There are many sources that provide the Air Quality Index (AQI). Oftentimes, different sites may provide similar readings, with slight discrepancies. So, how do you know which data source is the most accurate for the Spokane region?
To begin, it is important to know how Spokane Clean Air’s air monitoring network works. Our monitoring map on this page displays data from both monitors and SensWA sensors. Monitors require extensive testing and maintenance to meet rigorous performance standards. They are often referred to as ‘regulatory-grade’ monitors. Sensors cost much less than monitors to acquire and maintain. They are smaller and not required to meet the same performance standards because they are not used for regulatory decision-making. We only use monitors to report the overall AQI, which is the highest reading taken from our network of monitors. From our map, you can retrieve data from either a monitor or sensor located nearest you.
Other air quality reporting websites and phone apps may differ because they may be reporting data from other types of sensors that businesses and individuals can purchase and install themselves. This is considered ‘crowdsourced data’. For example, EPA’s AirNow Fire and Smoke map displays our monitors and sensors, but also includes Purple Air (PA) sensors. PAs are small, stationary sensors available for purchase by any member of the public. Because anyone can purchase and set up a PA sensor, the accuracy of the data they provide can be influenced by where the owner of the Purple Air sensor installed the device. Also, when you are reviewing PurpleAir data, there are options to select different timeframes for the data, such as near real-time, 10 min, 1 hour, etc. These factors can make comparing data difficult. While data from low-cost sensors may not be as accurate as data from our regulatory-grade monitors, the sensors can provide helpful insights for very localized air quality information.
So, what factors might result in discrepancies between AQI sources?
Data source
Simply put, different reporting sites get their data from different places. Many websites based in Washington, or sites supported by federal agencies, will use Spokane Clean Air’s monitors and sensors to report data. For example, the AirNow Fire and Smoke Map shows our monitors and sensors and reports the same data we do. The Washington State Department of Ecology map does the same.
It is common for non-government sites to also report air quality data. This data may vary for several reasons. IQAir is a popular air quality site that sells its own air quality sensors to add to its monitoring map. Unlike AirNow, IQAir uses the data reported by these sensors alongside regulatory-grade monitors and sensors to calculate and report the AQI. This may lead to data discrepancies caused by the accuracy of the IQAir sensors.
Breezometer is another popular provider of air quality data—in fact, it supplies data to the built-in Apple Weather app. This site self-describes how it collects data by combining “big data and machine learning technology to provide intuitive, personalised information on air quality and pollen levels.” It does not have an interactive map, and it also does not produce an individual report for each pollutant. Instead, it reports a hybrid output for all relevant pollutants.
Sites like Breezometer and IQAir may differ greatly from the data being reported by official sources due to the inclusion of additional, privately installed sensors, or differing ways of calculating the AQI.
Update Timing: Same source, different data
Data from our network can take some time to be uploaded to all the different sites that use our monitors and sensors. Spokane Clean Air’s monitoring map updates hourly at 35 minutes past the hour. Other sites may differ. For example, AirNow.gov and Spokane Clean Air report the same air quality data, which comes from the regulatory monitors in Spokane County. For short periods of time, the websites report different values only because the two websites update at slightly different times. If you are comparing data from two sites, it is important to keep in mind how the update timing may vary based on the site and the source of the data.
Concentration versus AQI: What’s the difference?
Oftentimes, handheld particulate counters do not report the AQI—they report the concentration of particulates. This is the same data that our monitors and sensors collect, but we convert that concentration into a number on the Air Quality Index to make it easier for everyone to understand. We often get asked why a particulate counter is reporting a number that is different than the AQI. For example, if a counter is showing the number 35, users may assume that it is reporting the AQI as being in the Good/Green range, while our website is reporting that the AQI is 99, which falls in the Moderate/Yellow range. This difference in numbers is because we have done the conversion calculation for you, but the particulate counter does not. If you were to convert that particulate concentration to the AQI, you would find that a concentration of 35 is equivalent to an AQI reading of 99. It is also important to note that a handheld counter will likely report a short-term average, or an instantaneous reading. The AQI is applied to concentration data averaged over a longer time period. If you have a particulate counter at home and want to determine the AQI using your handheld device, you can use the AirNow AQI Concentration Calculator.
Location: The AQI is Unhealthy, but when I look outside, I can’t see smoke…
Our AQI is determined by the highest reading on our monitoring network—so even if most of the area is reading lower, if there is one monitor displaying a very high reading, then that is the number we use to determine the AQI.
What has happened a lot recently, for example, is that our AQI will be largely sitting in an acceptable range except for our northernmost monitor in Colbert. In the situation depicted above, our website and other sites that report our monitoring data would list the AQI as being 184, or in the Unhealthy/Red range. In reality, depending on where you live in the county, that reading may not be representative of your localized air quality, and you would be fine to go outside without some of the protections required when the AQI is unhealthy.
If you are using our monitoring page to check the AQI, please scroll down to view the monitoring map and check the monitor or sensor that is closest to you. This will give you a more accurate representation of your air quality.
There are many things that can impact an AQI reading. It is important to know what can affect this reading and which sites are most accurate.
