Revised PM10 24-Hour Background Value

January 2, 2007

The DNR periodically reviews ambient monitoring data for particulate matter with an aerodynamic diameter less than or equal to 10 microns (PM10) to determine whether the current PM10 background values used for air dispersion modeling of the National Ambient Air Quality Standards (NAAQS) should be updated. The department recently reviewed the PM10 ambient monitoring data for the period 2003 through 2005 using the same methodology as in 1992 and in 2001.

Review of the PM10 ambient monitoring data indicated that the current 24-hour PM10 regional background value should be lowered from the current 52 ug/m3 down to 45 ug/m3. The effective date for the revised 24-hour background is January 2, 2007. The annual PM10 background value was not revised since the annual PM10 standard has been revoked by EPA.

Additional information on how the 24-hour PM10 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.