Uncertainty of nitrogen budget in China

Are electric vehicles really the optimal option for the transportation sector in China to approach pollution reduction and carbon neutrality goals?

Profound worldwide fleet electrification is thought to be the primary route for achieving the target of carbon neutrality. However, when and how electrification can help mitigate environmental impacts and carbon emissions in the transport sector remains unclear. Herein, the overall life-cycle environmental impacts and carbon saving range of two typical A-class vehicles in China, including electric vehicle (EV) and internal combustion engine vehicle (ICEV), were quantified by the life cycle assessment model for endpoint damage with localization parameters. The results showed that the EV outperformed the ICEV for the total environment impact after a travel distance of 39,153 km and for carbon emissions after 32,292 km. The ICEV was more carbon-friendly only when the driving distance was less than 3229 km/a. Considering a full lifespan travel distance of 150,000 km, the whole life-cycle average environmental impacts of EV and ICEV were calculated as 8.6 and 17.5 mPt/km, respectively, but the EV had 2.3 times higher impacts than the ICEV in the production phase. In addition, the EV unit carbon emission was 140 g/km, 46.8% lower than that of the ICEV. Finally, three potential reduction scenarios were considered: cleaner power mix, energy efficiency improvement and composite scenario. These scenarios contributed 19.1%, 13.0% and 32.1% reductions, respectively. However, achieving carbon peak and neutrality goals in China remains a great challenge unless fossil fuels are replaced by renewable energy. The research can provide scientific reference for the method and practice of emission reduction link identification, eco-driving choice and emission reduction path formulation.

A new perspective on anthropogenic nitrogen loss mitigation strategies: Integrated control via sustainable regional integration

Unregulated regional integrated development disrupts the reactive nitrogen (Nr) cycle, adding complexity to anthropogenic Nr environmental losses. The objective of this study was to establish a framework for mitigating anthropogenic Nr loss through a new regional integration perspective by analyzing anthropogenic Nr loss and integrated control strategies in the Yangtze River Delta (YRD) region from 2011 to 2020. The results revealed that the total Nr loss in the YRD ranged from 1780.7 to 1972.0 Gg N yr-1. Re-linking cropland and livestock is crucial for reducing Nr loss, as they act as the main sources of Nr loss. Spatial analysis at the regional scale revealed that regional integration has led to a dispersion of Nr loss, while uneven development among cities has resulted in a westward shift of 8.6 km in the Nr loss centroid, suggesting the need for the implementation of collaborative governance and integrated environmental regulation in the YRD. At the city scale, 27 cities were clustered into six types based on the similarity of Nr loss structural characteristics, allowing for the development of targeted reduction policies based on the specific Nr structural characteristics of each city. The results of driver and mitigation potential analysis indicated the feasibility of achieving the shared goal of sustainable regional integration and the application of optimal mitigation strategies in different cities and the YRD. Overall, the new-perspective framework established in this study provides valuable references for sustainable Nr management in the context of regional integration.

Decoding China's anthropogenic typical pollutant discharge patterns: Long-term dynamics and hotspot transitions driven by population, diet, and sanitation

Human activities have led to an alarming increase in pollution, resulting in widespread water contamination. A comprehensive understanding of the quantitative relationship between anthropogenic pollutant discharges and the escalating anthropogenic disturbances and environmental efforts is crucial for effective water quality management. Here we establish a Model for Estimating Anthropogenic pollutaNts diScharges (MEANS) and simulate the long-term dynamics of various types of anthropogenic discharges in China based on an unprecedented spatio-temporal dynamic parameter dataset. Our findings reveal that from 1980 to 2020, anthropogenic discharges exhibited an overall trend of initially increasing and subsequently decreasing, with the peak occurring around 2005. During this period, the dominant pollution sources in China shifted from urban to rural areas, thereby driving the transition of hotspot pollutants from nitrogen to phosphorus in the eastern regions. The most significant drivers of anthropogenic pollutant discharges gradually shifted from population size and dietary structure to wastewater treatment and agricultural factors. Furthermore, we observed that a significant portion of China's regions still exceed the safety thresholds for pollutant discharges, with excessive levels of total phosphorus (TP) being particularly severe. These findings highlight the need for flexible management strategies in the future to address specific pollution levels and hotspots in different regions. Our study underscores the importance of considering the complex interplay between anthropogenic disturbances, environmental efforts, and long-term anthropogenic pollutant discharges for effective water pollution control.

Evaluating the anthropogenic nitrogen emissions to water using a hybrid approach in a city cluster: Insights into historical evolution, attribution, and mitigation potential

Anthropogenic reactive nitrogen (Nr) emissions from agricultural production and food consumption in city clusters have caused water quality degradation and scarcity. In this study, anthropogenic Nr emissions to the water environment were quantitatively evaluated in the Yangtze River Delta city cluster from 2011 to 2020 using coupling nitrogen (N) flow analysis and the grey water footprint (GWF) method. The spatiotemporal characteristics of the GWF and the relative contributions of natural and human factors to the water pollution level (WPL) were analyzed. The results showed that from 2011 to 2020, the total N-related GWF decreased by 12.1 %, mainly driven by reduced fertilizer application and livestock numbers. In 2020, the primary pollution source changed from livestock to humans; however, non-point sources still dominated the GWF. The spatial clustering trend of the GWF was significant: high and low GWF were mainly concentrated in the northeast and southwest regions, respectively. From 2011 to 2020, the mean center of the GWF moved west due to the decrease and increase in the eastern and western regions, respectively, supporting the pollution haven hypothesis. The WPL ranged from 2.67 to 5.03 and fluctuated due to variations in precipitation. The relative contributions of natural and human factors to the WPL evolution were 72.9 % and 27.1 %, respectively. According to the scenario analysis, increasing the N use efficiency to 50 %, manure recycling rate to 80 %, and sewage treatment rate in urban and rural regions to 98 % and 40 %, respectively, could decrease GWF by 39.6 %. The present study establishes an open framework to evaluate anthropogenic N emissions to water, and the outcomes provide valuable references for sustainable N management in city clusters.

Nitrogen flow in the food production and consumption system within the Yangtze River Delta city cluster: Influences of cropland and urbanization

Intensive anthropogenic activities associated with the food production and consumption system (FPC) drive massive reactive nitrogen inputs to city clusters resulting in serious nitrogen (N) pollution. We conducted a substance flow analysis to examine N flows in the FPC within the Yangtze River Delta city cluster from 2011 to 2019. The total N input and output showed parabolic downward trends, with decreases from 4008.27 to 3472.57 Gg N yr^-1 and 3518.65 to 3061.29 Gg N yr^-1, respectively; chemical fertilizer (54.7%-57.3%) and N loss (87.1%-90.9%) were the primary components of N input and output, respectively. The decreased total N input was related to reductions in chemical fertilizers and livestock numbers. However, a notable increase in N input to the human subsystem was observed, and urbanization was associated with increased N inputs within the human subsystem via higher amounts of food N consumed per capita and proportions of animal-based food N consumed. Total N loss initially increased then decreased; Nantong, Jiaxing, Shanghai, Yancheng, Taizhou, and Yangzhou were the top six cities in N loss intensity. The proportion of cultivated land area, livestock numbers per unit area, and population density were important factors influencing the spatial heterogeneity of N loss intensity. Twenty-six cities were divided into six groups based on their N loss composition, and various N management strategies were proposed. This study highlights the strong influences of cropland and urbanization on N flows within the FPC, which can be used as a reference for N management at a city cluster scale.