A state implementation plan, or SIP, is a state’s blueprint for carrying out requirements of the Clean Air Act (CAA) essentially, but not exclusively, related to attainment and maintenance of the National Ambient Air Quality Standards (NAAQS). The NAAQS are set for six criteria pollutants: sulfur dioxide, ozone, carbon monoxide, lead, fine particulate matter and nitrogen dioxide, which are codified at 40 CFR Part 50. When EPA establishes a new NAAQS or revises an existing NAAQS, it sets in motion a series of actions to ensure that air quality throughout the country meets those standards. A SIP defines an individual state's role in this process.
Each state’s SIP is a federally enforceable plan required and approved by EPA under Section 110 of the CAA. The SIP is a dynamic document, requiring frequent updates to meet changing conditions related to air emissions, monitored air quality and federal requirements. Each revision of the SIP must undergo public review and receive the formal approval of EPA.
A SIP serves two main purposes:
Demonstrates that the state has the basic elements of an air quality management program in place to implement a new or revised NAAQS.
Identifies the emission control requirements the state will rely upon to attain and/or maintain the NAAQS.
The contents of a typical SIP include:
Regulatory components (enforceable control measures): rules/regulations or source-specific requirements, e.g., permit conditions, orders, and consent decrees.
Non-regulatory components: attainment plans, rate of progress plans, emission inventories, transportation control measures, statutes demonstrating legal authority, monitoring networks, etc.
Any additional requirements promulgated by EPA (in the absence of a commensurate state provision) to satisfy a mandatory Section 110 or Part D requirement.
The terms "state implementation plan," "SIP," "SIP revision" and "implementation plan" are often used interchangeably. For each state there is really only one SIP. Every SIP document produced since New Hampshire's original SIP was adopted in 1972 is actually a SIP revision.