I reached out to the author and they're using an uHoo Smart Air Monitor and will be writing a review of it in the future. Most reviews of air quality monitors seem to focus on details like the size of the screen, or whether the monitor app is easy to use, and fail to actually test the accuracy of monitor itself. Hopefully this author's review is different.
garrettgrimsley|4 years ago
See this EPA testing table for some measures of accuracy: https://www.epa.gov/air-sensor-toolbox/evaluation-emerging-a...