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Air Quality Dispersion Modeling

There was a time when air dispersion modeling was a minor subset of the services that ALL4 provided to our clients.  Modeling was typically conducted to support PSD permitting or state-specific air toxics requirements, for visibility analyses for assessing impacts on Class I areas, or to support the development of multi-pathway or inhalation health risk assessments.  All of that has changed with the establishment of the new short-term NAAQS for SO2, NOX and fine PM.  In 2011 U.S. EPA issued guidance directing states to include air dispersion modeling results along with available ambient monitoring data when establishing SO2 attainment designations.  When this approach was paired with the stringent new 1-hour standards, air quality modeling became a critical tool, not only for evaluating compliance, but as importantly, for strategic facility planning. 

As we observed this shift in the role that air quality dispersion modeling serves, ALL4 changed the approach we take in offering this service area.  All of our technical staff, from bottom to top, is now trained in air dispersion modeling and everyone here now has first-hand experience with this critical aspect of air quality expertise.  While air dispersion modeling is a critical component to air quality permitting projects and NAAQS compliance, it is often misunderstood.  ALL4 offers extensive experience applying air dispersion models, understanding and interpreting the results, and integrating the results into the permitting process, compliance demonstrations, or strategic planning for future operations. ALL4 has conducted air quality modeling studies in support of a variety of regulatory and permitting projects. These include the following:

  • NAAQS Analyses 
  • PSD/NSR Permitting Projects
  • PSD Increment Analyses 
  • Air Quality Related Values (AQRV) Analyses 
  • Long Range Transport and BART/Visibility Analyses 
  • State Air Toxics Programs 
  • Odor Assessments 
  • Human Health Risk Assessments 
  • Risk Management Programs (RMP) for accidental releases 
  • Minor source air permitting projects 
  • Wind tunnel results analysis 

ALL4 has worked closely with state meteorologists, U.S. EPA regulatory and technical staff and model developers. ALL4 understands the technical aspects of the models and the regulations governing the use of air dispersion models. ALL4 uses EPA-developed air dispersion models such as:

  • AERMOD 
  • CALPUFF 
  • ALOHA 
  • TRACE 
  • ISCST3 
  • ISCPrime 
  • CTDMPlus

Related Case Studies

Air Toxics Screening Tool
Dispersion Modeling Analysis