Frequently Asked Questions

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The Air Quality Index (AQI) is EPA's national information tool used to inform the public about the health risks of air pollution. The index uses color-coded categories to show when air quality is good, moderate, or unhealthy. The AQI value is based on recent hourly data collected at air monitoring stations by Ecology and our air monitoring partners.

Replacing WAQA with the Environmental Protection Agency’s Air Quality Index makes it easier for people to understand when their health is at risk. The Washington State departments of Health and Ecology also added more health protective messages to the associated hazard categories in our public health guidance and tools.

The Air Quality Index (AQI) is a unit-less index calculated from pollutant concentrations. The AQI is calculated for six cpollutants: PM2.5, PM10, O3, NO2, CO, and SO2. These pollutants are measured in different units, and their measured concentrations correspond to health risks at different levels. The AQI converts these measurements to a common scale based on health risk. For each pollutant, an AQI value of 50 or below is considered good air quality, and an AQI value of 101 and above is considered unhealthy for sensitive populations. At sites that measure multiple pollutants, the AQI value shown is the highest of the values from the different pollutants.

The following table summarizes recommended health actions when particle pollution (PM2.5) is the dominant pollutant in the AQI.
For health information about other pollutants, please see EPA’s Air Quality Index: A Guide to Air Quality and Your Health

Washington Air Quality Guide for Particle Pollution
Air Quality Index What should I do?
Good (0-50) It is a great day to be active outside.
This is a good time to make a plan if poor air quality is in the forecast.
Moderate (51-100) Some people are especially sensitive to lower levels of particle pollution and should reduce exposure.
For example, limit time outside and avoid strenuous outdoor activity.
All sensitive groups should watch for coughing, shortness of breath, and other symptoms.
Unhealthy for Sensitive Groups (101-150) Sensitive groups should take steps to reduce exposure.
Limit time outside, avoid strenuous outdoor activity, and follow tips for cleaner indoor air.
Everyone should watch for signs to reduce exposure like coughing, shortness of breath, and other symptoms.
Unhealthy (151-200) Everyone should reduce exposure.
Limit time outside, avoid strenuous outdoor activity, and follow tips for cleaner indoor air.
Very Unhealthy (201-300) Everyone should reduce exposure.
Stay inside and filter indoor air to keep it cleaner.
Go elsewhere for cleaner air, if needed.
Hazardous (>300) Everyone should reduce exposure.
Stay inside and filter indoor air to keep it cleaner.
Go elsewhere for cleaner air, if needed.

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There are several reasons the map displays a gray dot:

The website displays the most recent hour’s data even if it appears to be an hour or two behind. There are two reasons the data may not feel current. Here is why:

There are several ways to find meteorological data:

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The website includes reports that can be exported as a PDF or Excel.
Reports dropdown visual

  1. Click on Reports link on the main menu bar to display the list of reports.
  2. Select a report by clicking on it.
    • Some reports automatically generate data. Search boxes will filter the visible data to smaller datasets.
    • Others require data selections before running the report.
    • Click Display to launch the report.
    • The report will appear on the screen and displayed in table or graph format.
    • The icons in the top rightReport export buttons visual of the report header include options of viewing the report as a graph, table, and exporting. Most reports include Excel and some include pdf export options.

Data is also available from the Environmental Protection Agency (EPA) website at:

Near-Real Time (most recent) Information
The air quality map shows current air quality conditions. A dot represents a monitoring location and the color represents the current air quality at the location. In many cases, monitors closest to you will give you an indication of the air quality in your area. However, significant differences are also possible because of topographical and meteorological influences such as mountains and wind.

You can always click on a "dot" to get information that is more detailed on the pollutants measured, current concentrations, and monitor station information.

Data Reports
Reports are available in the "Reports" main menu bar. These reports present data in many different ways, and can be exported.

Ecology and our partners operate a large air monitoring network with approximately 80 monitoring sites throughout the state. While we cannot monitor everywhere, we prioritize our monitoring efforts based on factors such as community size and expected air quality impacts. In communities without a monitor, air quality scientists use the data collected from nearby sites and air pollution models to estimate air pollution levels. Ecology also uses temporary mobile monitoring to characterize air pollution in areas where models suggest a potential air pollution problem.

There are several reasons data may be missing:

  1. Power outages at the site
  2. Site telecommunication problems
  3. The monitor wasn't operating properly

It depends. The most recently collected data have yet to be thoroughly reviewed for validity and should be considered preliminary. Ecology's quality assurance process involves a thorough review of the collected data to ensure that the data are of sufficient quality for intended uses. It typically takes about two months to complete the quality assurance process. This means that the data are accurate (valid) about 2 months after they have been collected. Summaries of such data will also be considered accurate.

The full web site is accessible, but not optimized, for small screens. To view the website on a mobile device, visit our mobile friendly site (opens in new window).

Mobile apps are available for Android and iOS in their app stores.

Get it on Google Play Get it on the Apple Store

Visit our report help page for guidance and a glossary of terms.