Cutting ammonia emissions is cost-effective way to mitigate air pollution

Reducing ammonia emissions could be a more cost-effective way to limit fine particulate matter air pollution than focused nitrogen oxide reduction, researchers report. Ammonia is widely used in the production of agricultural fertilizers critical to grow much of the planet's food. Although pivotal in supporting global food security, agricultural ammonia emissions also negatively impact the environment and represent a significant source of air pollution. When released into the air, ammonia (NH₃) bonds with nitrogen oxides (NO_x) and sulfur dioxide to form fine particulates. These particulates, less than 2.5 micrometers in diameter (PM_2.5) are often associated with severe health impacts, including death. According to the World Health Organization, PM_2.5 air pollution is the single largest environmental threat to human health, making the mitigation of its precursors – NH₃ andNO_x – a priority for many nations worldwide. However, the relative global contribution of NH₃ and NO_x emissions to impacts on human health from PM2.5 has not yet been determined. While much effort has been focused on reducing NO_x emissions, the best and most cost-effective way to reduce PM_2.5 air pollution remains elusive. To address these unknowns, Baojing Gu and colleagues developed a novel metric they call the "N-share" of PM_2.5 pollution, which is the relative change of total PM_2.5 concentration with and without emissions from reactive nitrogen like NH_3, and evaluated its impact from 1990 to 2013. Gu et al. found that nitrogen emissions caused roughly 23.3 million years of life lost in 2013 – a total corresponding to an economic cost of $420 billion. According to the authors, the abatement cost for ammonia emission is only 10% of what it would take to eliminate an equivalent amount of NO_x. Thus, reducing NH₃ emissions would be a more cost-effective way to limit PM_2.5 and mitigate its harmful health impacts rather than solely focusing on reducing NO_x. "Gu et al. show that the global burden of disease associated with nitrogen air pollution exposure is estimated to cause millions of deaths and lost years of healthy life annually and, together with economic setbacks, will cost far more to fix tomorrow than it would if action is taken today," writes Jan Erisman in a related Perspective.