Ambitious nitrogen abatement is required to mitigate future global PM2.5 air pollution toward the World Health Organization targets

Abstract

Nitrogen oxides (NO_x) and ammonia (NH₃) contribute substantially to current global fine particulate matter (PM_2.5) pollution. Their future role remains unclear and is complicated by interactions with background emissions. Here, we show that under climate mitigation scenarios, by 2050, a hypothetical phaseout of anthropogenic NH₃ emissions would reduce PM_2.5 by 20%–60% locally and be more effective than phasing out NO_x. Reducing NH₃ by 25%, instead, would be less effective than 25% NO_x reduction for many regions. Future reductions of NO_x and sulfuric dioxides from clean energy transitions would shift the nonlinear chemical regime of secondary inorganic aerosol formation toward NH₃ saturation. The later NH₃ controls are installed, the deeper the required reductions will be to be effective, although for many regions such levels are still within technical feasibility, while NO_x controls will always remain effective. Nitrogen reductions remain useful for achieving the World Health Organization guideline target for PM_2.5, and NH₃ controls need to happen sooner rather than later.