GZA’s staff of environmental professionals routinely performs air quality impact analyses to assess the impacts of air emission releases to the ambient air. In many cases, GZA conducts these air quality impact analyses as part of the air permitting process for a new or modified facility. In order to obtain the permits that are necessary to construct and operate a facility, an air quality impact assessment must often be performed to demonstrate that the facility will not cause or contribute to an exceedance of any state or national ambient air quality standard. For major new emissions sources or for major modifications to existing emissions sources, a Prevention of Significant Deterioration (PSD) impact analysis is also required. These impact analyses are typically performed using air dispersion models.

Dispersion modeling is a highly-specialized field that requires expertise in meteorology, atmospheric chemistry, and fluid dynamics. GZA’s staff of meteorologists, air quality scientists and engineers has experience using a wide variety of EPA-recommended dispersion models, ranging from the simplest screening models such as SCREEN3 to the most sophisticated of the current generation of refined models, including AERMOD and CALPUFF. GZA staff also have experience utilizing other specialty models for unique applications such as odor and visibility impact assessments. Overall, GZA has conducted modeling studies for a wide range of emission sources including landfills, power plants, manufacturing plants, accidental chemical releases, cooling towers, and vehicular emissions.

GZA offers comprehensive air dispersion modeling and impact analysis services that go beyond simply “running” the models. In many cases, especially when initial modeling results are unfavorable, modeling results must first be technically interpreted and then, if necessary, modeling strategies can be changed. To be able to do this effectively requires a technical understanding of the model algorithms and an awareness of the shortcomings and idiosyncrasies of a particular model. GZA staff have these capabilities.

Other related services offered by GZA include:

• Modeling protocol development
• Good Engineering Practice (GEP) stack height evaluations
• Building wake effect and cavity impact analyses
• Meteorological data processing and evaluation
• Background air quality evaluations
• Health risk assessments.