SO2 Average Values for 2013-2015 in NC Counties

In 2010, EPA revised the sulfur dioxide (SO2) standard to a 1-hour standard at a level of 75 parts per billion (ppb). To determine if the standard is met, a continuous 3-year average concentration is calculated from daily measurements and compared to the requirements of the standard.

The table below shows the 3-year average SO2 concentrations for the 5 highest reported values by county for 2013-2015.

SO2 levels in North Carolina are low, ranging from 2.7 percent to 42.7 percent of the standard. These values are higher than the previous 3-year period.

Additionally, for many years, SO2 has been measured at several sites across the state on a rotating basis.  This monitoring is conducted at five sites operated for 12 months every 3 years.   For these sites we do not have continuous 3-year averages.  The overall monitoring conducted at those sites show no exceedances of the standard.

North Carolina Design Values in Counties with SO2 Monitors 2013-2015 (99th Percentile Averages)

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3-Year Average
(99th Percentile)


23 ppb


9 ppb


10 ppb

New Hanover

32 ppb


14 ppb


9 ppb