Large-scale, industrialized farming has contributed significantly to the increased global food supply to feed the fast-growing world population over the past few decades, but it also comes with severe threats to the environment. In particular, the excessive application of chemical fertilizer has led to large emissions of reactive nitrogen compounds into the atmosphere, where they become significant components of fine particulate matter (PM2.5) air pollution. Intercropping has been considered as a sustainable agricultural practice that can reduce the environmental impacts of agriculture, but its potential benefits beyond the farm scale have rarely been examined. Here we develop a new parameterization scheme for belowground mutualistic interactions between intercropped crops in the DeNitificaiton-DeComposition biogeochemical model, which is then used to simulate and quantify the benefits of nationwide adoption of maize–soybean systems in China in terms of gains in crop production, decreases in fertilizer consumption, and reductions in ammonia (NH3) emission. We further examine how such a decline in NH3 emission could lessen the downwind formation of PM2.5 using the GEOS-Chem chemical transport model. We show that annual mean inorganic PM2.5 concentrations can be reduced by up to 1.5 μg m–3 with the nationwide adoption of maize–soybean intercropping, with a corresponding annual net economic benefit of US$67 billion, of which US$13 billion arises from saved health costs from reduced air pollution. This study demonstrates the economic and environmental values of intercropping systems in dually promoting food security and environmental health, which can serve as a basis for policy consideration as governments and stakeholders explore more sustainable farming options.

Global food security is one of the most pressing issues affecting human wellbeing. The United Nations has projected that the world population will exceed 9.5 billion by 2050 (United Nations 2014), which is expected to double the global demand for food crops due to the rising population, a worldwide shift toward a more meat-intensive diet, food waste and food surplus-deficit disparity inherent in the current food distribution system (Tilman et al 2011, FAO et al 2012, Lam et al 2013, Hiç et al 2016). It is crucial to enhance the production of food and animal feed to cope with the rising demand, but the associated environmental costs could be substantial. Farmland expansion has already displaced more than half of grasslands and more than 30% of forests globally, with tremendous impacts on wildlife habitats, biodiversity and ecosystem services (Foley et al 2011, 2012, Tai et al 2013). If no measures are taken to reduce the global food demand, current trends in people's meat and dairy intake habit and food waste would raise the demand for croplands further by ~19% and ~6%, respectively, by 2050, despite higher crop production enabled by conventional agricultural intensification