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New Hampshire Department of Environmental Services


Air quality modeling uses computer programs, or models, to simulate the flow of air pollution in the atmosphere and to predict the associated health and environmental impacts. By utilizing mathematical equations that replicate weather patterns and characteristics of the physical atmosphere, models are able to simulate the release and transport of air pollutants from their sources. Air quality models can also incorporate chemical reactions that occur in the atmosphere, as well as account for the effects of precipitation and the gravitational settling of airborne particles. Using these methodologies, air quality models then produce an estimation of pollution concentrations or depositions at specific locations of concern.

NHDES performs two types of air quality modeling: permit modeling and regional modeling.

Permit Modeling

Permit modeling assesses the impacts associated with individual facilities for regulated air pollutants as part of the NHDES air permitting process. Permit modeling is used to address stationary sources of air pollution such as power plants and industrial facilities. Permit modeling evaluates the impact of these facilities on their surroundings and on local air quality. The modeling results are compared to state and federal health-based air quality standards for criteria and toxic air pollutants. If these results are above the standards, the source may be required to take permit restrictions that could result in production limits, stack modifications and/or the addition of control devices.

For permit modeling to be performed, sources need to provide the amount of pollutant being emitted from each stack (emission rates), the stack characteristics, a site plan (which includes the property line), stack locations and the dimensions of any nearby buildings. This information is processed with local meteorological data and site-specific terrain elevations in order to predict worst-case air pollution impacts. Updated background air quality data and the contributions from other nearby stationary sources are also incorporated into the analysis to estimate cumulative impacts.

Regional Modeling

Regional modeling looks at how sources of air pollution throughout large portions of the United States affect air quality in New Hampshire and New England. NHDES regional modeling efforts have addressed the immediate New England area as well as the states east of the Mississippi River. Regional models incorporate various types of emissions source categories, such as stationary point (large industries), mobile (cars and trucks), biogenic (natural sources of emissions) and area sources. Area sources include all of the smaller, more widespread sources of emissions that are not included in other categories. Unlike permit modeling, regional modeling can encompass point, mobile, biogenic and area sources from across North America. Land use and terrain, atmospheric chemistry and meteorological data are also important components of regional modeling. This type of modeling can be used to evaluate the effects of widespread pollution prevention measures and assess various control strategies and future regulations for stationary and mobile sources. In this manner, regional models can be used to predict how control strategies might improve the air quality in New Hampshire, New England and the eastern United States.

Air Quality Forecasting and Analysis

In addition to air quality modeling, the NHDES modeling and analysis unit makes daily predictions of air quality and is involved in the analysis of air pollution. Daily forecasts are available on the NHDES Web site and at 1-880-935-SMOG.

NH Department of Environmental Services | 29 Hazen Drive | PO Box 95 | Concord, NH 03302-0095
(603) 271-3503 | TDD Access: Relay NH 1-800-735-2964 | Hours: M-F, 8am-4pm

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