Long-Term Field Performance of Sensirion SEN54 and SPS30 Low-Cost Particle Sensors: Seasonal Variability and Correction Using Dew Point Deficit

Low-cost optical particle counters (OPCs) are increasingly used for supplementary air-quality monitoring, but their long-term performance remains insufficiently characterised. This study evaluated two pairs of Sensirion OPCs (SEN54 and SPS30) against a Palas Fidas 200S equivalent monitor (EM) over a 19-month field deployment. Sensor agreement was considerably lower for PM10 (mean R2 = 0.50, mean RMSE = 13.70 µg·m−3) than for PM2.5 (mean R2 = 0.87, mean RMSE = 5.53 µg·m−3). None of the sensors adequately captured elevated PM10 episodes associated with mineral dust, and removing these episodes moderately improved agreement with the EM. Both sensor types exhibited pronounced seasonal variability, with substantially better performance during the cold season. A large proportion of this variability was explained by atmospheric moisture conditions represented by the dew point deficit (DPD). MARS-based correction models combining sensor-reported PM concentrations and DPD improved performance to mean R2 values of 0.68 for PM10 (mean RMSE = 8.25 µg·m−3) and 0.92 for PM2.5 (mean RMSE = 3.29 µg·m−3). For SPS30 sensors, particle-count and DPD-based corrections further improved PM10 and PM2.5 performance, although high PM10 episodes remained challenging for some sensors. Residual warm-season underestimation suggests that aerosol-specific properties beyond atmospheric moisture continue to affect sensor accuracy.