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PM10 Average Values

In 2012, the United States Environmental Protection Agency (USEPA) reaffirmed the existing regulatory limit for PM10 concentrations.  The standard remained at 150 micrograms per cubic meter (ug/m3) averaged over a 24-hour period.  This value may not be exceeded more than once, on average, per year, over a 3-year period.  The Design Value for PM10 is defined as the number of times the standard is exceeded each calendar year averaged over a 3-year period. 

Since this number is zero for all counties in North Carolina, to produce a meaningful map, the NC Division of Air Quality began using the 2nd highest, 24-hour average concentration recorded during the latest 3-year period to illustrate PM10 concentrations across the state.  A 2nd highest value of more than 150 ug/m3 would indicate non-attainment of the USEPA standard.  Currently, all sites in North Carolina are in attainment. 

Please click here to open the map as a PDF.

Table 1 lists the 2nd highest, 24-hour average concentration of PM10 recorded at monitoring sites in North Carolina between 2015 and 2017.  In addition, the table lists the 2nd highest 24-hour average concentration of PM10 recorded through North Carolina’s Revolving Site Program.  The Revolving Site Program operates monitors on a 12-month basis to provide a snapshot of PM10 conditions across more areas of the state.  Data from these sites do not meet USEPA requirements for operation over a full 3-year period but have been included to provide a more complete picture of PM values.  Data from the revolving sites program are indicated by an asterisk (*).  The first column below lists the county where the monitoring site is located, and the second column lists the 2nd highest 24-hour average recorded for the period.  In counties with more than one PM10 monitoring site, the value reported is the 2nd highest measured for all sites in the county during the 3-year period.   



2nd Highest 24-Hour Concentration 2015- 2017

Cumberland [1]  


Forsyth [1]


Guilford [1]


Mecklenburg [1]


Wake [3]  


Durham [1]  


Alexander [2]*


Caswell [2]*


Lenoir [2]*  


Martin [2]*


New Hanover [2]*  


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 or urban.

[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 PM10 concentrations. The first column lists the county, the second lists the average value for that county. In Counties with more than one PM10 monitoring site, the value reported is the highest 3-year average among the inclusive sites.

County Average 98th Percentile
Catawba 28 µg/m3
Cumberland 25 µg/m3
Durham 26 µg/m3
Forsyth 25 µg/m3
Guilford 23 µg/m3
Mecklenburg 32 µg/m3
Wake 28 µg/m3