A52E-03 Warming-induced increases in agricultural soil NH3 and NOx emissions could worsen PM2.5 air quality

Abstract

Agricultural soils are an important source of ammonia (NH₃) and nitrogen oxides (NOₓ), key precursors of fine particulate matter (PM₂.₅). While land-use changes and fertilizer applications are commonly considered in emission inventories, the role of climate-driven changes in soil nitrogen emissions on PM_2.5 pollution remains underexplored. Using a customized Community Land Model (CLM5) and GEOS-Chem High Performance (GCHP), we simulate agricultural soil NH₃ and NOₓ emissions and their impacts on PM₂.₅ under two CMIP6 scenarios: SSP2-4.5 and SSP5-8.5. We find that end-of-century warming alone increases global annual mean agricultural NH₃ and NOₓ emissions by 33% (5.4 Tg N yr⁻¹) and 12% (0.27 Tg N yr⁻¹), respectively, under SSP5-8.5. These increases can raise annual mean PM₂.₅ concentrations by up to 4.8 µg m⁻³ locally. In the US, climate-induced increases in soil nitrogen emissions alone may increase the population living in areas of non-attainment of U.S. PM₂.₅ air quality standards by 18.2 millions (+21%) under 2018 anthropogenic emission background. Under 50% reductions in anthropogenic NOₓ and SO₂ emissions, such increases in population living in non-attainment area is even stronger (22.8 millions, +69%). This highlights a significant and underappreciated climate penalty on PM₂.₅, especially in regions with high agricultural and low other anthropogenic NOₓ and SO₂ emissions. Our results suggest that existing emission inventories and air quality policies may underestimate future PM₂.₅ risks unless climate-sensitive biogeochemical feedbacks are included. These findings call for greater integration of Earth system processes into future air quality management strategies.

Plain-language Summary

As the climate warms, farm soils could release more nitrogen gases like ammonia and nitrogen oxides into the air. These gases help form fine particle air pollution, or PM₂.₅, which is harmful to human health. Our research used advanced computer models to predict how much more of these gases soils might emit in the future, and how that could affect air quality. We found that climate change alone could increase global agricultural ammonia emissions by 33% and nitrogen oxides by 12% by the end of the century. These extra emissions could raise PM₂.₅ levels significantly, especially in farming regions. In the United States, this could cause tens of millions more people to live in areas that exceed national air quality standards—even if other air pollutants like industrial emissions are reduced. These results show that climate change could make it harder to clean up air pollution, unless we account for how warming affects emissions from the land itself.