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Draft Nitrogen Dioxide Background Concentrations for Rural Areas
Posted: 12/04/2013

In 2012 the statewide default background concentrations for use in dispersion modeling analyses were updated. At that time, the only two nitrogen dioxide (NO2) monitoring sites in Iowa were used to calculate an average NO2 background. Both of these sites are located in urban areas, where NO2 concentrations are generally higher. As such, the default NO2 background concentrations represent a conservative estimate for many portions of rural Iowa. In order to provide a more accurate estimate of the NO2 background levels in rural areas, the DNR has developed draft rural NO2 background concentrations.

The DNR is proposing to implement the following default rural NO2 background concentrations. The current default concentrations will remain in place for urban areas of the state, and are also listed below for comparison.

                Rural                                     Urban

1-hour 34 µg/m3 (18 ppb)           75 µg/m3 (40 ppb)

Annual 5 µg/m3 (3 ppb)                15 µg/m3 (8 ppb)

By default, modeling analyses conducted in Clinton, Linn, Polk, Pottawattamie, Scott, and Woodbury counties will use the existing urban background and all other areas of the state will use the rural background. However, portions of the “urban” counties that are separated from the urban core by a large enough distance will be allowed to use the rural background. A Google Earth file will be provided that depicts a more detailed division between urban and rural areas in these counties.

A technical support document describing the methodology used to determine the proposed background concentrations can be found on the Air Quality Bureau’s public input website.

Please contact Brad Ashton at, or by phone at (515) 725-9527, with any questions or comments by 12/18/2013.

This list serve article is intended for consultants, industries, environmental groups, general public, and other entities regulated under the Clean Air Act. It was written by the DNR Air Quality Bureau to share regulatory news, program updates and technical guidance.