Air Dispersion Modeling

The Approach

Permits are won on the modeling, and lost on the schedule

A dispersion modeling result that shows an exceedance late in a project is expensive in a way few other findings are. It can force equipment changes, stack redesign, or site relocation after the capital has been committed.

Modeling early, coordinating with the agency before you submit, and building the application on emissions calculations that hold up under review is how permits get issued on schedule. IES does the modeling and the permitting together, so the analysis is done by the people who know what the application has to survive.

AERMOD dispersion modeling

Refined modeling for criteria pollutants and air toxics: receptor grid design, terrain and building downwash, meteorological data selection and processing, and background concentration development.

Design-stage modeling

AERMOD dispersion modeling

Modeling is a design tool, not only a permit requirement. For new construction or modifications, running it during design shows which controls, stack heights, or stack locations will meet the standard while those choices are still inexpensive to change.

Modeling protocols and pre-coordination

Submitting a protocol and getting agency concurrence before the refined analysis is the highest-return step in most permitting projects. It converts a subjective review into an agreed set of assumptions.

Emissions calculations

Modeling protocols and pre-coordination

Potential-to-emit and actual emissions for engines, turbines, heaters, flares, tanks, loading, and fugitives. The calculation basis drives applicability, which drives your whole permit path.

Permit applications

Applicability and NSR analysis

Minor and major source applications, construction permits, general permit registrations, Title V applications and renewals, and modifications, prepared and shepherded through agency review.

Applicability and NSR analysis

Whether a project triggers New Source Review, whether netting applies, whether a modification is major, and whether Title V obligations attach.

When your site ends up in someone else's model

A site can be running normally, within its permit, and still end up in a modeled exceedance it had no part in starting.

When a new or modified source nearby goes through a PSD analysis, the cumulative modeling can include existing sources in the area. Yours may be one of them. If the combined results show an exceedance, your facility can draw agency attention, data requests, or pressure to reduce emissions, all triggered by another operator's project.

The inventory used to represent your site in that analysis is often the weak point. It may rest on permitted maximums rather than actual operation, outdated stack parameters, or equipment that has since been changed. We review how your facility was represented, correct what is wrong, run an independent analysis where it helps, and handle the response to the agency.

Context

Criteria pollutant permitting runs on its own track

Air permitting for criteria pollutants operates under NAAQS, New Source Review, and Title V, on authority separate from the greenhouse gas programs that have seen the most change.

State permitting programs are likewise independent. The obligations here have been stable, and demand has been growing as new generation and large-load projects come forward.

Facility types we permit

Compressor stations and gathering facilities
Natural gas processing plants
Production sites and central tank batteries
Backup and prime power generation, including data center and large-load projects
Other industrial facilities with combustion, storage, or process sources

These are examples, not a limit. If your facility carries a permit obligation, we can model it.

Process

How a permitting project runs

Applicability screening: What permit path the project is on and what triggers it.
Emissions inventory: Potential to emit, source by source.
Modeling protocol: Drafted and coordinated with the agency.
Refined modeling:AERMOD analysis and results.
Application preparation: Assembled, reviewed, submitted.
Agency response: Completeness review, technical questions, and public comment where applicable.

We flag exceedance risk at step two, not step four. That is the difference between a design adjustment and a project delay.

Start before the design is locked

The least expensive time to find a modeling problem is before equipment is ordered. Bring us the project early and we will tell you which permit path you are on.

Common questions

What is AERMOD?

AERMOD is EPA's preferred steady-state dispersion model for near-field regulatory applications. It predicts ambient concentrations from modeled sources at defined receptors, and results are compared against ambient standards or applicable increments.

When is dispersion modeling required for an air permit?

It depends on the permit type, the pollutants, and the state. Major source permits generally require it. Many minor source permits require modeling only above certain emission levels or for specific pollutants. Some states require it broadly. We determine this during applicability screening.

Why would my site show up in another facility's PSD analysis?

Cumulative modeling for a nearby project can include existing sources in the area. If your facility is represented with outdated or overstated inputs, it can appear to contribute to an exceedance that does not reflect how you actually operate.

Can modeling help before we build?

Yes, and that is often where it pays for itself. Modeling during design shows which controls, stack heights, and stack locations will meet the standard while those choices are still easy to change.

What if modeling shows an exceedance?

Options include refining inputs, revising stack parameters, changing equipment or controls, adjusting site layout, or accepting operating limits. Where the model is simply too conservative, ambient monitoring can demonstrate compliance with measured data instead.

When does ambient monitoring make sense?

When a facility cannot show compliance through modeling but may well be meeting the standard in reality. Monitoring requires an agreed protocol, a proper siting study, and sustained operation, so it is a longer commitment than modeling, but it replaces a conservative prediction with an actual measurement.

How long does air permitting take?

It varies widely, from weeks for a general permit registration to a year or more for a major source permit with refined modeling and public comment. Agency review time is usually the largest and least controllable component, which is why pre-coordination matters.

How do we get started?

Schedule a free consultation and IES will scope the engagement around your facilities, reporting obligations, and timeline.

Air Permitting and Dispersion Modeling

The Approach

Permits are won on the modeling, and lost on the schedule

What we do

AERMOD dispersion modeling

AERMOD dispersion modeling

AERMOD dispersion modeling

Design-stage modeling

AERMOD dispersion modeling

AERMOD dispersion modeling

Modeling protocols and pre-coordination

Modeling protocols and pre-coordination

Modeling protocols and pre-coordination

Emissions calculations

Modeling protocols and pre-coordination

Modeling protocols and pre-coordination

Permit applications

Applicability and NSR analysis

Applicability and NSR analysis

Applicability and NSR analysis

Applicability and NSR analysis

Applicability and NSR analysis

Measured emissions inputs

Measured emissions inputs

Measured emissions inputs

Measured emissions inputs

Measured emissions inputs

Cumulative modeling

Context

Criteria pollutant permitting runs on its own track

Facility types we permit

Process

How a permitting project runs

Start before the design is locked

Common questions

Ready to Take the Next Step?

Air Permitting and Dispersion Modeling

The Approach

Permits are won on the modeling, and lost on the schedule

What we do

AERMOD dispersion modeling

AERMOD dispersion modeling

AERMOD dispersion modeling

Design-stage modeling

AERMOD dispersion modeling

AERMOD dispersion modeling

Modeling protocols and pre-coordination

Modeling protocols and pre-coordination

Modeling protocols and pre-coordination

Emissions calculations

Modeling protocols and pre-coordination

Modeling protocols and pre-coordination

Permit applications

Applicability and NSR analysis

Applicability and NSR analysis

Applicability and NSR analysis

Applicability and NSR analysis

Applicability and NSR analysis

Measured emissions inputs

Measured emissions inputs

Measured emissions inputs

Measured emissions inputs

Measured emissions inputs

Cumulative modeling

Context

Criteria pollutant permitting runs on its own track

Facility types we permit

Process

How a permitting project runs

Start before the design is locked

Common questions

Ready to Take the Next Step?

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