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 an approach that combines measured air concentration and wet deposition data and modeled deposition velocity and dry deposition data. Wet deposition values are obtained from combining the National Trends Network (NTN) measured values of precipitation chemistry with precipitation estimates from the Parameter-elevation Regression on Independent Slopes Model (PRISM). Air concentration data from the Clean Air Status and Trends Network (CASTNET), the Ammonia Monitoring Network (AMoN), and the SouthEastern Aerosol Research and Characterization (SEARCH) network were included. Modeled data were obtained from the Community Multiscale Air Quality (CMAQ) model.

Details of the methodology for developing the data set as well as comparisons of deposition from this data set with other deposition estimates is provided in Schwede and Lear (2014). This data set is expected to be updated as the methodology evolves and as new data become available. Each version is denoted by a version number which includes the four digit year of release and a two digit version number. For example, the current release is version 2018.02 and contains files for the years 2000-2016. The data are available as ESRI ArcGRID exported gridded deposition fields and maps that can be downloaded using the links below.

Questions about the data should be directed to Donna Schwede ( or Greg Beachley (


TDep - Reports
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