EnviroNearby

Williamsburg County, South Carolina air quality history

Daily Air Quality Index summaries from EPA monitors in Williamsburg, South Carolina, 1991–2007.

72%
Good days in 2007
44
Median daily AQI, 2007
4
Days above 100 in 2007
245
Days with an AQI in 2007 (of 365)

In 2007, EPA reported a daily Air Quality Index (AQI) for Williamsburg, South Carolina on 245 days. 177 of those days (72%) were in the Good range, and the median daily AQI was 44. That median is lower than the typical monitored county in South Carolina (median 47 across 21 counties), and about the same as the typical monitored U.S. county (46). The main pollutant was ozone on 245 days. Across the years with fuller monitoring, the share of Good days held roughly steady: an average of 77% in 1991–1993 versus 76% in 2005–2007.

EPA did not report an AQI for every day of 2007 here (245 of 365 days). Figures describe monitored days only; seasonal monitoring (for example, ozone measured only in warmer months) can make a county look cleaner or dirtier than a full-year record would.

The most recent year with data for this county is 2007; EPA's files for 2008–2025 contain no row for it, which usually means its monitors stopped reporting.

How the days broke down each year

Each bar is one year. The colored segments show the share of monitored days that fell in each AQI category.

Share of monitored days in each AQI category, by year0%25%50%75%100%1991: Good 159 of 198 days1991: Moderate 33 of 198 days1991: Unhealthy for Sensitive Groups 6 of 198 days19911992: Good 280 of 334 days1992: Moderate 44 of 334 days1992: Unhealthy for Sensitive Groups 8 of 334 days1992: Unhealthy 2 of 334 days1993: Good 215 of 317 days1993: Moderate 73 of 317 days1993: Unhealthy for Sensitive Groups 28 of 317 days1993: Unhealthy 1 of 317 days19931994: Good 182 of 213 days1994: Moderate 25 of 213 days1994: Unhealthy for Sensitive Groups 6 of 213 days1995: Good 165 of 230 days1995: Moderate 61 of 230 days1995: Unhealthy for Sensitive Groups 4 of 230 days19951996: Good 195 of 236 days1996: Moderate 38 of 236 days1996: Unhealthy for Sensitive Groups 3 of 236 days1997: Good 132 of 176 days1997: Moderate 40 of 176 days1997: Unhealthy for Sensitive Groups 4 of 176 days19971998: Good 116 of 176 days1998: Moderate 48 of 176 days1998: Unhealthy for Sensitive Groups 12 of 176 days1999: Good 150 of 212 days1999: Moderate 50 of 212 days1999: Unhealthy for Sensitive Groups 12 of 212 days19992000: Good 145 of 223 days2000: Moderate 70 of 223 days2000: Unhealthy for Sensitive Groups 8 of 223 days2001: Good 203 of 242 days2001: Moderate 38 of 242 days2001: Unhealthy for Sensitive Groups 1 of 242 days20012002: Good 163 of 228 days2002: Moderate 55 of 228 days2002: Unhealthy for Sensitive Groups 9 of 228 days2002: Unhealthy 1 of 228 days2003: Good 180 of 221 days2003: Moderate 39 of 221 days2003: Unhealthy for Sensitive Groups 2 of 221 days20032004: Good 182 of 221 days2004: Moderate 38 of 221 days2004: Unhealthy for Sensitive Groups 1 of 221 days2005: Good 179 of 225 days2005: Moderate 45 of 225 days2005: Unhealthy for Sensitive Groups 1 of 225 days20052006: Good 165 of 218 days2006: Moderate 49 of 218 days2006: Unhealthy for Sensitive Groups 4 of 218 days2007: Good 177 of 245 days2007: Moderate 64 of 245 days2007: Unhealthy for Sensitive Groups 4 of 245 days2007
  • Good
  • Moderate
  • Unhealthy for Sensitive Groups
  • Unhealthy
  • Very Unhealthy
  • Hazardous

Typical and high-end AQI over time

The median is the middle day of the year. The 90th percentile is the level that only the highest 10% of days exceeded.

Median and 90th-percentile daily AQI, by year0501001991: 90th percentile AQI 741992: 90th percentile AQI 641993: 90th percentile AQI 1001994: 90th percentile AQI 641995: 90th percentile AQI 771996: 90th percentile AQI 671997: 90th percentile AQI 741998: 90th percentile AQI 971999: 90th percentile AQI 802000: 90th percentile AQI 842001: 90th percentile AQI 612002: 90th percentile AQI 842003: 90th percentile AQI 672004: 90th percentile AQI 612005: 90th percentile AQI 672006: 90th percentile AQI 712007: 90th percentile AQI 711991: Median AQI 381992: Median AQI 371993: Median AQI 401994: Median AQI 351995: Median AQI 401996: Median AQI 401997: Median AQI 421998: Median AQI 451999: Median AQI 412000: Median AQI 452001: Median AQI 402002: Median AQI 412003: Median AQI 372004: Median AQI 372005: Median AQI 382006: Median AQI 402007: Median AQI 44199119931995199719992001200320052007
  • Median daily AQI
  • 90th-percentile daily AQI

Main pollutant by day, 2007

On each monitored day, the AQI reflects whichever measured pollutant had the highest index. This counts how many days each pollutant set the AQI. A pollutant that was not measured here cannot appear.

PollutantDays as main pollutantShare of monitored days
Ozone245100%

Year-by-year data

Annual AQI summary by year
YearDays with AQIGoodModerateUnhealthy for Sensitive GroupsUnhealthyVery UnhealthyHazardousMedian AQI90th pct.Max AQIMain pollutant
20072451776440004471122Ozone
20062181654940004071136Ozone
20052251794510003867105Ozone
20042211823810003761112Ozone
20032211803920003767126Ozone
20022281635591004184151Ozone
20012422033810004061101Ozone
20002231457080004584140Ozone
199921215050120004180150Ozone
199817611648120004597140Ozone
19971761324040004274108Ozone
19962361953830004067112Ozone
19952301656140004077101Ozone
19942131822560003564147Ozone
1993317215732810040100151Ozone
19923342804482003764159Ozone
19911981593360003874150Ozone

What this data can and can’t tell you

It is a county-level summary. EPA reports one AQI per day for the county, based on the monitors operating there. Air at a particular street, school or home can differ, especially near roads, industry or wildfire smoke.

It is not a health assessment. The AQI is EPA’s scale for communicating daily air quality. A county’s history can’t tell you what the health risk is for any particular person. For daily conditions and health guidance, see AirNow.

Rules change over time. EPA has revised AQI breakpoints, most recently for fine particles in 2024, so some year-to-year change can reflect the scale rather than the air.

Counties in South Carolina with a similar median AQI in 2007

All monitored counties in South Carolina

Source: U.S. EPA AirData, “Annual AQI by County” files for 1991–2007 (EPA download page). EPA file dates: 2026-06-26. Imported into EnviroNearby November 5, 2026. How we use this data · Report a problem