Comparing Low- and Mid-Cost Particulate Matter Sensor Performance Indoors

Until recently, particulate matter (PM) monitoring instruments have been very expensive (>$10,000s), only permitting indoor air quality research over short periods of time in a select few locations and prohibiting the general public from assessing their indoor air quality. However, several low-cost ($100s) and mid-cost ($1,000s) sensors have recently entered the commercial market and are being widely deployed by the public. While low- and mid-cost sensors have expanded access to indoor air quality information, it is crucial that their limitations are fully understood so that they can be used to successfully mitigate exposure to poor air quality. In this study, we compare PM data reported by low-cost (Plantower PMS) and mid-cost (QuantAQ MODULAIR-PM) PM sensors in five different indoor environments on Georgia Tech’s campus: two classrooms, two academic common spaces, and a cafeteria. PM data were collected in the five indoor environments during a portion of the Fall semester every minute for three PM size bins: PM₁, PM_2.5, and PM₁₀. Compared to the MODULAIR-PM, the Plantower PMS only measures approximately 45% of PM₁, 70% of PM_2.5-1; 72% of PM_10-2.5 across all five indoor environments. Furthermore, the low-cost sensor data is only strongly correlated for PM₁ (R² > 0.93) but not PM_2.5 (R² <0.13) or PM₁₀ (R² <0.19) across all environments. Therefore, while the nephelometer performs well and can be used to assess exposure to indoor particles with diameters less than 1.0 micron, it fails to accurately assess exposure to indoor particles of larger diameters. This is very important because the mass fraction of large particlesto all particles is significant (7% on average) in all five indoor environments evaluated in this study. The Plantower PMS is expected to miss larger particles because the sensor’s capability is limited by its detection range: it only detects particles with diameters between 0.3 to 1.0 micron, a fraction of PM₁, and extrapolates this data to PM_2.5 and PM₁₀. Conversely, the MODULAIR-PM sensor can measure particles with diameters between 0.35 to 40.0 microns. With over 10,000 low- and mid-cost sensors installed globally and increasing scientific publications relying on low-cost sensor data, it is imperative for users to understand these sensors’ limitations to draw solid conclusions about the measured air quality.