About GCX Critical Loads
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EPA's GCX Critical Loads Mapper (CL Mapper) was developed to make information more accessible on effects from atmospheric deposition (precipitation of rain, snow or fog) of nitrogen (N) and sulfur (S). CL Mapper also helps users better understand local and regional vulnerability to atmospheric pollution, and how pollution levels and ecosystem effects are estimated both historically and for the future.
The CL Mapper is an interactive mapping tool that enables decision makers, researchers, and the public to easily access information for the conterminous U.S. on:
- atmospheric deposition of N and S (estimates through time are provided for several different air quality models),
- critical loads for terrestrial and aquatic ecosystems (from the National Atmospheric Deposition Program’s National Critical Loads Database), and
- critical load exceedances (defined as the deposition minus the critical load).
Areas where atmospheric deposition levels are higher than critical load (i.e., positive exceedances) indicate potential vulnerability to atmospheric deposition.
For more information on atmospheric deposition, critical loads, critical load exceedances, and how these concepts are used to support decision making, see the USFS CL Portal, the NPS’s Critical Loads for Resource Protection, and EPA's Integrated Science Assessment (ISA) for Oxides of Nitrogen, Oxides of Sulfur, and Particulate Matter (Ecological Criteria).
History of CL MAPPER
Below is a list of important milestones.
| Date | Milestone |
|---|---|
| Oct 2022 | EPA released version 2.1 of the CL Mapper which was updated to include BIA data. |
| Apr 2018 | CL Mapper was incorporated into the Global Climate Explorer set of tools and website. |
| Oct 2018 | EPA released verson 2.0 of the CL Mapper interactive tool, which included summary reports for Federally protected areas across the contiguous U.S. |
| Jun 2017 | EPA released the beta version (v.1.0) of the CL Mapper interactive tool. |
Publications
EPA Reports
Datasets and Geoprocessing
- Learn more about the CL Mapper datasets and geoprocessing underpinning the CL Mapper from the CL Mapper Tool Dataset Information Document.
- Learn more about the Critical Loads of Atmospheric Deposition (CLAD) Science Committee's National Critical Loads Database (NCLD), Version 3.1
Journal Articles Related to Critical Loads for Nitrogen and Sulfur Deposition
- Clark, C.M., Phelan, J., Doraiswamy, P., Buckley, J., Cajka, J.C., Dennis, R.L., Lynch, J., Nolte, G.N., & Spero, T.L. 2018. Atmospheric deposition and exceedances of critical loads from 1800-2025 for the conterminous United States. Ecological Applications, 28(4), 2018, pp. 978–1002. doi: 10.1002/eap.1703.
- McDonnell, T.C., S. Belyazid, T.J. Sullivan, M. Bell, C. Clark, T. Blett, T. Evans, W. Cass, A. Hyduke, and H. Sverdrup. 2018. Vegetation dynamics associated with changes in atmospheric nitrogen deposition and climate in hardwood forests of Shenandoah and Great Smoky Mountains national parks, USA. Environmental Pollution. 237:662-674. doi:10.1016/j.envpol.2018.01.112.
- Whitfield, C.J., Phelan, J.N., Buckley J., Clark, C.M., Guthrie, S, & Lynch, JA. 2018. Estimating Base Cation Weathering Rates in the USA: Challenges of Uncertain Soil Mineralogy and Specific Surface Area with Applications of the PROFILE Model. Water Air Soil Pollution (2018) 229:61. doi:10.1007/s11270-018-3691-7.
- Additional CLAD National Critical Load Database (NCLD) as reported on the National Atmospheric Deposition Program website.
Other Related Resources
- National Atmospheric Deposition Program (NADP) Critical Loads of Atmospheric Deposition (CLAD) Science Committee
- National Atmospheric Deposition Program (NADP) Total Deposition (TDep) Science Committee
For more information on datasets produced as part of this project, please visit the CL Mapper Interactive Tool.
For assistance/questions please use the Contact Us About the Critical Loads Mapper page. For general Global Climate Explorer questions, separate from the CL Mapper tool, please use the link below.