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Air Quality Modeling Program

Administered by the Division of Air Quality


Why Do We Need Models?

The Division of Air Quality regularly measures the concentration of specific air pollutants at selected monitoring locations. However, the Division also needs the ability to make future projections of air pollution levels. Computer models are a relatively inexpensive and expedient means of providing this air quality information. For example, models can be used to predict the future concentration of a particular pollutant after the implementation of a new pollution control program. The results of the modeling are then used to estimate the effectiveness of the control program and whether it is worth the cost of implementation. Because of their ability to evaluate a variety of options for managing air quality, models are an important planning tool.

What Exactly Are Models?

There are a wide variety of air quality models that have been developed for different pollution sources, meteorology, downwind distances, and other factors that affect how pollutants are dispersed in the atmosphere. In general, however, all of these models require two types of data: information about the source being modeled, including the pollutant emission rate, and information about the dispersing characteristics of the meteorology surrounding the source, such as wind speed and direction. The model uses this information to mathematically simulate the pollutant's downwind dispersion in order to derive estimates of concentration at a specified location. Some models even simulate the chemical transformations and removal processes that can occur along the transport path.

How Are Models Used?

Air pollution models are most frequently used during the permitting process to verify that a new source of air pollution will not exceed federal health-based standards. These standards, called the National Ambient Air Quality Standards (NAAQS), were established by the Federal Government to protect human health and the environment. These relatively simple models estimate downwind concentrations from a proposed facility prior to its construction.

Larger scale, regional models are sometimes used to simulate the air quality impacts from all sources in an urbanized area. This is a very complex analysis that is usually reserved for developing state plans to clean up large areas of nonattainment where air pollution exceeds the NAAQS. These models are very useful for determining the cost effectiveness of regional air pollution control strategies such as vehicle inspection programs or wood burning restrictions.