Design and Evaluation of a Calibration Chamber for Low-Cost PM Sensors–Part 1: Number Concentration-Based Assessment

Low-cost particulate matter (PM) sensors are widely deployed for air quality monitoring, but their accuracy varies significantly with aerosol properties and environmental conditions. This study presents a systematic intercomparison of two commercially available low-cost optical particle sensors viz., OPC-N3 and PMS5003 across a matrix of temperature and RH conditions in a calibration chamber. The calibration chamber provided stable and reproducible conditions with uniform flow, validated using CFD simulations. We evaluated the sensor-reported size-resolved particle number concentrations and their cumulative distributions to four aerosols with varied physicochemical properties, including PSL (inert, nonhygroscopic), NaCl and (NH4)2SO4 (inorganic, hygroscopic), and soot (organic, nonhygroscopic) aerosols under four distinct RH and temperature conditions. The results indicate that PMS5003 showed negligible sensitivity to aerosol type, concentration, or environmental conditions, suggesting that its number concentration response depends largely on its restricted side-scatter geometry and internal transfer functions. Its agreement with the reference monitor was relatively better for cumulative fractions dominated by submicron particles (PM1). In contrast, OPC-N3 exhibited higher size-resolving capability with improved accuracy in the submicron range for nonabsorbing aerosols under high RH conditions. However, substantial deviations were observed for soot (errors > −400%) due to low scattering, coincidence and agglomeration effects. These findings highlight the importance of aerosol-specific assessment and correction strategies for reliable LCS measurements.