An air quality analysis must be submitted for each pollutant that the construction permit applicant proposes to emit in excess of the de minimis emission thresholds or as requested by the director. Although each facility is unique, the methodology used to demonstrate compliance should be consistent, and at a minimum, should follow the recommendations contained within the Code of Federal Regulations, Title 40, Part 51, Appendix W.

Area designations and permit classification impact the extent and type of analysis that will be required. The topics discussed on the Ambient Air Quality Modeling website provide a general overview of the dispersion modeling procedures that should be followed when conducting Ambient Air Quality Impact Analyses (AAQIA) for construction permit applications within the State of Missouri. Prior to conducting the AAQIA, the applicant should submit a modeling protocol to the department’s Air Pollution Control Program in order to provide the staff from the Construction Permit Modeling Unit the opportunity to review and comment on the modeling methodology. The submission of a modeling protocol can prevent delays from occurring during the review process. Questions comments or data requests should be directed to the Construction Permit Modeling Unit at 573-751-4817.

General Topics

Screen Modeling vs. Refined Modeling

Simple screening procedures can be used to determine if a proposed source or modification poses a threat to the air quality within a region. If the screening analysis indicates that no threat to air quality is likely due to the construction of an emissions source; no further analysis is necessary and the compliance determination can be deemed complete. If, on the other hand, the screening results indicate potential adverse impacts, a refined air quality analysis will be required.  

It should be noted that if the following criteria are met, a screening analysis is not appropriate and should not be conducted:  the source configuration is complex; the emission rates are variable; multiple emission releases are under review; complex topographical features are present; or the existing air quality within the region is questionable. In these instances, a refined air quality analysis will be required. 

Definitions

Model Input Development

When conducting an ambient air quality impact analysis, the characteristics of the proposed sources must be defined within the air quality model. Differing source types are used to describe emission releases within the model and should reflect the actual design characteristics of the release point. In addition, information regarding the facility layout, property boundary and surrounding terrain must be provided and can impact the outcome of the air quality analysis. The following sections provide an overview of each component of the modeling study including any requirements that are specific to the State of Missouri.

Minor Source Modeling

Minor Source 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 a demonstration of compliance with the increment standards is not a required component of the minor source modeling program at the time of permitting for new sources of construction. In these instances, the permit granting authority will internally track increment consumption within baseline areas at five year intervals for oxides of nitrogen, particulate matter under ten microns, particulate matter under two and one-half microns and sulfur dioxides. Available increments will be allocated on a first-come, first-serve basis.

For existing sources that are undergoing a construction permit modification, the requirement to demonstrate compliance with the increment standards will be made on a case by case basis. Applicants should contact the department’s Air Pollution Control Program at 573-751-4817 to determine if an increment assessment will be required prior to permit issuance.  

Significant Impact 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 source or modification 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 (5)(F)3 Table 1, 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 Standard Compliance

A NAAQS compliance demonstration is required for all pollutants that exceed the significance levels outlined in 10 CSR 6.060 (5)(F)3 Table 1. 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

A demonstration of compliance with the increment standards is not a required component of the minor source modeling program at the time of permitting for new sources of construction. In these instances, the permit granting authority will internally track increment consumption within baseline areas at five year intervals. Available increments will be allocated on a first-come, first-serve basis.

For existing sources that are undergoing a construction permit modification, the requirement to demonstrate compliance with the increment standards will be made on a case by case basis. Applicants should contact the department’s Air Pollution Control Program at 573-751-4817 to determine if an increment assessment will be required prior to permit issuance. 

Hazardous Air Pollutant Risk Assessment

According to 10 CSR 10-6.060 (5)(D), an applicant must submit an air quality analysis if the project’s potential hazardous air pollutant (HAP) emissions exceed the Screening Modeling Action Levels (SMALs). Once it is determined that a HAP analysis is necessary, the applicant must submit a demonstration of compliance with the Risk Assessment Levels (RALs). The RAL compliance demonstration must consider emissions from the proposed source and existing sources at the facility. 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.  A separate RAL demonstration must be conducted for each pollutant that has a significant ambient impact or as requested by the Director.

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. 

Modeling Protocol Template

Major Source Attainment Area Modeling

Major Source 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 requires the submittal of 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. 

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 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 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 (5)(F)3 Table 1, 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 significant monitoring concentrations, preconstruction monitoring will be required for a minimum period of one year prior to permit issuance.

National Ambient Air Quality Standard Compliance Determinations

A NAAQS compliance demonstration is required for all pollutants that exceed the significance levels outlined in 10 CSR 6.060 (5)(F)3 Table 1. 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. 

Secondary Impact Analysis

Because ozone and PM2.5 can form in the presence of precursor emissions, all major source permit applications must perform a secondary impact assessment if the project emissions of SO2, NOx or VOC exceed 40 tons per year. 

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 (5)(F)3 Table 1. The purpose of the increment compliance determination 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 (5)(F)5 Table 2. 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 Risk Assessment

According to 10 CSR 10-6.060 (5)(D), an applicant must submit an air quality analysis if the project’s potential hazardous air pollutant (HAP) emissions exceed the Screening Modeling Action Levels (SMALs). Once it is determined that a HAP analysis is necessary, the applicant must submit a demonstration of compliance with the Risk Assessment Levels (RALs). The RAL compliance demonstration must consider emissions from the proposed source and existing sources at the facility. 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.  A separate RAL demonstration must be conducted for each pollutant that has a significant ambient impact or as requested by the Director.

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. 

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. 

Modeling Protocol Template

Major Source Nonattainment Area Modeling

According to 10 CSR 10-6.060 (7), any new major stationary source, or major modification to a stationary source, must obtain a Section 7 nonattainment area permit for each pollutant that it proposes to emit if the area has been designated nonattainment for that pollutant and the projected emission rate exceeds the major source thresholds. 

The Section 7 nonattainment area requirements differ from those that are required under the Section 8 Prevention of Significant Deterioration permitting program. In order to obtain a Section 7 nonattainment area permit, the applicant must agree to the following items:

  • Emissions must be controlled through the application of the lowest achievable emission rate. 
  • Emission offsets must be obtained.
  • All sources owned by the applicant must be in compliance with all applicable air quality standards.
  • A Class I visibility assessment must be made.

Because these requirements are pollutant specific, guidance pertaining to the air quality analysis and emissions offsets will not be provided on this website. If it is determined that a nonattainment area permit is required, the applicant should contact the department’s Air Pollution Control Program for guidance at 573-751-4817.

Major Source Hazardous Air Pollutant Modeling

Hazardous air pollutants (HAPs), also known as air toxics, are air pollutants associated with elevated cancer levels and other adverse health effects. New emission units, or modifications to existing emission units, that have the potential to emit HAPs may be required to obtain a construction permit before commencing construction. New emission units may also be subject to the federal standards found in 40 CFR Part 63, known as National Emission Standards for Hazardous Air Pollutants for sources that fall within the following categories: Maximum Achievable Control Technology and Generally Available Control Technology standards. The following document provides a summary of the permit review requirements for HAPs.

  • HAPs Guidance Document (under construction) 

Data Requests and Electronic Submittals

Meteorological Data Requests for Construction Permitting

Emissions Inventory Data Requests for Construction Permitting

Electronic Submittal of Modeling Files

  • For information on how to submit an ambient air quality impact analysis , please contact department staff at the Air Pollution Control Program at 800-361-4827 or 573-751-4817.  

In This Section:

Hazardous Air Pollutants (HAPs)

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