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Nitrogen Dioxide

Nitrogen Dioxide Implementation - Programs and Requirements for Reducing Oxides of Nitrogen

The Clean Air Act requires EPA to set National Ambient Air Quality Standards (NAAQS) for six criteria pollutants; nitrogen dioxide is one of these.  EPA works with partners at state, local, and tribal air quality agencies to meet these standards.

Under the Clean Air Act (CAA), as amended in 1990, each state must develop a plan describing how it will attain and maintain the NAAQS.  In other words, how it plans to clean up polluted areas and keep them clean.  This plan is called the State Implementation Plan (SIP) and is required under Section 110 of the CAA (40 CFR Part 51, Subparts F & G).  In general, the SIP is a collection of programs, including:

  • a monitoring program, which is a collection of monitoring devices throughout the country which provide actual measurements of the concentrations in the air, to identify whether an area is meeting the air quality standards, and if not, how much reductions are needed to meet those standards;
  • air quality calculations and computer modeling, which are used to predict future trends and the effects of emissions reduction strategies;
  • emissions inventories, which describe the sources and categories of emissions to the air for a given pollutant, and how much is emitted by each source or source category;
  • control strategy studies whose goal is finding the best way to reduce emissions in order to meet air quality standards;
  • formal adoption of measures (enforceable by EPA, States and citizens) which ensure that we will achieve the reductions deemed necessary in the planning process;
  • periodic review to evaluate whether those needed reductions were achieved in reality, and whether they had the predicted result.

The air quality agency responsible for the State Implementation Plan, (usually a state agency) must provide the public an opportunity to review the plan before sending it to EPA for approval.

In cases where the EPA fails to approve a state implementation plan, the Agency can issue and enforce a Federal Implementation Plan (FIP) to ensure attainment and maintenance of the NAAQS.   In addition, the Clean Air Act contains penalties, referred to as "sanctions" which EPA can impose in areas not satisfying the State Implementation Plan requirements. 

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