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EPA Research Partner Support Story: Atmospheric deposition of nitrogen

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Partners: Delaware Department of Agriculture, DC Department of Energy & Environment, Maryland Department of the Environment, Virginia Department of Environmental Quality, West Virginia Department of Environmental Protection
Challenge: Estimating the impact of atmospheric deposition on nutrient loading in Chesapeake Bay
Resource: Improved models for calculating historic and predicting future atmospheric deposition of nitrogen
Project Period: 2015 – Present

The Chesapeake Bay watershed includes parts of six states and the District of Columbia and is home to over 18 million people. It provides over $100 billion annually in economic benefits. However, the growth in industry, population, and agriculture in the watershed has degraded water quality, with much of the decline attributed to excessive nutrient loading.

"Science-based decision-making is at the core of the Chesapeake Bay Program Partnership and ORD's work to update the CMAQ airshed model provided the partnership with a better understanding of past progress and well as future opportunities for reducing atmospheric sources of pollution.” – Maryland Department of the Environment, Water and Science Administration Director Lee Currey

Consequently, in 2010, a Total Maximum Daily Load (TMDL) was established to reduce nutrient loading to the Chesapeake Bay watershed. Atmospheric deposition is among the largest pathways of nitrogen loading to the watershed, and the individual and combined impacts of climate and emissions changes on nitrogen loading from NH x  and NO x  to the watershed had not been well assessed.

Working in collaboration with the EPA Region 3 (Mid-Atlantic) Chesapeake Bay Program, EPA ORD scientists developed a consistent long term emissions dataset (Foley et al. 2023) and tailored the Community Multiscale Air Quality (CMAQ) modeling system (Hood et al. 2021) so that it could be used to estimate atmospheric nitrogen deposition for historical (2002 – 2019), and future (2035, 2050) scenarios projected using the GCAM USA model including planned reductions, state greenhouse gas targets, and a NetZero greenhouse gas emissions by 2050 target. The work was conducted to assist partner states and watershed managers.

ORD scientists have developed a set of annual North American emissions data for multiple air pollutants across 18 broad source categories for 2002 through 2019. The emissions datasets are designed to support regional air quality modeling for a wide variety of human health and ecological applications. The data were developed to support simulations of the CMAQ model but can also be used by other regional scale air quality models. The emissions data are one component of EPA's Air Quality Time Series Project which also includes air quality modeling inputs and outputs for the Conterminous US. The nitrogen deposition estimates generated are being used in the development of the Phase 7 version of the Chesapeake Bay Model and will be widely distributed among the federal, state, local and academic Chesapeake Bay Program research partners as they consider options for reducing nutrient loading.

Read the peer-reviewed publications:

  • The Chesapeake Bay program modeling system: Overview and recommendations for future development
  • 2002–2017 anthropogenic emissions data for air quality modeling over the United States
  • Long-term regional trends of nitrogen and sulfur deposition in the United States from 2002 to 2017

EPA Research to Support States

  • State Environmental Agencies' Research Needs
  • ORD Meetings with States and Regions
  • EPA Tools & Resources Webinar Series
  • EPA Tools & Resources Training Webinar Series
  • PFAS Resources for States
  • EPA Research Partner Support Stories
    • EPA Research Partner Support Stories Compilation Document
  • Collaborative Projects with State Environmental Health Experts
  • Videos: EPA ORD Collaborations with State Partners
  • ORD's Key State Partners
Contact Us About EPA Research to Support States
Contact Us to ask a question, provide feedback, or report a problem.
Last updated on April 14, 2025
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