Air Quality

The Clean Air Act (CAA) requires the U.S. Environmental Protection Agency (EPA) to identify and revise national ambient air quality standards (NAAQS) for air pollutants that may reasonably be anticipated to endanger public health.

To date, EPA has set NAAQS for six "criteria" air pollutants: ozone, carbon monoxide, nitrogen dioxide, sulfur dioxide, particulate matter (PM10), and lead. EPA and the State of Arizona share responsibility for ensuring all areas attain federal NAAQS by deadlines specified in the CAA. Arizona is required to monitor each of these pollutants and submit data used to determine whether geographic areas are in "attainment" for each. A geographic area that does not meet EPA air quality standards is classified as a nonattainment area.

Designation as a nonattainment area triggers a series of steps that must be taken to bring the area into compliance. Such as:

  • Preparing and executing a state implementation plan (SIP) to achieve and maintain NAAQS within their borders.

  • Establishing regional and enforceable measures for controlling air pollution from stationary and mobile sources. (Construction is considered an off road mobile source)

  • Transportation conformity which applies to all nonattainment and maintenance areas that fail to meet the NAAQS coordinates a regions transportation plan with its air quality plan. Transportation projects must demonstrate that they do not further degrade air quality in the region.

Currently Arizona has 16 areas in seven counties (Cochise, Gila, Maricopa, Pima, Pinal, Santa Cruz and Yuma) statewide designated as nonattainment areas or attainment areas with maintenance plans. Particulate Matter (PM10) is the predominant pollutant in most of these areas, other pollutants include (PM2.5), CO, SO2, Lead, and Ozone.

Pima, Pinal and Maricopa County have their own air pollution control programs and operate pursuant to agreements with ADEQ. In addition to ADEQ, two metropolitan planning organizations share in the responsibility of completing state implementation plan requirements for ozone, carbon monoxide, and particulate pollution.

Maricopa County PM10
Since 1999 Maricopa County has struggled to attain air quality standards. In 1999 over 77 measures were proposed and implemented in the serious area plan to reduce dust. Failing to attain, the region was required to prepare a five percent plan which means emissions must be reduced 5% annually until attainment is reached.

On December 31, 2006 the region submitted its plan with an additional 53 aggressive measures to reduce emissions, thereby designating the area as having the most stringent measures (MSM) in the nation for controlling dust.

In June 2012, EPA issued a completeness determination of the MAG 2012 Five Percent Plan which stopped the 18-month conformance freeze and sanctions for transportation funding and construction projects planned after 2014.

Due to the approval of the 2011 exceptional events package, the region now has a record of clean air for the previous three years from 2010-2012. (Exceptional events are emission activities, such as extraordinary high winds, outside the control of mankind.)

In 2014 EPA issued a clean data finding for the Region, which would allow officials to develop a maintenance plan for the region. EPA's finding was challenged in October 2014 by Arizona Center for Law in the Public Interest (ACLPI). The suit is now waiting to be heard. MAG has filed as an intervener to the case. The region must remain "clean" (no violations of the monitors) to stay out of nonattainment.

Pinal County
In 2009 after reviewing data indicating numerous violations at the monitors in Pinal County, EPA requested the state submit recommendations for designating areas of Pinal County as either in attainment, nonattainment or unclassifiable for PM10 and PM2.5.

On July 2, 2012, EPA re-designated a portion of western Pinal County from "unclassifiable" to "nonattainment" for the 24hour PM10 NAAQS. ADEQ and Pinal County are finalizing their SIP to submit to EPA in early 2016 with more stringent enforceable control measures on contributing sources, including additional measures on high wind event days.

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