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State Implementation Plan

Under the Clean Air Act, the U.S. Environmental Protection Agency (EPA) has established air quality standards to protect public health and the environment. EPA has set national ambient air quality standards (NAAQS) for the six primary air pollutants. These include: carbon monoxide (CO), lead (Pb), nitrogen dioxides (NO2), ozone (O3), particulate matter (PM10 and PM2.5), and sulfur dioxide (SO2).

When an area does not meet the air quality standard for one of the NAAQS pollutants, the area may be subject to the formal rulemaking process that designates the area as nonattainment. The Clean Air Act requires states with areas failing to meet the NAAQS to produce a state implementation plan (SIP).

A SIP is an enforceable plan developed at the state and local level that explains how the area will comply with the NAAQS according to the Clean Air Act. The SIP is the cumulative record of all air pollution strategies, state statutes, state and local rules, and local ordinances implemented under Title I of the Clean Air Act by governmental agencies within the state.

In general, a SIP will include historical background information, a description of the nonattainment area, an assessment of air quality conditions and ambient air quality data for the area, an emissions inventory of sources of pollutants, control strategies, an attainment demonstration, and contingency provisions.

The first Arizona SIP submittal was in 1972. Because there have been so many changes to federal, state and local air quality programs over the past 30 years, there is not a single definitive document that contains all of the SIP requirements. Rather than re-writing the entire SIP regularly, parts of the SIP are simply revised as needed.

Revisions are necessary when new federal or state requirements are enacted, when new data improves modeling techniques, when a specific area's attainment status changes, or when an area fails to reach attainment.

Revisions to Arizona's SIP must be submitted to the EPA by the director of the Arizona Department of Environmental Quality (ADEQ) on behalf of the governor. Once approved by EPA and published in the Federal Register, the provisions contained in the SIP revision become enforceable by the federal government as well as by the appropriate governmental entities of Arizona. The cumulative and complete record of SIP revisions that have been approved by EPA and federally enforceable in Arizona is called the "applicable Arizona SIP".


Attainment Status

Portions of Maricopa County have been designated nonattainment for three pollutants: particulate matter (PM10), carbon monoxide (CO) and ozone (O3).


Maricopa County PM10 Nonattainment Area


Attainment Status Designation: Serious Nonattainment

Maricopa County was reclassified as a serious PM10 nonattainment area on June 10, 1996. On July 9, 1999, the Maricopa Association of Governments (MAG) submitted to EPA the MAG 1999 Serious Area Particulate Plan for PM10 (Executive Summary), addressing both the 24-hour and annual standards.

A revised state implementation plan (SIP) was submitted in February 2000. The Plan, based on new most stringent measures, included an extension request for attainment no later than December 31, 2006. On January 10, 2002, EPA announced approval of Arizona's plan to attain the standards for PM10 in the metropolitan Phoenix area by 2006. EPA's approval granted a 5-year extension of the attainment date for both the 24-hour and annual PM10 standards to December. 31, 2006. Both decisions were published in the Federal Register on July 25, 2002 ( 67 FR 48718).

On July 2, 2002, EPA found that more work was needed to achieve attainment of the 24-hour standard in the area of the Salt River monitoring site. For more information on the "Salt River Study Area" see the Arizona Department of Environmental Quality Salt River PM10 State Implementation Plan Revision webpage.

Despite the most stringent measures and best available control measures adopted and implemented earlier, the nonattainment area failed to attain the NAAQS by the extended deadline of December 31, 2006. This failure triggered a special requirement under Section 189(d) of the Clean Air Act that SIP revisions provide for annual reductions of PM10 or PM10 precursors of not less than 5 percent of the most recent emissions inventory, until the NAAQS is attained, be submitted to EPA by December 31, 2007. This SIP revision was prepared by the Maricopa Association of Governments and submitted to EPA by the deadline.

The primary sources of particulate pollution in the area are construction activities, paved road dust, unpaved roads and parking lots, agricultural activities, windblown dust from disturbed vacant lots, construction sites, and agricultural fields, fires and open burning, dust from offroad recreational vehicles, leaf blowers, and exhaust from cars.


Maricopa County CO Attainment Area with Maintenance Plan


Attainment Status Designation: Attainment

On April 8, 2005, EPA redesignated the Phoenix metropolitan area to attainment for CO and approved the attainment demonstration and maintenance plan which shows maintenance of the CO NAAQS through 2015. The Phoenix metropolitan area was originally designated as a moderate CO nonattainment area under the Clean Air Act Amendments of 1990, with an attainment date of December 31, 1995. As a result of the area's failure to reach attainment by the end of 1995, EPA reclassified the area as a serious nonattainment area in 1996, with a new attainment date of December 31, 2000. The Phoenix metropolitan area has not had an exceedance of the CO NAAQS since 1996. Cars and other gasoline-powered motor vehicles cause more than 75 percent of the area's CO.


Maricopa County Ozone Nonattainment Areas


1-hour Ozone Attainment Area with Maintenance Plan

Attainment Status Designation:  Attainment

On June 14, 2005, EPA redesignated the Phoenix metropolitan area to attainment of the 1-hour ozone NAAQS and approved the attainment demonstration and maintenance plan which shows maintenance of the 1-hour ozone NAAQS through 2015. The 1-hour ozone NAAQS was revoked by EPA on June 15, 2005. However, certain control measures developed and implemented for the 1-hour NAAQS are required to remain in place to ensure continued progress toward attainment of the 8-hour NAAQS.


8-hour Ozone Nonattainment Area (1997 standard)

Attainment Status Designation: Subpart 1 Nonattainment

On June 15, 2004, the EPA designated a 4,880 square mile area located mainly in Maricopa and Pinal Counties as an 8-hour ozone nonattainment area (69 FR 23858 ; April 30, 2004).

EPA's rule for implementing the 1997 8-hour ozone NAAQS requires that the nonattainment area meet the NAAQS by 2009. The MAG Eight-Hour Ozone Plan for the Maricopa County Area, June 2007, which demonstrates how the area will attain the standard, was submitted to EPA on June 13, 2007. EPA action is pending.


8-hour Ozone 2008 standard

Attainment Status Designation: Pending

On May 27, 2008, EPA strengthened the air quality standards for ground-level ozone to improve public health protection (73 FR 16436; March 27, 2008). Specifically, EPA revised the level of the NAAQS to 0.075 parts per million (from 0.084 part per million). Recommendations from States regarding which areas do or do not meet the new standards were due to EPA March 12, 2009. See the Arizona Department of Environmental Quality 8-Hour Ozone webpage for details regarding ADEQ's boundary recommendations for Maricopa County. EPA will issue final designations of attainment, nonattainment and unclassifiable areas no later than March 2010. Nonattainment areas must submit SIPs outlining how they will reduce pollution to meet the standards by a 2013 (if EPA issues designations in 2010).


For more information:

The Arizona Department of Environmental Quality's Air Quality Plans website contains recent relevant documents pertaining to Arizona nonattainment and attainment areas with maintenance plans.

EPA Region 9's Arizona Air Actions website contains recent EPA air quality actions for Arizona.

EPA Region 9's Air Quality State Implementation Plan (SIP) website contains EPA action logs for the federally enforceable applicable SIPs in Arizona. Action logs list the state and local air pollution regulations that EPA has incorporated into the applicable SIP under section 110 of the Clean Air Act.