Practical Guidance for Using PurpleAir Particle Monitors for Indoor and Outdoor Measurements in Community Field Studies

Abstract

Low-cost particle monitors have been widely evaluated in laboratory and ambient monitoring settings, but we have less knowledge about their performance for long-term indoor and outdoor monitoring in residential settings. We seek to provide practical guidance for using a type of low-cost particle monitors that have become widespread for indoor and outdoor monitoring in community field studies, PurpleAir PA-II monitors. We base our insights on experiences in a community-led residential field study in and around homes of predominantly agricultural workers in California's San Joaquin Valley. Our guidance spans three categories: (1) providing tools for handling and merging disparate data structures resulting from Wi-Fi-transmitted data and data collected on onboard microSD cards, (2) assessing performance metrics of PA-II monitors from laboratory co-location and field measurements, and (3) assessing data collection success rates of Wi-Fi data transmission and microSD card data acquisition from our study locations. The post-processing methods we demonstrate can successfully align data from both Wi-Fi transmission and microSD cards. Laboratory co-location measurements demonstrated that > 90% of the tested monitors performed well relative to each other (high precision), with only a few problematic monitors that warranted further investigation or exclusion from use. The application of co-location factors generated using the mean of all co-located monitors as a reference did not significantly affect distributions of field-measured indoor or outdoor PM_2.5 concentrations. Relying solely on Wi-Fi data transmission in our study would have resulted in large data loss (i.e., < 50% success rate); using microSD card storage with PA-II-SD monitors increased the data collection success rate to over 80% in these settings. This work contributes to the growing body of knowledge on low-cost particle sensor performance and usability.

Supplementary information: The online version contains supplementary material available at 10.1007/s44408-025-00048-4.

Keywords: Data collection; Long-term indoor exposure assessments; Low-cost particle monitors; Performance; QA/QC.

Fig. 1

Examples of custom wooden mounting structure for PA-II monitors deployed indoors (a and b) and outdoors (c and d) in our residential field study

Fig. 2

Co-located PA-II monitors in a home garage setting (a and b) and a large research laboratory garage setting (c and d)

Fig. 3

An example of data extracted via the Wi-Fi API

Fig. 4

An example of data extracted from microSD card

Fig. 5

Comparison of post-processed SD data and Wi-Fi extracted data

Fig. 6

Histograms of slope and R² of pm2.5_alt from each monitor with an arbitrary reference monitor (a and b) and the mean of monitors as a reference (c and d) for co-locations conducted in the intervention year

Fig. 7

Field data capture rate of PA-II (Wi-Fi only) and PA-II-SD (Wi-Fi + SD) monitors, comparing data captured via Wi-Fi transmission, SD card storage, and the total data captured by the monitors. Plot is sorted by Wi-Fi data capture rate within each monitor type. FK = Fresno/Kings Counties; KE = Kern County

Fig. 8

Histograms of PM_2.5_alt measurements from laboratory co-location tests and field tests, both with and without co-location factors applied, combining all indoor and outdoor data together

Fig. 9

Distributions of indoor and outdoor PM_2.5_alt measurements and concurrent PM_2.5_alt indoor/outdoor (I/O) ratios measured in the field study, comparing raw (without co-location factors) and adjusted (with co-location factors). Box plots exclude outliers for visual clarity