Field evaluation of low-cost particulate matter (PM) sensor instruments in indoor and outdoor environments: A university lecture hall and urban southeastern United States

The increasing use of low-cost particulate matter (PM) sensors for air quality monitoring highlights the importance of understanding their performance across different environments. This study evaluated the performance of three low-cost sensor instruments—PurpleAir Plantower PMS5003 (PMS), Alphasense OPC-N3 (OPC-N3), and QuantAQ MODULAIR-PM—in indoor (university lecture hall) and outdoor (urban Atlanta) settings, focusing on measurements of PM₁, PM_2.5, and PM₁₀. Reference data were obtained from a Scanning Mobility Particle Sizer (SMPS), an Aerosol Chemical Speciation Monitor (ACSM), and EPA monitoring sites. The PMS underreported PM₁₀ compared to the MODULAIR-PM when the coarse fraction exceeded 0.4. Regarding PM₁, which accounted for the majority of PM_2.5, PMS agreed with SMPS outdoors but underreported PM₁ by up to 60% at low concentrations (PM₁ < 2.5 µg/m³), which was the majority of measurements in the lecture hall. An alternative correction factor improved PMS accuracy in clean environments but heavily depended on calibration (calibration factors varied from 2 to 7). The OPC-N3 struggled to detect particles <350 nm but detected coarse particles missed by the PMS. The MODULAIR-PM combined strengths of both sensors, aligning with EPA references. While there were no consistent trends between relative humidity (RH) and low-cost instrument performance, we clearly demonstrated a correlation between aerosol liquid water content and low-cost sensor instrument bias. This study underscores the continuing need for developing and testing comprehensive and adjustable correction models that account for aerosol composition, particularly liquid water content. Our results emphasize the importance of considering particle size distribution, mass concentration, and chemical composition when selecting specific low-cost sensors to use and interpreting the corresponding data. Copyright © 2025 American Association for Aerosol Research