Reactive nitrogen in and around the northeastern and Mid-atlantic US: Sources, sinks, and connections with ozone

Authors: HUANG, M - Goddard Space Flight Center; CARMICHAEL, G - University Of Maryland; CRAWFORD, J - National Aeronautics And Space Administration (NASA); BOWMAN, K - National Aeronautics And Space Administration (NASA); DE SMEDT, I - Royal Belgian Institute Of Natural Sciences (IRSNB/KBIN); COLLIANDER, A - California Institute Of Technology; Cosh, Michael; KUMAR, S - Goddard Space Flight Center; GUENTHER, A - University Of California Irvine; JANZ, S - Goddard Space Flight Center; STAUFFER, R - Goddard Space Flight Center; THOMPSON, A - Goddard Space Flight Center; FEDKIN, N - Goddard Space Flight Center

Submitted to: Atmospheric Chemistry and Physics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/23/2024
Publication Date: 2/3/2025
Citation: Huang, M., Carmichael, G.R., Crawford, J.H., Bowman, K.W., De Smedt, I., Colliander, A., Cosh, M.H., Kumar, S., Guenther, A.B., Janz, S.J., Stauffer, R.M., Thompson, A.M., Fedkin, N.M. 2025. Reactive nitrogen in and around the northeastern and Mid-atlantic US: Sources, sinks, and connections with ozone. Atmospheric Chemistry and Physics. 25:1449-1476. https://doi.org/10.5194/acp-25-1449-2025.
DOI: https://doi.org/10.5194/acp-25-1449-2025

Interpretive Summary: Regional earth system models are useful for understanding the impacts different parameters on the overall system. New parameters are updated with new information to focus on the improvements on reactive nitrogen. Three case studies were conducted and it was demonstrated that hydrological variability can have significant impacts on environmental fluxes related to reactive nitrogen. This will guide future investigations to show the value of hydrologic monitoring and field experimentation for model advancement.

Technical Abstract: This study applies a regional Earth system model (NASA-Unified Weather Research and Forecasting with online chemistry) with updated parameterizations for selected land-air exchange processes and multi-platform observations, to first estimate reactive nitrogen (Nr = oxidized NOy + reduced NHx) emissions from anthropogenic and natural sources, nitrogen dioxide (NO2) column densities and surface concentrations, total and speciated Nr dry or/and wet deposition fluxes during 2018–2023 over the northeastern and Mid-Atlantic US most part of which belong to nitrogen oxides-limited or transitional chemical regimes. The estimated multi-year Nr concentrations and deposition fluxes are then compared with and related to ozone (O3), in terms of the spatiotemporal variability and their key drivers as well as possible ecosystem impacts. Finally, through three sets of case studies, we identify and discuss about 1) the capability of land data assimilation (DA) to reduce the uncertainty in modeled land surface states at daily-to-interannual timescales, that can be propagated into the atmospheric chemistry fields; 2) the impacts of irrigation on land surface and atmospheric fields as well as pollutants’ ecosystem uptake and impacts; and 3) the impacts of transboundary air pollution during selected extreme events on pollutants’ budgets and ecosystem impacts. With the updated model parameterizations and anthropogenic emission inputs, the eastern US surface O3 modeled by this tool persistently agrees better with observations (i.e., with root-mean-square errors staying within 4–7 ppbv for the individual years’ May-June-July) than those in literature where model errors exceeded 20 ppbv. Based on model calculations, surface O3 correlates more strongly with early afternoon NO2 columns than formaldehyde columns (r=0.54 and 0.40, respectively). The O3 vegetative uptake shows clearer downward temporal changes than the total Nr deposition due to the declining NOy emission and deposition fluxes completing with the increasing NHx fluxes. It is highlighted that, temporal variability of Nr and O3 concentrations and fluxes on subregional-to-local scale respond to hydrological variability that can be influenced by precipitation and controllable human activities such as irrigation. Deposition processes and biogenic emissions that are highly sensitive to interconnected environmental and plants’ physiological conditions, as well as extra-regional sources (e.g., O3-rich stratospheric air and dense wildfire plumes from upwind regions), have been playing increasingly important roles in controlling pollutants’ budgets in this area as local emissions go down owing to effective emission regulations and COVID lockdowns. To better inform the design of mitigation and adaptation strategies, it is recommended to continue evaluating and improving the model parameterizations and inputs relevant to these processes in seamlessly coupled multiscale Earth system models using laboratory and field experiments in combination with satellite DA which would in turn benefit remote sensing communities.