Revised NOx Annual Background Value

Febraury 5, 2007

The DNR periodically reviews ambient monitoring data to determine whether the current background values used for air dispersion modeling of the National Ambient Air Quality Standards (NAAQS) should be updated. The department recently reviewed the NOx ambient monitoring data for the period 2003 through 2005 using a similar methodology as used for particulate matter with an aerodynamic diameter less than or equal to 10 microns (PM10).

Review of the NOx ambient monitoring data indicated that the current rural and urban annual NOx background values of 14 and 20 micrograms per cubic meter should be replaced by the reduced regional background value of 11 micrograms per cubic meter. The revised NOx background value applies to all locations in Iowa. The effective date for the revised annual background is February 1, 2007.

Additional information on how the annual NOx background value was determined or any other questions related to this action can be directed to Lori Hanson at (515) 281-8911 or by email at lori.hanson@dnr.iowa.gov.