Quantification Of CH4 Emissions Research Articles

Toward on-demand measurements of greenhouse gas emissions using an uncrewed aircraft AirCore system

Abstract. This paper evaluates the performance of a multirotor uncrewed aircraft and AirCore system (UAAS) for measuring vertical profiles of wind velocity (speed and direction) and the mole fractions of methane (CH4) and carbon dioxide (CO2), and it presents a use case that combines UAAS measurements and dispersion modeling to quantify CH4 emissions from a dairy farm. To evaluate the atmospheric sensing performance of the UAAS, four field deployments were performed at three locations in the San Joaquin Valley of California where CH4 hotspots were observed downwind of dairy farms. A comparison of the observations collected on board the UAAS and an 11 m meteorological tower show that the UAAS can measure wind velocity trends with a root mean squared error varying between 0.4 and 1.1 m s−1 when the wind magnitude is less than 3.5 m s−1. Findings from UAAS flight deployments and a calibration experiment also show that the UAAS can reliably resolve temporal variations in the mole fractions of CH4 and CO2 occurring over periods of 10 s or longer. Results from the UAAS and dispersion modeling use case further demonstrate that UAASs have great potential as low-cost tools for detecting and quantifying CH4 emissions in near real time.

Quantification of Methane Emissions from Cold Heavy Oil Production with Sand Extraction in Alberta and Saskatchewan, Canada.

Cold heavy oil production with sand (CHOPS) is an extraction process for heavy oil in Canada, with the potential to lead to higher CH4 venting than conventional oil sites, that have not been adequately characterized. In order to quantify CH4 emissions from CHOPS activities, a focused aerial measurement campaign was conducted in the Canadian provinces of Alberta and Saskatchewan in June 2018. Total CH4 emissions from each of 10 clusters of CHOPS wells (containing 22-167 well sites per cluster) were derived using a mass balance computation algorithm that uses in situ wind data measurement on board aircraft. Results show that there is no statistically significant difference in CH4 emissions from CHOPS wells between the two provinces. Cluster-aggregated emission factors (EF) were determined using correspondingly aggregated production volumes. The average CH4 EF was 70.4 ± 36.9 kg/m3 produced oil for the Alberta wells and 55.1 ± 13.7 kg/m3 produced oil for the Saskatchewan wells. Using these EF and heavy oil production volumes reported to provincial regulators, the annual CH4 emissions from CHOPS were estimated to be 121% larger than CHOPS emissions extracted from Canada's National Inventory Report (NIR) for Saskatchewan. The EF were found to be positively correlated with the percentage of nonpiped production volumes in each cluster, indicating higher emissions for nonpiped wells while suggesting an avenue for methane emission reductions. A comparison with recent measurements indicates relatively limited effectiveness of regulations for Saskatchewan compared to those in Alberta. The results of this study indicate the substantial contribution of CHOPS operations to the underreporting observed in the NIR and provide measurement-based EF that can be used to develop improved emissions inventories for this sector and mitigate CH4 emissions from CHOPS operations.

High potential for CH4 emission mitigation from oil infrastructure in one of EU's major production regions

Abstract. Ambitious methane (CH4) emission mitigation represents one of the most effective opportunities to slow the rate of global warming over the next decades. The oil and gas (O&G) sector is a significant source of methane emissions, with technically feasible and cost-effective emission mitigation options. Romania, a key O&G producer within the EU, with the second highest reported annual CH4 emissions from the energy sector in the year 2020 (Greenhouse Gas Inventory Data - Comparison by Category, 2022), can play an important role towards the EU's emission reduction targets. In this study, we quantify CH4 emissions from onshore oil production sites in Romania at source and facility level using a combination of ground- and drone-based measurement techniques. Measured emissions were characterized by heavily skewed distributions, with 10 % of the sites accounting for more than 70 % of total emissions. Integrating the results from all site-level quantifications with different approaches, we derive a central estimate of 5.4 kg h−1 per site of CH4 (3.6 %–8.4 %, 95 % confidence interval) for oil production sites. This estimate represents the third highest when compared to measurement-based estimates of similar facilities from other production regions. Based on our results, we estimate a total of 120 kt CH4 yr−1 (range: 79–180 kt yr−1) from oil production sites in our studied areas in Romania. This is approximately 2.5 times higher than the reported emissions from the entire Romanian oil production sector for 2020. Based on the source-level characterization, up to three-quarters of the detected emissions from oil production sites are related to operational venting. Our results suggest that O&G production infrastructure in Romania holds a massive mitigation potential, specifically by implementing measures to capture the gas and minimize operational venting and leaks.

Methane emission rates averaged over a year from ten farm-scale manure storage tanks

Methane (CH4) emissions from animal manure stored in outdoor tanks are difficult to predict because of several influencing factors. In this study, the tracer gas dispersion method (TDM) was used to quantify CH4 emissions from ten manure storage tanks, along with the collection of supporting information, in order to identify its emission drivers. The dataset included two tanks storing dairy cattle manure, six holding pig manure, and two with digestate from manure-based biogas plants. CH4 emissions from the tanks were measured six to 14 times over a year. Emissions varied from 0.02 to 14.30 kg h−1, or when normalised by the volume of manure stored, emission factors (EFs) varied from 0.05 to 11 g m−3 h−1. Annual average CH4 EFs varied greatly between the tanks, ranging from 0.20 to 2.75 g m−3 h−1. Normalised EFs are similar to literature values for cattle and digested manure, but at the high end of the interval for pig manure. The averaged manure temperature for all tanks varied from 10.6 to 16.4 °C, which was higher than reported in a previous Danish study. Volatile solids (VS) concentration was in average higher for cattle manure (ranging from 3.1 and 4.4 %) than pig manure (ranging from 1.0 to 3.6 %). CH4 emission rates were positively correlated with manure temperature, whereas this was not the case for VS concentration. Annual average EFs were higher for pig than for cattle manure (a factor of 2.5), which was greater than digested manure emissions (a factor of 1.2). For the pig manure storage tanks, CH4 emissions were higher for covered tanks than for uncovered tanks (by a factor of 2.3). In this study, manure storage tanks showed a large disparity in emission rates, driven not only by physical factors, but also by farm management practices.

CH4 emissions from a double-cropping rice field in subtropical China over seven years

Rice paddies are important sources of the greenhouse gas methane (CH4). However, it is difficult to precisely quantify CH4 emissions using the static chamber method because of their discontinuous measurements as well as the spatial and temporal variability of CH4 emissions. To precisely quantify CH4 emissions from rice paddies and gain deep insight into the emission rhythm and environmental effects, a seven-yearlong CH4 flux measurement was carried out continuously using the eddy covariance method in a double cropping rice paddy in subtropical China. The annual CH4 emissions were 42 ± 2 g C m−2. The half hourly CH4 flux was highly correlated with gross primary production (GPP) and environmental factors, such as soil temperature (Ts), and latent heat flux (LE), which explain 47–91% of the CH4 diurnal variation. However, the peak of CH4 generally appeared at dusk during the vigorous growth period, which was quite different from the GPP peak around noon. CH4 flux seasonal dynamic were more complex, with double peaks during the growing season and lower values during the fallow season. Interestingly, in contrast to previous studies of linear or exponential relationships with short-term datasets, daily CH4 and GPP showed a logarithmic relationship at the vegetative stage in this study with seven-year data, this is crucial in improving the model accuracy in estimating annual CH4 emissions. The result implies that long-term observation is necessary to accurately assess CH4 emissions from rice paddy.

Measurement report: Atmospheric CH4 at regional stations of the Korea Meteorological Administration–Global Atmosphere Watch Programme: measurement, characteristics, and long-term changes of its drivers

Abstract. To quantify CH4 emissions at policy-relevant spatial scales, the Korea Meteorological Administration (KMA) started monitoring its atmospheric levels in 1999 at Anmyeondo (AMY) and expanded monitoring to Jeju Gosan Suwolbong (JGS) and Ulleungdo (ULD) in 2012. The monitoring system consists of a cavity ring-down spectrometer (CRDS) and a new cryogenic drying method, with a measurement uncertainty (68 % c.i. (confidence interval)) of ± 0.7–0.8 ppb. To determine the regional characteristics of CH4 at each KMA station, we assessed the CH4 level relative to local background (CH4xs), analyzed local surface winds and CH4 with bivariate polar plots, and investigated CH4 diurnal cycles. We also compared the CH4 levels measured at KMA stations with those measured at the Mt. Waliguan (WLG) station in China and Ryori (RYO) station in Japan. CH4xs followed the order AMY (55.3 ± 37.7 ppb) > JGS (24.1 ± 10.2 ppb) > ULD (7.4 ± 3.9 ppb). Although CH4 was observed in well-mixed air at AMY, it was higher than at other KMA stations, indicating that it was affected not only by local sources but also by distant air masses. Annual mean CH4 was highest at AMY among all East Asian stations, while its seasonal amplitude was smaller than at JGS, which was strongly affected in the summer by local biogenic activities. From the long-term records at AMY, we confirmed that growth rate increased by 3.3 ppb yr−1 during 2006/2010 and by 8.3 ppb yr−1 from 2016 to 2020, which is similar to the global trend. Studies indicated that the recent global accelerated CH4-growth rate was related to biogenic sources. However, δ13CH4 indicates that the CH4 trend in East Asia is derived from both biogenic and fossil fuel sources from 2006 to 2020. We confirmed that long-term high-quality data can help understand changes in CH4 emissions in East Asia.

Assessment of Seasonal Variation in Methane Emissions of Mediterranean Buffaloes Using a Laser Methane Detector.

A direct assessment of the methane (CH4) emission level and its variability factors is needed in each animal species in order to target the best mitigation strategy for the livestock sector. Therefore, the present study aimed to (1) test a laser methane detector (LMD) for the first time in Italian Mediterranean buffaloes (IMB), a non-invasive tool to quantify CH4 emissions; (2) test the effect of season on the emissions; and (3) compare the results measured directly with the ones estimated with the existing equations. CH4 emissions of twenty non-productive IMB, under the same feeding regimen, were monitored for 12 days in summer and winter. Significantly higher THI (74.46 ± 1.88 vs. 49.62 ± 4.87; p < 0.001), lower DMI (2.24 ± 0.04 vs. 2.51 ± 0.03% DMI/kg live weight; p < 0.001) and lower emission intensities (0.61 ± 0.15 vs. 0.75 ± 0.13; p < 0.001) were found during the summer period when compared with winter. LMD was found to be a versatile tool to be used in buffaloes, and it was clear that a summer increase in THI could act as a stressor for the animals, influencing their emissions. In addition, measured emissions were significantly higher than when estimated with the existing equations (p < 0.001), suggesting the need for further research in this area.

Differentiating and Mitigating Methane Emissions from Fugitive Leaks from Natural Gas Distribution, Historic Landfills, and Manholes in Montréal, Canada.

Rapidly reducing urban methane (CH4) emissions is a critical component of strategies aimed at limiting climate change. Individual source measurements provide the details necessary to develop actionable mitigation strategies and are highly complementary to mobile surveys and other top-down methods. Here, we perform 615 individual source measurements in Montréal, Canada, to quantify CH4 emissions from historic landfills, manholes, and fugitive emissions from natural gas (NG) distribution systems. We find that in 2020, historic landfills produced 901 (452 to 1541, 95% c.i.) tons of CH4, manholes emitted 786 (32 to 2602, 95% c.i.) tons of CH4, and NG distribution systems emitted 451 (176-843, 95% c.i.) tons of CH4, placing them all within the top four CH4 sources in Montréal. Methane emissions from both historic landfills and manholes are not accounted for in any greenhouse gas inventory. We find that geochemistry alone cannot positively identify source subcategories (e.g., type of manhole or NG infrastructure) in almost all cases, although C2/C1 ratios can distinguish NG distribution sources from biogenic sources (historic landfills and manholes). Using our individual source measurement data, we show that historic landfills have the greatest potential for CH4 reductions but the highest mitigation costs, unless we target the highest emitting landfills. In contrast, CH4 emissions from manholes can be reduced at low costs, but reduction methods are commercially unavailable. For NG distribution, methods such as increasing repair rates for high-emitting industrial meters can greatly reduce mitigation costs and emissions. Overall, our results highlight the role of individual source measurements in developing actionable CH4 mitigation strategies to meet municipal, regional, and national climate action plans.

Emission Determination by Three Remote Sensing Methods in Two Release Trials

Concentrations of greenhouse gases such as carbon dioxide (CO2), nitrous dioxide (N2O) and methane (CH4) in the atmosphere are rising continuously. The first step to reduce emissions from landfills is to gain better knowledge about the quantities emitted. There are several ways to quantify CH4 emissions at landfills. Comprehensive quality analyses of individual methods for emission rate quantification at landfills are few to date. In the present paper, the authors conducted two field trials with three different remote sensing methods to gain more knowledge about the possibilities and challenges in quantification of CH4 emissions from landfills. One release trial was conducted with released N2O as tracer and CH4 for quality assessment of the methods. In the second trial, the N2O tracer was released on a landfill to gain experience under field conditions. The well-established inverse dispersion modelling method (IDMM) was used based on concentration data of TDLAS (Tunable Diode Laser Absorption Spectroscopy)-instruments and on concentration data of a partly drone based Fourier-Transformation-Infrared-Spectroscopy (FTIR)-instrument. Additionally, a tracer-method with N2O-tracer and FTIR measurements was conducted. In both trials, IDMM based on TDLAS data and FTIR data provided the best results for high emission rates (15% deviation) and low emission rates (47% deviation). However, both methods have advantages, depending on the field of application. IDMM based on TDLAS measurements is the best choice for long-term measurements over several hours with constant wind conditions (8% deviation). The IDMM based on drone based FTIR measurements is the means of choice for measurements under changing wind conditions and where no linear measurement distances are possible.

Quantifying methane emissions from coal mining ventilation shafts using an unmanned aerial vehicle (UAV)-based active AirCore system

A large quantity of CH4 is emitted to the atmosphere via ventilation shafts of underground coal mines. According to the European Pollutant Release and Transfer Register (E-PRTR), hard coal mines in the Upper Silesia Coal Basin (USCB) are a strong contributor (447 kt CH4 in 2017) to the annual European CH4 emissions. However, atmospheric emissions of CH4 from coal mines are poorly characterized, as they are dispersed over large areas. As part of the Carbon Dioxide and CH4 Mission (CoMet) pre-campaign, a study of the USCB's regional CH4 emissions took place in August 2017. We flew a recently developed active AirCore system aboard an unmanned aerial vehicle (UAV) to obtain CH4 mole fractions downwind of a single coal mining ventilation shaft. Besides CH4, we also measured CO2, CO, atmospheric temperature, pressure, and relative humidity. Wind-speed and wind-direction measurements were made using a lightweight balloon-borne radiosonde. Fifteen UAV flights were performed flying perpendicular to the wind direction at several altitude levels, to effectively build a ‘curtain’ of CH4 mole fractions in a two-dimensional plane at a distance between 150 and 350 m downwind of a single ventilation shaft. Furthermore, we have developed an inverse Gaussian approach for quantifying CH4 emissions from a point source using the UAV-based observations, and have applied it as well as the mass balance approach to both simulated data and actual flight data to quantify CH4 emissions. The simulated data experiments revealed the importance of having multiple transects at different altitudes, appropriate vertical spacing between the individual transects, and proper distance between the center height of the plume and the center flight transect. They also showed that the inverse Gaussian approach performed better than the mass balance approach. Our estimate of the CH4 emission rates from the sampled shaft ranges from 0.5 to 14.5 kt/year using a mass balance approach, and between 1.1 and 9.0 kt/year using an inverse Gaussian method. The average difference between the mass balance and the inverse Gaussian approach was 2.3 kt/year. Based on the observed correlation between CO2 and CH4 (R-squared > 0.69), the CO2 emissions from the shaft were estimated to be between 0.3 and 9.8 kt/year. This study demonstrates that the UAV-based active AirCore system provides an effective way of quantifying coal mining shaft emissions of CH4 and CO2.

Temporal and Spatial Variability of Methane Emissions from Texas Open-Lot Beef Cattle Feedyard Pens

HighlightsOpen-lot beef cattle feedyards are a source of greenhouse gas emissions.Pen surface methane emissions were quantified during the cool and warm seasons.Methane was generated in the lower anaerobic layers of the manure pack.Methane emissions decreased after rainfall due to methane oxidation or blocking of pore space.Pen surface methane emissions accounted for <1% of overall feedyard GHG as CO2eq.Abstract. Texas is one of the top beef-producing states, where annually more than five million beef cattle are finished in large feedyards on earthen-surfaced pens. Manure deposited on open-lot pen surfaces can contribute to greenhouse gas (GHG) emissions such as methane (CH4). Two week-long sampling campaigns were conducted in April (cool season) and August (warm season) to quantify CH4 emissions from the feedyard pen surface. Emissions were monitored before and after 12.7 mm simulated rainfall events. Temporal and spatial variabilities in emissions were quantified using automated recirculating flux chambers, a multiplexer system, and a real-time CH4 analyzer. During the cool season, mean CH4 flux was 1.09 (SD ±2.39) and 0.12 (±0.25) g animal-1 d-1 before and after rainfall, respectively. During the warm season, mean CH4 flux was 0.65 (±1.01) and 0.26 (±0.44) g animal-1 d-1 before and after rainfall, respectively. This suggested that CH4 was produced in the lower, anaerobic layer of the manure pack and CH4 emissions were inhibited following rainfall, most likely due to microbial oxidation of CH4 in the upper layers through methanotrophy or from slowing of diffusion by blocking the manure pore space. The overall mean pen surface CH4 flux was 0.53 g animal-1 d-1. This flux accounted for a small percentage (<1%) of the overall estimated feedyard GHG emissions expressed as CO2eq. Thus, efforts to mitigate GHG from open-lot beef cattle feedyards in the Texas Panhandle should focus on sources with higher percentages of overall GHG, such as enteric methane, pen surface nitrous oxide, and nitrous oxide from fertilized cropland. Keywords: Beef cattle, Flux chamber, Greenhouse gas, Manure, Methane, Rainfall.

Comparison of methods to measure enteric methane emissions from ruminants: an integrative review

The agricultural industry is the main emitter of methane (CH4) and nitrous oxide (N2O), gases that each have a global warming potential that is greater than that of CO2 by 23 and 298 times, respectively. On a global scale, enteric fermentation from ruminant animal production (especially of cattle and sheep) is responsible for between 21% and 25% of total anthropogenic CH4 emissions. The search for effective, simple, and fast methods to measure the production of CH4 and other products from ruminal fermentation has been the objective of several studies on ruminant nutrition. Thus, techniques have been developed under experimental conditions of Brazil and other international countries to quantify CH4 emissions of ruminants. The objective of this literature review is to discuss and compare the existing techniques of measuring enteric CH4 from ruminants. Each technique has a shortcoming or disadvantage in its characterization of ruminal fermentation. The ex-situ technique of measuring CH4 from ruminal fermentation has been quite promising, because it facilitates the measurement of CH4 and other fermentation products, such as short chain fatty acids (SOFA). CH4 detection by a portable laser is effective in monitoring fluctuations in emission and is recommended especially for short-term measurements of respiring and eructating animals reared in a feedlot system. Other methods are being improved and better adapted for practical use in the ongoing quest for more efficient uses of ruminal fermentation products.

Advancing Scientific Understanding of the Global Methane Budget in Support of the Paris Agreement

AbstractThe 2015 Paris Agreement of the United Nations Framework Convention on Climate Change aims to keep global average temperature increases well below 2 °C of preindustrial levels in the Year 2100. Vital to its success is achieving a decrease in the abundance of atmospheric methane (CH4), the second most important anthropogenic greenhouse gas. If this reduction is to be achieved, individual nations must make and meet reduction goals in their nationally determined contributions, with regular and independently verifiable global stock taking. Targets for the Paris Agreement have been set, and now the capability must follow to determine whether CH4 reductions are actually occurring. At present, however, there are significant limitations in the ability of scientists to quantify CH4 emissions accurately at global and national scales and to diagnose what mechanisms have altered trends in atmospheric mole fractions in the past decades. For example, in 2007, mole fractions suddenly started rising globally after a decade of almost no growth. More than a decade later, scientists are still debating the mechanisms behind this increase. This study reviews the main approaches and limitations in our current capability to diagnose the drivers of changes in atmospheric CH4 and, crucially, proposes ways to improve this capability in the coming decade. Recommendations include the following: (i) improvements to process‐based models of the main sectors of CH4 emissions—proposed developments call for the expansion of tropical wetland flux measurements, bridging remote sensing products for improved measurement of wetland area and dynamics, expanding measurements of fossil fuel emissions at the facility and regional levels, expanding country‐specific data on the composition of waste sent to landfill and the types of wastewater treatment systems implemented, characterizing and representing temporal profiles of crop growing seasons, implementing parameters related to ruminant emissions such as animal feed, and improving the detection of small fires associated with agriculture and deforestation; (ii) improvements to measurements of CH4 mole fraction and its isotopic variations—developments include greater vertical profiling at background sites, expanding networks of dense urban measurements with a greater focus on relatively poor countries, improving the precision of isotopic ratio measurements of 13CH4, CH3D, 14CH4, and clumped isotopes, creating isotopic reference materials for international‐scale development, and expanding spatial and temporal characterization of isotopic source signatures; and (iii) improvements to inverse modeling systems to derive emissions from atmospheric measurements—advances are proposed in the areas of hydroxyl radical quantification, in systematic uncertainty quantification through validation of chemical transport models, in the use of source tracers for estimating sector‐level emissions, and in the development of time and space resolved national inventories. These and other recommendations are proposed for the major areas of CH4 science with the aim of improving capability in the coming decade to quantify atmospheric CH4 budgets on the scales necessary for the success of climate policies.

Large Fugitive Methane Emissions From Urban Centers Along the U.S. East Coast.

Urban emissions remain an underexamined part of the methane budget. Here we present and interpret aircraft observations of six old and leak‐prone major cities along the East Coast of the United States. We use direct observations of methane (CH4), carbon dioxide (CO2), carbon monoxide (CO), ethane (C2H6), and their correlations to quantify CH4 emissions and attribute to natural gas. We find the five largest cities emit 0.85 (0.63, 1.12) Tg CH4/year, of which 0.75 (0.49, 1.10) Tg CH4/year is attributed to natural gas. Our estimates, which include all thermogenic methane sources including end use, are more than twice that reported in the most recent gridded EPA inventory, which does not include end‐use emissions. These results highlight that current urban inventory estimates of natural gas emissions are substantially low, either due to underestimates of leakage, lack of inclusion of end‐use emissions, or some combination thereof.

China's Urban Methane Emissions From Municipal Wastewater Treatment Plant

AbstractThe increased number and capacity of municipal wastewater treatment plants (WWTPs) in China has driven the emission of methane (CH4). Few studies have focused on quantification of CH4 emissions from municipal WWTPs of different cities and analysis of socioeconomic factors influencing the quantity of emissions. Here we estimated CH4 emissions from WWTPs in China for 229 prefectural‐level cities, based on data from 2,019 working municipal WWTPs. The results show the total CH4 emissions to be 1,169.8 thousand tons (29.2 MtCO2e) in 2014, which is over three times that of the municipal WWTPs in the United States in 2016. Large cities along the east coast regions had larger CH4 emissions in absolute and per capita terms. Correlation analysis shows that cities with higher gross domestic product, household food consumption expenditure, or household consumption expenditure produced more degradable organics in wastewater, thus more CH4 emissions. Measures to control the sources of degradable organics and regulate WWTP processes with less emission factor are key to mitigate CH4 emissions. In addition to aerobic or anaerobic wastewater treatment systems, factors such as wastewater temperature, length of sewer, and the addition of nitrate that influencing emission factor are suggested to be involved in CH4 emission modeling.

Methane Emissions from the Marcellus Shale in Southwestern Pennsylvania and Northern West Virginia Based on Airborne Measurements

AbstractNatural gas production in the United States has increased rapidly over the past decade, along with concerns about methane (CH4) fugitive emissions and its climate impacts. Quantification of CH4 emissions from oil and natural gas (O&NG) operations is important for establishing scientifically sound policies for mitigating greenhouse gases. We use the aircraft mass balance approach for three flight experiments in August and September 2015 to estimate CH4 emissions from O&NG operations over the southwestern Marcellus Shale. We estimate a mean CH4 emission rate as 21.2 kg/s with 28% coming from O&NG operations. The mean CH4 emission rate from O&NG operations was estimated to be 1.1% of total NG production. The individual best‐estimate emission rates from the three flight experiments ranged from 0.78 to 1.5%, with overall limits of 0% and 3.5%. These emission rates are at the low end of other top‐down studies, but consistent with the few observational studies in the Marcellus Shale region as well as the U.S. Environmental Protection Agency CH4 inventory. A substantial source of CH4 (~70% of observed CH4 emissions) was found to contain little ethane, possibly due to coalbed CH4 emitted either directly from coal mines or from wells drilled through coalbed layers in O&NG operations. Recent regulations requiring capture of gas from the completion‐venting step of hydraulic fracturing appear to have reduced the atmospheric release of CH4. Our study suggests that for a 20‐year time scale, energy derived from the combustion of natural gas extracted from this region likely exerts a net climate benefit compared to coal.

Large methane emissions from natural gas vehicles in Chinese cities

In recent years, cities in developing countries have become more and more reliant on natural gas as a clean energy source for transportation to reduce air pollution. In this study, we used street-level measurement of atmospheric CH4 and CO2 concentrations to quantify CH4 emissions from natural gas vehicles (NGVs) in China. These measurements were made in eight cities (Chengdu, Urumqi, Jinan, Nanjing, Lanzhou, Harbin, Guangzhou) with varying sizes of NGV fleet. A traffic CH4:CO2 emission ratio (TER) was determined via linear regression of CH4 versus CO2 concentration data obtained from each street transect. The TER value was combined with the ratio of NGVs in the street traffic in a mathematical model to obtain the CH4 emission factor for NGVs. Results show that the TER increases with increasing NGV ratio and decreases with increasing traffic speed. Overall, the NGV CH4 emission factor in these cities is 0.022 ± 0.0033 kg m−3, about 8 times the Intergovernmental Panel on Climate Change (IPCC) default factor for NGVs and is more than 100% higher than the mean NGV tailpipe emission factor found in the published literature. That the overall emission factor is much larger than the tailpipe emission factor indicates that on-road vehicle gas leakage is a widespread problem. A business-as-usual scenario suggests that NGVs may emit 1.23 Tg CH4 yr−1 in 2030, or about 3% of China's current total anthropogenic emission. Our study suggest that curbing the emissions from this sector should be a high priority for global climate mitigation efforts.

Year-round methane emissions from liquid dairy manure in a cold climate reveal hysteretic pattern

Liquid dairy manure storage is favourable for methane (CH4) production and a significant source of this greenhouse gas. Manure storage in cold climates faces large temperature variations over the course of a year, and added on-farm complexities in manure loading require year-round measurements which are currently lacking. The objectives of this study were to 1) quantify CH4 emissions from farm-scale liquid dairy manure storage in a cold climate, 2) investigate the effect of manure temperature on CH4 emissions, and 3) compare measured CH4 emissions with values derived from the USEPA temperature model. Methane fluxes were measured from Aug 2010 to early Nov 2011 on a commercial farm in Ontario, Canada, using a micrometeorological mass balance method which relied on 3 towers with air intakes at 4 heights placed around the storage tank. Manure temperature and volatile solid content (VS) were also measured. Monthly CH4 emissions scaled by VS decreased from 43.8 g CH4 kg−1 VS in Sep 2010 to 5.3 g CH4 kg−1 VS in Jan 2011, and were correlated with temperature (r2 = 0.94). Manure temperature increased starting in Feb 2011, but the increase in CH4 emissions was delayed to Jul 2011. Hence, the response of CH4 emissions to temperature showed a hysteretic pattern where emissions in the warming branch after the winter (Apr-Jun) were significantly lower than emissions in the cooling branch after the summer (Sep-Nov) despite similar temperatures. The temperature model predicted emissions during the cooling phase well, but overpredicted emissions during the warming phase, indicating other limiting factors for microbial CH4 production. Thus, the annual predicted CH4 emissions were about 2.3× larger than the measured values. The newly observed hysteresis effect should be considered when predicting CH4 emissions from stored manure.

Methane emissions from the Marcellus Shale in southwestern Pennsylvania and northern West Virginia based on airborne measurements.

Natural gas production in the U.S. has increased rapidly over the past decade, along with concerns about methane (CH4) leakage (total fugitive emissions), and climate impacts. Quantification of CH4 emissions from oil and natural gas (O&NG) operations is important for establishing scientifically sound, cost‐effective policies for mitigating greenhouse gases. We use aircraft measurements and a mass balance approach for three flight experiments in August and September 2015 to estimate CH4 emissions from O&NG operations in the southwestern Marcellus Shale region. We estimate the mean ± 1σ CH4 emission rate as 36.7 ± 1.9 kg CH4 s−1 (or 1.16 ± 0.06 Tg CH4 yr−1) with 59% coming from O&NG operations. We estimate the mean ± 1σ CH4 leak rate from O&NG operations as 3.9 ± 0.4% with a lower limit of 1.5% and an upper limit of 6.3%. This leak rate is broadly consistent with the results from several recent top‐down studies but higher than the results from a few other observational studies as well as in the U.S. Environmental Protection Agency CH4 emission inventory. However, a substantial source of CH4 was found to contain little ethane (C2H6), possibly due to coalbed CH4 emitted either directly from coalmines or from wells drilled through coalbed layers. Although recent regulations requiring capture of gas from the completion venting step of the hydraulic fracturing appear to have reduced losses, our study suggests that for a 20 year time scale, energy derived from the combustion of natural gas extracted from this region will require further controls before it can exert a net climate benefit compared to coal.

Factors affecting methane emissions from rice production in the Lower Mississippi river valley, USA

Rice (Oryza sativa L.) plays a key role in sustaining global food security; however, rice production also accounts for a significant proportion of global methane (CH4) emissions, a major greenhouse gas involved in altering global climate. Many previous studies have quantified the proportion of CH4 emissions by independently evaluating factors such as soil texture and cultivars – an approach that has led to potentially biased estimates of their actual contribution to total emissions. Most of these studies have not considered the influence of the preceding crop or growing-season weather that could lead to a significant variation in carbon budgets. The main objective of this study was to identify the key edaphic, cultivar, and environmental factors and determine their proportional contributions towards CH4 emissions in direct-seeded, rice-based cropping systems. A multiple regression model was developed to quantify CH4 emissions as a function of temperature (both day and night independently and in combination) and other weather variables, soil (silt-loam-surface-textured Albaqualf and clay-surface-textured Epiaquert), cultivar (conventional and hybrid), and cropping system (rice-rice and soybean [Glycine max L.]-rice). Results showed that (i) the Albaqualf emitted 211% more CH4-C than the Epiaquert (P<0.01; (ii) inbred cultivars accounted for 55 to 70% more CH4-C emissions than hybrid cultivars (P<0.01); (iii) soybean-rice rotations produced 58% less CH4-C emissions than rice-rice rotations (P<0.01); and (iv) future warming scenarios increased CH4-C emissions by up to 53%. To mitigate CH4 emissions, future research and crop production strategies that prioritize rice production on clay-surface-textured soils and use alternatives to a rice-rice rotation are recommended.