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Carbon Monoxide (CO) Pollution in Outdoor Air

Applying or Implementing the Outdoor Air Carbon Monoxide (CO) Standards

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Designations: how do we know if an area is not meeting CO standards?

Areas within each state are "designated" as either meeting (attaining) carbon monoxide (CO) standards or not meeting them. In some cases, an entire state may attain a standard. Those areas that exceed the standards are known as “nonattainment areas.”

As of 2010, there are no nonattainment areas for CO. However, some areas are designated as "maintenance" areas. Maintenance plans are prepared in areas that were initially designated nonattainment, but then are able to demonstrate attainment. Maintenance plans are the mechanism for ensuring that once the areas meets the standards, it will continue to attain the standards for the next 20 years (in two 10-year intervals).

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What are the state implementation plan (SIP) requirements?

Air quality standards get applied, or implemented, through controlling air pollution from emission sources. Each state is required to develop a plan for how they will control air pollution within their jurisdiction. This plan is called a State Implementation Plan (SIP).

In general, the SIP consists of:

  • air quality monitoring
  • air quality modeling
  • emission inventories
  • emission control strategies;
  • contingency measures; and
  • documents (policies and rules) that the state uses to attain and maintain the NAAQS.

A state must engage the public, through notices and public hearings, before sending the SIP to EPA for approval. Tribes may develop plans if they choose to do so, otherwise EPA will develop an implementation plan for them.

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How do states develop SIPs and start (or continue) attaining the standards?

  • An infrastructure SIP, or i-SIP, is a requirement for all states, regardless of designation. Even areas in attainment must demonstrate what controls they will continue to use and regulate in order to remain in attainment.
  • Redesignations and Clean Data Policy (CDP): States with areas that are starting to monitor attainment can demonstrate attainment using air quality modeling and other analyses.
  • EPA evaluates the submitted SIPs, then issues a notice, indicating that either the SIP has been approved or needs additional work. Once the SIP has been approved, the state implements its air pollution control strategies to gradually reduce CO pollution.

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