Total Deposition Science Committee (TDep)

The mission of the Total Deposition Science Committee (TDep) is to improve estimates of atmospheric deposition by advancing the science of measuring and modeling atmospheric wet, dry, and total deposition of species such as sulfur, nitrogen and mercury by providing a forum for the exchange of information on current and emerging issues within a broad multi-organization context including atmospheric scientists, ecosystem scientists, resource managers, and policy makers.

The specific charges of TDep are:

  • Support national networks that monitor atmospheric deposition by providing information on emerging measurement techniques, model development, and uncertainties associated with these approaches.
  • Identify and prioritize knowledge gaps in the field of measuring and modeling atmospheric deposition and advocate for research to address those gaps.
  • Coordinate with Critical Loads of Atmospheric Deposition Science Committee (CLAD) and other groups to advocate the use of the most scientifically defensible deposition estimates for critical loads and other environmental assessments.
  • Provide expertise and advice on present and potential decisions and regulatory actions pertaining to the field of measuring and modeling atmospheric deposition.
  • Encourage greater communication and collaboration between groups from different disciplines with interests in atmospheric deposition.

More information on the structure of TDep and its leadership roles and workgroups can be found here.

Total Deposition Maps
One of the goals of the NADP Total Deposition (TDep) Science Committee is to provide estimates of total sulfur and nitrogen deposition for use in critical loads and other ecological assessments.

The deposition estimates provided here were developed using a Measurement-Model Fusion (MMF) approach that combines measured air concentration and wet deposition data and modeled deposition velocity and dry deposition data. Fused dry deposition estimates are created from weekly air concentration measurements from the Clean Air Status and Trends Network (CASTNET) which are combined with spatially gridded modeled dry deposition velocities and fused with modeled dry deposition flux estimates from the EPA’s Community Multiscale Air Quality (CMAQ) model. The weekly fused gridded deposition maps are aggregated to annual estimates. Annual wet deposition estimates are obtained by combining the National Trends Network (NTN) measured values of precipitation chemistry with precipitation estimates from the Parameter-elevation Regression on Independent Slopes Model (PRISM). The wet and the dry annual deposition estimates are then combined to get total deposition.

The methodology was originally developed and is detailed in Schwede and Lear (2014). In 2021, the measurement-model fusion method was recoded with several updates and improvements. Details will be provided in a forthcoming manuscript which will be posted here once published. The new model version number is 2023.01 and gridded deposition fields are now in a GeoTIFF format and map images are available at the links below. The 2023.01 product spans the years from 2000-2022.


For questions regarding the total deposition maps please contact: Greg Beachley,

TDep - Reports
TDep - Working Groups

TDep is organized into workgroups to increase structure and organization and promote collaborative work on specific projects that meet the TDep mission. These workgroups have a more specific project-oriented focus and discuss and advance more specific details. The workgroups are expected to report on progress and achievements to the larger TDep audience at the spring and fall meetings.
The current workgroups include:

Stakeholder Workgroup

Lead: Ian Rumsey, US EPA

The TDep Stakeholder workgroup is focused on building collaboration across Federal and State agencies, academia, and non-profit groups to identify and address research knowledge gaps in the field of atmospheric deposition. The workgroup objectives are briefly:

  • Increase communication across scientific communities (i.e., atmospheric chemistry, ecology)
  • Create new opportunities for collaborative research by promoting the inclusion of deposition science in grant programs
  • Advance the integration of TDep science needs into existing research programs across stakeholder groups
  • Facilitate communication among program managers within stakeholder Agencies and user groups

Measurement Model Fusion (MMF) Workgroup

Lead: Greg Beachley, US EPA

The Measurement Model Fusion (MMF) workgroup serves as the caretakers of the TDep MMF script, grids, and product outputs. Workgroup members conduct research and have discussions to ensure that the TDep MMF stays current with the state of deposition science. The group will respond to any questions and requests involving the TDep MMF products. The workgroup has established focus taskgroups to further breakdown the workload and improve collaboration.

  • The Product Development Taskgroup will improve methods and efficiency of quality assurance/quality control procedures for evaluating the TDep MMF product.
  • The Outreach task-group will focus on the TDep Total Deposition maps website and product updates. This task-group will focus on messaging (i.e. social media alerts) and identifying new stakeholders and collaborators.
  • The Deposition Uncertainty and Improvements task-group will focus on long-term improvements to the TDep MMF and helping to keep the TDep MMF current with the state of the science. A key focus of this group will be is to better understand uncertainty in deposition measurements and models and how it effects the calculation and exceedance if critical loads. These questions are pursued through:
    • how deposition estimates and critical loads vary along environmental gradients and across ecosystems.
    • Assessing deposition measurement methods (filter-based samplers, bulk precipitation collectors, ion exchange resin (IER) columns, snowpack, and lichen tissue) in comparison to modeled values.
    • Evaluating deposition model estimates (CMAQ, TDEP, CAMx, and ADAGIO) and compare to measurements to assess the spatial variability of uncertainty.
    • Developing a framework to identify impacts of evaluating critical load (CLs) exceedances with a single deposition model when CLs were developed from different data sources.

Measurement Workgroup

Leads: Bret Schichtel and Kristi Morris, NPS

The Measurement Workgroup (MWG) serves to assess and advance air quality monitoring related to pollutant deposition in support of the National Atmospheric Deposition Program, the Total Deposition (TDep) Science Committee, and scientific and regulatory activities. Workgroup objectives include:

  • Support national networks relevant to atmospheric deposition by providing information on emerging measurement techniques and their uncertainties.
  • Identify and prioritize knowledge gaps in current direct and indirect monitoring of atmospheric deposition and promote research to address those gaps, including rural, suburban, and urban environments.
  • Promote and support the incorporation of monitoring data into TDep products and workgroups and scientific and regulatory assessments.
  • Facilitate communication between monitoring data generators and users. In the spring of 2023, the Urban Deposition Workgroup (CityDep) became incorporated into the Measurement Workgroup. For an informative brochure and minutes of past meetings, please follow the CityDep link).
TDep White Paper Seminars

06/17/2020 - Snow and atmospheric deposition/Remote sensing measurements of oxidized and reduced Nitrogen for application to Nr budgets

04/15/2020 - Modeling fluxes of reactive nitrogen using chemical transport models / Assessing uncertainty in total Nr deposition estimates for North American critical load applications


03/18/2020 - Development and Testing of Source, Receptor, and Hybrid-oriented Apportionment methods / Application of a bidirectional ammonia air-surface exchange model at NADP AMoN sites

02/19/2020 - Low-cost method for routine monitoring of air-surface exchange of reactive nitrogen compounds / Characterization of organic nitrogen in air and precipitation

11/20/2019 - National trends network data validation, completeness criteria and annual mean concentration weighting / Trends in Air Pollutant Deposition Compared to Changes in Emissions

10/16/2019 - Advancing throughfall methods for quantifying reactive nitrogen deposition / Occult deposition: What we know, don't know and should really know

09/18/2019 - Total atmospheric nitrogen deposition in urban areas / Measurements of air-surface exchange of reactive nitrogen in natural ecosystems across North America

Meeting Minutes