Air Quality

Air Dispersion Modeling

Sage modelers have years of experience in air dispersion modeling, having performed thousands of air dispersion modeling runs all over the world.


New Source Review (NSR) modeling, also referred to as construction permitting or preconstruction permitting, predicts the effect of a new source on air quality using tools such as air models as part of the permitting process. Sage has many years of experience in all facets of New Source Review modeling:

  • Prevention of Significant Deterioration (PSD) permits which are required for new major sources or a major source making a major modification in an attainment area
  • Nonattainment NSR permits which are required for new major sources or major sources making a major modification in a nonattainment area
  • Minor source permits

In addition to modeling for Federal National Ambient Air Quality Standards (NAAQS) and/or PSD increments, permit applications may require analyses for State standards (i.e., air toxics for example). Sage modelers are experienced at using the following air models:

  • Screening Models (SCREEN3, AERSCREEN, TSCREEN, VISCREEN, etc.)
  • Near-field Dispersion Models (ISCST3, AERMOD, and others)
  • Significantly Reduced AERMOD Run Time
  • Long-Range Transport Models (CALPUFF)
  • Risk Management Models and Utilities (RMP*Comp, CAMEO, ALOHA, MARPLOT, LandView)
  • Hazardous Release Models (ISCEV, SLAB, DEGADIS, ADAM, etc.)


Process and production upsets and unexpected events sometimes occur at a facility. In addition to reporting the event, air modeling can demonstrate the potential effects on air quality. This modeling analysis may have an important bearing on fines or penalties in some cases, assessing the worst-case impacts of an unexpected event. It can also accurately determine the areal coverage of the event and the duration of the exposure to various air pollution levels.

Sage has extensive experience in this kind of air modeling and can work quickly to determine the potential exposures of such an event. If air modeling can demonstrate that the event had insignificant effects on health and welfare concerns, then a company can move quickly to assuage the general public's concerns.


Mobile source modeling is often required by state and federal regulators to assess the impacts of new highways, transit centers, and traffic control systems. Emissions models such as MOBILE6 are used to provide estimates of current and future emissions from highway motor vehicles. MOBILE6 calculates average in-use fleet emission factors for:

  • Three criteria pollutants: hydrocarbons (HC); carbon monoxide (CO); and oxides of nitrogen (NOx).
  • Gas, diesel, and natural-gas-fueled cars, trucks, buses, and motorcycles.

Air models such as CALINE3 and CAL3QHC are used to predict air quality levels related to highways and intersections. Sage's modeling experts can help you with mobile source emissions calculations and mobile source modeling.


Owners and operators must implement a risk management program if their facility manufactures, uses, stores, or otherwise handles more than a threshold quantity of a listed regulated substance in a process. The Clean Air Act Section 112(r) addresses the requirements of the risk management plans (RMPs). Sage engineers and modelers are familiar with the requirements of the RMP program. Sage modelers can assist you with:

  • Risk Management Models and Utilities (RMP*Comp, CAMEO, ALOHA, MARPLOT, LandView)
  • Hazardous Release Models (ISCEV, SLAB, DEGADIS, ADAM, CHARM, etc.)
  • Risk Management Program and Plan (RMP) Off-Site Consequence Analysis Modeling
  • Determination of the Radius of Impact and Population Affected
  • Refined Modeling for More Realistic Impact Estimates
  • Modeling Results Analyses, Interpretation, Documentation, and Reporting


Complex air dispersion models are used in the development of state implementation plans (SIPs) and in the development of new regulations. Sage modelers have performed projects for an SO2 SIP and nonattainment evaluation study conducted in Oklahoma, as well as a study of a potential SO2 nonattainment area for Harris County, Texas. In addition, Sage has capability to help assess impacts of SIP changes to individual facilities.


Sage modelers have a wealth of experience in various areas of legal proceedings. Sage can assist your legal counsel with a team of experts. Our legal counsel support services include:

  • Contested-Case Permit Hearings
  • Expert witness testimony
  • Non-testifying expertise
  • Special dispersion modeling studies
  • Regulatory interpretation

Sage's experienced modelers have prepared expert witness reports and have provided testimony at dozens of contested case hearings and toxic tort cases. In addition, Sage's modelers have provided research support to attorneys preparing their cases. This work includes both technical support and interpretation of complex regulations.

Sage Serves You

Sage's modelers are experienced at conducting custom onsite and offsite training courses on all aspects of atmospheric dispersion modeling and air pollution meteorology. EnviroMod University, a Sage partner-company, also provides regularly scheduled environmental training and follow-up support to both government and industry personnel.

Sage's training topics include:

  • Air quality modeling (all aspects of New Source Review modeling, toxics modeling, emissions event modeling, risk management plan modeling, and special toxic tort modeling)
  • Air permitting
  • Reporting
  • Regulations

Sage's instructors strive to deliver knowledge and competence to each participant to increase their personal skills and to increase their value to their organization.

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