Project operated by Jason Snell jsnell@sixcolors.com with enormous contributions from Matt Silverlock, Rob Silverii, Adam Lickel, Alexander Ogilvie, Brian Donovan, Jon Sadka, and anonymous others!
This project generates a widget that displays local air quality on the home screen of devices running iOS or iPadOS 14. It is displayed via the Scriptable app by Simon Støvring.
The widget uses data from the PurpleAir network of low-cost, consumer air quality sensors. While in America the EPA has a large, established network of sensors, the nearest sensor to you may not be experiencing the same conditions as you are, especially in extreme events such as wildfires. This widget exists because the nearest EPA sensor to me (Jason Snell) did not accurately reflect my local air quality during heavy wildfire smoke conditions. You can read more about the origin of this project if you like.
To use this widget, make a new script inside Scriptable and paste in the contents of purpleair-aqi.js.
You can run the script from within the app, or add a new Small widget on your home screen, set it to Scriptable, and choose the script by tapping and holding on the widget, choosing Edit Widget, and choosing the script by tapping on the Script field.
If you don't specify the sensor ID of a nearby PurpleAir sensor, the script will attempt to display information from the active sensor that is closest to you. (To force the widget to use a specific PurpleAir sensor ID, tap and hold on the widget, choose Edit Widget, and enter the sensor ID in the Parameter section. To find a sensor ID, go to the PurpleAir map and tap or click on a station near you. The URL in your browser should change to the new selection. A four- or five-digit number will appear just after "select=" and that's the number to enter in to the Parameter field.)
This widget uses an EPA calculation designed for low-cost sensors like PurpleAir in areas where wood smoke is an issue, such as during wildfires. You can read about the backstory here and see the EPA document here.
PurpleAir refers to this calculation as US EPA, which you can choose from the Conversion popup on the PurpleAir web map.
In some extreme smoke situations the widget falls back to the AQANDU calculation method.
The words and colors! The real point of AQI isn't the number, it's the level -- the words and color. But we all like numbers, so it displays a number too. Also, the widget does display a trend if one exists, so if you're in volatile conditions, you should be able to tell at a glance if your air quality is improving or worsening.