Total Deposition (TDep) Science Committee

2026 Webinar Series Presents:

Constraining Long-Term NO_x Emissions over the United States and Europe using Nitrate Wet Deposition Monitoring Networks

April 30, 2026 11:00 AM – 12:00 PM EDT (Zoom Meeting)

Agenda

Presentation:
Constraining Long-Term NO_x Emissions over the United States and Europe using Nitrate Wet Deposition Monitoring Networks

Summary: Nitrogen oxides (NO_x = NO + NO₂) play a critical role in regulating tropospheric chemistry, yet NO_x emission estimates are subject to large uncertainties, casting doubt on our ability to accurately model secondary pollutants such as ozone. Here, we provide an additional constraint on NO_x emissions and trends using nitrate wet deposition (NWD) fluxes from the United States National Atmospheric Deposition Program (NADP) and the European Monitoring and Evaluation Programme (EMEP). We use these NWD measurements to evaluate anthropogenic and total NO_x trends and magnitudes in the global Community Emissions Data System (CEDS) emissions inventory and the GEOS-Chem chemical transport model from 1980–2020. Over both the United States and Europe, observed NWD trends track well with anthropogenic NO_x emissions from the CEDS inventory until 2010, after which NWD trends level out in contrast to continued decreases in CEDS. After 2010, NWD trends are able to reproduce total NO_x emissions trends when the influences of both anthropogenic and background sources are considered. Observed NWD fluxes also capture NO_x emissions decreases over the 2020 COVID-19 lockdown period and are consistent with satellite and surface measurements of NO₂. We further compare modelled and observed NWD to provide an additional line of evidence for potential overestimates of anthropogenic NO_x in emissions inventories. Over the United States, we find consistent overestimates of NO_x emissions in CEDS in summer from 1980–2017 averaging 15–20%. Over Europe, we find that NO_x is overestimated in all seasons, with the strongest average overestimates occurring in summer (175%) and fall (170%). These overestimates may be reduced by cutting anthropogenic NO_x emissions by 50% in CEDS over Europe. We find that NO_x emission reductions over Europe improve model ozone at the surface, reducing the model summertime ozone overestimate from 14% to 2%.

Presented by:
Dr. Amy Christiansen – University of Missouri – Kansas City

Dr. Amy Christiansen is an atmospheric chemist whose expertise lies in global chemical transport modeling. She holds a PhD in Chemistry from the University of California, Irvine, and completed a postdoctoral appointment at the University of Montana. In September 2022, she joined the School of Science and Engineering at the University of Missouri – Kansas City as an Assistant Professor of Chemistry. Dr. Christiansen’s research interests focus on long-term atmospheric measurements and modeling to understand how pollutant concentrations, distribution, and impacts have changed over time. Her favorite science is that which connects the chemical to the human: exploring the connections between atmospheric chemistry and climate change, public health, and environmental justice. Dr. Christiansen sits on the Climate Data Guide Board of Advisors for the National Center for Atmospheric Research, serves on the American Geophysical Union Early Career Committee, and is a contributing scientist to the United Nations Economic Commission for Europe’s Task Force on Hemispheric Transport of Air Pollution.

Zoom Registration

Past webinar:

Dr. Jesse Bash
March 3, 2026

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