Cumulative Emissions Research Articles

Groundwater level effects on greenhouse gas emissions from undisturbed peat cores

Peat soils store a large part of the global soil carbon stock, which can potentially be lost when they are drained and taken into cultivation, resulting in CO2 emission and land subsidence. Groundwater level (GWL) management has been proposed to mitigate peat oxidation, but may lead to increased emissions of nitrous oxide (N2O) and methane (CH4).The aim of this experiment was to study trade-offs between greenhouse gas emissions from peat soils as a function of GWL. We incubated 1 m deep, 24 cm diameter undisturbed bare soil cores, after removal of the grass layer, from three contrasting Dutch grassland peat sites for 370 days at 16 °C. The cores were subjected to drying-wetting cycles, with the GWL varying between near the soil surface to 160 cm below the surface. We measured gas fluxes of CO2, N2O and CH4 from the soil surface, extracted pore water for DOC and mineral nitrogen analysis, and measured soil hydraulic and shrinkage characteristics.Emissions of CO2 increased after lowering the GWL, but showed different GWL-response curves during rewetting of the soil. On average, highest CO2 emissions of 1.5 g C·m−2 day−1 were found at a GWL of 80 cm below the surface. However, the 0 cm GWL was the only treatment with significantly lower CO2 emissions than other GWLs. Cumulative CO2 emissions differed significantly between sampling sites. Emissions of N2O showed a different response, peaking at GWL heights above −20 cm, particularly after a recent GWL rise. Though not significantly different, the highest N2O emissions were measured at the 0 cm GWL treatment. We confirmed this pattern for N2O in un-replicated soil cores with grass sward, although emission values were lower in these cores due to the root uptake of mineral nitrogen. CH4 emissions or −uptake remained low under any GWL. We conclude that raising the GWL is a successful strategy to reduce CO2 emissions from peat oxidation. However, raising the GWL close to the soil surface could lead to N2O emissions that negate any gains in terms of global warming potential. Our results suggest that raising the GWL in peat grasslands to −20 cm creates such a risk. A constant GWL at the surface (0 cm) would be preferential for mitigating both CO2 and N2O emissions, although such conditions don’t allow for agricultural grass production (mowing or grazing).

Effects of inhibitors and slit incorporation on NH3 and N2O emission processes after urea application

The use of urea fertilizers in agriculture is associated with many negative environmental impacts and is a source of ammonia (NH3) and nitrous oxide (N2O) emissions. Such losses from urea fertilizer can be avoided by different mitigation techniques. Three different mitigation principles, urease inhibitor (N-(2-Nitrophenyl) phosphoric triamide, 2-NPT) (UI) alone and urease inhibitor in combination with nitrification inhibitors (N-[3(5)-methyl-1 H-pyrazol-1-yl) methyl] acetamide, MPA) (NI) and closed slit incorporation of urea fertilizer into the soil, were compared on a sandy loam soil at a soil water level of 70 % water-holding capacity. An in vitro microcosm approach with open dynamic incubation chambers was used to monitor NH3 emissions over two weeks with NH3 sampling by washing bottles. N2O emissions were studied over ten weeks in slow throughflow mesocosms with continuous gas chromatographic (GC) measurements. To get insights into N2O production and consumption processes, gas samples were taken after six weeks and N2O isotopocules were analyzed by isotope ratio mass spectrometry (IRMS). Slit injection showed the greatest effect on NH3 emission reduction by 79.6 % (40.6 % by UI, and 46.7 % by UINI) compared to surface applied urea. Minor pollution swapping to N2O was observed at the beginning of the trial due to incorporation but not in the cumulative emissions over the entire incubation time. The reduction effect of UINI on N2O emissions decreased over time with no cumulative emission reduction at the end of experimentation. N2O isotopocules confirmed the high contribution of nitrification to N2O production. In contrast and bacterial denitrification, nitrifier denitrification and fungal denitrification were involved on a much lower level and N2O reduction to N2 was not pronounced. All NH3 mitigation measurements where effective to decrease NH3 emissions while their effects on N2O emission varied over time. Factors as crop N uptake and rainfall would further modify the overall effect on N2O emissions and need to be considered for final pollution swapping assessment. Further research on the impact of NI on non-target microbial communities is warranted to elucidate potential environmental consequences and long-term efficacy of inhibitor compounds.

How megacities can achieve carbon peak through structural adjustments: an input–output perspective

Abstract There is still a huge gap between the emissions pathways of megacities and the pathways to meeting the targets set by the Paris agreement. Compared with technological emission reductions, structural emission reduction can provide cities with more stable and sustainable carbon-peaking solutions. This study constructs a scenario-based input–output optimization model, adopting a novel carbon emission accounting method for purchased electricity that considers shared responsibility, and systematically evaluates the decarbonization paths of megacities and their impacts on economic growth, energy consumption, and carbon emissions. The results show that (a) through industry substitution and manufacturing restructuring, Shenzhen is projected to peak at 57.68 MtCO2 emissions in 2026, with a 10.57% energy and a 19.55% carbon reduction by 2030. (b) Shenzhen can achieve its carbon emission peak target through the energy transition while accepting a loss of 0.97%–3.23% of GDP, requiring the maximum economic concession of 16.45% from the transportation sector (S10) in the early stage of transformation, while 12.24% from the extractive industry (S2) in the later stage. (c) The comprehensive structure adjustment proved to be more effective than other mitigation approaches, capable of achieving high-quality economic growth of 6.4% during the study period while reaching a peak target of 53.55 million tons of CO2 by 2026. (d) The emission reduction effect of the power sector was the most significant among all the scenarios, with emission reduction rates between 6.26% and 35.63%, and the cumulative emission reduction potential reached 38.1–110.6 MtCO2. The priority for emission reduction in the power sector is the coal phase-out plan, which is essential for achieving these significant reductions. This study provides an important reference for megacities facing similar challenges, especially those in developing countries, to achieve a stable and sustainable carbon peak pathway through structural adjustment.

Carbon emission measurement and regional decomposition analysis of China’s beef cattle farming industry

IntroductionWarming caused by greenhouse gas (GHG) emissions has become a global environmental issue of widespread concern, and China, as a responsible power, has the pressing task of reducing carbon emissions. China is one of the world’s major beef producers and consumers, and at the same time, beef cattle, as a large livestock, is the largest source of GHG emissions in the livestock industry.MethodsThis study considered the panel data of 31 provinces in China from 2008 to 2022. The kernel density estimation and Dagum Gini coefficient were used to analyze the spatiotemporal dynamic evolution patterns and influencing factors of carbon emissions from China’s beef cattle farming industry.Results(1) The carbon emission trajectory of beef cattle production follows a distinctive “ascend-descend-ascend” three-phase pattern. By 2022, the sector’s cumulative carbon emissions had burgeoned by 37.62% relative to 2008, reflecting an average annual escalation of 2.31%. Despite the overall upward trend in carbon emissions, significant regional differences were observed. The Central Plains region has witnessed a consistent decline, in stark contrast to the Southwest and Northeast regions, which have emerged as hotspots for heightened carbon emissions and intensified emission densities within China’s beef cattle production landscape, underscoring the intensifying significance of carbon mitigation measures. (2) The kernel density curve shows an overall rightward shift with a specific gradient effect on carbon emissions. In addition, the range of the right drag of the curve in 2022 was significantly reduced, which laterally reflects the narrowing of the difference between the provinces with the highest and lowest carbon emissions from beef cattle farming. The principal source of variance in the overall carbon emissions from beef cattle production is the disparities between regions, which accounts for an average annual contribution rate of 52.52%. Conversely, the within-region contribution rates have remained relatively stable, while those for the intensity of transvariation have witnessed a substantial rise, with annual averages of 18.31 and 28.96%, respectively. (3) Regarding the factors influencing carbon emissions reduction, environmental regulations and production efficiency significantly drive carbon emissions reduction in beef cattle farming.DiscussionRelevant government departments should actively guide farmers toward green production, establish perfect policies and regulations for low-carbon beef cattle farming, and promote low-carbon beef cattle farming models based on local conditions.

Biochar Applied in Places Where Its Feedstock Was Produced Mitigated More CO2 Emissions from Acidic Red Soils

Agricultural soil is the main source of greenhouse gas emissions, among which carbon dioxide (CO2) is an important greenhouse gas, impacting the global climate. In China, as a large rice-producing country, carbon sequestration and CO2 mitigation in paddy soil are crucial for the mitigation of global climate change. While biochar has been widely used in the mitigation of soil greenhouse gas emissions, the application site of biochar, i.e., whether or not it is the same as its feedstocks, may generate different effects on soil CO2 emissions due to the differences in the element and nutrient concentrations in its feedstocks, especially when applied in fertilized soil. In order to explore the effects of biochar application with different feedstocks on the mitigation of CO2 emissions from paddy soil, this experiment took paddy soil in a red soil area as the research object, using rice straw and Camellia oleifera fruit shell as raw materials to produce biochar (adding an amount of 40 g kg−1 soil) and urea as an external nitrogen source (adding an amount of 200 mg kg−1 soil). The effects of two different types of biochar derived from feedstocks with different producing origins on the CO2 emissions from paddy soil were studied via laboratory control incubation studies. The results showed that (1) the effects of rice straw biochar addition on the soil pH, NO3−-N and total available nitrogen (AN) content were significantly higher than those of Camellia oleifera fruit shell biochar (the scale of the increase was higher by 6.40%, 579.7% and 180.1%, respectively). (2) The CO2 emission rate and cumulative emissions of soil supplemented with rice straw biochar were significantly lower than in that supplemented with Camellia oleifera fruit shell biochar (decreases of 28.0% and 27.5%, respectively). Our findings suggest that the efficiency of emission mitigation of rice straw biochar is better than that of Camellia oleifera fruit shell applied to paddy soil. While future studies considering more types of greenhouse gases will be necessary to expand these findings, this study indicates that biochar prepared from in situ feedstock can be used to reduce greenhouse gas emissions in rice fields, so as to ensure sustainable development and achieve energy conservation and emission reduction goals. This study will benefit future agricultural practices when choosing biochar as a greenhouse gas mitigation strategy in the context of global warming, as well as other global changes following global warming, caused by elevated atmospheric greenhouse gases.

Phosphorus fertilization promotes carbon cycling and negatively affects microbial carbon use efficiency in agricultural soils: Laboratory incubation experiments

Soil organic carbon (SOC) loss from intensive agriculture represents a major global concern. Consequently, strategies to improve soil management to mitigate or abate SOC losses and enhance carbon (C) sequestration are urgently needed. Nutrient availability, especially nitrogen (N) and phosphorus (P), regulates soil C cycling and storage. While N effects are well studied, less is known about how soil P status and different fertilizer types affects SOC dynamics. This laboratory incubation assessed how two common P fertilizers, diammonium phosphate (DAP) and single superphosphate (SSP), affected microbial activity and C immobilization in the zone of soil directly around the fertilizer granule (prillosphere) across three contrasting agricultural soils (Inceptisol, Vertisol, Alfisol). Soils were amended with DAP or SSP granules and C turnover assessed with 14C-labeled glycine, malic acid or glucose, alongside unfertilized controls. After three weeks, soil pH, electrical conductivity (EC), Olsen-P and microbial C use efficiency (CUE) were measured. DAP increased pH in the Inceptisol (acidic soil), while SSP decreased pH in all soils. Both fertilizers increased EC and Olsen-P, but SSP enhanced Olsen-P more than DAP. Cumulative 14CO2 emissions were 19–20 % higher with P fertilizers compared to the control, with DAP stimulating faster initial C mineralization rates than SSP, except in the Alfisol. P addition reduced microbial CUE by 23–34 % across all soils and substrates versus the unfertilized control. We ascribe this reduction in CUE to an alleviation of nutrient limitation or a fertilizer-induced osmotic stress. The co-addition of N either in DAP or glycine did not alter the P-induced CUE response suggesting that P was more important than N in regulating microbial CUE in these soils. We conclude that P fertilization increased short-term C turnover and may lead to reduced C storage in soil, however, further long-term (>1 year) research is needed to identify optimum P management strategies to minimize C losses in agricultural soils.

Biochanin A feed supplementation alters dynamics of trace gas emissions from lamb urine-amended soil.

Sustainable growth in livestock production requires reductions in trace gas emissions on grazing lands. Urine excreta patches are hot spots for accelerated emissions of carbon and nitrogen. Ruminant dietary supplementation with the isoflavone biochanin A (BCA) has been shown to improve cattle weight gain. To determine if BCA supplementation affects urine N excretion and soil trace gas emissions, soil in microcosms was amended with urine from lambs fed 0, 0.45, or 0.90g BCA day-1. Soil gas emissions were measured over 60 days and analyzed with a linear mixed-effects model with repeated measures. On 2 days during the incubation, BCA addition across doses significantly reduced nitrous oxide emissions by 73% and methane by 98% compared to urine from non-dosed lambs. Cumulative ammonia volatilization was significantly reduced by 33% but cumulative nitrous oxide and methane emissions were not. Alterations in trace gas emissions occurred despite no change in urine N content with BCA feed supplementation. A separate laboratory incubation using urine from a non-supplemented lamb that was exogenously spiked with varying BCA concentrations supported these results: BCA significantly altered ammonia and methane emission dynamics and reduced cumulative nitrous oxide emissions by up to 41%. BCA did not change soil microbial community structure, suggesting alterations to other processes, such as soil enzyme activity, were affecting soil trace gas emissions. Overall, lamb BCA supplementation did not affect urine N but reduced ammonia volatilization, which may contribute to greater sustainability in livestock production systems.

Microplastic contamination accelerates soil carbon loss through positive priming

The priming effect, i.e., the changes in soil organic matter (SOM) decomposition following fresh organic carbon (C) inputs is known to influence C storage in terrestrial ecosystems. Microplastics (particle size <5 mm) are ubiquitous in soils due to the increasing use and often inadequate end-of-life management of plastics. Conventional polyethylene and bio-degradable (PHBV) plastics contain large amounts of C within their molecular structure, which can be assimilated by microorganisms. However, the extent and direction of the potential priming effect induced by microplastics is unclear. As such, we added 14C-labeled glucose to investigate how background polyethylene and PHBV microplastics (1 %, w/w) affect SOM decomposition and its potential microbial mechanisms in a short-term. The cumulative CO2 emission in soil contaminated with PHBV was 42–53 % higher than under Polyethylene contaminated soil after 60-day incubation. Addition of glucose increased SOM decomposition and induced a positive priming effect, as a consequence, caused a negative net soil C balance (−59 to −132 μg C g−1 soil) regardless of microplastic types. K-strategists dominated in the PHBV-contaminated soils and induced 72 % higher positive priming effects as compared to Polyethylene-contaminated soils (160 vs. 92 μg C g−1 soil). This was attributed to the enhanced decomposition of recalcitrant SOM to acquire nitrogen. The stronger priming effect associated in PHBVs can be attributed to cooperative decomposition among fungi and bacteria, which metabolize more recalcitrant C in PHBV. Moreover, comparatively higher calorespirometric ratios, lower substrate use efficiency, and larger enzyme activity but shorter turnover time of enzymes indicated that soil contaminated with PHBV release more energy, and have a more efficient microbial catabolism and are more efficient in SOM decomposition and nutrient resource uptake. Overall, microplastics, (especially bio-degradable microplastics) can alter biogeochemical cycles with significant negative consequences for C sequestration via increasing SOM decomposition in agricultural soils and for regional and global C budgets.

PSLBII-28 Effects of dietary protein manipulation on greenhouse gases and ammonia emissions from feedlot beef steers

Abstract Black Angus steers [n = 112; body weight (BW) = 401 ± 3.6 kg] were used in a randomized incomplete block design to evaluate the effects of 3 rumen available protein to microbial crude protein ratios (RAP:MCP) on growth performance, and gaseous emissions from feedlot steers. Steers were blocked by initial BW and randomly assigned to 1 of 3 treatment rations. Diets were fed rations either Deficient (-150 gּ animal-1ּ d-1; DEF), Balanced (0 gּ animal-1ּ d-1; BAL), or Excess (+150 gּ animal-1ּ d-1; EXS) in RAP: MCP. Steers were allocated and housed in cattle pen enclosures (CPE), and treatment diets were delivered daily as a total mixed ration. The present study consisted of two 42-d periods. Refusals were collected weekly and BW every 14 d. Gas measurements were obtained daily in sequential order from all CPE. Data were analyzed with R statistical software (4.2.3). The linear mixed effect model procedure within the “lme4” package was used with CPE as the experimental unit, treatment and week as fixed effects, and block and period as random effects. A contrast coefficient matrix was constructed to test for linear and quadratic effects. Initial, intermediary and final BW were not different for steers receiving the varying RAP:MCP (P ≥ 0.239). A treatment effect (P = 0.004) was observed for mean dry matter intake (DMI) where EXS steers consumed 0.46 kg more DM compared with BAL steers, but DEF steers had similar DMI to those fed EXS and BAL (P = 0.189). Average daily gain (ADG) was only affected by treatment (P = 0.007) on d 0 to 14 where steers receiving DEF gained 0.6 kg more than those fed BAL (P = 0.010), but those fed EXS had similar ADG. Similar to ADG, gain to feed (G:F) was affected by treatment (P = 0.012) only during d 0 to 14. Mean CH4 production from steers fed DEF and EXS were 20% and 13% greater (P = 0.010) compared with those fed BAL, respectively; however, CH4 from EXS vs. DEF steers was not different (P = 0.149). Mean cumulative NH3 emissions increased linearly by treatment with EXS steers emitting up to 52% more NH3 compared with those receiving DEF (P &amp;lt; 0.001). Similarly, EXS steers had increased SO2 emissions by up to 44% compared with those fed DEF (P &amp;lt; 0.001). Emissions of CO2, N2O, and H2S were similar (P &amp;gt; 0.100). The manipulation of RAP:MCP in the diets of feedlot steers can drastically reduce NH3 emissions without affecting growth performance and may be a valuable tool to reduce air pollution from beef production systems.

The Physics of the Carbon Cycle: About the Origin of CO2 in the Atmosphere

Aims: Examination of the correctness of some assumptions of IPCC regarding climate. Discussion of consequences. Methodology: Explanation of terms used by IPCC and clarification of consequences, identification of prerequisites for the validity/applicability of these terms and scrutiny of their fulfillment under real-world conditions, discussion of consequences. Results: Based on the laws of physics and logic, two central terms used by IPCC, i.e. the fixed "airborne fraction", and the constant "CO2-budget” cannot exist in reality. The first states that about 50 % of the CO2 emitted by humans (the “airborne fraction”) stay in the atmosphere for centuries or longer (the other about 50 % leaving it within maximum a few years), the latter is the maximum value of cumulative net global anthropogenic emissions that is allowed, if global warming should be kept below a given level, for example 2 °C. According to their definition, both values are independent of the temporal distribution of the anthropogenic emissions. But physics speaks against their existence. And also the “Bern Cabon Cycle Model”, used by IPCC as an alternative method to analyze the carbon cycle, cannot be correct, because it is based on incorrect physical boundary conditions. The inadmissibility of the two terms is also supported by observations of the fast decay of 14CO2 after the atomic bomb test stop agreement. Conclusion: If the considerations made here are correct, IPCC's assessment of the sharp increase in CO2 concentration being a consequence of anthropogenic releases implodes. Consequently, the assessment of global warming to be man-made is justified no more, and the necessity to terminate all anthropogenic releases of CO2 for climate protection reasons becomes superfluous. The considerations made here appear to be very reliable, but in view of the far-reaching consequences, a careful review by the scientific community seems to be urgently needed.

Natural grassland restoration exhibits enhanced carbon sequestration and soil improvement potential in northern sandy grasslands of China: An empirical study

Vegetation restoration is an effective measure for restoring degraded ecosystems. Soil carbon mineralization, a crucial indicator for evaluating the effectiveness of vegetation restoration, is essential in soil carbon cycling. However, the response of soil carbon mineralization to different vegetation restoration types remains unclear. In this study, grassland (Leymus chinensis and Stipa bungeana), shrubland (Corethrodendron fruticosum), and forestland (Ulmus pumila) with 20 years of consistent restoration in the Xilingol sandy grassland were selected to determine the effects of vegetation restoration types on soil carbon mineralization. The results showed that the soil cumulative carbon dioxide emissions (CCE) and microbial respiration rate (SMR) in grassland and forestland were significantly higher than those in shrubland, while soil carbon mineralization efficiency (CME) and microbial metabolic quotient (MQ) were significantly lower than those in shrubland. Furthermore, soil organic carbon (SOC) and its fractions were influenced considerably by vegetation restoration types, with grassland exhibiting the highest SOC content. The ratios of soil total effective nutrients (C/N, N/P, and C/P) and the content of active organic carbon (DOC, MBC, EOC, and POC) can effectively reflect the changes in soil carbon mineralization and the stability of SOC pools. The variations in CCE were influenced by litter biomass, macroaggregates organic carbon, mineral-associated organic carbon (MAOC), and dissolved organic carbon (DOC), while the changes in SMR were affected by aboveground biomass (AGB), soil total nitrogen and phosphorus ratios (N/P), and microaggregate organic carbon and microbial biomass carbon. The changes in CME were affected by AGB, N/P, pH, MAOC, and DOC, while the changes in MQ were influenced by AGB, N/P, DOC, MAOC, and easily oxidizable organic carbon. Given the higher carbon sequestration benefits and soil quality improvement capability of naturally restored grassland, this study suggests that grassland could be considered the primary vegetation restoration type in the Xilingol sandy grassland.

Increased global warming potential during freeze-thaw cycle is primarily due to the contribution of N2O rather than CO2

While freeze-thaw cycle (FTC) can influence greenhouse gas emissions, the specific greenhouse gas that responds most strongly to FTC, as well as the underlying mechanisms, remain unclear. Here, we conducted a meta-analysis to explore the responses of global warming potential (GWP) and the fluxes of CO2 and N2O to FTC. Our results showed that FTC treatment significantly increased GWP, N2O flux, cumulative GWP, and cumulative N2O emissions by 23.1 %, 53.2 %, 14.5 %, and 164.6 %, respectively, but did not affect CO2 flux, indicating that the enhanced GWP during the FTC period may be primarily due to the contribution of N2O flux rather than CO2 flux. The responses of GWP (+68.6 %), CO2 (+21.0 %), and N2O fluxes (+136.3 %) in croplands was higher than those in other ecosystems, exhibiting a strong dependence on ecosystem types. The effect size of FTC treatment on greenhouse gas emissions escalated with decreasing freezing temperature and diminished with increasing FTC frequency. Moreover, mean annual temperature (MAT) and FTC patterns were key factors influencing GWP during the FTC period. These findings provide critical insights into the variations in greenhouse gas emissions due to FTC and its influencing factors, allowing for more accurate predictions of the future impact of global climate change on GWP.

Long‐term tillage and cover cropping differentially influenced soil nitrous oxide emissions from cotton cropping system

AbstractClimate‐smart agricultural practices, such as no‐tillage (NT) and cover cropping, have been widely adopted and are anticipated to yield multiple benefits, including soil carbon sequestration, enhancing soil health, and crop yield stability. However, their influence on nitrous oxide (N2O) emissions varies, with the potential of both increasing and decreasing N2O emissions. Increasing N2O emissions under these practices may potentially offset the climate mitigation benefits from increased soil carbon sequestration. We investigated N2O emissions in response to 42 years of long‐term adoption of NT and legume cover crop, under nitrogen (N) rates of 0 and 67 kg N ha−1, in a continuous cotton system in the Southeastern United States. Intensive manual chamber‐based measurements were conducted over two growing seasons (2021–2022 and 2022–2023). Long‐term NT did not significantly affect cumulative N2O emissions during the study period (p &gt; 0.05). Hairy vetch cover crop‐grown plots emitted two to three times more N2O than those without cover crops in 2021–2022, with no significant effect observed in 2022–2023. Cumulative emissions in cover crop plots were greater compared to those in no cover crop plots when fertilized with 67 kg N ha−1 in 2021–2022; however, this trend did not persist in 2022–2023. While interannual variability exists, our results generally suggest that long‐term NT may not increase N2O emissions, hence its adoption could enhance its broader soil health and climate benefits via soil carbon sequestration, whereas managing legume cover crop residues in N‐fertilized systems is critical to mitigate N2O emissions.

Early Opportunities for Onshore and Offshore CCUS Deployment in the Chinese Cement Industry

The promotion of deep decarbonization in the cement industry is crucial for mitigating global climate change, a key component of which is carbon capture, utilization, and storage (CCUS) technology. Despite its importance, there is a lack of empirical assessments of early opportunities for CCUS implementation in the cement sector. In this study, a comprehensive onshore and offshore source–sink matching optimization assessment framework for CCUS retrofitting in the cement industry, called the SSM-Cement framework, is proposed. The framework comprises four main modules: the cement plant suitability screening module, the storage site assessment module, the source–sink matching optimization model module, and the economic assessment module. By applying this framework to China, 919 candidates are initially screened from 1132 existing cement plants. Further, 603 CCUS-ready cement plants are identified, and are found to achieve a cumulative emission reduction of 18.5 Gt CO2 from 2030 to 2060 by meeting the CCUS feasibility conditions for constructing both onshore and offshore CO2 transportation routes. The levelized cost of cement (LCOC) is found to range from 30 to 96 (mean 73) USD·(t cement)−1, while the levelized carbon avoidance cost (LCAC) ranges from −5 to 140 (mean 88) USD·(t CO2)−1. The northeastern and northwestern regions of China are considered priority areas for CCUS implementation, with the LCAC concentrated in the range of 35 to 70 USD·(t CO2)−1. In addition to onshore storage of 15.8 Gt CO2 from 2030 to 2060, offshore storage would contribute 2.7 Gt of decarbonization for coastal cement plants, with comparable LCACs around 90 USD·(t CO2)−1.

Effects of Organic Fertilizer and Biochar on Carbon Release and Microbial Communities in Saline–Alkaline Soil

Climate change and aridification have increased the risk of salinization and organic carbon loss in dryland soils. Enrichment using biochar and organic fertilizers has the potential to reduce salt toxicity and soil carbon loss. However, the effects of biochar and organic fertilizers on CO2 and CH4 emissions from saline soils in dryland areas, as well as their microbial mechanisms, remain unelucidated. To clarify these issues, we performed a 5-month incubation experiment on typical soda-type saline soil from the western part of the Songnen Plain using five treatments: control treatment (CK), 5% urea (U), straw + 5% urea (SU), straw + 5% urea + microbial agent (SUH), and straw + 5% urea + biochar (SUB). Compared with the SU treatment, the SUH and SUB treatments reduced cumulative CO2 emissions by 14.85% and 35.19%, respectively. The addition of a microbiological agent to the SU treatment reduced the cumulative CH4 emissions by 19.55%, whereas the addition of biochar to the SU treatment increased the cumulative CH4 emissions by 4.12%. These additions also increased the relative abundances of Proteobacteria, Planctomycetes, and Ascomycota. Overall, the addition of biochar and organic fertilizer promoted CO2 emissions and CH4 uptake. This was mainly attributed to an improved soil gas diffusion rate due to the addition of organic materials and enhanced microbial stress due to soil salinity and alkalinity from the release of alkaline substances under closed-culture conditions. Our findings have positive implications for enhancing carbon storage in saline soils in arid regions.

Dynamic evolution of particulate and gaseous emissions for typical residential coal combustion

Residential coal combustion still accounts for half of the heating energy consumption in many developing countries. The dynamic variation during the combustion process importantly determines the combustion facility design and appropriate air quality assessment, which was omitted in conventional studies. This study investigated the emissions of particulate and gaseous pollutants during the combustion process for typical coal types using online monitoring. During the first pyrolysis stage with temperature climbing, the organic aerosols (OA) and gases reached peak concentration. The second fierce combustion stage had the highest temperature and produced the highest cumulative emissions, particularly a substantial amount of black carbon for coals with higher volatile content. Using higher-quality coals will undoubtedly reduce PM emissions, by a factor of 10 from bituminous to anthracite coal. However, more ultrafine particles (d < 0.1 μm) from cleaner coal may pose additional health risks. Anthracite and honeycomb coal had approximately twice the energy content and emitted more CO2 per unit mass of fuel and had more persistent SO2 emissions throughout the burnout stage. The oxygenation of OA and organic gases remained increased during combustion, suggesting the pyrolysis products underwent oxidation before being emitted. The investigation of the coal combustion process suggests the importance of reducing volatiles to control PM emissions, but the potential negative synergistic effects between PM reduction and increased carbon emissions should also be considered.

Partial organic substitution increases soil quality and crop yields but promotes global warming potential in a wheat-maize rotation system in China

Excessive application of synthetic fertilizer has resulted in serious soil degradation and significant greenhouse gases (GHGs) fluxes in farmlands. Partial organic substitution for synthetic fertilizer was considered as a possible strategy for sustainable agricultural development, but its potential effects on soil quality, GHGs emissions, and crop productivity remain unclear. A field experiment across 3-year was conducted to evaluate the responses of soil quality, nitrous oxide (N2O), carbon dioxide (CO2), and methane (CH4) emissions, and crop yields to different ratios of organic fertilizer (OF) to synthetic fertilizer (SF). Six treatments were included: non-fertilization (CK); total SF; total OF; 15 %, 30 %, and 45 % organic substitution (LO, MO, and HO). Soil cumulative N2O emission was decreased with increasing organic substitution ratios, mainly attributing to the reducing soil NH4+ content. However, organic substitution increased soil CO2 and CH4 emissions due to the high manure-driven C input, consequently promoting global warming potential (GWP). Meanwhile, soil organic C, total N, P, available P, K, and C-acquisition enzyme activities were increased with organic substitution, resulting the higher soil quality index (SQI) under HO and OF. HO enhanced the annual yield of wheat and maize by 7.2 % and 13.0 % compared with SF and OF, respectively. The positive relationship between crop yield and SQI indicated that the yield-enhancing effect with partial organic substitution was mainly attributed to the improved synchronization in nutrient supply and soil fertility. Overall, partial organic substitution, especially 45 % organic substitution represents a viable strategy to improve soil quality and crop productivity while mitigating N2O emission in wheat-maize rotation systems. However, organic substitution promoted the GWP through stimulating soil CO2 and CH4 emissions. Further investigations of optimize fertilization managements are still needed to reduce manure-induced CO2 and CH4 emissions to achieve higher climate change mitigation.

Characterization of carbon dioxide emissions from late stage windrow composting

As organic waste is converted to usable amendments via composting, there are large CO2 emissions associated with the decomposition of organic matter via microorganisms. While the active composting phase produces the largest emissions over a short duration, compost can often be stored during and after the maturation phase for much longer periods of time, increasing cumulative emissions. As such, the objectives of this study were to examine the spatial and temporal variability associated with in situ emissions sampling while identifying the environmental and chemical controls on emissions in windrow composting facilities during and after the maturation phase. A total of 665 flux measurements were taken from four windrows representing different ages and compositions between June and November 2020. Factorial analysis of covariance (ANOVA) was used to determine the variability between sampling locations, while multiple linear regression was used to identify those parameters which had the most influence on CO2 flux. Emissions showed significant variability over time that were attributed to ambient temperatures. During the summer, each windrow reached peak emissions between 5.0 and 32.3 g CO2 m-2 hr-1. As temperatures cooled, the windrows saw a 62%–86% decline in emissions, generally falling below 2 g CO2 m-2 hr-1. Significant differences occurred between the top-most sampling location and all others on the windrow, emitting between 33%–100% more CO2. The environmental controls of surface temperature, moisture content, and internal temperature showed the highest influence on emissions (R2 = 0.62). Chemical properties including organic nitrogen, carbon, pH, magnesium, and nitrate also showed significant influence (R2 = 0.43). This research has shown that environmental factors including temperature and moisture show the strongest influence over emission rates in mature compost. A significant negative effect of organic nitrogen on CO2 flux was found, indicating that increased presence of organic nitrogen would aid in the retention of carbon after the maturation phase, acting to lower total emissions.

Composted maize straw under fungi inoculation reduces soil N2O emissions and mitigates the microbial N limitation in a wheat upland

Enhancement of microbial assimilation of inorganic nitrogen (N) by straw addition is believed to be an effective pathway to improve farmland N cycling. However, the effectiveness of differently pretreated straws on soil N2O emissions and soil N-acquiring enzyme activities remains unclear. In this study, a pot experiment with four treatments (I, no addition, CK; II, respective addition of maize straw, S; III, composted maize straw under no fungi inoculation, SC; and IV, composted maize straw under fungi inoculation, SCPA) at the same quantity of carbon (C) input was conducted under the same amount of inorganic N fertilization. Results showed that the seasonal cumulative N2O emissions following the SCPA treatment were the lowest at 4.03 kg N ha−1, representing a significant reduction of 19 % compared with the CK treatment. The S and SC treatments had no significant effects on N2O emissions. The decrease of soil N2O emissions following the SCPA treatment was mainly attributed to the increase of microbial N assimilation and the increased abundance of functional genes related to N2O reductase. The SCPA treatment significantly decreased soil alkaline phosphatase (ALP) activity and increased leucine aminopeptidase (LAP) activity at the basal fertilization, while increased soil ALP and LAP activity, decreased soil N-Acetyl-β-D-Glucosidase (NAG) activity at harvest. Compared with the CK treatment, the S, SC, and SCPA treatment significantly increased soil β-glucosidase (β-GC) activity at harvest. The decrease in the (NAG+LAP)/ALP ratio following the SCPA treatment indicated that the composted maize straw under fungi inoculation alleviated microbial N limitation at harvest. Moreover, PICRUSt analysis also suggested that the SCPA treatment increased the abundance of bacterial genes associated with N assimilation and N2O reduction, whereas the S and SC treatment did not significantly affect the abundance of N2O reduction genes compared with the CK treatment. Our results suggest that the composted maize straw under fungi inoculation would reduce the risk of N2O emissions and effectively mitigate the microbial N limitation in dryland wheat system.

Exploring Synergistic GHG Emissions Mitigation Potential and Costs of Room Air Conditioners.

This study explores the potential of synergistically reducing direct (refrigerant) and indirect (electricity) greenhouse gas (GHG) emissions in the global room air conditioning (RAC) sector, based on 80% of global RAC manufactured in China. Three scenarios are evaluated: Business-as-usual (BAU) based on maintaining refrigerant and energy efficiency levels from 2021 China RAC sales shares, Kigali Amendment compliant with 10% energy efficiency improvement by 2025 (KAE), and accelerated refrigerant transition and energy efficiency improvement (ATE). Each scenario considers the costs of refrigerant and efficiency measures for export market groups based on Kigali Amendment classifications. BAU predicts around 1 Gt CO2-eq average annual global RAC emissions (2022-2060). Cumulative emission reductions in China's RAC manufacturing under KAE and ATE are 12.2 and 17.2 Gt CO2-eq A5II and A5I (except China), presenting cost-effective abatement measures, with average costs of -$51.4 and -$68.8/t CO2-eq in KAE and ATE. Cumulative average abatement costs are around $18 and $4/t CO2-eq globally. KAE and ATE scenarios would avoid surface temperature rises of 0.023 (±0.002) °C and 0.027 (±0.003) °C, respectively, versus BAU. Collaboration between China and importing countries is urged to enhance energy efficiency in RACs traded, ensuring sustainable mitigation aligned with the Kigali Amendment.