Agricultural Nitrogen Emissions and Interconnections with Air Quality

Reactive nitrogen emissions (Nr; including nitrogen oxides, NO_x, and ammonia, NH₃) are important precursors of airborne PM_2.5 and ozone that adversely affect human and ecosystem health. Understanding their impacts is crucial for synergistic policies on climate and air pollution mitigation. Here we will present modeling studies to quantify the interconnections between agricultural nitrogen emissions and air quality. Using a metric called “N-share” of PM_2.5 pollution to represent the contribution of Nr compounds to total PM_2.5 concentration, we show that nitrogen accounted for 39% of global PM_2.5 exposure in 2013, increasing from 30% in 1990 with rising reactive nitrogen emissions and successful controls on sulfur dioxide. Controlling NH₃ tends to be more effective than NO_x for deep emission controls. Improving agricultural nitrogen management through strategies such as reduced nitrogen fertilizer use and improved manure management would reduce agriculture NH₃ emissions by 23%-39% in China. From the consumption aspect, eliminating global food loss and waste in 2015 would equivalently reduce anthropogenic NH₃ emissions associated with food production by 11.4 Tg (16%), decrease local PM_2.5 concentrations by up to 5 μg m^-3, and mitigate nitrogen critical load exceedances in global biodiversity hotspots by up to 19%. We also identify optimal Nr control pathways for Europe by integrating air quality modeling and cost data. When costs are considered, strategies for both western and eastern Europe shift in favor of NH₃ controls, as NH₃ controls up to 50% remain 5-11 times more cost-effective than NO_x per unit PM_2.5 reduction there.