Data / Rankings / Share of days unhealthy for sensitive groups or worse (US EPA AQI) / Counties in South Carolina

Counties in South Carolina by share of days unhealthy for sensitive groups or worse (US EPA AQI)

Chester County had the highest share of days unhealthy for sensitive groups or worse (US EPA AQI) of 26 counties in 2005, at 11.9%. Williamsburg County had the lowest, at 0.4%. The median was 3.5%. Source: EPA.

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Highest11.9Chester County
Lowest0.4Williamsburg County
Median3.526 counties

Map of counties, 2005

Abbeville County: 6.9 %Aiken County: 4.4 %Anderson County: 9 %Barnwell County: 1.9 %Beaufort County: 2.2 %Berkeley County: 0.9 %Charleston County: 4.4 %Cherokee County: 4.5 %Chester County: 11.9 %Chesterfield County: 3.7 %Colleton County: 2.8 %Darlington County: 5.9 %Edgefield County: 1.8 %Florence County: 1.8 %Georgetown County: 0.9 %Greenville County: 3.3 %Greenwood County: 0.9 %Horry County: 0.8 %Lexington County: 0.8 %Oconee County: 2.5 %Pickens County: 6.8 %Richland County: 6.6 %Spartanburg County: 9 %Union County: 5.5 %Williamsburg County: 0.4 %York County: 6.6 %
  • Under 0.9
  • 0.9 to 2.5
  • 2.5 to 4.4
  • 4.4 to 6.6
  • 6.6 and over
  • No data
%, 2005. Hatched areas have no value for this period. Source: Invokely calculation with data from EPA. Boundaries: U.S. Census Bureau cartographic boundary files.

All counties, 2005

Chester County: 11.9 %Chester County11.9Anderson County: 9 %Anderson County9Spartanburg County: 9 %Spartanburg County9Abbeville County: 6.9 %Abbeville County6.9Pickens County: 6.8 %Pickens County6.8Richland County: 6.6 %Richland County6.6York County: 6.6 %York County6.6Darlington County: 5.9 %Darlington County5.9Union County: 5.5 %Union County5.5Cherokee County: 4.5 %Cherokee County4.5Aiken County: 4.4 %Aiken County4.4Charleston County: 4.4 %Charleston County4.4Chesterfield County: 3.7 %Chesterfield County3.7Greenville County: 3.3 %Greenville County3.3Colleton County: 2.8 %Colleton County2.8Oconee County: 2.5 %Oconee County2.5Beaufort County: 2.2 %Beaufort County2.2Barnwell County: 1.9 %Barnwell County1.9Edgefield County: 1.8 %Edgefield County1.8Florence County: 1.8 %Florence County1.8Berkeley County: 0.9 %Berkeley County0.9Georgetown County: 0.9 %Georgetown County0.9Greenwood County: 0.9 %Greenwood County0.9Horry County: 0.8 %Horry County0.8Lexington County: 0.8 %Lexington County0.8Williamsburg County: 0.4 %Williamsburg County0.4Chester County: 11.9 %Chester County11.9Anderson County: 9 %Anderson County9Spartanburg County: 9 %Spartanburg County9Abbeville County: 6.9 %Abbeville County6.9Pickens County: 6.8 %Pickens County6.8Richland County: 6.6 %Richland County6.6York County: 6.6 %York County6.6Darlington County: 5.9 %Darlington County5.9Union County: 5.5 %Union County5.5Cherokee County: 4.5 %Cherokee County4.5Aiken County: 4.4 %Aiken County4.4Charleston County: 4.4 %Charleston County4.4Chesterfield County: 3.7 %Chesterfield County3.7Greenville County: 3.3 %Greenville County3.3Colleton County: 2.8 %Colleton County2.8Oconee County: 2.5 %Oconee County2.5Beaufort County: 2.2 %Beaufort County2.2Barnwell County: 1.9 %Barnwell County1.9Edgefield County: 1.8 %Edgefield County1.8Florence County: 1.8 %Florence County1.8Berkeley County: 0.9 %Berkeley County0.9Georgetown County: 0.9 %Georgetown County0.9Greenwood County: 0.9 %Greenwood County0.9Horry County: 0.8 %Horry County0.8Lexington County: 0.8 %Lexington County0.8Williamsburg County: 0.4 %Williamsburg County0.4
%. Source: Invokely calculation with data from EPA. Retrieved 2026-10-12.

Full ranking

RankCounties2005 (%)Change on 2004
1Chester County11.9+11 pts
2Anderson County9+3 pts
2Spartanburg County9+2.6 pts
4Abbeville County6.9+3.3 pts
5Pickens County6.8+2.5 pts
6Richland County6.6-2.7 pts
6York County6.6+5 pts
8Darlington County5.9+3.1 pts
9Union County5.5+3.4 pts
10Cherokee County4.5+3.9 pts
11Aiken County4.4-0.5 pts
11Charleston County4.4+2.5 pts
13Chesterfield County3.7+0.9 pts
14Greenville County3.3+2.2 pts
15Colleton County2.8+1.1 pts
16Oconee County2.5+0.5 pts
17Beaufort County2.2+1.2 pts
18Barnwell County1.9-0.3 pts
19Edgefield County1.8+0.1 pts
19Florence County1.8+1.8 pts
21Berkeley County0.9-0.7 pts
21Georgetown County0.9+0.3 pts
21Greenwood County0.90 pts
24Horry County0.8+0.8 pts
24Lexington County0.8+0.2 pts
26Williamsburg County0.4-0.1 pts

Other periods

About this ranking

Days with a daily Air Quality Index above 100 (unhealthy for sensitive groups, unhealthy, very unhealthy or hazardous) as a percentage of the days of the year with an AQI in a US county. Calculated by Invokely from the day counts in the EPA AirData annual summaries; the counts are stored with each value.

Use the share rather than the number of days to compare counties, since the days with an AQI differ. United States counties with air quality monitors only, about 1,000 of some 3,100 in recent years; a county without monitors has no value. The number of days with an AQI differs between counties because some monitors run only in the ozone season.

Every value in the ranking comes from the same publisher and the same period, so the counties are compared on one definition. 2 counties with data in other periods have no value for 2005 and are left out rather than filled from another source. Equal values share a rank.

How to cite

U.S. Environmental Protection Agency, Air Quality System, AirData. EPA AirData annual AQI by county: days with an AQI above 100 as a share of days with an AQI, calculated with stored counts. https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual. Retrieved 2026-10-12.

Citation styles

The publisher is the author. Invokely is named only as the place the figures were read, where a style asks for it.

APA 7

U.S. Environmental Protection Agency. (2026). EPA AirData annual AQI by county: days with an AQI above 100 as a share of days with an AQI, calculated with stored counts (Counties in South Carolina by share of days unhealthy for sensitive groups or worse (US EPA AQI), 2005) [Data set]. Retrieved October 12, 2026, from https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual

MLA 9

EPA AirData annual AQI by county: days with an AQI above 100 as a share of days with an AQI, calculated with stored counts, Counties in South Carolina by share of days unhealthy for sensitive groups or worse (US EPA AQI), 2005. U.S. Environmental Protection Agency, 13 July 2026, https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual. Invokely, https://invokely.ai/rankings/unhealthy-air-quality-days-share/south-carolina-counties?period=2005. Accessed 12 Oct. 2026.

Chicago (author-date)

U.S. Environmental Protection Agency. 2026. EPA AirData annual AQI by county: days with an AQI above 100 as a share of days with an AQI, calculated with stored counts. Counties in South Carolina by share of days unhealthy for sensitive groups or worse (US EPA AQI), 2005. Dataset. Accessed October 12, 2026. https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual. Also distributed by Invokely, https://invokely.ai/rankings/unhealthy-air-quality-days-share/south-carolina-counties?period=2005.

Harvard

U.S. Environmental Protection Agency (2026) EPA AirData annual AQI by county: days with an AQI above 100 as a share of days with an AQI, calculated with stored counts, Counties in South Carolina by share of days unhealthy for sensitive groups or worse (US EPA AQI), 2005 [Dataset]. Available at: https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual, via Invokely: https://invokely.ai/rankings/unhealthy-air-quality-days-share/south-carolina-counties?period=2005 (Accessed: 12 October 2026).

BibTeX
@misc{environmental_counties_in_south_carolina_2005,
  author = {{U.S. Environmental Protection Agency}},
  title = {{EPA AirData annual AQI by county: days with an AQI above 100 as a share of days with an AQI, calculated with stored counts: Counties in South Carolina by share of days unhealthy for sensitive groups or worse (US EPA AQI), 2005}},
  year = {2026},
  howpublished = {Data set},
  url = {https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual},
  urldate = {2026-10-12},
  note = {Accessed via Invokely, https://invokely.ai/rankings/unhealthy-air-quality-days-share/south-carolina-counties?period=2005. Publisher attribution: U.S. Environmental Protection Agency, Air Quality System, AirData. EPA AirData annual AQI by county: days with an AQI above 100 as a share of days with an AQI, calculated with stored counts. https://aqs.epa.gov/aqsweb/airdata/download\_files.html\#Annual. Retrieved 2026-10-12.},
}
RIS
TY  - DATA
AU  - U.S. Environmental Protection Agency
TI  - EPA AirData annual AQI by county: days with an AQI above 100 as a share of days with an AQI, calculated with stored counts: Counties in South Carolina by share of days unhealthy for sensitive groups or worse (US EPA AQI), 2005
PY  - 2026
DA  - 2026/07/13
PB  - U.S. Environmental Protection Agency
DB  - Invokely
UR  - https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual
L2  - https://invokely.ai/rankings/unhealthy-air-quality-days-share/south-carolina-counties?period=2005
Y2  - 2026/10/12
N1  - Accessed via Invokely, https://invokely.ai/rankings/unhealthy-air-quality-days-share/south-carolina-counties?period=2005.
N1  - Publisher attribution: U.S. Environmental Protection Agency, Air Quality System, AirData. EPA AirData annual AQI by county: days with an AQI above 100 as a share of days with an AQI, calculated with stored counts. https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual. Retrieved 2026-10-12.
ER  -
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Questions

Which county has the highest share of days unhealthy for sensitive groups or worse (US EPA AQI)?

Chester County, with 11.9% in 2005, according to EPA.

Which county has the lowest share of days unhealthy for sensitive groups or worse (US EPA AQI)?

Williamsburg County, with 0.4% in 2005.

Where does this ranking come from?

Every value comes from one source and one period, so the places are comparable: U.S. Environmental Protection Agency, EPA AirData annual AQI by county: days with an AQI above 100 as a share of days with an AQI, calculated with stored counts. Retrieved 2026-10-12. 2 counties have no value for 2005 and are not ranked.

Share of days unhealthy for sensitive groups or worse (US EPA AQI): other rankings

Counties in South Carolina: more rankings