Substantial nitrogen pollution embedded in international trade

Anthropogenic emissions of reactive nitrogen to the atmosphere and water bodies can damage human health and ecosystems(1,2). As a measure of a nation's contribution to this potential damage, a country's nitrogen footprint has been defined as the quantity of reactive nitrogen emitted during the production, consumption and transportation of commodities consumed within that country, whether those commodities are produced domestically or internationally(3). Here we use global emissions databases(4,5), a global nitrogen cycle model(6), and a global input-output database of domestic and international trade(7,8) to calculate the nitrogen footprints for 188 countries as the sum of emissions of ammonia, nitrogen oxides and nitrous oxide to the atmosphere, and of nitrogen potentially exportable to water bodies. Per-capita footprints range from under 7 kg N yr(-1) in some developing countries to over 100 kg N yr(-1) in some wealthy nations. Consumption in China, India, the United States and Brazil is responsible for 46% of global emissions. Roughly a quarter of the global nitrogen footprint is from commodities that were traded across country borders. The main net exporters have significant agricultural, food and textile exports, and are often developing countries, whereas important net importers are almost exclusively developed economies. We conclude that substantial local nitrogen pollution is driven by demand from consumers in other countries.