NO2 Average Values

For many years there were only two NO2 monitors in NC using a "federal reference method." Those sites were in Forsyth and Mecklenburg Counties and were operated by Local Programs. Beginning in 2014, additional NO2 monitoring sites began operation in Wake and Lee Counties. As of 2018, there are four NO2 sites, and all are operated as defined in the Annual Monitoring Network Plan for North Carolina Air Quality.

Please click here to open the NO2 Design Values Map as a PDF.

For NO2, the United States Environmental Protection Agency (USEPA) uses a 3-year average of the 98th percentile of the daily maximum concentration to determine the design value for this pollutant.  The table below shows 3-year averages for the 98th percentile of daily maximum NO2 concentrations. The first column lists the county, the second lists the 3-year average 98th percentile value, the third column lists the site with the highest 3-year average.  The fourth column lists the arithmetic mean value of all hourly averages for that county. The fifth column lists the site with the highest mean value.  In Counties with more than one NO2 monitoring site, the value reported is the highest average among the inclusive sites.  An asterisk (*) has been added to indicate those sites which have not operated for the entire 3-year period, but whose data has been included in this summary.


Average 98th Percentile

Site Name

Arithmetic Mean

Site Name


36 ppb [a]

Hattie Avenue [1]

7 ppb

Hattie Avenue [1]


8 ppb [a]

Blackstone [2]

1 ppb

Blackstone [2]


39 ppb

Remount Road [1]

11 ppb

Remount Road [1][*]


36 ppb

Millbrook [1]

9 ppb

Triple Oak [1]

[*] Indicates the site does not satisfy the summary criteria

Purpose of Monitor

[1] SLAMS – (State and Local Monitoring Stations) Network of monitoring stations that monitor ambient air concentrations for pollutants for which standards have been established. The scale of these sites can be either Neighborhood/Area Wide or Micro-scale/Near Road (Remount Road and Triple Oak). Hattie Avenue is a Neighborhood Scale Regional Administrator Required Monitoring Site.

[2] SPM – (Special Purpose Monitors) SPMs allow the capability of providing monitoring for various reasons such as special studies, modeling verification or compliance status, and other objectives. These monitors are not committed to any one location or for any specified period.

[3] NCORE – (National Core) Community-oriented multi-pollutant monitoring station used to evaluate the regional air quality models used in developing emission strategies and to track trends in air pollution abatement control measures’ impact on improving air quality.




Table 1. The following table shows 3-year averages for the 98th percentile of daily maximum NO2 concentrations. The first column lists the county, the second lists the average value for that county.

County Average 98th Percentile
Forsyth 41 ppb
Mecklenburg 41 ppb
Previous Years