Share of days with unhealthy air
The percentage of days when the Air Quality Index was over 100, which is unhealthy for sensitive groups or worse. The index runs from 0 to 500 and is set by the worst pollutant that day. Smoke from wildfires and summer ozone cause most of these days. It counts only the days the monitors gave a reading, and a year counts only if there were at least 274 of them. Only about 800 counties have a monitor, mostly the larger ones.
Reported for803areas, in 51 states — none in CT
Link to density0.25not mostly about how urban a place is
Nearby places alike0.43Moran’s I: strongly, neighbouring places tend to be similar
Typerate% of days
How it has moved
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Every state, every year
Nothing to draw here: this measure has no state figures. Its publisher reports it for counties. This site does not add county numbers up into state figures, since a home-made figure could clash with one an agency publishes itself. The chart above covers the whole country, year by year.
Where it comes from
EPA Air Quality System · EPA AQS annual_aqi_by_county, Unhealthy for Sensitive Groups + Unhealthy + Very Unhealthy + Hazardous Days, divided by Days with AQI
Days rated unhealthy for sensitive groups or worse (AQI above 100), as a share of the days with an AQI. It covers only monitored counties, so it cannot be added up into a state or metro figure. Only counties with an air monitor, about 800 a year lately, and only years with an AQI on at least 274 days.
Combining areas: it cannot be combined, so it is shown only where its publisher works it out.
What it goes with
The strongest links that have a page of their own. Unadjusted is the link before adjusting for anything, from −1 (opposite) to +1 (in step). Adjusted compares places with the same population density, income and education levels, so those differences can’t explain the link. This list leaves out the 3 pairs built from the same numbers or the same model as this measure, since they are bound to match.
| Measure | Unadjusted | Adjusted |
|---|---|---|
| Share of days with unhealthy air and Population (WONDER)Where Share of days with unhealthy air is higher, Population (WONDER) tends to be higher: a moderate link that holds when only places with similar density, income and education are compared. Population (WONDER) by US county | +0.53 | +0.56 |
| Share of days with unhealthy air and Tests takenWhere Share of days with unhealthy air is higher, Tests taken tends to be higher: a moderate link that holds when only places with similar density, income and education are compared. Tests taken by US county | +0.55 | +0.54 |
| Share of days with unhealthy air and Women who gave birth in the past yearWhere Share of days with unhealthy air is higher, Women who gave birth in the past year tends to be higher: a moderate link that holds when only places with similar density, income and education are compared. Women who gave birth in the past year by US county | +0.51 | +0.52 |
| Share of days with unhealthy air and UnemployedWhere Share of days with unhealthy air is higher, Unemployed tends to be higher: a moderate link that holds when only places with similar density, income and education are compared. Unemployed by US county | +0.53 | +0.52 |
| Share of days with unhealthy air and People who did not moveWhere Share of days with unhealthy air is higher, People who did not move tends to be higher: a moderate link that holds when only places with similar density, income and education are compared. People who did not move by US county | +0.50 | +0.49 |
| Share of days with unhealthy air and PopulationWhere Share of days with unhealthy air is higher, Population tends to be higher: a moderate link that holds when only places with similar density, income and education are compared. Population by US county | +0.49 | +0.49 |
| Share of days with unhealthy air and Population for whom poverty status is determinedWhere Share of days with unhealthy air is higher, Population for whom poverty status is determined tends to be higher: a moderate link that holds when only places with similar density, income and education are compared. Population for whom poverty status is determined by US county | +0.50 | +0.49 |
| Share of days with unhealthy air and Population in the same house one year agoWhere Share of days with unhealthy air is higher, Population in the same house one year ago tends to be higher: a moderate link that holds when only places with similar density, income and education are compared. Population in the same house one year ago by US county | +0.50 | +0.49 |
| Share of days with unhealthy air and People covered by a tax returnWhere Share of days with unhealthy air is higher, People covered by a tax return tends to be higher: a moderate link that holds when only places with similar density, income and education are compared. People covered by a tax return by US county | +0.49 | +0.49 |
| Share of days with unhealthy air and Population (firearm measures)Where Share of days with unhealthy air is higher, Population (firearm measures) tends to be higher: a moderate link that holds when only places with similar density, income and education are compared. Population (firearm measures) by US county | +0.49 | +0.49 |
40 more pairs with share of days with unhealthy air have a page: Population · Total population · Women aged 15 to 50 · Population for whom poverty status is determined · Population below the poverty line · Population, decennial census · Population below the poverty line · Workers aged 16 and over who commute · Population aged 15 and over · Population aged 18 and over · Owner-occupied housing units · Labour force · Employed · Population aged 25 and over · Tax returns filed · Presidential votes cast, 2024 · Occupied housing units · Presidential votes cast, 2020 · Housing units · Aggregate travel time to work · Children in the mobility cohort · Children with below-median parental income · Presidential votes cast, 2016 · Presidential votes cast, 2008 · Presidential votes cast, 2012 · Population aged 65 and over · Presidential votes cast, 2004 · Private jobs · Presidential votes cast, 2000 · Business establishments · Business establishments opened · Business establishments closed · Personal income · Population with a bachelor's degree or higher · Foreign-born population · New homes permitted · Gross domestic product · New single-family homes permitted · Yearly precipitation · New homes permitted in buildings of 5 or more units.
Population makeup
How this measure varies with the racial and ethnic makeup of counties. Every group is shown, whatever its rank. These are links across counties: they describe places, not people. They say nothing about any person’s risk or behaviour based on their race. Counties with a larger share of one group also differ in much else, such as income, segregation, region and history. The adjusted figure only accounts for density, income and education.
Highest and lowest
Of 803 counties reporting it. These are the two ends of a national ranking. For most measures, that ranking mostly sorts places by income and how urban they are. That is why the place pages compare each place with similar places instead.
Highest
- San Bernardino County, CA — 32.3
- Riverside County, CA — 31.2
- Los Angeles County, CA — 23.8
- Tulare County, CA — 22.5
- Kern County, CA — 19.2
Lowest
The middle area reports 1.1. The middle half of counties falls between 0.277 and 2.47 (the 25th to 75th percentile).
US Counties With the Highest Share of Days with Unhealthy Air · US Counties With the Lowest Share of Days with Unhealthy Air
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