Air Quality Index
Air Quality Forecast
Monitoring Air Quality
Particulate Matter is measured in micrograms per cubic meter of air (UG/M3)
Ozone is measured in parts per billion (PBB)
About the Air Quality Index (AQI)
The AQI is a tool for reporting how clean or polluted the air is and the potential health effects. Think of the AQI as a yardstick that runs from 0 to 500. The higher the value, the greater the level of air pollution and the greater the health concern. An AQI value greater than 100 means air quality is not within health-based air quality standards established by the EPA.
The AQI is divided into these six categories:
Good – Air quality is considered satisfactory, and air pollution poses little or no risk.Numeric Value: 0-50
Moderate – Air quality is acceptable; however, for some pollutants there may be a moderate health concern for a very small number of people who are unusually sensitive to air pollution.Numeric Value: 51-100
Unhealthy for Sensitive Groups – Members of sensitive groups may experience health effects. The general public is not likely to be affected.Numeric Value: 101-150
Unhealthy – Everyone may begin to experience health effects; members of sensitive groups may experience more serious health effects.Numeric Value: 151-200
Very Unhealthy – Health alert: everyone may experience more serious health effects.Numeric Value: 201-300
Hazardous – Health warnings of emergency conditions. The entire population is more likely to be affected.Numeric Value: 301-500
Air Quality Monitoring & Forecasting: Frequently Asked Questions
What does the Air Quality Index (AQI) reported at the top of this page represent?
Spokane Clean Air’s air monitors report concentrations of PM2.5, PM10, and ozone each hour. These hourly data are used to calculate “Current Air Quality” (or “NowCast”) index values for each PM2.5, PM10, and ozone monitor in SRCAA’s network of air monitoring stations. The highest among these hourly index values is the designated “Current Air Quality Index” for the Spokane region as a whole, the corresponding air pollutant (PM2.5, PM10, or ozone) being the predominant air pollutant in the Spokane region for that hour.
How does the AQI work?
The Air Quality Index (AQI) was developed by the U.S. Environmental Protection Agency (EPA) as a tool to report local air quality for community members. It uses a color-coded scale of 0 to 500. Hourly concentrations of air pollutants collected at air monitoring stations are converted to the AQI scale. This allows the pollutants to be normalized to a common scale that is easy to understand and provides health-based guidance.
The higher the AQI value, the more polluted the air is and the greater the health concern. For example, an AQI value of 50 or below represents good air quality, while an AQI value over 300 represents hazardous air quality. The colors make it easy for people to quickly determine if air quality is reaching unhealthy levels in their communities so that they can make choices to protect their health.
How is the AQI calculated for the Current Air Quality?
Each pollutant has its own health-based standard. For particulate matter, it is a 24-hour average. For ozone, it is the max 8-hour running average for the day. This means the official daily AQI is not known until the following day. This isn’t very useful when conditions are rapidly changing, such as a dust storm or wildfire smoke. To report air quality that is near real-time, EPA developed the NowCast or what is referred to as “current air quality” on SpokaneCleanAir.org.
The NowCast calculation is designed to be responsive to rapidly changing air quality conditions. More recent hourly air pollution readings (e.g., last three hours) are given greater weight in determining the NowCast index value when air quality is changing more rapidly, as may be the case when wildfire smoke affects air quality.
The NowCast is a very effective tool to report near real-time air quality that correlates to the health-based standards.
Why is the AQI updated only once an hour?
Our air quality monitors collect data hourly. That data is automatically uploaded to the statewide air quality monitoring telemetry system and then to EPA’s AirNow.gov. Data goes through a quality check, and then at :35 past each hour, our website is updated with the most recent hour of data. So, the Current AQI updated at 1:35 pm is monitored data from Noon-1pm. At 2:35 pm, the 1-2 pm data is reported. The delay enables our system to ensure we are providing the best quality data. If a monitoring site has a malfunction, this potentially “bad data” can be removed from the reporting so that the AQI isn’t erroneously reported.
What does Unhealthy for Sensitive Groups mean? What are sensitive groups?
If the AQI is over 100 then it is in the Unhealthy for Sensitive Groups/Orange range. This means the air quality is not meeting the federal, health-based air quality standard.
Inhaling smoke is not good for anyone, even healthy people. Most people are likely to have minor symptoms. Several groups of people, especially those with pre-existing heart and lung conditions, are more at-risk for severe health impacts. People most likely to have health problems from breathing smoke include:
- Lung diseases such as asthma or chronic obstructive pulmonary disease (COPD), including bronchitis and emphysema.
- Respiratory infections, such as pneumonia, acute bronchitis, bronchiolitis, colds, or flu.
- Existing heart or circulatory problems, such as dysrhythmias, congestive heart failure, coronary artery disease, and angina.
- Prior history of heart attack or stroke.
- Infants and children under 18 because their lungs and airways are still developing and they breathe more air per pound of body weight than adults.
- Adults over age 65 because they are more likely to have unrecognized heart or lung diseases.
- Pregnant women because both the mother and fetus are at increased risk of health effects.
- Smokers because they are more likely to already have lower lung function and lung diseases.
- People with low socioeconomic status because they are more likely to have higher exposures and less likely to have access to healthcare.
How does Spokane Clean Air measure air pollution?
We operate a network of monitoring sites in Spokane County, each with sophisticated instrumentation that collects concentrations of air pollutants every hour, around the clock. The pollution concentrations are submitted to the state department of Ecology and the US Environmental Protection Agency (EPA). Cities across our country are required to meet health-based air quality standards for specific pollutants commonly found in ambient air that pose a risk to human health and the environment.
How is the 2-day Air Quality Forecast developed?
A member from our experienced air quality monitoring section develops a two-day air quality forecast each morning. Air quality forecasting is challenging, especially for wildfire smoke because conditions can change so rapidly. Several sources of data and information are reviewed and considered when developing the daily forecast, including:
- The current air quality trends
- Weather reports, trends and forecasts
- Smoke and active fire maps and models (during wildfire season)
- Satellite images
- Conference calls with other air quality and weather agencies during widespread events such as wildfires and dust storms.
Why isn’t there an air monitoring station closer to my home?
There are specific ambient air quality monitoring protocols outlined by the EPA that air quality agencies must follow. These requirements ensure that a community’s ambient air quality is measured effectively to determine if air quality standards are being met. Ambient air quality monitoring is done at the neighborhood scale (representative of neighbor air quality) and at the community scale. While air quality can vary somewhat neighborhood to neighborhood, locations are selected to represent air quality over broad areas. For example, there are two monitoring sites that represent neighborhood air quality and others that represent community air quality. The emphasis is on areas expected to have the worst pollution as well as to avoid redundancies among locations.
Why is the air quality reported at AirNow.gov sometimes different than what is reported at SpokaneCleanAir.org?
AirNow.gov and Spokane Clean Air report the same air quality data which come from the regulatory monitors in Spokane County. For short periods of time, the websites report different values only because the two websites update at different times.
Your monthly air quality report lists AQI values lower than I recall seeing on the current Air Quality webpage. Why?
The monthly air quality reports provide a summary of each day of the month’s Air Quality Index. This is because the nationaly, health-based standard for particulate matter is a 24-hour average, midnight to midnight. For ozone, it is the max 8-hour running average for the day. While you may see slighlty higher hourly AQI reported as the Current Air Quality Index, the data hasn’t been averaged to calculate the daily AQI. To read more information related to this topic, review the 4th & 5th questions/answers provided above.
What is the difference between the WAQA and the AQI?
The Washington State Department of Ecology (Ecology) developed the Washington Air Quality Advisory (WAQA) tool to use instead of the AQI.
The WAQA uses the same color-coded categories as the AQI to show when air quality ranges from good to hazardous. However, for fine particle pollution (PM2.5), the WAQA has lower pollutant concentration thresholds than the AQI. For example, you might see “orange/unhealthy for sensitive groups” reported for Spokane if you are on Ecology’s air monitoring data page, compared to “yellow/moderate” being reported on Spokane Clean Air’s webpage.
Spokane Clean Air reports the national, standardized AQI but some areas of Washington have chosen to report the WAQA.
What are personal air sensors?
Personal air sensors are lower in cost, portable and easier to operate than regulatory-grade monitors. Their popularity is gaining across the United States and there are many studies underway to provide the latest science on their performance, operation, and best practices. Visit EPA’s air sensor webpage for addition information.
Why doesn’t data from my PurpleAir sensor align with what Spokane Clean Air is reporting?
There are a few reasons why PurpleAir data and from Spokane Clean Air are different. Studies have shown that PurpleAir devices can report PM2.5 at concentrations that are about double what regulatory air quality monitors report. It is also important to remember that the PurpleAir devices are not subject to the strict maintenance that regulatory air monitors receive. This can also add to the difference in reported data. Additionally, PurpleAir data can report in different time increments, whereas regulatory monitors capture hourly data. This is why it is important to y look at the data details. Here are some tips:
If you are looking at the Purpleair.com/map and want to compare Purple Air sensor data with regulatory, stationary monitoring site data, an equation has been developed by agencies, including EPA, that helps corrects the PurpleAir data. When looking at the PurpleAir map, in the lower left corner there is a box where you can select “Conversion” then select “US EPA” and then “one hour average graphs” to see the most comparable data to what is reported at SpokaneCleanAir.org and AirNow.gov and which corresponds to health-based air quality standards.