Ambient BackgroundsContact: Stephanie Hengesbach, 517-284-6746Agency: Environmental Quality
Modeling for sources emitting criteria pollutants may be required to demonstrate compliance with National Ambient Air Quality Standards (NAAQS). If a demonstration is needed, guidelines specify that ambient backgrounds be added to predicted concentrations. Ambient backgrounds are calculated via data made available from various air monitoring stations located across the region.
The appropriate selection of a particular air monitoring station depends on several factors including, but not limited to, the following:
- proximity of the monitor to the modeled source,
- location of the monitor with respect to the modeled source (e.g. upwind or downwind based on prevailing winds),
- available years of data,
- sighting objective of the monitor,
- completeness of data, and
- availability of data from a potentially more representative monitor.
When calculating a background it is desirable that data from the last three years be used. Data from the last three years will not always be available. In these cases, the AQD can be consulted as to which alternatives can be considered.