Mitigation potential of global ammonia emissions and related health impacts in the trade network Nature Communications 12, Article number: 6308 (2021) Cite this article Ammonia (NH3) emissions, mainly from agricultural sources, generate substantial health damage due to the adverse effects on air quality. NH3 emission reduction strategies are still far from being effective. In particular, a growing trade network in this era of globalization offers untapped emission mitigation potential that has been overlooked. Here we show that about one-fourth of global agricultural NH3 emissions in 2012 are trade-related. Globally they induce 61 thousand PM2.5-related premature mortalities, with 25 thousand deaths associated with crop cultivation and 36 thousand deaths with livestock production. The trade-related health damage network is regionally integrated and can be characterized by three trading communities. Thus, effective cooperation within trade-dependent communities will achieve considerable NH3 emission reductions allowed by technological advancements and trade structure adjustments. Identification of regional communities from network analysis offers a new perspective on addressing NH3 emissions and is also applicable to agricultural greenhouse gas emissions mitigation. With air pollution being reduced globally by controlling pollutants from industrial sectors, the far-less-regulated ammonia (NH3) emissions consequently become an important driver for fine particulate matter (PM2.5) pollution1,2,3,4. NH3 emissions contribute to PM2.5 pollution through the chemical formation of particulate ammonium sulfate and ammonium nitrate4,5 and lead to tens of thousands of deaths annually6. Nearly 90% of global NH3 emissions are emitted from agricultural sources1, including ammonia-based fertilizers and animal manure. Unfortunately, regulations for agricultural NH3 emissions are overall ineffective worldwide1. Outpacing many industrial sectors, agriculture is the leading sector in driving anthropogenic PM2.5 pollution in Europe and the eastern USA4,6,7. NH3 emissions are currently not regulated over high NH3 emitting regions, e.g., China1, although recent research shows that improving agricultural nitrogen management can achieve 34% reductions and reduce PM2.5 by up to 8 μg m−3 (ref. 8) More importantly, future increases in agricultural production to accommodate food demand of a growing population will increase the health risks from NH3-related environmental consequences9,10. As such, developing strategies to reduce NH3 emissions is urgent and would generate substantial environmental and health benefits1,6,8,11.Substantial efforts have already been made to reduce pollutant emissions at local scales1,8. In a globalized world, however, localized agricultural production is increasingly connected to foreign consumption owing to the expanding agricultural trade in order to meet food and nutritional demands around the world12. The current trade volume of global agricultural commodities accounts for over 20% of global agricultural production13, mostly occurring between Organisation for Economic Cooperation and Development (OECD) and non-OECD countries (such as China, India, and other Asian countries). Substantial NH3 emissions are related to international exports of agricultural commodities by mostly developing countries to meet the growing food demand of the developed world14. Understanding NH3 emissions embodied in international trade offers considerable potential to abate NH3 emissions.NH3 emission transfers through the global trade network can be quantified by global multiregional input–output (MRIO) models, which have been applied to measure trade-induced emissions of greenhouse gases15,16,17,18, primary PM2.5, and secondary PM2.5 precursors19,20,21,22,23,24,25. Oita et al.14 reported that about 26% of NH3 emissions in 2010 were embodied in the international trade of commodities. However, little attention was paid to the related public health burden, except for several recent analyses on the health impact of trade-related primary PM2.523,24,25 and secondary PM2.5 precursors22. Although these studies shed light on the international dimension of consumption-driven environmental pollution and related health risks, their insights into each type of air pollutant have been counteracted because of the different sources and mitigation potential. Especially, previous studies focused mainly on pollutant emissions from industrial sectors, and agricultural NH3 emission transfers and their environmental and health outcomes are still not fully understood1.Furthermore, transfers of the health burdens from trade-related NH3 emissions are determined by the structure of the international trade of agricultural commodities. Comparative advantages, such as availability of arable land, water resources, technologies, and geographical location, prompt various economies to participate in the production, processing, and trade of agricultural commodities. Those interregional activities transfer NH3 emissions and their health outcomes, together weaving a complex network26. Unveiling the network characteristics of health-effect transfers can target important regions, production sectors, consumption categories, and communities for reducing NH3 emissions and mitigating health damages.In this work, we aim to explore the mitigation potential of global ammonia emissions by analyzing the role of the international trade network. We show the trade-induced global agricultural NH3 emissions, consequent PM2.5 formation and related health impacts of the year 2012 in 181 economies, demonstrating large NH3 mitigation potential in international trade and associated benefits. We identify the role of leading communities in transferring the health impacts through international trade. We further demonstrate the potential of technological advancements and trade structure adjustments within leading countries in reducing trade-related NH3 emissions. These findings point out the importance of international collaborative efforts for the formulation of comprehensive international environmental policies and actions for addressing NH3 that are overlooked.Global trade-induced NH3 emissions of the year 2012 are assessed using the MRIO model with detailed NH3 emissions estimates from the Emissions Database for Global Atmospheric Research (EDGAR v4.3.2) inventory27 (see ‘Methods’). Since agricultural NH3 emissions (52,325 Gg) account for 89% of the global NH3 emissions (58,671 Gg) in 2012, we focus on NH3 emissions from the agricultural sector in this study. The embodied NH3 emissions in international trade balance (EEB) can be obtained as the difference of import-related emissions (EEI, total emissions in other regions related to domestic consumption) and export-related emissions (EEE, the total domestic emissions related to final consumption in other regions) (see Fig. 1 and ‘Methods’). An economy with a positive value of EEB is a net importer of embodied NH3 emissions, while that with a negative EEB is a net exporter. By linking the local emissions to global consumption, an estimated 23% (11,840 Gg) of global agricultural production-based emissions (PBEs), namely emissions caused by domestic production, are associated with international exports (Fig. 1a and Supplementary Data 1). Our estimation is consistent with the previously reported 26% of NH3 emissions embodied in the international trade in 201014. Owing to such substantial agricultural NH3 emissions embodied in international trade, the PBE of NH3 in most economies are remarkably different from their consumption-based emissions (CBEs), which allocate emissions occurring during food production and distribution to final consumers (Fig. 1b and Supplementary Data 2). It thus means that global transfers of agricultural NH3 emissions (Supplementary Data 3 and Supplementary Table 1) can reallocate PM2.5 and public health burdens across borders, i.e., improving (harming) air quality and health in importing (exporting) countries.Fig. 1: Global agricultural NH3 emissions associated with production, consumption, and trade.a Production-based emissions (PBEs) of NH3 (shaded) and export-related emissions (EEEs) of NH3 (pie charts) (Gg) in 2012. Pie charts inserted in (a) are the countries (highlighted by country’s abbreviation) with high EEE NH3 emissions from livestock and crop cultivation, respectively. b Consumption-based (CBE) and import-related emissions (EEIs) of NH3 (Gg) in 2012. Detailed results for each country are provided in the Supplementary Data files. The three-letter country abbreviations inserted in the plot are detailed in Supplementary Data 6. Maps were created by using ArcGIS version 10.7.1 (ESRI https://www.esri.com/en-us/arcgis/about-arcgis/overview).We quantify the contribution of trade-related NH3 emissions to PM2.5 exposure by utilizing a global chemical transport model (CTM) (GEOS-Chem) by perturbing NH3 emissions embodied in exported products (export-related emissions) for 181 countries (see ‘Methods’). Figure 2a shows that NH3 emissions resulting from producing final products that are ultimately consumed abroad occur in many developing countries, with adverse effects on local air quality. About 1–2 μg m−3 of PM2.5 in eastern China is contributed by agricultural NH3 emitted during the production of food that is exported. We found a similar magnitude of contributions to local PM2.5 for export in other countries, i.e., 0.6–1.2 μg m−3 in northern India and Pakistan, 0.6–1.5 μg m−3 in northern Italy and eastern European countries (e.g., Poland, Belarus, Ukraine), and 0.3–0.9 μg m−3 in the eastern USA and central Canada.Fig. 2: Air quality and health impacts of export-related NH3 emissions in 2012.a PM2.5 concentrations (μg m−3) induced by export-related NH3 emissions in 2012 are calculated by GEOS-Chem simulations. Attributable premature mortality density (deaths per 0.1° × 0.1° a−1) due to export-related NH3 emissions from b crop production and c livestock production. The attributable premature mortality is determined by GEOS-Chem modeled fractional contributions of export-driven NH3 emissions to total PM2.5 and the calibrated high-resolution PM2.5 data from GBD 201326. Premature mortality on a resolution of 0.1° × 0.1° is estimated following the methods of the GBD study to estimate the premature deaths from ambient PM2.5 exposure (see ‘Methods’). Maps were created by using the NCAR Command Language, version 6.4.0 (NCAR, https://doi.org/10.5065/D6WD3XH5).The associated public health burden is estimated using the integrated exposure–response (IER) functions following the method of the Global Burden of Disease (GBD) study28 (see ‘Methods’). The estimated premature deaths attributed to ambient PM2.5 exposure is a function of export-related NH3 emissions, local PM2.5 levels, population densities, and baseline mortality for different diseases. Here we consider the impacts from the four leading causes of death: ischemic heart disease, chronic obstructive pulmonary disease, cerebrovascular disease, and lung cancer. We estimated the mortality contribution from sectoral export-related agricultural NH3 emissions based on an assumption that the contribution of one sector to the disease burden of PM2.5 is directly proportional to its share of PM2.5 concentration.For a given country, the premature deaths from its sectoral export-related NH3 emissions can be calculated by multiplying its fractional contribution of sectoral export-related NH3 emissions to PM2.5 concentration by the total PM2.5 concentration-related mortalities for each 0.1° × 0.1° grid cell. The fractional contribution of sectoral export-related NH3 emissions to PM2.5 was estimated by the GEOS-Chem simulations (see ‘Methods’). The export-related NH3 emissions are related to 61 thousand premature deaths, especially in many developing countries (Supplementary Fig. 1 and Supplementary Table 2). High premature mortality is found in China (26.3 thousand deaths) and India (6.2 thousand deaths), due to their higher PM2.5 concentrations from export-related agricultural NH3 emissions and population densities. In Southeast Asia, premature mortality is estimated at about 2.0 thousand deaths, of which Bangladesh and Vietnam account for ~45% (0.9 thousand deaths) and 32% (0.7 thousand deaths). In Pakistan, ~37% of agricultural NH3 emissions and 0.9 thousand deaths are related to exports. PM2.5 pollution from export-related NH3 emissions is responsible for 2.1 thousand deaths in the USA. In Europe, the estimated premature mortality in Eastern European countries (9.7 thousand deaths) is much higher than those in Western Europe (3.9 thousand deaths).Figure 2b, c shows the health burdens estimated from sectoral export-related NH3 emissions. Premature mortality induced by export-related livestock production is 36 thousand deaths, and by export-related crop production is 25 thousand deaths. It suggests that NH3 emissions from trade-related livestock production need more strict control due to its higher overlap with residential regions that are populated and have high emissions of NOx and SO2, particularly over Mainland China and India (Fig. 2). Supplementary Table 3 shows the top 20 trading pairs of sectoral NH3 trade-related health impacts. We found that Mainland China and India suffer substantial health costs via exporting to developed countries. Moreover, there are large variations in the health effects across different regions of each country due to differences in local PM2.5 levels, population densities and agricultural production activities. For example, 73% (90%) of health burden from crop sector (livestock sector) in the USA was found on eastern USA (east of 95°W), and 58% (78%) of health burden from crop sector (livestock sector) was concentrated in northern India (north of 24°N). Northern China (north of 30°N) is the hotspot of China’s related premature deaths, accounting for about 70% from the crop sector or livestock sector. These results suggest that the health effects related to the livestock sector are more likely to be regionally concentrated, so place-based strategies on regional emission reduct
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Mitigation potential of global ammonia emissions and related health impacts in the trade network
