Search

China has shut down and abandoned a substantial number of coal mines since 1999, which have been releasing methane (CH 4 ) for many years. However, the characteristics of China's abandoned mine methane (AMM) emissions are still unclear; this is a concerning knowledge gap because coal mines are the largest contributor to China's anthropogenic CH 4 emissions. This study used two methods to estimate China's historical AMM emissions over the past 40 years (1980-2020) and to project its AMM emissions to 2060 which is the target year for China's carbon neutrality goal. The results show that China's AMM emissions increased substantially from 0.11 ± 0.03 million tons per year (Mt/yr) (3.1 ± 0.84 Mt/yr CO 2 -eq) in 1980 to 4.7 ± 0.94 Mt/yr (131 ± 26 Mt/yr CO 2 -eq) in 2020. An accelerated growth rate was found during 1998-2005, with AMM emissions rapidly increasing by approximately three times, which was consistent with the high number of mine shutdowns. In 2019, we found that AMM emissions had become the fourth largest anthropogenic source in China, higher than the national anthropogenic CH 4 emissions of individual United Nations Framework Convention on Climate Change Annex I countries excluding the United States of America and the Russian Federation. If unabated, China's AMM emissions are projected to peak at 8.7 ± 2.6 Mt/yr in 2040 and reach approximately one-third of China's anthropogenic carbon dioxide emissions in 2060. This study reveals that understanding AMM emissions can help more accurately quantify China's total CH 4 emissions and guide their future mitigation., (Copyright © 2022 Elsevier Inc. All rights reserved.)

Abstract: Methane is a greenhouse gas with a global warming potential 25-fold that of CO2, and animal agriculture is recognized as a source of CH4 to the atmosphere. Dairy farms on the southern High Plains of New Mexico and Texas (USA) are typically open lot, and sources of CH4 are enteric emissions from cattle and wastewater lagoons. Uncovered anaerobic lagoons are identified by the US Environmental Protection Agency as a source of CH4 in dairy manure management systems. Our objective was to quantify summer CH4 emissions from wastewater lagoons of a commercial dairy farm in eastern New Mexico. Research was conducted during 8 days in August (2009) at a 3500 cow open lot dairy farm with flush alleys. Methane concentration over three lagoons (total area of 1.8ha) was measured using open path laser spectroscopy. Background CH4 concentration was measured using a back-flush gas chromatography system with flame ionization. Wind and turbulence data were measured using a three-axis sonic anemometer. Emissions were estimated using an inverse dispersion model. Methane concentrations in the air over the lagoons ranged from 3 to 12ppm, and averaged 5.6ppm, with a background CH4 concentration of 1.83ppm. Methane flux density (i.e., emission rate/unit area) ranged from 165 to 1184μg/m2/s, with a mean daily CH4 flux density of 402kg/ha/d. Methane emission rate averaged 0.211kg/head/d. Uncovered anaerobic lagoons were a source of CH4 emitted from this southern High Plains dairy farm, and lagoons could be a control point for emission reductions. This article is part of the special issue entitled: Greenhouse Gases in Animal Agriculture – Finding a Balance between Food and Emissions, Guest Edited by T.A. McAllister, Section Guest Editors; K.A. Beauchemin, X. Hao, S. McGinn and Editor for Animal Feed Science and Technology, P.H. Robinson. [Copyright &y& Elsevier]

Atmospheric methane, a more effective heat-trapping gas than CO2 that may affect climate change, has its greatest man-made source in the US from municipal solid waste (MSW) landfills. Consequently, the wise management of landfills can reduce these greenhouse gas emissions to the atmosphere. Methane from modern MSW landfills built with composite covers is frequently vented directly to the atmosphere. Biofiltration of landfill gas could oxidize CH4 to CO2 and water. Methane oxidation in old landfills with conventional soil covers can be effective in reducing the amount of CH4 emitted. In this study, comparison of methane emissions from three different landfill covers was conducted. Methane emissions from old landfills constructed with conventional soil covers, modern MSW landfills constructed with composite covers, and modern MSW landfills constructed with composite covers plus biofilters were calculated using the calculated CH4 oxidation rates. The results showed that an average of only 14% of the generated CH4 was emitted from landfills with modern composite covers plus biofilters, and an average of 85% of the generated CH4 was emitted from landfills with conventional covers when 100% of the generated CH4 emissions to the atmosphere from landfills with modern composite covers was assumed. By comparing the CH4 emission rates from three different landfill types, the use of a properly sized biofilter should be an effective technique to reduce CH4 emissions from landfills across the USA and potentially in many other areas of the world. [ABSTRACT FROM AUTHOR]

Measurements focused on seasonal contribution of rice productivity to methane emission were made in three experiments conducted in Texas flooded paddy soils during 1994 and 1995 growing seasons. A total of five rice cultivars representing two distinct groups in methane emission were involved. Over a 10-week period after permanent flooding, total seasonal methane emission was positively correlated with rice above-ground biomass (r2 = 0.845, n = 11). A very strong dependence of daily methane emission on above-ground vegetative biomass (r2 = 0.887, n = 93) and on root biomass (r2 = 0.816, n = 33) was also observed. Calculation from three developmentalperiods (vegetative, reproductive and ripening) of rice plant indicated that more than 75% of total seasonal methane was emitted during the last 5-week period in concert with reproductive and ripening stages, while rice biomass production during the same period-amounted to (approx.) 50% of the seasonal total. According to the correlation of cumulative methane emission with above-ground biomass increment between every two-week interval (r2 = 0.490, n = 93, P = 0.000),the carbon released as methane is approximately equivalent to 3% and4.5% of photosynthetically fixed carbon in the biomass for low and high emission cultivars, respectively. A further investigation showed that these fractions are related to plant growth and development. Thecarbon ratio of methane emitted to net photosynthetic production during vegetative, reproductive, and ripening periods averaged 0.9%, 3.6% and 7.9%, respectively, for low emission cultivars, and 2.0%, 5.0% and 8.3%, respectively, for high emission cultivars. Moreover, the ratio was strongly dependent on plant biomass, resulting in r2 values from 0.775 to 0.907. [ABSTRACT FROM AUTHOR]

Methane emissions at different rice productivity levels were observed from Texas rice paddy soils during the years 1991--95. Analysis of field measurements showed that seasonal methane emission (E) was strongly dependent on soil, cultivar, and rice grain yield. The relationship can be quantitatively described by E (g m-2) = 0.048 xSI x VI x GY. SI is a soil index to characterize the relative effectof soil texture on emission and is linked with soil sand percentage.VI is a variety index to identify the intervarietal difference in methane emission and is related to the amount of methane emission per unit grain yield. GY is grain yield (g m-2). Constant 0.048was derived from the measurements of 10 cultivars planted in 1993. Computed emission applying the relationship is well matched with measured data. The comparison of computed with measured seasonal methane emission over an 80-day period using a total of 32 data sets yields a correlation coefficient r2 of 0.800. In addition, the ratio of seasonal methane emission to net primary productivity was calculated on a carbon to carbon basis, which produces an average value of 2.8%, ranging from 1.2% to 5.4%. A further investigation indicated that the ratio is soil and variety dependent and can be quantitatively explained by C[CH4]/C[NPP] (%) = 3.21 x SI x VI + 0.12 (r2 = 0.738, n = 32). Under the condition of 30% soil sand, this ratio is (approx.) 3% for the majority of cultivars. [ABSTRACT FROM AUTHOR]