Ammonia reduction should be prioritized in Europe’s fight against air pollution

Pollution particles of less than 2.5 micrometers in diameter in the air around us, also known as fine particles or PM_2.5, is one of the leading environmental risk factors for premature deaths worldwide, including in Europe. Despite successful reductions in the emissions of air pollutants such as sulfur dioxide, particulate matter, and nitrogen oxides, the new World Health Organization (WHO) air quality guidelines are still exceeded in many parts of the continent.

According to the authors of the new study just published in Nature Communications, phasing out emissions of ammonia and nitrogen oxides could reduce concentrations of PM_2.5 by 2.3 µg/m³ over Europe on annual average and avoid about 100,000 premature deaths each year. When it comes to reducing pollution, cutting down on nitrogen oxide has a steady impact. However, reducing ammonia is not as effective at first, but it becomes crucial when aiming for significant pollution reduction. Moreover, abating ammonia emissions is about five to ten times as cost-efficient for the same reduction in PM_2.5 making it clear that a focus on ammonia reductions will be vital to achieve deep cuts in pollution over all of Europe.

“We were able to identify different chemical regimes in our modeling approach. The effects originally differ in different parts of Europe as the initial chemical composition of the atmosphere varies,” explains Zehui Liu, lead author of the study and a researcher at the Laboratory for Climate and Ocean-Atmosphere Studies at Peking University in China. “We see the same effect when abatement kicks in successfully – once nitrogen oxide reductions are in place, it becomes increasingly more important to remove ammonia.”

The authors agree that their results will help establish policy priorities. “Most nitrogen oxide emissions come from factories and vehicles, and we've already taken steps to control them. However, when it comes to agriculture, which is the main source of ammonia emissions, we haven't made much progress. This means there's an opportunity to achieve positive results by implementing effective measures in the agricultural sector,” notes Wilfried Winiwarter, a study coauthor and senior research scholar in the IIASA Pollution Management Research Group

“We found that air quality improvements differ from one region to another. Additionally, achieving further improvements in air quality levels for particulate matter would also demand stricter control measures for pollutants other than nitrogen oxides and ammonia,” adds Harald Rieder, another study coauthor and Professor at the University of Natural Resources and Life Sciences (BOKU) Vienna.

“We can also learn for other parts of the world, such as China and India. Having successfully initiated air pollution reductions in China, we now need to determine the next steps of emission reductions,” concludes study coauthor Lin Zhang, a Professor at Peking University.

Reference
Liu, Z., Rieder, H.E., Schmidt, C., Mayer, M., Guo, Y., Winiwarter, W., and Zhang, L. (2023). Optimal reactive nitrogen control pathways identified for cost-effective PM_2.5 mitigation in Europe. Nature Communications 14, 4246. DOI: 10.1038/s41467-023-39900-9