NO2 Attainment Status and Trends

Overview
The Clean Air Act defines an area as attainment or nonattainment based on a “design value” (see Criteria Pollutants). Please read below for information about nitrogen dioxide (NO2) attainment status and design value trends.

New Hampshire’s Attainment Status
New Hampshire is currently designated as attainment statewide for NO2. Because there has never been a nonattainment designation for NO2 in New Hampshire, there are no maintenance areas.

Historical Trends
The chart below compares New Hampshire’s maximum one-hour NO2 design values and 98th percentiles to the standard in effect at that time. The current one-hour NO2 design value, which has been in effect since 2010, is defined as the three-year average of each year’s 98th percentile based on hourly concentrations.

These data show that maximum design values fell significantly around 1990 and have remained well below the NAAQS since that time. The most recent drop in concentrations is primarily due to a move in the monitoring of NO2 from Manchester to Nashua.

New Hampshire 1-hour nitrous oxide design values