Fossil-Fuel and Food Systems Equally Dominate Anthropogenic Methane Emissions in China

Dynamic Methane Emissions from China's Fossil-Fuel and Food Systems: Socioeconomic Drivers and Policy Optimization Strategies

In response to the 2023 "Action Plan for Methane Emission Control" in China, which mandates precise methane (CH4) emission accounting, we developed a dynamic model to estimate CH4 emissions from fossil-fuel and food systems in China for the period 1990-2020. We also analyzed their socioeconomic drivers through the Logarithmic Mean Divisia Index (LMDI) model. Our analysis revealed an accelerated emission increase (850.4 Gg/year) during 2005-2015, compared to 570.4 Gg/year in the preceding period (1990-2005), with a downward trend (-1216.6 Gg/year) detected after 2015. The fossil-fuel system was the primary contributor to these changes, with emissions positively correlated with per capita GDP and negatively influenced by energy intensity at the production stage and wastewater discharge intensity at the disposal stage. In the food system, CH4 emission intensity and waste treatment practices were the most significant negative drivers at production and disposal stages, respectively. Urbanization also played a notable role, contributing to 19.3% and 18.1% in livestock and rice cultivation emission reductions, respectively. Despite the observed changes, coal mining, livestock, and rice remain the dominant sources of CH4 emissions. Our findings suggest that effective CH4 emission mitigation can be achieved through strategies such as reducing energy intensity, improving agricultural production efficiency, and advancing urbanization efforts.

Satellite-Based Monitoring of Methane Emissions from China's Rice Hub

Rice cultivation is one of the major anthropogenic methane sources in China and globally. However, accurately quantifying regional rice methane emissions is often challenging due to highly heterogeneous emission fluxes and limited measurement data. This study attempts to address this issue by quantifying regional methane emissions from rice cultivation with a high-resolution inversion of satellite methane observations from the Tropospheric Monitoring Instrument (TROPOMI). We apply the method to the largest rice-producing province (Heilongjiang) in China for 2021. Our satellite-based estimation finds a rice methane emission of 0.85 (0.69-1.03) Tg a-1 from the province or an average emission factor of 22.0 (17.8-26.6) g m-2 a-1 when normalized by rice paddy areas. The satellite-based analysis reveals a 2 to 4 times lower bias in widely used global and national inventories, which lack up-to-date regional information. The inversion reduces the uncertainty of regional rice emissions by 73% relative to bottom-up estimates based on field flux measurements. The satellite inversion also shows that the highest rice methane emissions occur in June during the tillering stage of rice, decreasing toward ripening, indicating that the predominant water management practice in the region involves drainage and intermittent flooding after initial flooding. Process-based modeling further suggests that this practice can lead to a reduction of methane emissions by more than 50% compared to continuous flooding of rice paddies and natural wetlands.

Heterogeneous evolution and driving forces of multiple hazardous air pollutants and GHGs emissions from China's primary aluminum industry

The booming of China's primary aluminum industry (PAI) brought substantial emissions of hazardous air pollutants (HAPs) and greenhouse gases (GHGs). By using life cycle assessment and bottom-up method, a comprehensive emission inventory for multiple typical HAPs and GHGs from China's PAI during 1990-2021 was developed and explored for the first time. Our results show that spatial-temporal emissions trends of HAPs and GHGs from PAI in China diverse significantly. The conventional atmospheric pollutants (including SO2, NOx and particulate matter (PM)), fluoride and per fluorinated compound (PFCs) had been effectively suppressed since 2007 due to the implementation of various environmental policies; while, emissions of CO, VOCs, CH4, heavy metals and CO2 had increased at different rates unexpectedly. From the spatial distribution perspective, Henan, Shanxi, Guizhou, Guangxi and Shandong dominated the emissions of PAI in China, but with consumption expansion and environmental constrains, PAI plants start to expand to northwest and southwest areas where are richer in sufficient and cheaper power resources, thus bring significant emission increasing there, particular for conventional atmospheric pollutants in northwest and CO and VOCs in southwest China. By underlying driving forces of PAI emissions, results show that end-of-pipe control measures at various stages have played different roles to reduce emissions of the concerned species at each period, but its reduction effect diminished gradually. Future reduction should seek underlying changes in production technology and energy system. Under constrains of environmental regulation and resource endowment, promoting circular economic development for PAI would be a key strategy to reduce HAPs and GHGs emissions simultaneously in PAI.

Tracking Carbon and Ammonia Emission Flows of China's Nitrogen Fertilizer System: Implications for Domestic and International Trade

China is the world's largest producer, consumer, and exporter of synthetic nitrogen (N) fertilizer. To assess the impact of domestic demand and international exports, we quantified the life-cycle CO2eq and ammonia (NH3) emissions by tracking carbon (C) and nitrogen (N) flows from coal/gas mining through ammonia production to N fertilizer production, application, and export. In 2020, China's N fertilizer system emitted 496.04 Tg of CO2eq and 3.74 Tg of NH3, with ammonia production and N fertilizer application processes contributing 36 and 85% of the life-cycle CO2eq and NH3 emissions, respectively. As the largest importers of N fertilizer, India, Myanmar, South Korea, Malaysia, and the Philippines collectively shifted 112.41 Tg of CO2eq. For every ton of N fertilizer produced and used in China, 16 t of CO2eq and 0.18 t of NH3 were emitted, compared to 9.7 t of CO2eq and 0.13 t of NH3 in Europe. By adopting currently available technologies, improving N fertilizer utilization efficiency and employing nitrification inhibitors could synergistically reduce CO2eq emissions by 20% and NH3 emissions by 75%, while energy transformation efforts would primarily reduce CO2eq emissions by 59%. The production of ammonia using green electricity or green hydrogen could significantly enhance the decarbonization of China's N fertilizer system.

Air quality and health benefits for different heating decarbonization pathways in China

The urgent need for decarbonization in China's heating system, comprised of approximately one hundred thousand boilers, is imperative to meet climate and clean air objectives. To formulate national and regional strategies, we developed an integrated model framework that combines a facility-level emission inventory, the Community Multiscale Air Quality (CMAQ) model, and the Global Exposure Mortality Model (GEMM). We then explore the air quality and health benefits of alternative heating decarbonization pathways, including the retirement of coal-fired industrial boilers (CFIBs) for replacement with grid-bound heat supply systems, coal-to-gas conversion, and coal-to-biomass conversion. The gas replacement pathway shows the greatest potential for reducing PM2.5 concentration by 2.8 (2.3-3.4) μg/m3 by 2060, avoiding 23,100 (19,600-26,500) premature deaths. In comparison, the biomass replacement pathway offers slightly lower environmental and health benefits, but is likely to reduce costs by approximately two-thirds. Provincially, optimal pathways vary - Xinjiang, Sichuan, and Chongqing favor coal-to-gas conversion, while Shandong, Henan, Hebei, Inner Mongolia, and Shanxi show promise in CFIBs retirement. Henan leads in environmental and health benefits. Liaoning, Heilongjiang, and Jilin, rich in biomass resources, present opportunities for coal-to-biomass conversion.

Methane emission and influencing factors of China's oil and natural gas sector in 2020-2060: A source level analysis

The Chinese oil and gas industry requires targeted policies to reduce methane emissions. To achieve this goal, it is necessary to predict future methane emission trends and analyze the factors that influence them. However, changing economic development patterns, insufficient analysis of various factors influencing emissions, and inadequate resolution of methane emission inventories have made these goals difficult to achieve. Accordingly, this study aims to expand the methane emission estimation method to compile source-level emission inventories for future emissions, analyze the factors influencing them, and form a mechanistic understanding of the methane emissions from the local oil and gas industry. The research results indicate that methane emissions deriving from this industry will increase rapidly before 2030, after which they will decline slowly in all scenarios. The production and utilization processes in the natural gas supply chain, i.e., compressors and liquid unloading, include the main sources of methane emissions. Emissions are affected significantly by total production and consumption. Change in the overall supply and demand of natural gas affects change in methane emissions more significantly than adopting new technologies and strengthening facility maintenance, i.e., the overall supply and demand of natural gas are the dominant factors in controlling methane emissions. This study suggests that controlling the total demand for oil and gas should be at the core of the methane emission control policy for the local oil and gas industry. Moreover, equipment maintenance and emission reduction technologies should be used more effectively to reduce total emissions.

Tracking Carbon Flows from Coal Mines to Electricity Users in China Using an Ensemble Model

Accurately tracking carbon flows is crucial for preventing carbon leakage and allocating responsibility for reducing CO2eq emissions. In this study, we developed an ensemble model to effectively track carbon flows within China's power system. Our approach integrates coal quality tests, individual power plant datasets, a dynamic material-energy flow analysis model, and an extended version of an interconnected power grid model that incorporates transmission and distribution (T&D) losses. Our results not only provide accurate quantification of unit-based CO2eq emissions based on coal quality data but also enable the assessment of emissions attributed to T&D losses and emission shifts resulting from interprovincial coal and electricity trade. Remarkably, for CO2eq emissions from coal-fired units, the disparity between the guideline and our study can be as high as [-95%, 287%]. We identify Guangdong, Hebei, Jiangsu, and Zhejiang provinces as the major importers of both coal and electricity, responsible for transferring nearly half of their user-based emissions to coal and power bases. Significantly, T&D losses, often overlooked, contribute to 15-20% of provincial emissions at the user side. Our findings emphasize the necessity of up-to-date life cycle emissions and spatial carbon shifts in effectively allocating emission reduction responsibilities from the national level to provinces.

Tracking Carbon Flows in China's Iron and Steel Industry

Accurately tracking carbon flows is the first step toward reducing the climate impacts of the iron and steel industry (ISI), which is still lacking in China. In this study, we track carbon flows from coal/mineral mines to end steel users by coupling the cross-process material and energy flow model, point-based emission inventory, and interprovincial trade matrices. In 2020, ISI emitted 2288 Tg of CO2 equivalent (CO2eq, including CH4 and CO2), 96% of which came from energy use and 4% from raw material decomposition. Often overlooked off-gas use and CH4 leakage in coal mines account for 25% of life-cycle emissions. Due to limited scrap resources and a high proportion of pig iron feed, the life-cycle emission intensity of the electric arc furnace (EAF) (1.15 t CO2eq/t steel) is slightly lower than the basic oxygen furnace (BOF) (1.58 t CO2eq/t steel) in China. In addition, over 49% of producer-based emissions are driven by interprovincial coal/coke/steel trade. In particular, nearly all user-based emissions in Zhejiang and Beijing are transferred to steelmaking bases. Therefore, we highlight the need for life-cycle and spatial shifts in user-side carbon management.