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Last Updated: Thursday, January 17, 2013 10:28 AM

Carbon Monoxide Hot Spot Analysis

Hot spot analysis for carbon monoxide (CO) is required under the US Environmental Protection Agency (EPA) Transportation Conformity regulations for projects that are not either "Table 2" exempt projects (40 CFR 93.126) or Signal Synchronization Projects (40 CFR 93.128) in Federal nonattainment or maintenance areas for CO. For environmental review (NEPA and CEQA) purposes, CO hot spot analysis is required in all areas. The hot spot analysis process for conformity provides a good framework for CO analysis in general at the project level, and the CO Protocol is accepted for CO analysis under most air district CEQA procedures..

The Transportation Conformity regulations, at 40 CFR 93.116 and 123, specify CO analysis criteria and procedures. In general, projects that are not exempt from all conformity requirements must be modeled using appropriate emission factors and an approved dispersion model to determine whether sensitive receptors will experience new or worsened violations of the Federal CO standard. If a project will create or make worse a CO violation, it cannot proceed to Federal funding or other approval.

In 1997, EPA approved the CO Protocol for use as an alternative hot spot analysis method in California. Statewide and regional interagency consultation groups also reviewed the Protocol and approved it for conformity use. The Protocol provides a screening procedure for determining when a project may be of concern for CO violations, and a standardized method of using the CALINE4 dispersion model for detailed analysis if necessary. The CO Protocol is strongly recommended for CO hot spot analysis in California; however, CO hot spot modeling based on EPA's standard Modeling Guidance is acceptable if EMFAC is used to generate emission factors instead of EPA's MOBILE or MOVES models.

EPA's Final Rule of March 10, 2006, dealing with particulate matter (PM) hot spot analysis, did not change any criteria or procedures related to CO. Use of the CO Protocol remains the recommended analysis method for CO in California.

Guidance References

• CO Protocol
• CALINE4 model
• CALINE4 manual
• EPA March 10, 2006 Final Rule (PM Hot Spots)
• EPA January 24, 2008 Final Rule (mostly SAFETEA-LU related changes)
• EPA Modeling Guidance
• EPA Support Center for Regulatory Air Modeling
• Map of Federal CO Nonattainment and Maintenance Areas in California
  • Display version (GIF format)
  • Print version (PDF format)
  • CO Map at EPA Region 9 Air Quality Maps web site

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