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Air Quality Improvement Planning

Nogales | PM 2.5 Maintenance Area

Revised On: Oct. 16th, 2026 - 02:06 pm

County Affected:

Parts of Santa Cruz County | View eMap >

Pollutant of Concern:

2006 24-hour PM2.5 (fine particulate matter 2.5 microns or less in diameter) National Ambient Air Quality Standard (NAAQS)

Nonattainment Area Designation and Reclassification Dates:

  • Nov. 13, 2009 - Designation as Nonattainment for the 2006 24-hour PM2.5 NAAQS |  View 74 FR 58688 >
  • June 2, 2014 - Classification as Moderate Nonattainment for the 2006 24-hour PM2.5 NAAQS | View 79 FR 31566 >
  • Aug. 15, 2022 - Reclassification from nonattainment to attainment for the 2006 24-hour PM2.5 NAAQS | View 87 FR 49997 >

Classification Level:

Attainment/Maintenance (2006 24-hour PM2.5 NAAQS)

Summary: 

The Nogales area was designated nonattainment under the 2006 24-hour PM2.5 NAAQS in 2009 and subsequently classified as moderate in 2014. Since then, air quality has improved, and the area has attained the standard. 

Improvements to the Mariposa Port of Entry, which reduced commercial truck idling and wait times, along with increasingly stringent federal light-duty vehicle standards and fuel standards, have contributed to significant reductions in PM2.5 concentrations. 

Because all applicable nonattainment area planning requirements were met, the  U.S. Environmental Protection Agency (EPA) redesignated the area from nonattainment to attainment in 2022. The most recent State Implementation Plan (SIP) revision (Nogales 2006 24-hour PM2.5 NAAQS Maintenance Plan and Redesignation Request, submitted April 2021) demonstrates that the area will maintain the standard through 2032 and includes contingency measures for potential violations of the 2006 24-hour PM2.5 standard. A second 10-year Maintenance Plan is due in 2030. 

Regulatory Background:

In December 2006, the EPA strengthened the primary and secondary 24-hour PM2.5 NAAQS. Pursuant to Section 107(d) of the Clean Air Act (CAA), the standards required states to submit recommendations within one year of promulgation for areas meeting, not meeting, or unable to be classified under the new or revised NAAQS. 

In December 2007, Arizona submitted its initial designation recommendations to the EPA. In its submission, Arizona recommended designating the Nogales area in Santa Cruz County as nonattainment for the 2006 24-hour PM2.5 NAAQS.

On Nov. 13, 2009, the EPA designated the Nogales area as nonattainment for the 2006 24-hour PM2.5 NAAQS, relying on 2004-2007 monitoring data that showed the area was not attaining the standard (74 FR 58688). Following this designation, air quality in the area improved as permanent upgrades to the commercial vehicle port of entry, alongside increasingly stringent federal light-duty vehicle and fuel standards. 

On Jan. 7, 2013, the EPA finalized a clean data determination (CDD) for the Nogales area based on 2009-2011 monitoring data (78 FR 887). This CDD suspended certain nonattainment area planning requirements for as long as the area continued to attain the standard, including the requirements for an attainment demonstration, a reasonably available control measure demonstration, a reasonable further progress demonstration, and contingency measures. 

The CDD did not, however, suspend the requirement to submit emissions inventories to the EPA under CAA section 172(c)(3). In September 2013, ADEQ submitted a SIP revision containing 2008 and 2010 emissions estimates for PM2.5 and its precursors (nitrogen oxides, volatile organic compounds, sulfur dioxide, and ammonia), which the EPA approved on Feb. 9, 2015 (80 FR 6907). 

On June 2, 2014, the EPA classified all areas designated nonattainment for the 1997 and/or 2006 PM2.5 NAAQS as Moderate, including the Nogales area (79 FR 31566). Subsequently, in May 2017, the EPA determined, based on 2013-2015 monitoring data, that the Nogales area had attained the 2006 24-hour PM2.5 NAAQS by the statutory attainment date of Dec. 31, 2015 (82 FR 21711). 

On April 13, 2021, ADEQ submitted the Nogales 2006 24-hour PM2.5 NAAQS Maintenance Plan and Redesignation Request to the EPA as a revision to the Arizona SIP to demonstrate compliance with all CAA requirements needed to redesignate the area from nonattainment to attainment. On Aug. 15, 2022, the EPA issued a final action approving the Nogales Maintenance Plan as a revision to the Arizona SIP (87 FR 49997). In doing so, the EPA determined that:

  • The area will continue to attain the 2006 24-hour PM2.5 NAAQS for 10 years beyond redesignation, and 
  • The contingency measures included in the plan met all applicable requirements in section 175A(d) of the CAA to promptly correct any violation of the PM2.5 NAAQS that may occur after redesignation.

In the same action, the EPA also granted ADEQ’s request to redesignate the Nogales planning area from nonattainment to maintenance/attainment for the 2006 PM2.5 NAAQS (CAA section 107(d)(3)(D)). This decision was based on the following findings: 

  • The area had attained the 2006 24-hour PM2.5 NAAQS; 
  • The relevant portions of the Arizona SIP were approved; 
  • The air quality improvements were a result of permanent and enforceable control measures; 
  • Arizona had met all requirements applicable to the Nogales area with respect to section 110 and part D of the CAA; and

The Nogales Maintenance Plan for the 2006 24-hour PM2.5 NAAQS met all applicable requirements for Maintenance Plans under section 175A of the CAA. A second maintenance plan for the Nogales area for the 2006 PM2.5 NAAQS is due in 2030.

Submitted SIPs for the Nogales PM2.5 Nonattainment Area:
  • Arizona State Implementation Plan Revision for the Nogales PM2.5 Nonattainment Area, Submitted Sept. 6, 2013
  • Nogales 2006 24-hour PM2.5 NAAQS Maintenance Plan and Redesignation Request, Submitted April 13, 2021

All plans are available upon request from the ADEQ Records Center | Submit a Records Request >

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