Nr Emissions Research Articles

Towards sustainable fruit production: Identifying challenges and optimization strategies

CONTEXTThe transition to sustainable fruit production is vital for global sustainability and agricultural development. However, implementing these insights into practice faces significant challenges. OBJECTIVESPomelo (Citrus maxima), a prominent citrus species in tropical and subtropical regions, has been cultivated to enhance farmer profitability but increasing yields often comes at the cost of environmental degradation. This study uses pomelo as a case study to assess key factors influencing pomelo production and establish optimal practices that meet consumption-based food while co-benefits for environmental and economic sustainability. METHODSA comprehensive study was conducted by combining 1155 farm surveys (from 2010, 2018, and 2022) with 31 field experiments. Life cycle assessment (LCA), classification and regression tree (CART) analysis, and scenario analysis were employed to develop pathways for sustainable pomelo production in Pinghe County, Fujian Province, China. RESULTS AND CONCLUSIONSResults show no significant differences in pomelo yield across the three years; however, pomelo production in 2022 demonstrated a 60 %–67 % lower in environmental footprints and a 64 %–76 % higher benefit-cost ratio (BCR) compared to 2010 and 2018. Tree age was identified as a critical factor influencing pomelo yield, with optimal yields observed in trees older than 12.5 years. The rate of phosphorus fertilizer application was a key determinant of the phosphorus footprint (PF), which was positively correlated with phosphorus fertilizer rates. Similarly, nitrogen fertilizer application significantly impacted both carbon and nitrogen footprints (CF and NF) as well as the BCR. CF and NF increased with higher nitrogen fertilizer rates, while BCR exhibited a negative correlation with nitrogen fertilizer application. Implementing Science and Technology Backyards (STB) followed by farmer training of slightly more than pomelo nutrient requirements practice (SNRP) or coordinate management by farmers and researchers of matching pomelo nutrients requirement practice (MNRP) had 50 %–91 % lower environmental footprints per ton of pomelo produced and 15 %–44 % higher BCR compared to current farming practices (FP) via reducing 46 %–77 % N, 49 %–92 % P2O5, and 42 %–73 % K2O per hectare. Moreover, adopting 100 % MNRP in pomelo production, along with sustainable fertilizer practices and the implementation of innovative fertilizers, could reduce greenhouse gas (GHG) emissions (0.76 Tg), reactive nitrogen (Nr) emissions (8.76 Gg), phosphorus (P) losses (0.84 Gg), and augment net ecosystem economic benefits (NEEB) (0.94 billion CNY) at the county scale. SIGNIFICANCEOur study provides evidence-based strategies for achieving sustainable pomelo production through multi-stakeholder collaboration of STB, government, enterprises, and smallholders.

Characteristics of reactive nitrogen emissions from solid waste and its environmental impact in the Yellow River Basin, China

ABSTRACT One of the topics of concern on a global scale is the source, fate, and environmental effects of solid waste nitrogen (N). Quantitative calculation and evaluation of solid waste N (SWN) generation and its reactive N (Nr) emission characteristics, as well as their environmental effects in the basin ecosystem, are essential for the sustainable management of SWN and the improvement of the ecological environment. The accounting framework for the production of SWN and associated Nr emission was established using the Yellow River Basin of Henan section as an example. The findings revealed that SWN, with an annual average of 265.3 Gg N yr−1, grew by 17.2% over the previous ten years. The largest contributors were domestic waste N (82.5%) and livestock and poultry waste N (12.9%), with the remaining sources making up roughly 4.5%. The majority of the sources of Nr emissions were NH3 (63.2%), NOx (18.9%), and Nr lost to groundwater (12.3%), whereas N2O contributed just 5.7%. To mitigate Nr emissions from solid waste in the basin, enhancing solid waste classification, recycling, and composting treatment while reducing dumping and landfilling is vital. The study offers a scientific basis for the management and prevention of SWN in the basin.

Aspirational nitrogen interventions accelerate air pollution abatement and ecosystem protection.

Although reactive nitrogen (Nr) emissions from food and energy production contribute to multi-dimensional environmental damages, integrated management of Nr is still lacking owing to unclear future mitigation potentials and benefits. Here, we find that by 2050, high-ambition compared to low-ambition N interventions reduce global ammonia and nitrogen oxide emissions by 21 and 22 TgN/a, respectively, equivalent to 40 and 52% of their 2015 levels. This would mitigate population-weighted PM2.5 by 6 g/m3 and avoid premature deaths by 817 k (16%), mitigate ozone by 4 ppbv, avoid premature deaths by 252k (34%) and crop yield losses by 122 million tons (4.3%), and decrease terrestrial ecosystem areas exceeding critical load by 420 Mha (69%). Without nitrogen interventions, most environmental damages examined will deteriorate between 2015 and 2050; Africa and Asia are the most vulnerable but also benefit the most from interventions. Nitrogen interventions support sustainable development goals related to air, health, and ecosystems.

Role of reactive nitrogen species in changing climate and future concerns of environmental sustainability.

The nitrogen (N) cycle is an intricate biogeochemical process that encompasses the conversion of several chemical forms of N. Given its role in food production, the need for N for life on Earth is obvious. However, the release of reactive nitrogen (Nr) species throughout different biogeochemical processes contributes to atmospheric pollution. Several human activities generate many species, including ammonia, nitrous oxide (N2O), nitric oxide, and nitrate. The primary reasons for this change are the use of nitrogen-based fertilizers, industrial activities, and the burning of fossil fuels. N2O poses a significant threat to environmental sustainability on our planet, with its global warming potential approximately 298 times greater than that of CO2. It has direct or indirect impacts on the environment, agroecosystem, and human life on earth. Solar, hydroelectric, geothermal, and wind turbines must be used to reduce Nr emissions. In addition, enterprises should install catalytic converters to minimize nitrogen gas emissions. To reduce Nr emissions, strategic interventions like fertilizer balancing are needed. This work will serve as a comprehensive guide for researchers, academics, and policymakers. Additionally, it will also assist social workers in emphasizing the Nr issue to the public in order to raise awareness within worldwide society.

Tracking social-economic system nitrogen flow in China for emissions reduction and efficiency improvement

The increasing human demand have driven intensive reactive nitrogen (Nr) use, leading to high emissions and low efficiency in entire social-economic system. Herein, we accomplished a social-economic Nr flow model to trace the multi-sectorial Nr use, efficiency, and emissions in China from 1980 to 2020. The results showed that Nr use intensity increased 3.1-fold within four decades, with the decreasing proportions of Nr recovery from 32.7 % to 16.8 %. The Nr use pathways of production, consumption and waste management stages showed low resources use efficiency in agriculture and industrial production, high degree of consumption loss, insufficient waste treatment characteristics currently. Nr emissions peaked in 2012 and declined 12.7 % to 2020 owing to the nitrogen oxides control and mitigating overuse of fertilizers, and will continuously decrease under strategies in 2040 (41.7 % compared with 2012), indicating the large potential for emission reduction and efficiency improvement in next few decades.

A Decadal Change in Atmospheric Nitrogen Deposition at a Rural Site in Southern China

Elevated atmospheric reactive nitrogen (Nr) emissions and the subsequent nitrogen (N) deposition have negatively impacted the global environment, particularly in China. In order to assess the long-term trends in atmospheric N deposition in the south of China, Taojiang County in Hunan Province was selected as a representative rural area for study. We analyzed interannual variation in atmospheric Nr, including gaseous ammonia (NH3), nitrogen dioxide (NO2), nitrate acid (HNO3) vapor, particulate ammonium (NH4+), and nitrate (NO3−) in air and NH4+-N and NO3−-N in precipitation from 2011 to 2020. The 10-year average atmospheric wet-plus-dry N deposition was 41.9 kg N ha−1 yr−1, which decreased by approximately 24% after 2012, indicating that NH3 and NOx emissions were effectively reduced by emission controls introduced in 2013. Wet deposition accounted for approximately 74% of the total N deposition and was significantly influenced by annual precipitation amount. Reduced N (NH3, pNH4+, and NH4+ in rainwater) was the dominant form, comprising approximately 58% of the total N deposition, while oxidized N (pNO3−, NO2, HNO3, and NO3− in rainwater) accounted for 42% of the total N deposition. Atmospheric HNO3, NO2, and NH3 concentrations and deposition declined by 30–80% over the decade, while particulate NH4+ and NO3− concentrations and deposition remained at relatively stable levels, which suggests that ongoing research and policy should focus on rural particulate pollution. Future strategies must concentrate on the integrated control of NH3 and NOx emissions to mitigate air pollution and protect human health, particularly in rural areas because current abatement efforts are primarily directed toward urban areas and the industrial sector, whereas non-point source NH3 pollution, influenced mainly by agricultural activities, dominates in rural regions.

Impacts assessment of nitrification inhibitors on U.S. agricultural emissions of reactive nitrogen gases

Fertilizer-intensive agriculture leads to emissions of reactive nitrogen (Nr), posing threats to climate via nitrous oxide (N2O) and to air quality and human health via nitric oxide (NO) and ammonia (NH3) that form ozone and particulate matter (PM) downwind. Adding nitrification inhibitors (NIs) to fertilizers can mitigate N2O and NO emissions but may stimulate NH3 emissions. Quantifying the net effects of these trade-offs requires spatially resolving changes in emissions and associated impacts. We introduce an assessment framework to quantify such trade-off effects. It deploys an agroecosystem model with enhanced capabilities to predict emissions of Nr with or without the use of NIs, and a social cost of greenhouse gas to monetize the impacts of N2O on climate. The framework also incorporates reduced-complexity air quality and health models to monetize associated impacts of NO and NH3 emissions on human health downwind via ozone and PM. Evaluation of our model against available field measurements showed that it captured the direction of emission changes but underestimated reductions in N2O and overestimated increases in NH3 emissions. The model estimated that, averaged over applicable U.S. agricultural soils, NIs could reduce N2O and NO emissions by an average of 11% and 16%, respectively, while stimulating NH3 emissions by 87%. Impacts are largest in regions with moderate soil temperatures and occur mostly within two to three months of N fertilizer and NI application. An alternative estimate of NI-induced emission changes was obtained by multiplying the baseline emissions from the agroecosystem model by the reported relative changes in Nr emissions suggested from a global meta-analysis: −44% for N2O, −24% for NO and +20% for NH3. Monetized assessments indicate that on an annual scale, NI-induced harms from increased NH3 emissions outweigh (8.5–33.8 times) the benefits of reducing NO and N2O emissions in all agricultural regions, according to model-based estimates. Even under meta-analysis-based estimates, NI-induced damages exceed benefits by a factor of 1.1–4. Our study highlights the importance of considering multiple pollutants when assessing NIs, and underscores the need to mitigate NH3 emissions. Further field studies are needed to evaluate the robustness of multi-pollutant assessments.

Integrated straw-derived biochar utilization to increase net ecosystem carbon budget and economic benefit and reduce the environmental footprint

ContextCrop residues are often returned to the soil to achieve soil carbon (C) sequestration in the agricultural sector, thereby mitigating climate change and soil degradation. However, direct straw incorporation may increase the risks of greenhouse gas (GHG) and reactive nitrogen (Nr) emissions. Objective and methodsTo comprehensively evaluate whether straw-derived biochar is a feasible alternative to straw for increasing grain yields and soil C sequestration while reducing GHG and Nr emissions in cropland, we conducted a two-factor field trial on maize farmland in northwest China during 2019–2021. Factor one comprised three straw incorporation methods (straw removal (T), total straw incorporation (S), and straw-derived biochar incorporation (B; biochar application at a straw/biochar ratio of 33%)) and factor two comprised two nitrogen (N) fertilizer application rates (0 and 300 kg ha–1). The relative benefits of the treatments for the maize productivity, net ecosystem carbon budget (NECB), carbon footprint (CF), nitrogen footprint (NF), and net ecosystem economic benefits (NEEB) were comprehensively evaluated by using the life cycle assessment (LCA) and Z-score methods. ResultsN fertilizer application was the main factor that increased maize productivity, NECB, NF, and NEEB in the maize agroecosystem. Under conventional N application, NECB increased by 244.0% (1647.37 kg C ha–1 yr–1) under SN compared with TN, and heterotrophic respiration (Rh) and N2O emissions increased by 70.3% and 34.9%, respectively. By contrast, BN increased NECB by 295.8% (1996.79 kg C ha–1 yr–1), and decreased Rh and N2O emissions by 8.2% and 20.9%, respectively. Hence, BN reduced the net global warming potential (NGWP) and greenhouse gas intensity (GHGI) of the farmland ecosystems by 56.4% (1609.49 kg CO2-eq ha–1 yr–1) and 46.5%, respectively, compared with SN. Moreover, the grain yield, water use efficiency (WUE) and N use efficiency increased significantly under BN compared with TN. Compared to SN, integrated straw-derived biochar utilization (pre-farm abatement + BN management on the farm) reduced the average CF and NF of the maize agroecosystem by 350.2% (4004.85 kg CO2-eq ha–1 yr–1) and 16.5% (12.68 kg N-eq ha–1 yr–1), respectively, and improved NEEB by $ 624.7 ha–1 yr–1. ConclusionsIntegrated straw-derived biochar utilization may be applied as a sustainable and economical straw alternative to straw for enhancing soil C sinks and reducing GHG and Nr emissions. Implications or significanceIntegrated straw-derived biochar utilization is an economically friendly and sustainable method for straw utilization in dryland maize production, and highly significant for mitigating climate and environmental degradation.

Mitigating life-cycle environmental impacts and increasing net ecosystem economic benefits via optimized fertilization combined with lime in pomelo production in Southeast China

Excessive fertilization is acknowledged as a significant driver of heightened environmental pollution and soil acidification in agricultural production. Combining fertilizer optimization with soil acidity amendment can effectively achieve sustainable crop production in China, especially in Southeast China. However, there is a lack of long-term studies assessing the environmental and economic sustainability of combining fertilizer optimization with soil acidity amendment strategies, especially in fruit production. A four-year field experiment was conducted to explore pomelo yield, fruit quality, and environmental and economic performance in three treatments, e.g., local farmer practices (FP), optimized NPK fertilizer application (OPT), and OPT with lime (OPT+L). The results showed that the OPT+L treatment exhibited the highest pomelo yield and fruit quality among the three treatments. The OPT treatment had the lowest net greenhouse gas (GHG) emissions among the three treatments, which were 90.1 % and 42.6 % lower than those in FP and OPT+L, respectively. It is essential to note that GHG emissions associated with lime production constitute 40.7 % of the total emissions from fertilizer production. The OPT+L treatment reduced reactive nitrogen (Nr) emissions and phosphorus (P) losses, compared to FP and OPT. Moreover, the OPT+L treatment increased the net ecosystem economic benefit by 220.3 % and 20.3 % compared with the FP and OPT treatments, respectively. Overall, the OPT and OPT+L treatments underscore the potential to achieve environmentally friendly and economically sustainable pomelo production. Our study provides science-based evidence to achieve better environmental and economic performance in pomelo production through optimized NPK fertilization and alleviating soil acidification by lime.

Agroecosystem modeling of reactive nitrogen emissions from U.S. agricultural soils with carbon amendments

Fertilizer-intensive agriculture is a leading source of reactive nitrogen (Nr) emissions that damage climate, air quality, and human health. Biochar has long been studied as a soil amendment, but its influence on Nr emissions remains insufficiently characterized. More recently, the pyrolysis of light hydrocarbons has been suggested as a source of hydrogen fuel, resulting in a solid zero-valent carbon (ZVC) byproduct whose impact on soil emissions has yet to be tested. We incorporate carbon amendment algorithms into an agroecosystem model to simulate emission changes in the year following the application of biochar or ZVC to the US. fertilized soils. Our simulations predicted that the impacts of biochar amendments on Nr emissions would vary widely (− 17% to + 27% under 5 ton ha−1 applications, − 38% to + 18% under 20 ton ha−1 applications) and depend mostly on how nitrification is affected. Low-dose biochar application (5 ton ha−1) stimulated emissions of all three nitrogen species in 75% of simulated agricultural areas, while high-dose applications (20 ton ha−1) mitigated emissions in 76% of simulated areas. Applying zero-valent carbon at 20 ton ha−1 exhibited similar effects on nitrogen emissions as biochar applications at 5 ton ha−1. Biochar amendments are most likely to mitigate emissions if applied at high rates in acidic soils (pH < 5.84) with low organic carbon (< 55.9 kg C ha−1) and inorganic nitrogen (< 101.5 kg N ha−1) content. Our simulations could inform where the application of carbon amendments would most likely mitigate Nr emissions and their associated adverse impacts.Graphical

Contrasting change trends in dry and wet nitrogen depositions during 2011 to 2020: Evidence from an agricultural catchment in subtropical Central China

Over the past decade, China has experienced a decline in atmospheric reactive nitrogen (Nr) emissions. Given that China's subtropical region is a significant nitrogen (N) deposition hotspot, it is essential to accurately quantify the ten-year variations in dry and wet N depositions in the context of reductions in atmospheric Nr emissions. Here, we evaluated the spatiotemporal variation in N deposition on forest, paddy field and tea field ecosystems in a typical subtropical agricultural catchment from 2011 to 2020. Our findings indicated a significant decrease in total N deposition in both the tea field ecosystem (41.5–30.5 kg N ha−1) and the forest ecosystem (40.8–25.7 kg N ha−1) (P < 0.05), but no significant change in the paddy field ecosystem (29.3–32.9 kg N ha−1). Specifically, dry N deposition exhibited significant declines except in the paddy field ecosystem, whereas wet N deposition had no significant change. The reduction in total oxidized and reduced N depositions in forest and tea field ecosystems is attributed to the decrease in NOx and NH3 emissions. Additionally, The ratio of NHx deposition to total N deposition all exceeded 0.5 in three ecosystems and the NHx/NOy ratio had an increasing trend (P < 0.05) in the paddy field, indicating that reactive N emissions from agricultural sources were the primary contributor to overall N deposition. Our study emphasizes that despite the decreasing trend in N deposition, it still exceeds the critical loads of natural ecosystems and requires stringent N emissions control, particularly from agricultural sources, in the future.

Insight into Municipal Reactive Nitrogen Emissions and Their Influencing Factors: A Case Study of Xiamen City, China

Reactive nitrogen (Nr) has been confirmed as an indispensable nutrient for the city ecosystem, but high-intensity human activities have led to nitrogen pollution in cities, especially in coastal cities, jeopardizing ecosystem services and human health. Despite this, the characteristics and influencing factors of Nr remain unclear in coastal cities, particularly in the context of rapid urbanization. This study used the material flow analysis method to estimate Nr emissions in Xiamen from 1995 to 2018 and evaluated the characteristics of excessive Nr emissions. The STIRPAT model was used to identify and explore factors contributing to observed Nr levels in coastal cities. As indicated by the results, (1) the quantity of Nr generated by human activities increased 3.5 times from 1995 to 2018. Specifically, the total Nr entering the water environment showed a general increase with fluctuations, exhibiting an average annual growth rate of 3.1%, increasing from 17.2 Gg to 35.1 Gg. (2) Nr loads in the nearby sea increased notably from 8.1 Gg in 1995 to 25.4 Gg in 2018, suggesting a threefold augmentation compared with surface waters and groundwater. (3) NOx was the gaseous Nr with the greatest effect on the atmosphere in Xiamen, which was primarily due to fossil fuel consumption. (4) Population and per capita GDP were major factors contributing to Nr load in the water environment, while Nr emission to the atmosphere was influenced by population and energy consumption. These findings provide valuable insights for tailored approaches to sustainable nitrogen management in coastal cities.

Mitigation of reactive nitrogen loss from arable soils through microbial inoculant application: A meta-analysis

Excessive N fertilizer application contributes to a surge in reactive N (Nr) emissions from agroecosystems, consequently threatening global ecosystems’ quality and security. Adding functional microorganisms to agricultural soils, namely microbial inoculants (MI), is a promising method for ensuring sustainable agriculture, but general assessment of microorganism-driven N losses and mediating factors (such as climate conditions, soil properties, and field management practices) remains unclear. Therefore, a comprehensive meta-analysis on the effect of MI addition on NH3 volatilization, N2O emissions, and N leaching in soil-crop systems was conducted by integrating 50 published articles (188 paired observations). The MI application significantly reduced N2O emissions and NH3 volatilization by 29.8% and 24.9%, respectively. The boosted regression tree model showed that the soil organic carbon (SOC) and soil pH significantly affected the efficacy of MI application on both NH3 and N2O loss mitigation. The effects of MI application on N leaching were not clear due to limited data points. Additionally, MI addition significantly increased the abundance of denitrification functional genes (nirK, nirS, and nosZ). In conclusion, MI application presented a high potential to reduce Nr from croplands, future adoption of MI techniques should consider the effects of soil properties and field practices on its efficacy in order to achieving sustainable N management in crop production systems.

The nitrogen and carbon footprints of ammonia synthesis in China based on life cycle assessment

The global nitrogen (N) cycle has emerged as an earth system process with more serious artificial disruption than climate change. Artificially synthesized reactive nitrogen (Nr) already accounts for nearly 50% of the total Nr in the earth system. The massive anthropogenic conversion of inert nitrogen (N2) to Nr is a major driver of imbalance and disruption of the earth's N cycle, where the artificial ammonia (NH3) synthesis process is the main trigger. Existing studies on life cycle environmental impacts of ammonia synthesis mainly focused on the greenhouse effect but lacked or underestimated the interference with the nitrogen cycle due to currently incomplete nitrogen footprint frameworks. In addition, the comprehensive evaluation of the nexus between nitrogen and carbon footprint of NH3 synthesis systems is also insufficient. Attempting to solve the above-mentioned problems, life cycle assessment models of seven ammonia synthesis systems were established considering different raw material pathways and production technologies under China's context, assisted by the Brightway2 platform. The general framework of nitrogen footprint accounting (GFNFA) that was established by the authors previously was employed to assess the ammonia synthesis on nitrogen footprint covered all ecosphere. The performance and hotspots of the system nitrogen footprint, carbon footprint (CF) and nitrogen-carbon nexus were then systematically quantified and analyzed. Results indicated that electrolysis-based ammonia powered by renewable and nuclear energy had the lowest Nr emission (0.499–1.148 kg Nr/t NH3) and carbon emission (592.822–1045.494 kg CO2-eq/t NH3). Among the seven ammonia synthesis systems investigated, biomass-based ammonia had the largest Nr emission and system nitrogen accumulation, and it converts the most N2 to Nr per ton ammonia produced, due to the extensive resources consumption and emissions during straw growth and direct Nr emission in gasification process. Thus, it caused the most significant disturbance to the earth's nitrogen cycle. The nexus between nitrogen and carbon footprints was revealed that the system's energy consumption was found to be a common driver through hotspots and contribution analysis. NH3 synthesis efficiency was the most determining factor in the system's Nr and carbon emissions. With a 15% increase in synthesis efficiency, nitrogen and carbon footprints can be reduced by more than 12.5%. This study can help researchers better understand the life cycle impacts of ammonia synthesis systems on earth's nitrogen and carbon cycle from multidisciplinary ecological origins.

Soil Emissions of Reactive Nitrogen Accelerate Summertime Surface Ozone Increases in the North China Plain.

Summertime surface ozone in China has been increasing since 2013 despite the policy-driven reduction in fuel combustion emissions of nitrogen oxides (NOx). Here we examine the role of soil reactive nitrogen (Nr, including NOx and nitrous acid (HONO)) emissions in the 2013-2019 ozone increase over the North China Plain (NCP), using GEOS-Chem chemical transport model simulations. We update soil NOx emissions and add soil HONO emissions in GEOS-Chem based on observation-constrained parametrization schemes. The model estimates significant daily maximum 8 h average (MDA8) ozone enhancement from soil Nr emissions of 8.0 ppbv over the NCP and 5.5 ppbv over China in June-July 2019. We identify a strong competing effect between combustion and soil Nr sources on ozone production in the NCP region. We find that soil Nr emissions accelerate the 2013-2019 June-July ozone increase over the NCP by 3.0 ppbv. The increase in soil Nr ozone contribution, however, is not primarily driven by weather-induced increases in soil Nr emissions, but by the concurrent decreases in fuel combustion NOx emissions, which enhance ozone production efficiency from soil by pushing ozone production toward a more NOx-sensitive regime. Our results reveal an important indirect effect from fuel combustion NOx emission reduction on ozone trends by increasing ozone production from soil Nr emissions, highlighting the necessity to consider the interaction between anthropogenic and biogenic sources in ozone mitigation in the North China Plain.

Optimal reactive nitrogen control pathways identified for cost-effective PM2.5 mitigation in Europe

Excess reactive nitrogen (Nr), including nitrogen oxides (NOx) and ammonia (NH3), contributes strongly to fine particulate matter (PM2.5) air pollution in Europe, posing challenges to public health. Designing cost-effective Nr control roadmaps for PM2.5 mitigation requires considering both mitigation efficiencies and implementation costs. Here we identify optimal Nr control pathways for Europe by integrating emission estimations, air quality modeling, exposure-mortality modeling, Nr control experiments and cost data. We find that phasing out Nr emissions would reduce PM2.5 by 2.3 ± 1.2 μg·m−3 in Europe, helping many locations achieve the World Health Organization (WHO) guidelines and reducing PM2.5-related premature deaths by almost 100 thousand in 2015. Low-ambition NH3 controls have similar PM2.5 mitigation efficiencies as NOx in Eastern Europe, but are less effective in Western Europe until reductions exceed 40%. The efficiency for NH3 controls increases at high-ambition reductions while NOx slightly decreases. When costs are considered, strategies for both regions uniformly shift in favor of NH3 controls, as NH3 controls up to 50% remain 5-11 times more cost-effective than NOx per unit PM2.5 reduction, emphasizing the priority of NH3 control policies for Europe.

Exploring a sustainable rice-cropping system to balance grain yield, environmental footprint and economic benefits in the middle and lower reaches of the Yangtze River in China

Environmental degradation and resource scarcity are serious challenges faced by global rice production. Although rice production is crucial to ensure global food security, it is also one of the principal sources of greenhouse gas (GHG) and reactive nitrogen (Nr) emissions. Exploring rice-cropping systems with a low environmental footprint and high grain yield and economic benefits is a crucial strategy to improve the sustainability of rice production. Here, life cycle assessment was used to compare the performance of middle-season rice (MR), double-season rice (DR) and ratoon rice systems (RR) based on farmer-reported data in the middle and lower reaches of the Yangtze River of China. The average annual grain yields of DR, MR, and RR were 13.68, 8.96 and 11.97 t ha−1, respectively. Although RR produced 12.5% lower grain yield, it had 41.2% lower global warming potential (GWP) and 33.8% smaller eutrophication potential (EP) than DR, which resulted in lower greenhouse gas intensity (GHGI) and reactive nitrogen intensity (NrI). The lower GWP and EP in RR were mainly attributed to lower agricultural inputs, smaller CH4 and N2O emissions and less Nr losses. Compared with MR, RR had higher GWP and EP, but significantly higher grain yield (33.6%) in RR contributed to lower GHGI and similar NrI. In all three cropping systems, CH4 emissions and NH3 volatilization had the highest contributions to GWP and EP, respectively. Compared with the other two cropping systems, RR exhibited the highest net economic income (NEI), benefit-cost ratio and eco-efficiency. Overall, our results suggested that RR is a sustainable rice-cropping system that can coordinate grain yield, environmental footprint and economic benefits.

Driving reactive nitrogen emissions in China: Competition between scale and efficiency

AbstractReactive nitrogen (Nr) emissions aggravate air and water pollution across the world. The factors influencing Nr emissions have not been clearly uncovered, especially for regions under rapid economic growth. Here we modeled total Nr emissions in mainland China and analyzed factors driving their growth during the decade (2000–2010) of fastest socioeconomic development. Results show that total Nr emissions increased from 24.9 terrogram (Tg) to 35.2 Tg, a 41.7% increase with an average annual growth rate of 3.5%. Agricultural activities, including crop planting and livestock and poultry breeding, together took a substantial but decreasing share, from 75.2% in 2000 to 61.4% in 2010. Industrial wastewater discharge, energy use, and crop production are the three largest sources contributing to the Nr emissions growth. Factors related to scale (e.g., the amount of industrial energy use) led to a growth in Nr emissions, and factors related to efficiency (e.g., industrial energy use per unit of economic output) contributed to reduction. The decreasing effect of efficiency gains, however, was still unable to overcome the increasing effect of the activity scale. More in‐depth research studies on mitigation strategies are required, to inform the decoupling between socioeconomic development and Nr emissions.

Accounting for the nitrogen footprint of food production in Chinese provinces during 1998–2018

Excessive emission of reactive nitrogen (Nr) in the environment has a negative impact on human health and biodiversity and aggravates the greenhouse effect. Food production and consumption is the primary source of anthropogenic Nr emissions. Currently, the research on China's nitrogen footprint lacks the exploration of regional differentiation, and the local virtual Nitrogen factor (VNF) is also insufficient. In this study, we developed localized VNF at the provincial level in China and then applied them to measure the per capita food production Nitrogen footprint of 31 provinces in mainland China from 1998 to 2018 by employing a modified N-Calculator model. We found that the national per capita food production N footprint varied from 15.30 to 21.09 kg/year over the past 20 years. Per capita food production N footprint of 29 provinces increased, ranging from 13% to 113%. The dominance of the food production N footprint of meat gradually increased, and the differences between regions showed a decreasing trend. Finally, we compared the results with different countries based on VNF and 2018 food consumption data. Although the limitations of the underlying data and parameters pose challenges to the accuracy of the estimation, our study provides an original data contribution to nitrogen footprint research to scientific communities and policymakers.

Reducing food-system nitrogen input and emission through circular agriculture in montane and coastal regions

Reducing biogeochemical flows (e.g., reactive nitrogen [Nr]) is essential for a sustainable food system. Previous studies lack tailored strategies for Nr reduction in smaller-scale agricultural production. We developed a framework coupling material flow analysis and system dynamics modeling to establish a pathway for Nr reduction. We applied this framework to Fujian, southeast China, a mountainous and coastal province with fragmented small-scale agricultural and large-scale aquaculture production. Crops, livestock, and aquaculture accounted for 44.03%, 31.11%, and 23.69%, respectively, of Nr input in 2019. Thus, crop and livestock production accounted for approximately 70% of total Nr emissions. Only 8.66% of the total Nr inputs were recycled from livestock to cropland, and the Nr use efficiency of all three food categories was less than 20%. A balanced diet among residents increased (by 15.5%) Nr emissions, whereas minimized food loss and waste partially neutralized (reduced by 17.9%) the increase in Nr emission from dietary changes. By contrast, recycling kitchen waste, manure, and straw would eliminate 39.5% of the regional-food-system Nr emissions. We conclude that a circular agricultural system with Nr recycling is effective to reduce Nr input and emissions through more unified crop and livestock production in montane and coastal regions of Fujian.