Performance Assessment of Two Low-Cost PM 2.5 and PM 10 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 PM 10 daily concentrations in the Padana Plain (Northern Italy). A total of 19 LC stations for PM 2.5 and 20 for PM 10 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 PM 10 than PM 2.5 reference observations, while lower accuracy was shown in terms of RMSE, MAE and R 2 . AirQino stations under-estimated both PM 2.5 and PM 10 reference concentrations (MB = -4.8 and -2.9 μg/m 3 , respectively), while PurpleAir stations over-estimated PM 2.5 concentrations (MB = +5.4 μg/m 3 ) and slightly under-estimated PM 10 concentrations (MB = -0.4 μg/m 3 ). PurpleAir stations were finer than AirQino at capturing the time variation of both PM 2.5 and PM 10 daily concentrations (R 2 = 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 /PM 10 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. PM 10 outputs.