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About CL Mapper

EPA's GCX Critical Loads Mapper (CL Mapper) was developed to make information more accessible on effects from atmospheric deposition 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:

  1. atmospheric deposition of N and S (estimates through time are provided for several different air quality models),
  2. critical loads for terrestrial and aquatic ecosystems (from the National Atmospheric Deposition Program’s National Critical Loads Database), and
  3. 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).

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History of CL MAPPER

Below is a list of important milestones.

Date Milestone
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.

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EPA Reports

Datasets and Geoprocessing

Journal Articles Related to Critical Loads for Nitrogen and Sulfur Deposition

Other Related Resouces

For more information on datasets produced as part of this project, please visit the CL Mapper Interactive Tool.

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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.