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Using natural gas as a fuel in the road freight sector instead of diesel could cut greenhouse gas and air quality emissions but the switch alone is not enough to meet UK climate targets. A life cycle assessment (LCA) has been conducted comparing natural gas trucks to diesel, biodiesel, dimethyl ether and electric trucks on impacts to climate change, land use change, air quality, human health and resource depletion. This is the first LCA to consider a full suite of environmental impacts and is the first study to estimate what impact natural gas could have on reducing emissions form the UK freight sector. If LNG is used, climate change impacts could be up to 33% lower per km and up to 12% lower per kWh engine output. However, methane emissions will eliminate any benefits if they exceed 1.5–3.5% of throughput for typical fuel consumption. For non-climate impacts, natural gas exhibits lower emissions (11–66%) than diesel for all indicators. Thus, for natural gas climate benefits are modest. However, emissions of CO, methane and particulate matter are over air quality limits set for UK trucks. Of the other options, electric and biodiesel trucks perform best in climate change, but are the worst with respect to land use change (which could have significant impacts on overall climate change benefits), air quality, human toxicity and metals depletion indicators. Natural gas could help reduce the sector's emissions but deeper decarbonization options are required to meet 2030 climate targets, thus the window for beneficial utilisation is short. Unlabelled Image • LNG trucks have 17–21% lower GWP than diesel per km. • LNG has lower impacts than diesel across all indicators per km. • CNG has higher impacts than diesel across most indicators. • Methane slip must be <3.5% for LNG to have lower GWP than diesel. • Natural gas itself not enough to help UK meet emission targets. [ABSTRACT FROM AUTHOR]

Abstract Greenhouse gases (GHGs) produced by the extraction of natural gas are an important contributor to lifecycle emissions and account for a significant fraction of anthropogenic methane emissions in the USA. The timing as well as the magnitude of these emissions matters, as the short term climate warming impact of methane is up to 120 times that of CO 2. This study uses estimates of CO 2 and methane emissions associated with different upstream operations to build a deterministic model of GHG emissions from conventional and unconventional gas fields as a function of time. By combining these emissions with a dynamic, techno-economic model of gas supply we assess their potential impact on the value of different types of project and identify stranded resources in various carbon price scenarios. We focus in particular on the effects of different emission metrics for methane, using the global warming potential (GWP) and the global temperature potential (GTP), with both fixed 20-year and 100-year CO 2 -equivalent values and in a time-dependent way based on a target year for climate stabilisation. We report a strong time dependence of emissions over the lifecycle of a typical field, and find that bringing forward the stabilisation year dramatically increases the importance of the methane contribution to these emissions. Using a commercial database of the remaining reserves of individual projects, we use our model to quantify future emissions resulting from the extraction of current US non-associated reserves. A carbon price of at least 400 USD/tonne CO 2 is effective in reducing cumulative GHGs by 30–60%, indicating that decarbonising the upstream component of the natural gas supply chain is achievable using carbon prices similar to those needed to decarbonise the energy system as a whole. Surprisingly, for large carbon prices, the choice of emission metric does not have a significant impact on cumulative emissions. [ABSTRACT FROM AUTHOR]

Abstract Wastewater treatment is an important source of methane (CH 4) emissions. In most large-size aerobic treatment plants, the excess sludge is digested in anaerobic reactors (AD), with the concomitant CH 4 emissions. The guidelines of the Intergovernmental Panel on Climate Change (IPCC) have been adopted worldwide for quantifying the national emission inventories, which include wastewater treatment plants (WWTP) as a key category. The IPCC recommends using default emission factors (Tier 1) for countries with limited available data (such as Mexico and most developing countries). However, these estimates have a high degree of uncertainty, owing to the lack of reliable information about the operation process and local environmental conditions. In order to reduce uncertainty in the estimation of CH 4 emission from WWTP in Mexico, a country-specific emission factor was determined for AD associated with activated sludge process. This was accomplished with on-site data obtained from the AD of six activated sludge WWTP. In addition, the measured CH 4 emissions were compared to those resulting from the application of the IPCC Tier 1 method, using the recommended default methane correction factor (MCF: 0.8) as well as alternate values (0.32 and 0.26) recently proposed by the authors. Results show that the IPCC Tier 1 method, using the recommended MCF, highly overestimate CH 4 emissions compared with the values obtained on-site. In contrast, the alternate MCF achieved better estimations than the IPCC-recommended MCF, much closer to the observed emission values. The CH 4 emission factor proposed as country (Mexico) specific value is 0.49 kg CH 4 /kg BOD rem , which would allow the application of IPCC Tier 2 method. By doing so, the uncertainty associated with CH 4 emission from aerobic treatment plants with AD would be reduced. This, in turn, would provide important information for implementing appropriate CH 4 mitigation strategies for the water sector. Graphical abstract Unlabelled Image Highlights • Improved estimates of national CH 4 emission inventories from wastewater are needed. • A country-specific CH 4 EF for anaerobic sludge digesters is proposed for Mexico. • IPCC Tier 1 method, with the recommended MCF, generally overestimates CH 4 emissions. • Tier 1 method using alternate MCF reached closer estimations to on-site emissions. • It is recommended to adopt the alternate MCF for anaerobic sludge digesters (Tier 1). [ABSTRACT FROM AUTHOR]

Wastewater treatment (WWT) may be an important source of methane (CH 4 ), a greenhouse gas with significant global warming potential. Sources of CH 4 emissions from WWT facilities can be found in the water and in the sludge process lines. Among the methodologies for estimating CH 4 emissions inventories from WWT, the more adopted are the guidelines of the Intergovernmental Panel on Climate Change (IPCC), which recommends default emission factors (Tier 1) depending on WWT systems. Recent published results show that well managed treatment facilities may emit CH 4 , due to dissolved CH 4 in the influent wastewater; in addition, biological nutrient removal also will produce this gas in the anaerobic (or anoxic) steps. However, none of these elements is considered in the current IPCC guidelines. The aim of this work is to propose modified (and new) methane correction factors (MCF) regarding the current Tier 1 IPCC guidelines for CH 4 emissions from aerobic treatment systems, with and without anaerobic sludge digesters, focusing on intertropical countries. The modifications are supported on in situ assessment of fugitive CH 4 emissions in two facilities in Mexico and on relevant literature data. In the case of well-managed centralized aerobic treatment plant, a MCF of 0.06 (instead of the current 0.0) is proposed, considering that the assumption of a CH 4 -neutral treatment facility, as established in the IPCC methodology, is not supported. Similarly, a MCF of 0.08 is proposed for biological nutrient removal processes, being a new entry in the guidelines. Finally, a one-step straightforward calculation is proposed for centralized aerobic treatment plants with anaerobic digesters that avoids confusion when selecting the appropriate default MCF based on the Tier 1 IPCC guidelines. [ABSTRACT FROM AUTHOR]

Crop straw incorporation has become a prevailing agricultural practice that guarantees the food production and security. There is a significant body of work on the effects of straw incorporation on the methane (CH 4 ) emissions in paddy fields. However, it is unclear whether there are diverse links between CH 4 emission dynamics and incorporations of different organic compound classes of straw to paddy fields. In this study, soil incubations were conducted to assess the respective effect of incorporations of hydrolysable amino acid (HAA), dilute-acid extractable carbohydrate (DAC), lipid and acid-insoluble organic matter (AIOM) fractions of rice straw on the CH 4 emission in paddy soil. It is revealed that incorporations of HAA and DAC fractions exert the greatest intensities to stimulate the CH 4 emissions, which mainly takes place in the early period of incubation; on contrary, the incorporation of lipid fraction exerts the lowest intensity and mainly takes place in the late period. The pattern of CH 4 emission after incorporation of AIOM fraction occurs peaks both in the early and late periods of incubation. Our findings highlight that the time of occurrence and intensity of effects of rice straw incorporation on CH 4 emissions vary significantly depending on the different organic compound classes of rice straw, which may be key to proposing a promising management strategy for mitigating CH 4 emissions in paddy fields in the context of straw incorporation. [ABSTRACT FROM AUTHOR]

An emerging approach to limit rice uptake and grain As targets the shared root-uptake pathway between As(III) and Si. We amended rice paddy mesocosms with Si-rich rice residues (husk and husk char) or silicate fertilizer to evaluate the impact of different Si sources on rice uptake of Si and As including As speciation in grain under background soil As. For a systems-approach, we also measured plant biomass, rice yield, porewater chemistry, mesocosm-scale CH 4 and CO 2 fluxes, plant concentrations of nutrients and metals, and root Fe plaque mineralogy. Relative to the control, Si-rich amendments increased plant Si and proportion of ferrihydrite on root plaque, decreased root-to-shoot Mn transfer and As uptake, and shifted grain As from inorganic to organic As. The charred husk treatment, which resulted in the most Si accumulation in rice shoots, most decreased plant As and grain As. Husk treatment led to the highest CH 4 emissions, but all treatments had lower CH 4 emissions than has been reported for straw treatments. Collectively, Si-rich amendments performed similarly across several biogeochemical benchmarks, with charred husk best restricting plant As, suggesting these amendments can be used to reduce toxicity of As from rice grain while maintaining yield. [ABSTRACT FROM AUTHOR]

Methane (CH 4 ) emissions by human activities have more than doubled since the 1700s, and they contribute to global warming. One of the sources of CH 4 is produced by incomplete oxidation of feed in the ruminant's gut. Domestic ruminants produce most of the emissions from animal sources, but emissions by wild ruminants have been poorly estimated. This study (i) scales CH 4 against body mass in 503 experiments in ruminants fed herbage, and assesses the effect of different sources of variation, using published and new data; and (ii) it uses these models to produce global estimates of CH 4 emissions from wild ruminants. The incorporation of phylogeny, diet and technique of measuring in to a model that scales log 10 CH 4 g d − 1 against log 10 body mass (kg), reduces the slope, from 1.075 to 0.868, making it not significantly steeper than the scaling coefficient of metabolic requirements to body mass. Scaling models that include dry matter intake (DMI) and dietary fiber indicate that although both increase CH 4 , dietary fiber depresses CH 4 as the levels of DMI increases. Cattle produces more CH 4 per unit of DMI than red deer, sheep or goat, and there are no significant differences between CH 4 produced by red deer and sheep. The average estimates of global emissions from wild ruminants calculated using different models are smaller (1.094–2.687 Tg y − 1 ) than those presented in the reports of the Intergovernmental Panel on Climate Change (15 Tg yr − 1 ). Potential causes to explain such discrepancy are the uncertainty on the world's wild ruminant population size, and the use of methane output from cattle, a high methane producer, as representative methane output of wild ruminants. The main limitation researchers' face in calculating accurate global CH 4 emissions from wild ungulates is a lack of reliable information on their population sizes. [ABSTRACT FROM AUTHOR]

In comparative life cycle assessments of agricultural production systems, analyses of both the trade-offs between environmental impacts and crop productivity and of the uncertainties specific to agriculture such as fluctuations in greenhouse gas (GHG) emissions and crop yields are crucial. However, these two issues are usually analyzed separately. In this paper, we present a framework to link trade-off and uncertainty analyses; correlated uncertainties are integrated into environment-productivity trade-off analyses. We compared three rice production systems in Japan: a system using a pelletized, nitrogen-concentrated organic fertilizer made from poultry manure using closed-air composting techniques (high-N system), a system using a conventional organic fertilizer made from poultry manure using open-air composting techniques (low-N system), and a system using a chemical compound fertilizer (conventional system). We focused on two important sources of uncertainties in paddy rice cultivation—methane emissions from paddy fields and crop yields. We found trade-offs between the conventional and high-N systems and the low-N system and the existence of positively correlated uncertainties in the conventional and high-N systems. We concluded that our framework is effective in recommending the high-N system compared with the low-N system, although the performance of the former is almost the same as the conventional system. [ABSTRACT FROM AUTHOR]

Cold heavy oil production with or without sand (CHOPS, or CHOP) are prevalent methods of oil extraction in western Canada. CHOP(S) sites account for over 40% of all reported vented methane (CH 4 ) from oil production in Alberta, and high rates of CH 4 emissions have been confirmed in independent measurement studies. In this study, we used truck-based surveys coupled with qualitative optical gas imaging (OGI) to quantify and characterize methane emission rates and sources at nearly 1350 and 940 well sites in two major CHOP(S) developments respectively in 2016 and 2018. The studies were conducted in Lloydminster, Alberta, where produced gases are sweet (i.e., <0.5% sulfur) and non-olfactory, and Peace River, Alberta, where regulations were implemented in 2017 to manage sour (i.e., >0.5% sulfur) odorous emissions (hydrogen sulfide, BTEX, etc.). Based on results from all surveys, in Peace River, 43% of measured sites were emitting CH 4 , compared to 37% in Lloydminster. The measured CH 4 emission rates in Peace River were, however, significantly lower than in Lloydminster for both years, and had fallen from 2016 to 2018. In 2018, emissions in Lloydminster were fairly unchanged relative to previous measurements taken in 2016. OGI showed that tanks in Peace River continue to emit CH 4 despite regulatory interventions and a reported venting rate of zero. The continued emissions were thus classified as "unintended venting", which can be a consequence of the non-routine malfunction (e.g., inappropriate operator action or poor equipment design/sizing) of vapor recovery equipment. Mitigation strategies implemented in Peace River targeting olfactory compounds were beneficial in reducing and keeping CH 4 emissions lower, since these gases are co-emitted, and could even be co-regulated provincially. Reciprocal to that, we might expect future air quality improvements as a consequence of the new provincial requirements to reduce CH 4 emissions under amended Directives 060 and 017., Competing Interests: Declaration of competing interest The authors declare no competing financial interests. The research presented in this manuscript was exclusively under the contracts to the authors' academic affiliations., (Copyright © 2021 Elsevier B.V. All rights reserved.)

With the expansion of economic globalization and the growth of international trade, the pulling effect of household consumption to global anthropogenic CH 4 emissions related to production activities is becoming increasingly evident. This paper adopts a new perspective from the household-consumption side to investigate the CH 4 emissions of major economies in 2014 and compares it with the scenario under the final-demand-based perspective by combing the world input-output database and the latest emission data from the UNFCCC and EDGAR v5.0 database. Budgets of CH 4 emissions for 43 economies are established and trade connections & balances among major economies are explored. Results show that consumption-driven economies are allocated more CH 4 emissions in the household-consumption-based accounting (HCBA) framework compared to the final-demand-based accounting (FDBA) framework. The total trade-related transfer of CH 4 emissions is shown to sum up to 19% and 27% of the global total under the HCBA and FDBA frameworks, respectively. The household-consumption-based CH 4 emissions of China, India, Indonesia and Mexico are much lower than their final-demand-based CH 4 emissions, while the converse is true for the United States, Russia, Japan, the United Kingdom and Germany. The new accounting framework provides a new view to understand trade-related CH 4 emissions of major economies and to identify the role of household consumption in global supply chains, offering important implications for greenhouse gas emission mitigation. Unlabelled Image • Latest CH 4 emission inventories for major economies in 2014 are provided. • Household-consumption-based accounting of CH 4 emissions is firstly conducted. • The findings are compared with those under the final-demand-based accounting. • Consumption-oriented economies should take more responsibility for CH 4 reduction. [ABSTRACT FROM AUTHOR]

The use of sulfuric acid (SA) for reducing greenhouse gases (GHGs, mainly CH 4) emissions in manure management encounters with problems related with safety issue and increased H 2 S emissions. In the present study, citric acid (CA) as an alternative to SA was assessed in the lab-scale experiment at various dosages (pH 5.0–7.0), and then confirmed in the pilot-scale tank (effective volume of 30 ton). During 35 d of pig slurry (PS) storage at 30 °C, it was found that the CA addition to initial pH down to 6.5 could lead negligible reduction, while 85–99% and 48–72% reduction of CH 4 and H 2 S emissions were achieved at pH ≤ 6.0, respectively. The similar reduction performance was confirmed (control vs. pH 6.0) in the pilot-scale test, but, interestingly, two times higher CH 4 emissions of 123.7 kg CO 2 eq./ton PS was detected caused by the automatic temperature increase (≥35 °C). The pH of acidified PS did not exceed 6.5 during the whole storage period, while it was maintained 7.3–7.7 in the control. A continuous AD reactor fed with acidified PS exhibited a higher CH 4 yield of 10.0 m3 CH 4 /ton PS, compared to the control (5.7 m3 CH 4 /ton PS), due to the preservation of organic matters and added CA. In overall, about 8.5 [(4.4, storage) + (4.1, biogas)] kg of CH 4 /ton PS was generated from raw PS and it was reduced to 7.8 [(0.7, storage) + (7.1, biogas)] kg of CH 4 /ton PS by CA-acidification. Despite the carbon footprint for manufacturing CA, it was calculated that GHG reduction of 107 kg CO 2 eq./ton PS could be attained by CA-acidification. In terms of economic profit, it was estimated that 6.3 USD/ton PS can be gained by CA-acidification, while it was 2.4 USD/ton PS in case of control. Unlabelled Image • Citric acid addition for reducing CH 4 and H 2 S emissions during pig slurry storage. • CH 4 and H 2 S emissions reduction by 85–99% and 48–72% at pH ≤ 6.0, respectively. • Two times higher CH 4 emissions in the pilot-scale test compared to lab-scale one. • Digester fed with stored acidified-slurry exhibited 1.7 times higher CH 4 yield. • Further GHG reduction of 107.3 kg CO 2 eq./ton PS and profit of 3.9 USD/ton PS [ABSTRACT FROM AUTHOR]

We tested the effect of increasingly diverse combinations of tanniferous legumes (birdsfoot trefoil-BFT, sainfoin-SF) and alfalfa (ALF) on cattle performance, methane (CH 4) emissions and nitrogen (N) balance. Pairs of heifers (401 ± 49.6 kg) grazed three spatial replications of 7 treatments (n = 3/treatment): monocultures (BFT, SF, ALF) and all possible 2- and 3-way choices among strips of these legumes in a completely randomized block design of two 15-d periods during 2 consecutive years. Average daily gains (ADG) of heifers grazing the tanniferous legumes (1.05 kg/d) were 40% greater (p < 0.10) than of heifers grazing ALF (0.74 kg/d) during the first year. Heifers grazing the 3-way choice had greater intakes (10.4 vs 7.8 kg/d; p = 0.064) and ADG (1.21 vs. 0.95 kg/d, p = 0.054) than those grazing monocultures, suggesting a nutritional synergism among legumes. The average CH 4 emissions for legume monocultures vs. 2- and 3- way choices was 222 vs. 202 and 162 g/kg BW gain (p > 0.10), respectively. For heifers grazing SF and BFT compared with ALF, blood urea N was less (14.3 and 16.8 vs 20.8 mg/dL; p < 0.05) as were urinary N concentrations (3.7 and 3.5 vs 6.0 g/L; p < 0.05), but fecal N concentrations were greater (34.5 and 35.5 vs 30.5 g/kg, respectively; p < 0.05). Combining both tanniferous legumes (SF-BFT) led to the greatest declines in urinary N (2.24 g/L) and urea-N (1.71 g/L) concentration, suggesting that different types of tannins in different legumes result in associative effects that enhance N economy. In addition, heifers grazing 3-way choices partitioned less N into urine (40.7 vs 50.6%; p = 0.037) and retained more N (36.1 vs 25.2%, p = 0.046) than heifers grazing monocultures. In summary, combinations of tanniferous legumes with alfalfa improved animal performance and reduced environmental impacts relative to monocultures, resulting in a more sustainable approach to beef production in pasture-based finishing systems. Unlabelled Image • Beef production is criticized due to environmental pollution and emissions of GHG. • Tanniferous legumes may reduce urinary N excretions relative to alfalfa. • Grazing tanniferous legumes along with alfalfa increase N retention and BW gains. • Associative effects between different tannins led to the lowest urinary [N]. • Grazing a diversity of legumes reduces environmental impacts relative to monocultures. [ABSTRACT FROM AUTHOR]

Methane is considered to be one of the main causes of global warming. Quantifying methane emissions from landfills is the subject of many studies, especially emphasizing the role of two parameters: methane generation potential capacity (L 0), methane generation rate (k). In this study, we propose a system of integrated environmental information and mathematical model named EnLandFill (EN vironmental information – model integrated system for air emission and dispersion estimation from LandFill) that allows calculation L 0 from database and experimentally to determine optimal k. To perform experimental calculations, meteorological data were extracted from the WRF model and verified with real measurements. The novelty of this study lies in the inferred database system, the math model bank, especially the dispersion model, taking note account the complex topography, meteorological factors that change by the hour. EnLandFill was applied to Phuoc Hiep Landfill (PHLF) in Ho Chi Minh City as a case study, the results have identified the amount of methane released that is equal to 44,094,697.88 m3/year in 2019, but EnLandFill is designed to be general, applicable to other landfill entities. Unlabelled Image • Proposed a system of integrated environmental information and mathematical model named EnLandFill that allows calculate the potential methane generation capacity and experimentally to determine optimal methane generation rate. • The proposed system allows the assessment of the scope and extent of impacts caused by the dispersion of toxic substances from landfills. • Using the proposed system it is allowed calculate the amount of methane emitted from Phuoc Hiep landfill (PHLF) - the largest waste treatment complexes in Hochiminh city for 2019 is 44,094,697.88 m3/year. [ABSTRACT FROM AUTHOR]

Intensively managed grasslands are large sources of the potent greenhouse gas nitrous oxide (N 2 O) and important regulators of methane (CH 4) consumption and production. The predicted increase in flooding frequency and severity due to climate change could increase N 2 O emissions and shift grasslands from a net CH 4 sink to a source. Therefore, effective management strategies are critical for mitigating greenhouse gas emissions from flood-prone grasslands. We tested how repeated flooding affected the N 2 O and CH 4 emissions from 11 different plant communities (Festuca arundinacea, Lolium perenne, Poa trivialis, and Trifolium repens in monoculture, 2- and 4-species mixtures), using intact soil cores from an 18-month old grassland field experiment in a 4-month greenhouse experiment. To elucidate potential underlying mechanisms, we related plant functional traits to cumulative N 2 O and CH 4 emissions. We hypothesized that traits related with fast nitrogen uptake and growth would lower N 2 O and CH 4 emissions in ambient (non-flooded) conditions, and that traits related to tissue toughness would lower N 2 O and CH 4 emissions in flooded conditions. We found that flooding increased cumulative N 2 O emissions by 97 fold and cumulative CH 4 emissions by 1.6 fold on average. Plant community composition mediated the flood-induced increase in N 2 O emissions. In flooded conditions, increasing abundance of the grass F. arundinacea was related with lower N 2 O emissions; whereas increases in abundance of the legume T. repens resulted in higher N 2 O emissions. In non-flooded conditions, N 2 O emissions were not clearly mediated by plant traits related with nitrogen uptake or biomass production. In flooded conditions, plant communities with high root carbon to nitrogen ratio were related with lower cumulative N 2 O emissions, and a lower global warming potential (CO 2 equivalent of N 2 O and CH 4). We conclude that plant functional traits related to slower decomposition and nitrogen mineralization could play a significant role in mitigating N 2 O emissions in flooded grasslands. Unlabelled Image • Flooding increases N 2 O from managed grasslands • Plant community composition explains flood-induced N 2 O • Festuca arundinacea decreased, and Trifolium repens increased, flood-induced N 2 O • Higher root C:N is related to lower flood-induced N 2 O [ABSTRACT FROM AUTHOR]

As the world's largest CH 4 emitter, China's CH 4 emissions contribute to climate change more than the amount emitted by many developed countries combined. The rapid growth of China's coal demand has important implications for CH 4 emissions from coal mining or coal mine methane (CMM) emissions. This paper aims to present an overview of bottom-up estimation of China's CMM emissions, including the trend in the last four decades and the limitations of current understanding on CH 4 emissions. Although characterized by significant differences in inventory compilation, statistically, the total CMM emissions rose from 4.64 to 16.41 Tg with a peak of 21.48 Tg from 1980 to 2016. Large discrepancies of inventory results existed in previous studies, which were affected by the coverage of emission sources, emission factors and activity-level data. The disagreements can be largely attributable to the emission factors of underground mining, which contain substantial variances in both spatial and temporal dimensions. To develop more reliable CMM inventories and make targeted mitigation measures, more attention should be paid to the transparency of the estimated results, coal statistics, on-site CMM emission factors, and the emissions from abandoned coal mines. As the leading CH 4 emission source in China, the estimations of CMM emissions urgently need to overcome existing and emerging challenges for compiling a consistent and accurate inventory. Unlabelled Image • We perform an overview of current bottom-up estimation of China's CMM emissions. • CMM emissions over 1980–2016 rose from 4.64 to 16.41 Tg with a peak of 21.48 Tg. • Inventory results were improved along with large discrepancies and disagreements. • We discuss the types of emission source, emission factors and activity-level data. • The limits of current understanding and future research prospects are provided. [ABSTRACT FROM AUTHOR]