Temperature-Associated SD Card Logging Failures in PurpleAir Monitors: Findings from the Strong Heart Air Study

Low-cost air quality monitors are increasingly used in environmental health studies. We report the deployment and evaluation of low-cost, fine particulate matter (PM2.5) monitors in an ongoing investigation of air quality and cardiovascular health in three climatologically distinct American Indian communities. Prior to deploying large numbers of PurpleAir monitors for this work, we conducted pilot collocations of ten monitors at each study site to evaluate performance under field conditions. Monitors were configured to store data locally on SD cards rather than upload via WiFi to avoid cloud-based data ownership concerns in partner American Indian communities. During pilot collocations, we observed substantial data loss in colder regions: data recovery was 57% in Oklahoma and 10% in South Dakota, compared with 100% in Arizona. SD card logging commonly failed when ambient temperatures fell to mean (standard deviation) levels of 4.4 (3.2) °C in Oklahoma and 7.7 (2.0) °C in South Dakota. Follow-up outdoor experiments suggested that WiFi connection improves SD card reliability at low temperatures, while controlled 4 °C cold-room experiments confirmed logging failures without WiFi. Our findings demonstrate temperature-related limitations of PurpleAir monitors when used without WiFi and provide practical guidance for low-cost PM2.5 monitoring in cold climates.