Critical Loads - Protocols

The following protocols and guidance documents are available on this page to provide additional instructions to end users of the Air Quality Portal.

  • Critical Loads Implementation Strategy: This document outlines the process for calculating and assessing CLs and CL exceedances on a national forest.
  • Target Loads Strategy: This document outlines the process for developing target loads on a national forest, when CL exceedances have been determined to be significant and reliable.
  • Monitoring Strategy: This document outlines guidance specific to the resource and deposition data collection needs for improving CL estimates.
  • Management Strategy: This document outlines some of the management options available to reduce critical load exceedances and mitigate the effect of air pollution on national forests.
  • National Forest Exceedance Table: This table documents critical load exceedances occurring on every national forest and grassland on the continental U.S.  For each type of national CL hosted on the Portal, if any part of the national forest or grassland exceeds the CL, the CL is considered to be in exceedance.  Step 6 of the Critical Load Implementation Strategy guides examination of the extent and severity of this exceedance.
  • ArcGIS Mapping Protocols: This document outlines the protocols that should be followed to display and map the CLs and CL exceedance data provided on the Portal within ArcMap.
  • Critical Load Exceedance Metrics Protocol: This document outlines guidelines for examining critical load exceedance patterns across a forest to understand the extent and severity of potential impacts to resources, including the reliability of specific critical load estimates.
  • Critical Load Exceedance Calculation Documentation for Nationwide CL Efforts: This document outlines the methods used to calculate the CL exceedance values available in the nationwide critical loads spatial data.
  • Critical Load Exceedance Calculation Protocol: This document outlines the steps a user should follow when calculating their own CL exceedance values using CLs or deposition data not available in the Air Quality Portal.
  • Interpreting Multiple Critical Load Exceedances: This document outlines guidelines for interpreting CL exceedances when different types of CLs (different approaches to CL calculation) yield exceedances simultaneously.
  • Deposition Trend Protocol: This document provides additional information about the atmospheric deposition information available on the portal (2006 CMAQ), as well as guidance on evaluating trends in deposition (as discussed in Step 5 of the CL Implementation Strategy).
  • Empirical CL for Nutrient N GTR User’s Guide for CL Refinement: This document guides users through the process of identifying empirical CLs for nutrient nitrogen relevant to their both location and receptor(s) of interest, based on NRS GTR-80.
  • Critical Loads of Nutrient Nitrogen for Lichens Briefing Paper: All national forests have at least a small exceedance (in extent and/or severity) of the empirical CLs for nutrient nitrogen for lichens.  This briefing paper describes these critical loads: how to interpret them and why they are important to your forest and your Line Officer.
  • Published Sources of Critical Loads: This document lists the references of available published CLs nationally and by FS region, and provides a summary of important considerations for each reference.  References for ozone critical levels and references for published deposition estimates are also included.
  • Published Sources of Dynamic Modeling with Target Loads: This document lists the available published references of where dynamic modeling was used to set TLs, and provides a summary of important considerations for each reference.