The Maricopa County Air Quality Department (MCAQD) has been hard at work revising its new source review related rules. During a
workshop held on March 12, 2025, MCAQD gave stakeholders an update on the progress of this revision work for MCAQD Rule 230, General Permits, and MCAQD Rule 240, Federal Major New Source Review. MCAQD’s tentative goal is to submit a state implementation plan (SIP) revision containing the updated versions of these rules for Environmental Protection Agency (EPA) approval for incorporation into Maricopa County’s SIP by August 2025. With August approaching and many facilities within Maricopa County being subject to these rules, it is critical to review the proposed changes.
Updates Bring Clarity to General Permits
MCAQD Rule 230 establishes general air quality permits, which are those covering a facility class that contains large numbers of sources that perform the same operation, emit similar air pollutants, and are subject to similar rules. MCAQD offers general permits as an alternative to individual air permits (i.e., Non-Title V for minor sources or Title V for major sources) for facilities which meet the applicability criteria for existing categories. MCAQD offers general permits that cover the following facility classes:
- Asphalt Kettle Operations
- Crematories
- Dry Cleaning Operations
- Fuel Burning Operations
- Gasoline Dispensing Operations
- Graphic Arts Operations
- Stationary Dust Generating Operations
- Stationary Emergency Internal Combustion Engines
- Surface Coating and/or Abrasive Blasting Operations
- Vehicle and Mobile Equipment Refinishing Operations
- Wastewater Treatment Plant
- Wood Furniture, Fixture and Millwork Operations
Since General Permits for these facility classes are already developed, applying for an Authority to Operate (ATO) under a General Permit offers speed and cost advantages over applying for an individual source permit. Currently, over 2,400 ATOs are active in Maricopa County, meaning changes to Rule 230 will impact many facilities. It must be noted that general permits have pre-defined conditions, such as specific compliance demonstration methods, that may not suit every facility’s needs. General permits may also be more restrictive in allowing operational or regulatory changes. Based on your particular facility’s needs, a general permit may not be the most appropriate.
Rule 230 updates were originally proposed by MCAQD in the December 2019 round of SIP revisions. The updates were rejected by the EPA on the grounds that Rule 230 language lacked public notice, procedural, and operational clarity. In response to the EPA disapproval, MCAQD is proposing to clarify language in Section 300 of the Rule. Most importantly for sources, MCAQD added language confirming that a source that operates under a General Permit is not required to also obtain an individual source permit. MCAQD also explicitly listed the conditions under which a General Permit holder may make changes, which include:
- The changes are limited to those authorized in the General Permit, including installing a replacement emissions unit and adding or replacing air pollution control equipment;
- The changes do not require the source to obtain an individual non-Title V or Title V permit; and
- Written notification of the changes are provided to the Control Officer.
The proposed changes to Rule 230 will provide value to General Permit holders by spelling out the limits of what can and cannot be done under a General Permit. No matter how clear the language is made, it is still the responsibility of permit holders to familiarize themselves with their permit conditions.
Public notice procedures for those general permits which are subject to public notice requirements (i.e., Title V sources) are also being amended to ensure sufficient information is being provided to the public. The following information will be provided with public notice statements:
- Approximate number and general location of sources likely to obtain the General Permit.
- Overall expected emissions covered by each General Permit.
- A copy of the notification is sent to all other state and local air pollution control agencies having jurisdiction where emission units are located.
Updates Solidify Major New Source Review Requirements Ahead of Serious Ozone Nonattainment
MCAQD Rule 240 establishes federal new source review (NSR) requirements that apply to new major sources and major modifications to existing major stationary sources in nonattainment, attainment, and unclassifiable areas. With the anticipated
redesignation of the Phoenix-Mesa area to “serious” ozone nonattainment in 2025, Rule 240 must align with federal NSR requirements applicable to serious ozone nonattainment areas (i.e., Nonattainment NSR requirements).
MCAQD is therefore undergoing a rulemaking effort to incorporate Sections 182(c)(6), 182(c)(8), and 182(f)(1) of the Clean Air Act (CAA) into Rule 240, which MCAQD is proposing in its Rule 240 revisions to the EPA. The proposed amendments to Rule 240 confirm the stricter NSR requirements anticipated as a result of the upcoming redesignation of the Phoenix-Mesa area to “serious” ozone nonattainment. The implementation of these CAA sections will result in the 240 changes below
- A lower threshold for what is considered a “significant” volatile organic compound (VOC) and nitrogen oxides (NOx) emissions increase in the ozone nonattainment area. The significant emission rate (SER) will be lowered from 50 tons per year (tpy) to 25 tpy.
- Addition of special provisions for modifications at existing major sources of NOx and/or VOC in serious and severe ozone nonattainment areas, as noted in Table 1.
- Removal of the existing Rule section allowing for Interprecursor Trading (IPT) for Ozone (i.e., NOx and VOC offsets will no longer be authorized to be used interchangeably for meeting Nonattainment NSR requirements).
Table 1. Special Modification Provisions Added to Rule 240
| PTE of Major Source Being Modified | Elected Emission Offset Ratio for Modification | Subject to Nonattainment NSR Major Modification Requirements? (Y/N) | Control Technology Evaluation |
| Subject to Best Available Control Technology (BACT)? (Y/N) | Subject to Lowest Achievable Emission Rates (LAER)? (Y/N) |
| < 100 tpy NOx/VOC | 1.3:1 (Internal) | N | N | N |
| 1.2:1 (General) | Y | Y | N |
| > 100 tpy NOx/VOC | 1.3:1 (Internal) | Y | N | N |
| 1.2:1 (General) | Y | N | Y |
In addition to the key updates above, MCAQD is continuing rule order standardization efforts as well as rewording and restructuring sections for clarity.
Trinity’s 2022 article offers a comprehensive summary of the impacts from the Phoenix-Mesa redesignation to serious ozone nonattainment to facilities with air permits and remains an excellent resource for understanding changes in MCAQD requirements from the current moderate nonattainment status.
Conclusion
The sections above provide a summary of the proposed changes in MCAQD Rules as a result of EPA recommendations and the approaching ozone nonattainment reclassification. The proposed changes to Rule 230 and Rule 240 will affect a large number of facilities once approved and included in the SIP. If you have questions or would like to discuss how these changes may impact your facility, please email Trinity’s Phoenix office or call 602.274.2900.
