EnviroNearby

Crook County, Wyoming air quality history

Daily Air Quality Index summaries from EPA monitors in Crook, Wyoming, 2008–2012.

40%
Good days in 2012
58
Median daily AQI, 2012
12
Days above 100 in 2012
131
Days with an AQI in 2012 (of 366)

In 2012, EPA reported a daily Air Quality Index (AQI) for Crook, Wyoming on 131 days. 53 of those days (40%) were in the Good range, and the median daily AQI was 58. That median is higher than the typical monitored county in Wyoming (median 44.5 across 16 counties), and higher than the typical monitored U.S. county (44). The main pollutant was ozone on 131 days.

EPA did not report an AQI for every day of 2012 here (131 of 366 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 2012; EPA's files for 2013–2025 contain no row for it, which usually means its monitors stopped reporting.

Years with fewer than 120 monitored days (2008) are shown in the table but left out of comparisons and trend statements.

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%2008: Good 86 of 108 days2008: Moderate 22 of 108 days20082009: Good 143 of 166 days2009: Moderate 23 of 166 days20092010: Good 133 of 152 days2010: Moderate 18 of 152 days2010: Unhealthy for Sensitive Groups 1 of 152 days20102011: Good 144 of 153 days2011: Moderate 9 of 153 days20112012: Good 53 of 131 days2012: Moderate 66 of 131 days2012: Unhealthy for Sensitive Groups 12 of 131 days2012
  • 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 year0501002008: 90th percentile AQI 612009: 90th percentile AQI 542010: 90th percentile AQI 512011: 90th percentile AQI 482012: 90th percentile AQI 1002008: Median AQI 452009: Median AQI 432010: Median AQI 432011: Median AQI 392012: Median AQI 5820082009201020112012
  • Median daily AQI
  • 90th-percentile daily AQI

Main pollutant by day, 2012

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
Ozone131100%

Year-by-year data

Annual AQI summary by year
YearDays with AQIGoodModerateUnhealthy for Sensitive GroupsUnhealthyVery UnhealthyHazardousMedian AQI90th pct.Max AQIMain pollutant
201213153661200058100129Ozone
201115314490000394880Ozone
20101521331810004351101Ozone
2009166143230000435487Ozone
200810886220000456174Ozone

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 Wyoming

Source: U.S. EPA AirData, “Annual AQI by County” files for 2008–2012 (EPA download page). EPA file dates: 2026-06-26. Imported into EnviroNearby November 5, 2026. How we use this data · Report a problem