Air Pollution Control Program

Section 6 Modeling Requirements

An applicant for an air construction permit is required to conduct an ambient air quality impact analysis for each pollutant that exceeds the de minimis emission thresholds outlined in 10 CSR 10-6.020 (3)(A) Table 1. The level of analysis that is conducted is dependent upon the complexity of the project and its potential impact on air quality within the region. It is important to note that 10 CSR 10-6.060 (6)(A) 3 requires all applicants to demonstrate compliance with the increment standards for oxides of nitrogen, particulate matter under ten microns, particulate matter under two and one-half microns and sulfur dioxides if the de minimis emissions thresholds for any of these pollutants are exceeded.

Minor source permit applicants are required to maintain compliance with the National Ambient Air Quality Standards (NAAQS) and the Prevention of Significant Deterioration 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.

Significant Impact Area Determinations

A 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 sources or modifications 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. 

National Ambient Air Quality Standards 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 department's 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 risk assessment level 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. 

Checklist and Flowchart|

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 6 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.