EnviroNearby

Marshall County, Oklahoma air quality history

Daily Air Quality Index summaries from EPA monitors in Marshall, Oklahoma, 1999–2002.

69%
Good days in 2002
44
Median daily AQI, 2002
16
Days above 100 in 2002
275
Days with an AQI in 2002 (of 365)

In 2002, EPA reported a daily Air Quality Index (AQI) for Marshall, Oklahoma on 275 days. 189 of those days (69%) were in the Good range, and the median daily AQI was 44. That median is higher than the typical monitored county in Oklahoma (median 41.5 across 18 counties), and about the same as the typical monitored U.S. county (44). The main pollutant was ozone on 275 days.

EPA did not report an AQI for every day of 2002 here (275 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 2002; EPA's files for 2003–2025 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%1999: Good 121 of 230 days1999: Moderate 69 of 230 days1999: Unhealthy for Sensitive Groups 34 of 230 days1999: Unhealthy 6 of 230 days19992000: Good 168 of 271 days2000: Moderate 72 of 271 days2000: Unhealthy for Sensitive Groups 26 of 271 days2000: Unhealthy 5 of 271 days20002001: Good 101 of 160 days2001: Moderate 44 of 160 days2001: Unhealthy for Sensitive Groups 13 of 160 days2001: Unhealthy 2 of 160 days20012002: Good 189 of 275 days2002: Moderate 70 of 275 days2002: Unhealthy for Sensitive Groups 16 of 275 days2002
  • 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 year0501001501999: 90th percentile AQI 1192000: 90th percentile AQI 1052001: 90th percentile AQI 1002002: 90th percentile AQI 871999: Median AQI 502000: Median AQI 462001: Median AQI 462002: Median AQI 441999200020012002
  • Median daily AQI
  • 90th-percentile daily AQI

Main pollutant by day, 2002

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
Ozone275100%

Year-by-year data

Annual AQI summary by year
YearDays with AQIGoodModerateUnhealthy for Sensitive GroupsUnhealthyVery UnhealthyHazardousMedian AQI90th pct.Max AQIMain pollutant
200227518970160004487150Ozone
2001160101441320046100172Ozone
2000271168722650046105192Ozone
1999230121693460050119200Ozone

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.

All monitored counties in Oklahoma

Source: U.S. EPA AirData, “Annual AQI by County” files for 1999–2002 (EPA download page). EPA file dates: 2026-06-26. Imported into EnviroNearby November 5, 2026. How we use this data · Report a problem