On January 22, 2010, the EPA issued a new primary National Ambient Air Quality Standard for nitrogen dioxide. The new standard is based on a criterion for the highest one-hour average per sampling day. Monitors for which the 98th percentiles of such daily maximums averaged over three consecutive years exceeds 100 parts per billion are likely to be deemed not attaining this standard. Previously, both the primary and secondary NAAQS were attained when the annual arithmetic mean concentration was not greater than 53 PPB. This criterion is still used as a secondary NAAQS.

To aid in planning for attainment of the 1-hour NO₂ standard, the following North Carolina maps have been drawn showing the 3-year-average 98th percentile of maximum 1-hour concentrations in each county. Click on links for printer-friendly (PDF) version.

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