• ^a Not to be exceeded more than once per year.
• ^b Three year average of the annual 98^th percentile values.
• ^c Three year average of the annual fourth-highest daily maximum 8-HR concentration.
• ^d Not to be exceeded more than once per month.,
• ^e Not to be exceeded more than once on average over a three year period.
• ^f Average of annual concentrations for three calendar years.
• ^g Three year average of annual concentrations.
• ^h Three month arithmetic mean within a three year period.
• ⁱ Three year average of the annual 98^th percentile (8^th highest) of the daily maximum 1-HR average concentration in a year.
• ^j Three year average of the annual 99^th percentile (4^th highest) of the daily maximum 1-HR averages.
• ^k Note that in NDAC 33.1-15-02-04 Table 1 (effective July 2020), the annual and 24-hour SO₂ standards have been removed. These standards were removed from the NAAQS effective August 23, 2010 (see Fed Reg. Vol. 75, No. 119, 35520, Tuesday, June 22, 2010).

Note that values are corrected to a reference temperature of twenty-five degrees Celsius (25°C/298 K) and a reference pressure of seven hundred sixty millimeters of mercury (760 mmHg/101.3 kilo-pascals).

• ^a Modeled concentration is the highest-sixth-highest (H6H) 24-HR average across five years of NWS MET data.
• ^b Modeled concentration is the highest annual average across five years of NWS MET data.
• ^c Modeled concentration is the 98^th or highest-eighth-highest (H8H) of the annual distribution of maximum 24-HR concentrations averaged across five years of NWS MET data.
• ^d Modeled concentration is the highest-second-highest (H2H) concentration of five years of NWS MET data.
• ^e Modeled concentration is the 99^th or highest-fourth-highest (H4H) of the annual distribution of maximum 1-HR concentrations averaged across five years of NWS MET data.
• ^f Modeled concentration is the 98^th or highest-eighth-highest (H8H) of the annual distribution of maximum 24-HR concentrations averaged across five years of NWS MET data.
• ^g Note that in NDAC 33.1-15-02-04 Table 1 (effective July 2020), the annual and 24-hour SO₂ standards have been removed. These standards were removed from the NAAQS effective August 23, 2010 (see Fed Reg. Vol. 75, No. 119, 35520, Tuesday, June 22, 2010).

SILs are always highest value.

• ^a Modeled concentration is the highest annual average across five years of NWS MET data.
• ^b Modeled concentration is the highest-second-highest (H2H) 24-HR average across five years of NWS MET data.

SILs are always highest value.

Ambient Data can be accessed through EPA's Air Quality System (AQS) or EPA's GIS Server .

Notes:

• Anemometer height for all stations is 10.0 meters.
• Surface data is in the CD144 format.
• Upper-air station data is in FSL format.
• Station ID has been changed to WBAN code from abbreviated WMO code (ID is also changed in CD144 met files, 1/18/12), for compatibility with AERMET Version 11059 and newer.

Notes:

• Upper-air station data is in FSL format.
• Station ID has been changed to WBAN code from abbreviated WMO code (ID is also changed in CD144 met files, 1/18/12), for compatibility with AERMET Version 11059 and newer.

Notes 1/07/2011:

Files of hourly NO₂ and SO₂ concentrations from NDDoH monitoring sites listed above may be used as hourly background concentrations directly input to AERMOD or may be used to calculate other types of background values, e.g., annual, seasonal, or monthly averages. Monitoring sites with data in these folders represent the NDDoH's preferred sites for providing background concentration data, even though data from other monitoring sites may be used.

Files with designation "0408S2" have substitutions entered for all missing hours. Therefore, use of these hourly background files are preferred for use with NDDoH post-processing software.

Notes 8/14/2015:

Somewhat because of recent EPA guidance on background concentrations used with the new 1-hour NAAQS, the NDDoH does not recommend using hourly concentration data as a first choice for use in regulatory AERMOD modeling in North Dakota. For this reason, the background NO₂ and SO₂ concentration data listed above have not been updated with 2009-2013 monitoring data.

The NDDoH currently prefers use of a constant background concentration or input of matrices of seasonal, monthly, diurnal, or similar concentrations for use with AERMOD as a 1st and 2nd Tier background. Use of hourly monitoring data as background concentrations input to AERMOD will be considered on a case-by-case basis. Please contact the NDDoH Modeling Program for further information about options for background data.

Files included in ZIP package:

• ABRUAF*.FIL
• BISUAF*.FIL
• CMET58*.INP (AERMOD Input File)
• CMET58*.LST
• GEO3KM.DAT
• GGWUAF*.FIL
• INLUAF*.FIL
• PRCP0102.DAT
• RAPUAF*.FIL
• SURF.DAT

Note: * is for the year, i.e. 20– 00, 01, 02