Air Quality Permitting I Control Technology EvaluationsI Atmospheric Dispersion ModelingI Emissions Inventory

Air Quality Permitting Air quality permitting can be a complicated and expensive process. At Zephyr, we simplify this task for our clients by focusing on their needs and providing only those services necessary to meet their objectives. The engineers and scientists at Zephyr have prepared more than 1,500 approved permit applications, permit amendments, permit exemption applications, and related studies over the past 30 years. Our permitting project experience includes the preparation of:

  • State minor source permit applications
  • Federal New Source Review (PSD and Non-attainment) permit applications
  • Title V operating permit applications
  • Exemption applications
  • Permitting strategies
  • Feasibility evaluations

Control Technology Evaluations   Zephyr's staff stays abreast of the latest emissions control technologies available to industry and routinely assists its clients in selecting the most appropriate technologies for controlling their emission sources. Zephyr provides the following services in this area:

  • Abatement equipment specification and conceptual design
  • Recommendations for modification of existing controls
  • Pollution prevention through process optimization and improvements
  • RACT, BACT, MACT, and LAER analyses
  • Input to regulatory agencies in the evaluation of emissions control strategies

Atmospheric Dispersion Modeling   Zephyr's meteorologists are recognized experts in atmospheric dispersion modeling evaluations. We have developed, tested, and gained regulatory agency approval for model algorithms to simulate the dispersion of releases to the atmosphere from our clients' facilities. In addition, our meteorologists have published articles on atmospheric dispersion modeling techniques and applications and have taught college-level dispersion modeling courses. To maintain our capabilities as state-of-the-art, Zephyr staff members routinely attend and present papers at technical conferences. Zephyr's modeling professionals provide a variety of modeling services, including:

  • Accidental release and dense gas dispersion modeling
  • Building and structure wake effects evaluations
  • Good Engineering Practice stack height evaluations
  • Simple and complex terrain modeling
  • Toxics/health effects modeling
  • Hazardous release modeling
  • Line source and mobile source modeling
  • Radius-of-impact determinations
  • Federal and State regulation compliance modeling


Zephyr's mathematical modeling services typically are based on the use of EPA Guideline models, including ISCST3 and SCREEN3. In addition, we use other public domain models, such as SLAB and RMP-COMP, for specialized applications. We have been instrumental in the development and testing of AERMOD, the state-of-the-art dispersion model currently proposed by EPA for regulatory applications, and are experts in its use.

Emission Inventories   Zephyr's staff has prepared emission inventories for bulk fuels terminals, chemical manufacturing facilities, oil and gas facilities, electric generating stations, petroleum refineries, non-ferrous smelters, microelectronics manufacturing facilities, cement plants, pharmaceutical manufacturing plants, food processing operations, general manufacturing facilities, and numerous other industries throughout the United States. These inventories have been used for annual state submittals, compliance tracking tools, strategic planning, Title V permit applications, and regulatory applicability analyses. In many instances, Zephyr has automated all or part of the inventory process to minimize extensive manual data entry and calculation.