Modeling the interinfluence of fertilizer-induced NH 3 emission, nitrogen deposition, and aerosol radiative effects using modified CESM2

Abstract. Global ammonia (NH3) emission is expected to continue to rise due to intensified fertilization for growing food to satisfy the increasing demand worldwide. Previous studies focused mainly on estimating the land-to-atmosphere NH3 injection but seldom addressed the other side of the bidirectional nitrogen exchange – deposition. Ignoring this significant input source of soil mineral nitrogen may lead to an underestimation of NH3 emissions from natural sources. Here, we used an Earth system model to quantify NH3-induced changes in atmospheric composition and the consequent impacts on the Earth's radiative budget and biosphere, as well as the impacts of deposition on NH3 emissions from the land surface. We implemented a new scheme into the Community Land Model version 5 (CLM5) of the Community Earth System Model version 2 (CESM2) to estimate the volatilization of ammonium salt (NH4+) associated with synthetical fertilizers into gaseous NH3. We further parameterized the amount of emitted NH3 captured in the plant canopy to derive a more accurate quantity of NH3 that escapes to the atmosphere. Our modified CLM5 estimated that 11 Tg-N yr−1 of global NH3 emission is attributable to synthetic fertilizers. Interactively coupling terrestrial NH3 emissions to atmospheric chemistry simulations by the Community Atmospheric Model version 4 with chemistry (CAM4-chem), we found that such emissions favor the formation and deposition of NH4+ aerosol, which in turn disrupts the aerosol radiative effect and enhances soil NH3 volatilization in regions downwind of fertilized croplands. Our fully-coupled simulations showed that global-total NH3 emission is enhanced by nitrogen deposition by 2.4 Tg-N yr−1, when compared to the baseline case with 2000-level fertilization but without deposition- induced enhancements. In synergy with observations and emission inventories, our work provides a useful tool for stakeholders to evaluate the intertwined relations between agricultural trends, fertilize use, NH3 emission, atmospheric aerosols, and climate, so as to derive optimal strategies for securing both food production and environmental sustainability.