Air Pollution Control Program

Section 8 Attainment Area Modeling Requirements

According to 10 CSR 10-6.060 (8), any new major stationary source, or major modification to a stationary source, that proposes to locate within an area that is classified as attainment or unclassifiable must obtain a Prevention of Significant Deterioration (PSD) permit prior to commencing construction. 

The PSD program was established under the 1977 amendments to the Clean Air Act in order to prevent large industrial sources from deteriorating existing air quality in regions that were in compliance with the National Ambient Air Quality Standards (NAAQS).  Three primary goals were established under the program:  1. Ensure economic growth while preserving existing clean air resources, 2. preserve public health from adverse impacts that could occur due to an increase in ambient air pollutants, and 3. preserve, protect and enhance air quality within Class I areas.

Once it is determined that a facility is subject to the PSD requirements, any pollutant that exceeds the de minimis emissions thresholds becomes subject to review and will be required to submit an ambient air quality analysis.  The ambient air quality impact analysis must include a review of both the Class I and Class II areas that are affected by the proposed facility.  Additional impact analyses are also required and are described in the following documents. 

Major source permit applicants are required to maintain compliance with the NAAQS and the PSD increment standards regardless of the inclusion of the facility emissions in a modeling demonstration at the time of permit issuance.  The department’s Air Pollution Control Program reserves the right to request an ambient air quality impact analysis if it is determined that air quality issues are evident.

Class I Areas 

Class I areas are afforded the most protection under the PSD program and little air quality deterioration is allowed in these regions.  Congress identified mandatory Class I regions throughout the United States based upon national/regional value due to natural, scenic, recreational, and/or historic worth.  There are three Class I areas that can trigger a review for Missouri applicants, Hercules Glades Wilderness Area and the Mingo Wildlife Refuge that are located within the State of Missouri and Upper Buffalo Wilderness Area located in the State of Arkansas.

Class II Areas 

With the exception of the two Class I areas noted above, the remainder of the State of Missouri has been designated as a Class II area that is allowed moderate air quality deterioration.  Class II areas are often associated with managed economic growth that allows for increased air quality impacts due to the construction of manufacturing facilities.   

Significant Impact Area Determinations

Any facility that proposes to emit any pollutant above the thresholds outlined in 10 CSR 10-6.020 (3) (A) Table 1 must submit an ambient air quality impact analysis to the permit granting authority.  In order to determine if a full impact model analysis is necessary, a facility must complete a preliminary model analysis.  This analysis should only include the proposed source(s) or modification(s) so it can be determined if a significant modeled impact will take place.  If the model predicts the high first high to be below the thresholds outlined in 10 CSR 10-6.060 (11)(D) Table 4, no further analysis is necessary and the modeling study can be deemed complete provided it follows the EPA’s minimum modeling requirements.    

Preconstruction Monitoring Requirements 

Any facility that proposes to emit any pollutant above the thresholds outlined in 10 CSR 10-6.020 (3) (A) Table 1 must submit an ambient air quality impact analysis to the permit granting authority.  In order to determine if preconstruction monitoring is necessary, a facility must complete a preliminary model analysis.  This analysis should only include the proposed source(s) or modification(s) so it can be determined if a significant modeled impact will take place.  If the maximum modeled concentration exceeds the thresholds outlined in 10 CSR 10-6.060 (11)(B) Table 2, preconstruction monitoring will be required for a minimum period of one year prior to permit issuance. 

National Ambient Air Quality Standards (NAAQS) Compliance Determinations

A NAAQS compliance demonstration is required for all pollutants that exceed the significance levels outlined in 10 CSR 6.060 (11) (D) Table 4.  Unlike a significance determination, the NAAQS compliance demonstration must consider emissions from the proposed source, existing sources at the facility and interactive sources that contribute to background pollutant concentrations.  The modeled emission rates must reflect the maximum allowable operating conditions based upon federally enforceable emission limits and operating levels, for each pollutant, and averaging time. 

Missouri Air Quality Standards

In addition to the NAAQS, 10 CSR 10-6.010 establishes ambient air quality standards for two additional pollutants, hydrogen sulfide and sulfuric acid, that must be met in order to provide protection to the public and to maintain the health of the environment.  A third pollutant, fluoride, is also regulated under the New Source Review Program and can trigger an analysis if the de minimis threshold in 10 CSR 10-6.020(3) (A) Table 1 is exceeded.  The modeled emission rates must reflect the maximum allowable operating conditions based upon federally enforceable emission limits and operating levels, for each pollutant, and averaging time. 

Increment Compliance Determinations 

An increment compliance demonstration is required for all pollutants that exceed the significance levels outlined in 10 CSR 6.060 (11) (D) Table 4.  The purpose of the increment compliance determinations is to demonstrate that the facility, in conjunction with interactive sources, will not deteriorate the air quality beyond the limits outlined in 10 CSR 10-6-060 (11) (A) Table 1.  The increment compliance demonstration must consider emissions from any source that has had an emission increase since the establishment of the minor source baseline date.  The modeled emission rates for the proposed source or modification must reflect the maximum allowable operating conditions based upon federally enforceable emission limits and operating levels, for each pollutant, and averaging time.  It should be noted that the modeled emission rates for existing sources, that are not undergoing modification, should reflect the two-year average actual emissions that result from each piece of equipment that has been permitted. 

Hazardous Air Pollutant (HAP) Risk Assessment

Under the departments’ Air Pollution Control Program guidelines, a facility must submit an air quality analysis for all emission points within a facility when a refined analysis for a HAP is required.  This requirement was introduced to ensure that any applicable RAL is not violated near a facility since background concentrations are not a required component of a HAP analysis.  It is important to note that background concentrations are not currently required because they are virtually unknown for most HAPs, thereby making a background assessment impossible. 

Additional Impact Analyses 

In addition to determining compliance with the air quality standards, major source permit applicants are required to determine if the emissions due to the construction and operation of the new source or modification will result in visibility impairment, vegetation damage or pollutant deposition in the soil.  The applicant must also determine if additional emissions due to localized growth will occur and cause adverse ambient impacts. 

The air quality modeling checklist should be completed and included in the ambient air quality impact analysis that is submitted in support of the Section 8 construction permit.  Each element within the checklist should be addressed and must include an explanation if the modeling procedures outlined within the document are not followed.

Permit Amendments and Model “True-ups” 

If significant alterations to the project design are evident upon completion of construction, the applicant may be required to submit an updated ambient air quality impact analysis that continues to demonstrate compliance with the air quality standards.  The department’s Air Pollution Control program reserves the right to request the use of the most up to date air quality model regardless of the model version that was used in the original compliance demonstration.  Alterations to the meteorological database will not be made unless a significant amount of time has passed since the issuance of the construction permit. 

If an applicant submits a permit application for a new project and is required to submit an air quality impact analysis, the model version and meteorological database are likely to be updated.