Air Pollution Control Program

Modeling Overview

In 1977, the Clean Air Act was amended to include provisions for the establishment and implementation of a permitting program referred to as New Source Review (NSR).  The NSR program requires stationary sources to obtain a permit prior to the construction or modification of equipment that will result in the creation of air pollution.  Air pollution permits are legal documents that may contain special conditions that must be met in order to ensure that the new source of pollution will not cause or contribute to violations of the air quality standards.  Under the NSR program, three differing permit types have been established and are based upon the attainment status of a region, the amount of pollutant being emitted and the type of pollution being emitted:  Prevention of Significant Deterioration permits, non-attainment NSR permits and minor source permits.

Typically, state and local agencies are granted the authority to issue NSR permits on behalf of the federal government through the establishment of state implementation plans (SIPs) that must be pre-approved by the Environmental Protection Agency.  Through the SIP process, each state is allowed to develop its own procedures for implementing permitting programs provided the program meets the minimum criteria outlined in the Clean Air Act and the Code of Federal Regulations.           

The provisions contained within the SIP for the State of Missouri require the Department of Natural Resources to determine compliance with the air quality standards, prior to the issuance of a NSR permit, through the use of air quality modeling.  An applicant for an air construction permit is required to conduct an ambient air quality impact analysis (AAQIA) when the pollutant emissions exceed the de minimis emission thresholds outlined in 10 CSR 10-6.020 (3)(A) Table 1.

Additionally, the director may request that an applicant provide an AAQIA to the permit granting authority if it is likely that the new source or modification could appreciably affect air quality within a region or the air quality standards are being appreciably exceeded, regardless of the projected emissions of the construction.  

The objective of the AAQIA is to demonstrate that the proposed project, in conjunction with other emission sources, will not cause or significantly contribute to a violation of the National Ambient Air Quality Standards, or NAAQS, the Prevention of Significant Deterioration (PSD) increments or the Missouri Risk Assessment Levels (RALs). 

An AAQIA must be submitted for each pollutant that the air construction permit applicant proposes to emit in excess of the de minimis emission thresholds noted above 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, entitled "The Guideline on Air Quality Models."

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 website provide a general overview of the dispersion modeling procedures that should be followed when conducting AAQIAs 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.



Protocol Templates

*Air Pollution Control Program
P.O. Box 176
Jefferson City, MO 65102