A. Example of Data Collected by Padova Smart City
Figs. 4 and 5 report an example of the type of data that can be collected with the Padova Smart City system. The four plots show the temperature, humidity, light, and benzene readings over a period of 7 days. Thin lines show the actual readings, while thick lines are obtained by applying a moving average filter over a time window of 1 h (approximately, 10 readings of temperature, humidity, and light, and 120 readings of the benzene sensor, whose sampling rate is larger since the node is powered by the grid). It is possible to observe the regular pattern of the light measurements, corresponding to day and night periods. In particular, at daytime, the measure reaches the saturation value, while during nighttime, the values are more irregular, due to the reflections produced by vehicle lights. A similar pattern is exhibited by the humidity and temperature measurements that, however, are much more noisy than those for light. The benzene measurements also reveal a decrease of the benzene levels at nighttime, as expected due to the lighter night traffic, but quite surprisingly there is no evident variations in the daytime benzene levels during the weekend (October 26–27). It is also interesting to note the peak of benzene measured in the early afternoon of October 29. Examining the readings of the other sensors in the same time interval, we can note a sharp decrease of light intensity and temperature, and an increase in humidity. These readings suggest that a quick rainstorm has temporarily obscured the sunlight, while producing congestion in the road traffic and, in turn, a peak of benzene in the air.