Advanced Air Modeling

CPP Wind > What We Do > Air Modeling Services > Advanced Air Modeling

The Clean Air Act (CAA) was established in 1970 by Congress to protect public health and welfare. Since then, it’s undergone two amendments and has achieved many milestones. The United States’ air pollution has significantly decreased as a result of the CAA and more recent air quality regulations.

However, some air quality regulations, such as the National Ambient Air Quality Standards (NAAQS), have become more complex and stringent in the last few years, which poses a significant challenge to economic activity.

For example, the recent short-term NAAQS are much more difficult to meet than the original longer-term standards. This is because the conservative assumptions in AERMOD (the EPA’s accepted regulatory model) are more critical when dealing with these very stringent short-term standards. Many studies have shown that the results from AERMOD significantly overestimate ambient concentrations.

Some of the currently used assumptions that can cause significant overpredictions include:

  • Unrealistic building downwash effects calculated by the Building Profile Input Program for PRIME (BPIP) used by AERMOD
  • Assuming continuous maximum emissions
  • Pairing maximum background concentrations with the modeled (predicted) values
  • Simplistic haul road characterization
  • Inappropriate wind speeds to characterize wind-blown dust from storage piles
  • Inappropriate friction velocity to characterize low-speed winds under stable conditions

If your project has stalled because of air modeling requirements or if you need an alternative to less-accurate, overly-conservative modeling methods, we have scientifically-based, validated alternatives that can support your project while protecting air quality.

Our advanced modeling services include:

  • Equivalent Building Dimensions (EBD)
  • Haul road characterizations based on site-specific dispersion
  • Fugitive dust and particulate emissions from storage piles and exposed areas
  • Many more services

Unlike any other wind engineering consulting firm, we promote advanced techniques to alleviate excessive conservatism in permit modeling to a reasonable level that still protects public health.

With experience dating back to the inception of the Clean Air Act, our experts do more than run the models; we understand the theory, know where the models work, and recognize where they don’t work. If a model doesn’t work, we have unique tools to overcome these areas. This difference will save you time and money.

We use verified methods to reduce excess conservatism that lead to highly unrealistic results, while meeting NAAQS requirements and protecting air quality.

Equivalent Building Dimensions (EBDs) Studies

The effect on plumes caused by wind flowing around nearby buildings and/or structures is called building downwash. In AERMOD these effects are commonly calculated with BPIP. However, BPIP was developed for a specific range of building dimensions, and its accuracy is uncertain outside of this range. As an alternative to BPIP, EBDs can be determined through wind tunnel modeling and used in AERMOD for more accurate results. Another potential benefit to using EBDs instead of BPIP is achieving lower predicted concentrations. This could mean significant savings due to reduced costs in pollution control equipment and shorter stacks.

Fugitive Dust Emissions from Aggregate/Grain Handling, Storage Piles, and Exposed Areas

We provide more accurate wind-driven particulate emissions estimates using on-site testing. This method helps evaluate mitigation strategies since it accounts for local features that reduce wind speed. We can also determine site-specific dispersion coefficients for coke pits and aggregate or grain loading operations.

The Adjusted Friction Velocity Option in AERMET

This is a beta option that EPA added in AERMET to correct issues with friction velocity under low wind speed hours. According to recent comments from EPA, this option could soon be included as a regulatory (non-default) option in AERMET.

Good Engineering Practice (GEP) Stack Height

Many believe that GEP stack height is limited to 65m or 2.5 times the height of the building. This is not true. Depending on the surroundings and the details of the project, wind tunnel testing can justify heights above the formula or, in some cases, show that the higher stack is not actually needed for compliance.

Emission Variability Processor (EMVAP)

Current air modeling practices assume that emission units operate at full load every hour of the year. This assumption leads to unrealistic concentrations, especially for units that operate infrequently, at variable loads, or that have infrequent high emissions. EMVAP uses a statistical method to address the variability of emissions in dispersion modeling for more realistic predicted concentrations.

Background Concentrations

NAAQS permit modeling requires the inclusion of background concentrations to the predicted values obtained from AERMOD. Current practices pair the extreme values from representative ambient monitors with the predicted values from AERMOD. This assumes that two extremely unusual events occur at the same time. A more realistic method combines the median monitored value with the predicted concentrations from AERMOD. This is statistically valid and produces more accurate results.

These methods obtain more realistic concentration estimates that still comply with NAAQS. Using advanced modeling and analysis, we help your project overcome regulatory challenges to meet deadlines. Our expertise can also save you money by avoiding unnecessary emission controls and excessive stack heights.

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