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Air quality and the UV index

Weather 3 min read Beginner Updated

Weather is not part of 4Birds. It runs on 4search.com and 4conservative.com. You can read this guide here, and use Weather on 4search.com.
On this page
  1. Air quality
  2. The UV index
  3. Common questions

Two numbers on a place's page are about your health outdoors rather than the weather itself. The air quality index says how clean the air is, and the UV index says how strong the sun's ultraviolet light is.

#Air quality

The Air quality box is on the Today page of U.S. places that have an air quality reporting area nearby.

The Air quality box: a coloured number for the air quality index, its category and main pollutant, a coloured scale with a marker, what the category means and the next days' forecast

The air quality box: the index, its category and main pollutant, the scale, and the next days.

  1. 1The air quality index
  2. 2The category and the main pollutant
  3. 3Where it falls on the scale
  4. 4The next days
  • The number in the colored circle is the air quality index (AQI). Lower is cleaner.
  • The category beside it, such as Good, and the pollutant that sets the number, such as ozone or fine particles (PM2.5).
  • The scale with a marker shows where today falls, from green to purple.
  • A sentence under the scale says what the category means, in the words of the air quality agencies.
  • Forecast lists the next days' categories, with Action day when the local agency has called one.
  • The note names the reporting area and how long ago it reported. The data comes from AirNow, run by the U.S. Environmental Protection Agency with state, local and tribal partners, and is preliminary.
AQI Category
0 to 50 Good
51 to 100 Moderate
101 to 150 Unhealthy for Sensitive Groups
151 to 200 Unhealthy
201 to 300 Very Unhealthy
301 and above Hazardous

If no reporting area is near the place, or its last report is too old, the box is left out or shows only the forecast. An Air Quality Alert from the National Weather Service appears with the other alerts. See Weather alerts.

#The UV index

The UV index appears in Current conditions, in the hourly table's UV column and in each day of the 10-Day tab, when the forecast has it. A colored tag shows the number with a word:

UV index Shown as
0 to 2 Low
3 to 5 Moderate
6 to 7 High
8 to 10 Very high
11 and above Extreme

At night and on heavily overcast days the index is low. It is highest around midday.

#Common questions

Why is there no air quality box for my place?

The box needs a reporting area nearby, and it is shown for places in the United States. Places without one do not have it.

Why does the air quality look fine when it is smoky outside?

The index is reported for an area, at intervals, and the reading can be an hour or more old. Conditions can change faster than the report.

Where does the UV index come from?

From MET Norway's forecast, for places in the United States and elsewhere. See Where the weather comes from.

Read next

Weather Read a place's forecast page A place's Today page shows conditions now, the forecast in words, the next hours and days, radar, air quality, sun and moon, an almanac and local news. Weather Hourly and 10-day forecasts The Hourly tab charts the next 48 hours and tabulates every hour. The 10-Day tab shows each day in detail, day and night, with totals, sun and moon. Weather Where the weather comes from and how fresh it is Weather uses public sources such as the National Weather Service, NOAA, NASA, AirNow and MET Norway. See which gives what, and how fresh each figure is. Weather Weather alerts, watches, warnings and advisories See the National Weather Service's watches, warnings and advisories for a place, a state or the country, most urgent first, with the full text and what to do.