Critical Loads of Atmospheric Deposition Science Committee (CLAD)

CLAD meets twice yearly at the spring and fall NADP meetings, and welcomes all NADP participants and interested parties. The goals of CLAD are to:

  • Facilitate technical information sharing on critical loads topics within a broad multi-agency/entity audience;
  • Fill gaps in critical loads development in the US;
  • Provide consistency in development and use of critical loads in the US;
  • Promote understanding of critical loads approaches through development of outreach and communications materials.

For more information about critical loads and CLAD, refer to the follow information and summary documents:

CLAD Documents
Meeting Minutes and Presentations
CLAD Annual Reports

The Annual Report documents CLAD activities and products that occurred during the year spanning October 1st – September 31st. These include: summary of CLAD accomplishments; progress of the CLAD scientific Working Groups; new CLAD products; summary of Fall and Spring CLAD meetings; summary of the United Nations Economic Commission for Europe (UNECE) International Cooperative Programme (ICP) Modelling and Mapping (M&M) Working Group on Effects (WGE) Coordination Centre for Effects (CCE) annual meeting; and critical load--related publications added to the CLAD website during the year.

Critical Load Maps

The Critical Load Map Summary is a collection of critical load maps with supporting critical load information for the United States. These maps were developed by CLAD members using publicly-available critical load data that are included in the NADP CLAD National Critical Load Database v3.1 (NCLD).

Scientific Working Groups

Scientific working groups (WGs) have been a component of CLAD since 2011. The objectives of the WGs are to increase our understanding and ability to estimate and represent critical loads of deposition in the United States. To date, there are five active CLAD WGs:

  • WG-1: Adding new data and critical loads to the CLAD NCLD
    • produce, adopt, and practice a standardized method for review and incorporation of new published data and critical loads into the NCLD
    • Contact: Jason Lynch
  • WG-2: Characterizing uncertainty in critical load estimates
  • WG-3: Synthesizing multiple critical loads
    • develop a repeatable and defensible method for representing multiple critical loads in the same geographical area
    • Contact: Michael Bell and Linda Pardo
  • WG-4: Deposition uncertainty
    • develop an understanding of the range of uncertainty that is associated with measured versus modeled deposition and how it relates to critical loads
    • Contact: Michael Bell
  • WG-5: Critical Load Communications and Outreach (CLOC)
    • To develop an outreach and communication strategy to communicate the concept and use of critical loads to stakeholder groups
    • Contact: Linda Geiser
  • WG-6: Coordinate research efforts of ozone effects on ecosystems and develop ozone Critical Levels for North America



Critical Load Web Resources

The below are websites/tools related to critical load resources. These resources are not products of the NADP and CLAD, but instead developed by government agencies in the US and Europe and other organizations. Any opinions, findings, conclusions, or recommendations as part of these resources do not necessarily reflect the views of CLAD, NADP, and/or respective members’ affiliations.


US Forest Service Critical Loads Video Series

An ecosystem is a community of living and nonliving things. The plants, animals, air, water, soil, and sunlight all work together to create balanced, healthy ecosystems. These ecosystems are essential life-support systems for our own well-being and livelihoods. They provide us with vital goods and services, such as fish, timber, and clean water. To maintain a healthy ecosystem, land managers must be able to predict when and where environmental threats occur on the landscape. Air pollution is one of these environmental threats. When pollutants containing nitrogen and sulfur are deposited to the environment as components of rain, snow, clouds, fog, gases, and fine particles, they can cause ecosystem harm. Scientists use the concept of critical loads to identify when an ecosystem, or a part of an ecosystem, begins to experience harm from this deposition. This video series looks at how air pollution, specifically excess nitrogen and sulfur deposition, affects species and ecosystems. It also highlights how land managers can use critical loads to assess ecosystem health and guide resource management decisions. The series includes seven videos. A playlist is available here Critical Loads Video Series Playlist and individual links below.

Geiser, L.H. and Outka-Perkins, L., editors. 2021. Air Pollution Effects on Ecosystems: Critical Loads Video Series. Script text authors: Bill Jackson, Jason Lynch, Mike Bell, Emmi-Felker Quinn, Chris Clark, Robert Sabo, Jill McMurray, Claire O’Dea. Editing and filming by Lisa O-P and Ian Grob, animated graphics by Circuit Media, production by USDA. Videos are finished and were posted by the US Forest Service Chief’s Office of Communications to YouTube and to the FS National Technology and Development Program’s on-line library.

Critical Load Web Videos

The below are links to critical load videos. These resources are not products of the NADP and CLAD, but instead developed by government agencies, Universities, and other organizations. Any opinions, findings, conclusions, or recommendations as part of these products do not necessarily reflect the views of CLAD, NADP, and/or respective members’ affiliations.

Critical Load Videos from Washington State University

Nitrogen Deposition Effects on Alpine Lakes at Mount Rainier

Nitrogen Deposition Effects on Alpine Plants at Mount Rainier