Laboratory and field evaluation of real-time and near real-time PM _2.5 smoke monitors

Field Evaluation of Low-Cost Particulate Matter Sensors for Measuring Wildfire Smoke

“…All sensors exhibited a high bias, consistent with other field evaluations of the PA [ 7 , 16 , 21 , 29 , 30 ] and other optical-based sensors [ 8 , 15 , 16 , 19 ]. Additionally, the sensors evaluated here had higher correlations to the reference than most field studies using optical-based sensors (0.3 < r 2 < 0.95) [ 10 ].…”

“…The increasing popularity of these sensors is demonstrated by widespread use in many parts of the U.S. and the news media using the PurpleAir map as a source for local estimates of PM 2.5 concentrations during wildfires [ 6 ]. However, there is limited information on the performance of PM sensors during wildfires compared to the monitors currently used in temporary networks or at regulatory monitoring sites [ 7 , 8 ]. Therefore, the ability of a PM sensor to accurately represent smoke air quality impacts is unknown, limiting the utility of these low-cost sensors for public health decisions.…”

“…Laboratory studies have shown that many PM sensors have a high correlation with a reference instrument, which is often an optical-based research-grade instrument calibrated to filter mass or a designated regulatory instrument that has been validated against filter measurements [ 10 ]. Additionally, some PM sensors maintain linearity at concentrations as high as 500 µg/m 3 [ 7 , 11 , 12 , 13 , 14 ] with a quadratic response to concentrations as high as 10,000 µg/m 3 [ 11 , 14 ]. However, sensor performance has varied by manufacturer and model, even when using the same original equipment manufacturer (OEM) sensor, demonstrating the importance of the physical configuration of the sensor package, sensor design (e.g., laser, light detector, flow path, etc.…”

“…Additionally, environmental conditions can impact accuracy [ 20 , 21 ]. Some sensors have exhibited a high bias (up to 50%) with increasing temperature (T) [ 16 ] and increasing relative humidity (RH) (up to 90% when RH exceeded 75%) [ 7 , 10 , 20 , 21 ]. The sensitivity to RH may depend on particle composition, with PM hygroscopicity playing an important role [ 19 , 20 ].…”

“…More recently, Delp and Singer [ 23 ] found that five different models of low-cost PM sensor provided accurate measurements with a linear response to wildfire smoke concentrations as high as 150 µg/m 3 , but they each required a correction factor that differed between sensors even when using the same OEM sensing unit (Plantower PMS5003). A laboratory study by Mehadi et al [ 7 ] was able to achieve much higher concentrations (883 µg/m 3 ) with simulated smoke in the evaluation of two low-cost sensors (PurpleAir and Dylos). They found a low correlation between the PurpleAir and the reference instrument (r 2 = 0.33), and that the ratio of the sensor to reference PM 2.5 concentrations varied from about 1.5 to 3.5 with increasing smoke concentration.…”