Disparities in Growth of Low-Cost Air Pollution Sensor Deployment

Abstract

Background: Low-cost air quality sensors offer the capability to measure and generate a large volume of real-time air pollution data. Two of the most popular low-cost sensors are PurpleAir, a stationary outdoor/indoor monitor; and AirBeam, a portable monitor paired with a smartphone app. Despite the low cost of entry, the popularity and usage of low-cost air quality sensor usage are not yet quantified, and it is unclear where they are being deployed. Methods: Geocoded data from PurpleAirs and AirBeams were downloaded and processed through their respective application programming interfaces. We examined the growth of the numbers of outdoor PurpleAir units and AirBeam mobile sampling sessions over time around the globe. We also evaluated whether there exist disparities in the number of low-cost sensors in the U.S across geographic, racial, and socioeconomic factors at the census tract-level. Results: In 2017 there were approximately 800 outdoor PurpleAir units, and by the end of 2019 this number grew to 5700 units. The total number of AirBeam sampling sessions grew from 1300 in 2013 to more than 80000 by 2019. Most of the sensors were deployed in North America and Europe, although there was significant growth in Africa and Asia in 2019. In the U.S., PurpleAirs were mostly located in the Western states, and within census tracts with high socioeconomic status and majority white populations. AirBeam sessions were mostly carried out in densely populated census tracts and in areas with lower median incomes. Conclusions: The rapid growth of the low-cost sensor deployment across the globe highlights the interest in high-resolution air pollution data. In the U.S., there were noticeable disparities across race, socioeconomic status, and urbanicity for low-cost sensor usage. The observed differences between PurpleAir and AirBeam suggest that their user-profiles and usage purpose are likely to differ.