This dataset contains the observations of air quality collected within two experimental campaigns conducted in summer 2017 (07 August 2017-26 September 2017) and winter 2018 (15 January 2018-15 February 2018) in two street canyons in the city of Bologna, to verify the effectiveness of vegetation in altering ventilation levels and pollutant concentration in real-world street canyons. The dataset also contains the meteorological data collected during non-synoptic periods, representing the ideal condition to assess the behavior of the local circulation and turbulence. The experimental field campaigns were setup under WP3 (“Planning and evaluation of PCS solutions”) and conducted under WP5 (“Monitoring and Evaluation of the Interventions”) of the iSCAPE project. Briefly, two parallel urban street canyons characterized by a different occurrence of vegetation, i.e. one almost free of vegetation (Marconi St.) and one with a tree line along both sides of the street (Laura Bassi St.), were instrumented for measurements of meteorology and turbulence variables at three height levels, while pollutant concentrations were monitored at ground level inside both canyons. This dataset is linked to the paper “Disentangling the effect of vegetation on ventilation and air quality in urban street canyons: the Bologna iSCAPE experimental campaigns” by Di Sabatino et al., which will be submitted for publication on “Science of the Total Environment” edited by Elsevier, and to the paper “Characteristic Scales for Turbulent Exchange Processes in a Real Urban Canopy” by Barbano et al., which is under review for publication on “Boundary-Layer Meteorology” edited by Springer. If you use this dataset for your research or work purposes, we ask that you acknowledge us in the use of your data, which can be done by including a proper citation in any documents or publications using these data.

Sensor based monitoring systems have been indicated as a promising tool to increase information on spatio-temporal distribution of air pollution but several issues have been raised about the accuracy of such monitors when used in the field. The study aimed at assessing the performance of sensor based systems after multiple relocation in different seasons and sites. The systems included electrochemical sensors to measure NO2 and O-3 concentrations. The approach consisted in two-week field calibration of each device at a reference monitoring station and the test of the calibrated device at different reference station sites. The main specific goal was a comparison of sensor performance considering site-specific (SS) and no site-specific (no SS) calibration, i.e. calibration and testing carried out or not at sites with similar characteristics. Calibration was performed by season using random forest (RF) models. Very good performance was found for calibrated O-3 sensors with R-2 >= 0.82 regardless of seasons and sites. Mean normalized root mean square error (nRMSE) was around 7% and 6% in winter and summer tests, respectively. Very good performance of sensor systems was observed also for NO2 during winter (R-2 >= 0.84) with much better accuracy for SS compared to no SS calibration (nRMSE equal to 6% and 17%, respectively). A marked decrease of performance was observed for NO2 sensors during summer. Our results show a good potential of sensor based systems after SS field calibration in increasing information on the distribution of air pollution at high spatial and temporal resolution.

In order to assess the impact of traffic on local air quality a microscale simulation of pollutant concentration fields was produced for two busy intersections, in Reggio Emilia and in Modena, Italy. The simulation was performed by the model suite Micro-Swift-Spray, a Lagrangian particle dispersion model accounting for buildings. Direct measurements of traffic flow were continuously collected in Reggio Emilia over the period January 13–24, 2014 by a two channel radar traffic counter and in Modena from October 28 to November 8, 2016 by four single channel radar traffic counters and used for the hourly modulation of vehicular emissions. Combining radar counts with vehicular fleet composition for each municipality, specific emission factors were obtained. For both cities, simulated concentration fields were compared to local air quality measurements at the nearest urban traffic and urban background sites. The simulated NOx showed large correlation with the observations, notwithstanding some underestimation. The results proved the reliability of the procedure and provided a fair estimate of the NO2 mass fraction of total NOx (primary NO2) due to vehicular emissions in the investigated traffic sites.