You are here:
An analysis of degradation in low-cost particulate matter sensors
Citation:
deSouza, P., K. Barkjohn, A. Clements, J. Lee, R. Kahn, AND B. Crawford. An analysis of degradation in low-cost particulate matter sensors. Environmental Science: Atmospheres. Royal Society of Chemistry, Cambridge, Uk, , NA, (2023). https://doi.org/10.1039/D2EA00142J
Impact/Purpose:
The use of PM2.5 air sensor networks has grown exponentially in recent years. As these networks age, their performance may change. It is important to understand the lifespan of these monitors to determine when they should be replaced, and when measurements from these devices should or should not be used for various applications. This paper will provide valuable information to a variety of air sensor users.
Description:
Low-cost sensors (LCS) are increasingly being used to measure fine particulate matter (PM2.5) concentrations in cities around the world. The PurpleAir is one of the most commonly deployed LCS with ~ 15,000 monitors deployed in the United States. PurpleAir measurements are widely used by the public to evaluate PM2.5 levels in their neighborhoods. They are also increasingly being integrated into models by researchers to develop large-scale estimates of PM2.5. However, the performance of these monitors over time has not been well studied. It is important to understand the lifetime of these monitors to determine when they should be replaced, and when measurements from these devices should or should not be used for various applications. This paper fills in this gap by leveraging the fact that: (1) Each PurpleAir monitor is comprised of two identical sensors and the divergence between their measurements can be observed, and (2) There are several PurpleAir monitors within ~ 50 meters of regulatory monitors allowing us to compare measurements between these instruments, to propose empirically-derived degradation outcomes for the PurpleAir monitors. We evaluate how these outcomes change over time. On average, we find that the number of ‘flagged’ measurements, where the two sensors within a PurpleAir monitor diverge, increases with time to ~ 4% after 4 years of operation. We identified and report PurpleAir IDs of permanently degraded monitors. We also find that the bias of PurpleAir monitors, i.e., the difference between calibrated PM2.5 levels and the corresponding reference measurements increases over time by -0.12 (95% CI: -0.13, -0.11) μg/m3 per year. The average bias increases dramatically after 3.5 years. Climate zone is a significant modifier of the association between degradation outcomes and time.
