1.2 to 0.6 g CH(4)-C m(-2)y(-1)), but no clear trend was observed for N(2)O which kept negative value as annual rates at three sites.     

Methane and nitrous oxide emissions from an irrigated rice of North India

Upland rice was grown in the kharif season (June-September) under irrigated condition in New Delhi, India (28 degree 40'N and 77 degree 12'E) to monitor CH4 and N2O emission, as influenced by fertilizer urea, ammonium sulphate and potassium nitrate alone (at 120 kg ha-1) and mixed with dicyandiamide (DCD), added at 10% of applied N. The experimental soil was a typic ustochrept (Inceptisol), clay loam, in which rice (Oryza sativa L., var. Pusa-169, duration: 120-125 days) was grown and CH4 and N2O was monitored for 105 days by closed chamber method, starting from the 5 days and 1 day after transplanting, respectively. Methane fluxes had a considerable temporal variation (CV=52-77%) and ranged from 0.05 (ammonium sulphate) to 3.77 mg m-2 h-1 (urea). There was a significant increase in the CH4 emission on the application of fertilizers while addition of DCD with fertilizers reduced emissions. Total CH4 emission (105 days) ranged from 24.5 to 37.2 kg ha-1. Nitrous oxide fluxes were much lower than CH4 fluxes and had ranged from 0.18 to 100.5 g m-2 h-1 with very high temporal variation (CV=69-143%). Total seasonal N2O emission from different treatments ranged from 0.037 to 0.186 kg ha-1 which was a N loss of 0.10-0.12% of applied N. All the fertilizers significantly increased seasonal N2O emission while application of DCD reduced N2O emissions significantly in the range of 10-53%.     

Key factors affecting spatial variation of methane emissions from freshwater marshes

To understand the mechanism for spatial variation of CH(4) emissions from marshes grown with different type of plants in a region and plots within a certain marsh grown with one type of plants, we measured CH(4) emissions from a region in which eutrophic freshwater marshes were divided into three types: Carex lasiocarpa, Carex meyeruana and Deyeuxia angustifolia according to plant type as well as CH(4) concentration in porewater, aboveground plant biomass and stem density in situ in Sanjiang Plain of Northeast China in August 2001. Spatial variation of CH(4) emissions from both different marshes in a region and different plots within a certain marsh was high. The flux rates of CH(4) emissions from three marshes ranged from 17.2 to 66.5 mg CH(4) m(-2)h(-1) with 34.76% of variation coefficient, whereas the values in Carex lasiocarpa, Carex meyeriana and Deyeuxia angustifolia marshes varied from 21.6 to 66.5 (39.61%), from 17.2 to 45.0 (29.26%) and from 19.1 to 33.0 mg CH(4) m(-2)h(-1) (17.51%), respectively. Both the flux rates and spatial variation of CH(4) emissions strongly increased as standing water depth increased significantly. Standing water depth greatly governed the spatial variation of CH(4) emissions from different marshes in a region by changing the amount of plant litters inundated in standing water, which provided labile organic C for methanogens and controlled CH(4) concentrations in porewater. Moreover, the aboveground plant biomass determined spatial variation of CH(4) emissions from plots within a certain marsh by controlling the pathways (stem density) of CH(4) emissions from the marsh into the atmosphere.     

Methane balance of a bioreactor landfill in Latin America

This paper presents results from a methane (CH4) gas emission characterization survey conducted at the Loma Los Colorados landfill located 60 km from Santiago, Chile. The landfill receives approximately 1 million metric tons (t) of waste annually, and is equipped with leachate control systems and landfill gas collection systems. The collected leachate is recirculated to enable operation of the landfill as a bioreactor. For this study, conducted between April and July 2000, a total of 232 surface emission measurements were made over the 23-ha surface area of the landfill. The average surface flux rate of CH4 emissions over the landfill surface was 167 g x m(-2) x day(-1), and the total quantity of surface emissions was 13,320 t/yr. These values do not include the contribution made by "hot spots," originating from leachate pools caused by "daylighting" of leachate, that were identified on the landfill surface and had very high CH4 emission rates. Other point sources of CH4 emissions at this landfill include 20 disconnected gas wells that vent directly to the atmosphere. Additionally, there are 13 gas wells connected to an incinerator responsible for destroying 84 t/yr of CH4. The balance also includes CH4 that is being oxidized on the surface of the landfill by meth-anotrophic bacteria. Including all sources, except leachate pool emissions, the emissions were estimated to be 14,584 t/yr CH4. It was estimated that less than 1% of the gas produced by the decomposition of waste was captured by the gas collection system and 38% of CH4 generated was emitted to the atmosphere through the soil cover.     

Methane emissions from 20 landfills across the United States using vertical radial plume mapping

Landfill fugitive methane emissions were quantified as a function of climate type and cover type at 20 landfills using US. Environmental Protection Agency (EPA) Other Test Method (OTM)-10 vertical radial plume mapping (VRPM) with tunable diode lasers (TDLs). The VRPM data were initially collected as g CH4/sec emission rates and subsequently converted to g CH4/m2/ day rates using two recently published approaches. The first was based upon field tracer releases of methane or acetylene and multiple linear regression analysis (MLRM). The second was a virtual computer model that was based upon the Industrial Source Complex (ISC3) and Pasquill plume stability class models (PSCMs). Calculated emission results in g CH4/m2/day for each measured VRPM with the two approaches agreed well (r2 = 0.93). The VRPM data were obtained from the working face, temporary soil, intermediate soil, and final soil or synthetic covers. The data show that methane emissions to the atmosphere are a function of climate and cover type. Humid subtropical climates exhibited the highest emissions for all cover types at 207, 127, 102, and 32 g CH4/m2/day, for working face (no cover), temporary, intermediate, and final cover, respectively. Humid continental warm summers showed 67, 51, and 27 g CH4/m2/day for temporary, intermediate, and final covers. Humid continental cool summers were 135, 40, and 26 g CH4/m2/day for the working face, intermediate, and final covers. Mediterranean climates were examined for intermediate and final covers only and found to be 11 and 6 g CH4/m2/day, respectively, whereas semiarid climates showed 85, 11, 3.7, and 2.7 g CH4/m2/day for working face, temporary, intermediate, and final covers. A closed, synthetically capped landfill covered with soil and vegetation with a gas collection system in a humid continental warm summer climate gave mostly background methane readings and average emission rates of only 0.09 g CH4/m2/day flux when measurable.     

Methane production and consumption in an active volcanic environment of Southern Italy

Methane fluxes were measured, using closed chambers, in the Crater of Solfatara volcano, Campi Flegrei (Southern Italy), along eight transects covering areas of the crater presenting different landscape physiognomies. These included open bare areas, presenting high geothermal fluxes, and areas covered by vegetation, which developed along a gradient from the central open area outwards, in the form of maquis, grassland and woodland. Methane fluxes decreased logarithmically (from 150 to -4.5 mg CH4 m(-2)day(-1)) going from the central part of the crater (fangaia) to the forested edges, similarly to the CO2 fluxes (from 1500 g CO2 m(-2)day(-1) in the centre of the crater to almost zero flux in the woodlands). In areas characterized by high emissions, soil presented elevated temperature (up to 70 degrees C at 0-10 cm depth) and extremely low pH (down to 1.8). Conversely, in woodland areas pH was higher (between 3.7 and 5.1) and soil temperature close to air values. Soil (0-10 cm) was sampled, in two different occasions, along the eight transects, and was tested for methane oxidation capacity in laboratory. Areas covered by vegetation mostly consumed CH4 in the following order woodland>macchia>grassland. Methanotrophic activity was also measured in soil from the open bare area. Oxidation rates were comparable to those measured in the plant covered areas and were significantly correlated with field CH4 emissions. The biological mechanism of uptake was demonstrated by the absence of activity in autoclaved replicates. Thus results suggest the existence of a population of micro-organisms adapted to this extreme environment, which are able to oxidize CH4 and whose activity could be stimulated and supported by elevated concentrations of CH4.     

Methane consumption by soils of dryland rice agriculture: influence of varieties and N-fertilization

Growth of three rice varieties (Heera, Dhala Heera and Narendra-118) and their relationship with methane consumption was investigated under rainfed (dryland) condition. Overall methane flux rates ranged between -0.58 to 1.25 mg m(-2) h(-1) across varieties, treatments, and dates of measurements. Except for two days when soil was saturated, the soil consumed 0.05-0.58 mg CH4 m(-2) h(-1); these rates were inversely related with soil moisture. N-fertilization reduced consumption rates. Although all plant growth parameters, except for number of tillers, exhibited relationship with methane consumption in control plots, only root porosity did so in fertilized plots. Combinations of plant growth characteristics explained 74-92% variability in seasonal CH4 consumption in unfertilized plots. It was concluded that methane consumption by dryland soils was influenced by rice variety, soil moisture and nitrogen fertilization.     

Tetrachloroethylene emissions and exposure in dry cleaning

Tetrachloroethylene (PCE) emissions and the exposure of workers in six commercial and three industrial dry-cleaning establishments that use dry-to-dry machines were determined. The personal samples and area samples [8-hr time-weighted average (TWA) and short-term exposure] were collected with charcoal tubes and passive monitors. The temporal variation of PCE concentration in the workplace air was monitored using a Fourier transform infrared analyzer (FTIR). The PCE emission rates were determined by multiplying the average PCE concentration in the room and the total airflow rate in the room. The PCE emissions were related to the cleaning rate in units of kg/hr. The operators' mean TWA exposure in commercial shops and industrial establishments was 28 (4.1 ppm) and 32 mg/m3 (4.6 ppm), and the pressers' exposure was 3.4 (0.5 ppm) and 7.7 mg/m3 (1.1 ppm), respectively. The customer service personnel had the lowest TWA exposure with a mean value of 0.8 mg/m3 (0.1 ppm). The highest peak concentration (2300 mg/m3; 334 ppm) was observed during cleaning of the lint and button trap, during which operation respirators were used. The PCE emission rates ranged from 4 to 118 g/hr corresponding to emission factors (mass of solvent evaporated per mass of cleaned cloths) of 0.3-3.6 g/kg. The workers' exposure to PCE was below the occupational limit values in the United States [according to the American Conference of Governmental Industrial Hygienists (ACGIH)] and in Finland. The outdoor PCE emissions were clearly below the limit values given in the European Union volatile organic compound (VOC) directive requirements.     

Determining seasonal greenhouse gas emissions from ground-level area sources in a dairy operation in central Texas

Greenhouse gas (GHG) emissions from agricultural production operations are recognized as an important air quality issue. A new technique following the U.S. Environmental Protection Agency Method TO-14A was used to measure GHG emissions from ground-level area sources (GLAS) in a free-stall dairy operation in central Texas. The objective of this study was to quantify and report GHG emission rates (ERs) from the dairy during the summer and winter using this protocol. A weeklong sampling was performed during each season. A total of 75 and 66 chromatograms of air samples were acquired from six delineated GLAS (loafing pen, walkway, barn, silage pile, settling basin, and lagoon) of the same dairy during summer and winter, respectively. Three primary GHGs--methane (CH4), carbon dioxide (CO2), and nitrous oxide (N2O)--were identified from the dairy operation during the sampling periods. The estimated overall ERs for CH4, CO2, and N2O during the summer for this dairy were 274, 6005, and 7.96 g head(-1)day(-1), respectively. During the winter, the estimated overall CH4, CO2, and N2O ERs were 52, 7471, and 3.59 g head(-1)day(-1), respectively. The overall CH4 and N2O ERs during the summer were approximately 5.3 and 2.2 times higher than those in the winter for the free-stall dairy. These seasonal variations were likely due to fluctuations in ambient temperature, dairy manure loading rates, and manure microbial activity of GLAS. The annualized ERs for CH4, CO2, and N2O for this dairy were estimated to be 181, 6612, and 6.13 g head(-1)day(-1), respectively. Total GHG emissions calculated for this dairy with 500 cows were 2250 t of carbon dioxide equivalent (CO2e) per year.     

Methane emission from fields with differences in nitrogen fertilizers and rice varieties in Taiwan paddy soils

Flooded rice fields are one of the major biogenic methane sources. In this study, methane emission rates were measured after transplanting in paddy fields with application of two kinds of nitrogen fertilizers (ammonium sulfate, NH4+-N and potassium nitrate, NO3(-)-N) and with two kinds of rice varieties (Japonica and Indica). The experiment was conducted in fields located at Tainan District Agricultural Improvement Station in Chia-Yi county (23 degrees 25'08"N, 120 degrees 16'26"E) of southern Taiwan throughout the first and the second crop seasons in 1999. The seasonal methane flux in the first crop season with NH4+-N and NO3(-)-N ranged from 2.48 to 2.78 and from 8.65 to 9.22 g CH4 m(-2); and the values ranged 24.6-34.2 and 36.4-52.6 g CH4 m(-2) in the second crop season, respectively. In the first crop season, there were significantly increased 3.1-3.7-fold in methane emission fluxes due to plantation of Indica rice. In comparison of two rice varieties, the Indica rice variety showed a tendency for larger methane emission than the Japonica rice variety in the second crop season. Moreover, ammonium sulfate treatment significantly reduced CH4 emissions by 37-85% emissions compared to potassium nitrate plots. It was concluded that the CH4 emission was markedly dependent on the type of nitrogen fertilizer and rice variety in Taiwan paddy soils.     

Geologic emissions of methane to the atmosphere

The atmospheric methane budget is commonly defined assuming that major sources derive from the biosphere (wetlands, rice paddies, animals, termites) and that fossil, radiocarbon-free CH4 emission is due to and mediated by anthropogenic activity (natural gas production and distribution, and coal mining). However, the amount of radiocarbon-free CH4 in the atmosphere, estimated at approximately 20% of atmospheric CH4, is higher than the estimates from statistical data of CH4 emission from fossil fuel related anthropogenic sources. This work documents that significant amounts of "old" methane, produced within the Earth crust, can be released naturally into the atmosphere through gas permeable faults and fractured rocks. Major geologic emissions of methane are related to hydrocarbon production in sedimentary basins (biogenic and thermogenic methane) and, subordinately, to inorganic reactions (Fischer-Tropsch type) in geothermal systems. Geologic CH4 emissions include diffuse fluxes over wide areas, or microseepage, on the order of 10(0)-10(2) mg m(-2) day(-1), and localised flows and gas vents, on the order of 10(2) t y(-1), both on land and on the seafloor. Mud volcanoes producing flows of up to 10(3) t y(-1) represent the largest visible expression of geologic methane emission. Several studies have indicated that methanotrophic consumption in soil may be insufficient to consume all leaking geologic CH4 and positive fluxes into the atmosphere can take place in dry or seasonally cold environments. Unsaturated soils have generally been considered a major sink for atmospheric methane, and never a continuous, intermittent, or localised source to the atmosphere. Although geologic CH4 sources need to be quantified more accurately, a preliminary global estimate indicates that there are likely more than enough sources to provide the amount of methane required to account for the suspected missing source of fossil CH4.