Ozone Boundaries

Ozone Standard: SC Boundary Designations

2015 Ozone Standard Boundaries

November 16, 2017

The EPA published a Final Rule [82 FR 54232] in the Federal Register which designated all counties in South Carolina as “Attainment/Unclassifiable”, indicating that the entire state attained the 2015 Ozone NAAQS.

September 30, 2016

The design value, or DV, is the metric that the EPA uses to determine if an area meets the NAAQS. In the case of ozone, the DV is defined as the three year average of the annual 4th highest daily maximum 8 hour average ozone concentration at each monitor in an area. The highest DV for an area is compared with the NAAQS. If the highest DV is higher than the NAAQS, currently 70 ppb, then the area could be designated as "nonattainment." Most South Carolina monitors have shown a continuous improvement in DV since 2005, as shown in the chart below.

Ozone DV 2009-2018 Graph


The state made a recommendation to the EPA that all areas of South Carolina be designated attainment. This recommendation was based on 2013-2015 ozone monitoring results in accordance with the Clean Air Act. Two monitors, N. Spartanburg Fire Station #2 and Ashton, did not meet the 90% data completeness criterion in 40 CFR part 50 Appendix U over the 3-year period. DHEC also submitted a demonstration to show that on the missing days no conditions existed conducive to ozone concentrations above the 2015 NAAQS. The complete package submitted to EPA is here.

October 1, 2015

The binding Final Rule was signed. The Final Rule sets 0.070 ppm (70 ppb) for both primary and secondary standards. For more information on the new ozone NAAQS see the EPA's webpage.

November 26, 2014

The US Environmental Protection Agency (EPA) completed the federally mandated 5-year review of the national ambient air quality standard (NAAQS) for ozone and proposed a revised ground-level ozone standard range of 0.065-0.070 parts per million (ppm).

2008 Ozone Standard Boundaries

May 21, 2012

EPA published the implementation rule (77 FR 30160) for the 2008 ozone standard, which included the area classifications approach, attainment deadlines and revocation of the 1997 ozone standard for transportation conformity purposes. The effective date of this rule is July 20, 2012.

April 30, 2012

EPA has designated all of South Carolina as unclassifiable/attainment for the 2008 ozone standard, except for a portion of York County. Although the monitor in York County is meeting this standard, EPA included the eastern, urbanized area of York County in the Charlotte-Rock Hill, NC-SC nonattainment area because of its proximity to Charlotte.

This is the same portion of York County that EPA designated as nonattainment for the 1997 ozone standard, with the exception of the Catawba Indian Nation Reservation. EPA included the Catawba Indian Nation Reservation in the 1997 nonattainment area, but the EPA designated it as unclassifiable/attainment for the 2008 ozone standard. Learn more about the EPA's attainment/nonattainment designations for South Carolina.

February 29, 2012

DHEC responded to EPA's December 8, 2011, proposed boundary for the 2008 ozone standard.

February 7, 2012

EPA proposed the implementation rule for the 2008 ozone standard.

December 20, 2011

EPA announced a public comment period for its responses to states' and tribes' boundary recommendations for the 2008 ozone standard. On January 12, 2012, EPA extended the comment period deadline from January 19, 2012, to February 3, 2012.

December 9, 2011

DHEC certified the ozone monitoring data for the 2011 Ozone Season, further substantiating the attainment recommendation for each county of the entire State of South Carolina for the 2008 ozone standard.

December 8, 2011

EPA responded to DHEC's October 11, 2011, boundary recommendation for the 2008 ozone standard. EPA intends to modify DHEC's recommendation so that a portion of York County would be a part of the Charlotte-Gastonia-Salisbury, NC-SC nonattainment area. This is the same portion of York County that EPA designated nonattainment for the 1997 ozone standard. For more information, see EPA's website.

October 11, 2011

DHEC submitted an amendment to the 2008 boundary recommendations to EPA recommending all counties of the entire state be designated attainment.

September 22, 2011

EPA announced that it will implement the 2008 ozone standard. In this announcement, EPA discussed the designation process for the 2008 standard.

January 19, 2010

EPA announced it was extending by one year the deadline that it was extending by one year the deadline for promulgating designations for the 2008 ozone standard that were promulgated in March 2008. The new deadline was set for March 2011.

September 16, 2009

EPA announced it would reconsider the 2008 ozone standard.

July 12, 2009

DHEC submitted an errata to the 2008 boundary recommendations to EPA.

March 12, 2009

Upon delegation of Governor Mark Sanford's authority, DHEC submitted South Carolina's boundary recommendations for the 2008 ozone standard to EPA.

Previous Ozone Standards - History

1997 8-Hour Ozone Standard

In 1997, EPA promulgated an 8-hour ozone standard to replace the 1-hour standard. EPA revised the standards to establish the more stringent 8-hour standard at a level of 0.08 ppm. This was done to reflect the latest understanding of the effects of ozone exposure and to provide public health protection with an adequate margin of safety.

1997 8-hour Ozone Early Action Compact (EAC) process

On July 14, 2000, in accordance with the requirements of Section 107 of the Clean Air Act, DHEC submitted initial boundary recommendations for the 1997 8-hour ozone standard. These were based upon 1997 through 1999 monitored ozone data. DHEC recommended that the boundaries of seven Metropolitan Planning Organizations (MPOs) be designated nonattainment areas. EPA then proposed changes, recommending that whole counties be designated nonattainment, and requested more information and further documentation to adequately support the state's partial county recommendations.

On July 14, 2003, the state submitted a revised proposal to EPA for nonattainment area designations. In April 2004, EPA designated three areas in South Carolina as nonattainment but deferred the effective date for two of these areas because of their participation in the Early Action Compact process.

In April 2008, EPA redesignated these areas to attainment.

Additional Resources


Mary Peyton Wall, Manager, (803) 898-4064