Field calibration of a low-cost sensors network to assess traffic-related air pollution along the Brenner highway

This paper presents the results of a field campaign aiming at testing the ability of a network of low-cost electrochemical sensors to measure nitrogen dioxide concentration levels alongside one of the major Italian highway arteries. The results of a double on-field calibration, allowing for investigating the performance of the sensors under a broad range of weather conditions, are first shown and discussed. Different regression models are tested and their performance is widely assessed. Then, the measurements of the calibrated sensors are analyzed during a year-long field campaign, testing their performance against reference air quality stations and paying particular attention to different statistical indices. Results show a satisfactory performance of the low-cost sensors, highlighting their suitability to complement measurements from standard air quality stations, to reach a wider spatial coverage and to monitor pollutant concentrations in critical situations, when standard measurements are usually not feasible. Moreover, the dataset available from the year-long field campaign allows to extensively investigate nitrogen dioxide concentrations alongside the highway, pointing out in particular the strict relationship between pollutant concentration patterns and meteorological phenomena typical of Alpine valleys, such as daily-periodic thermally-driven wind systems.