Performance Assessment of Two Low-Cost PM_2.5 and PM₁₀ Monitoring Networks in the Padana Plain (Italy)

Two low-cost (LC) monitoring networks, PurpleAir (instrumented by Plantower PMS5003 sensors) and AirQino (Novasense SDS011), were assessed in monitoring PM_2.5 and PM₁₀ daily concentrations in the Padana Plain (Northern Italy). A total of 19 LC stations for PM_2.5 and 20 for PM₁₀ concentrations were compared vs. regulatory-grade stations during a full "heating season" (15 October 2022-15 April 2023). Both LC sensor networks showed higher accuracy in fitting the magnitude of PM₁₀ than PM_2.5 reference observations, while lower accuracy was shown in terms of RMSE, MAE and R². AirQino stations under-estimated both PM_2.5 and PM₁₀ reference concentrations (MB = -4.8 and -2.9 μg/m³, respectively), while PurpleAir stations over-estimated PM_2.5 concentrations (MB = +5.4 μg/m³) and slightly under-estimated PM₁₀ concentrations (MB = -0.4 μg/m³). PurpleAir stations were finer than AirQino at capturing the time variation of both PM_2.5 and PM₁₀ daily concentrations (R² = 0.68-0.75 vs. 0.59-0.61). LC sensors from both monitoring networks failed to capture the magnitude and dynamics of the PM_2.5/PM₁₀ ratio, confirming their well-known issues in correctly discriminating the size of individual particles. These findings suggest the need for further efforts in the implementation of mass conversion algorithms within LC units to improve the tuning of PM_2.5 vs. PM₁₀ outputs.