March 2021 Working Paper 007.2021

The second is the number of days in the year in which the concentration exceeded safeguard limits, computed as the simple average of the reported number of days in exceedance across the stations in the city i. [...] In the case of the spatial trend, the test compares the model with the trend (c) and the model without (b), and the p-value (reported in square brackets) suggests rejecting the null hypothesis that the geographical position of the city does not affect its pollutant exceedance. [...] In the case of geographical 10 coordinates, the figure appears as a set of level curves, each level representing the value of the smooth term: the higher the value of the smooth term (the trend), the higher is the level of the curve. [...] The coefficient estimates of the linear part of the deterministic component of the model; hence, the control variables and the meteorological variables are consistent with the results of the other models, from which they retain sign and significance. [...] In the horizontal axis the value of the variable is reported, in the vertical axis the value of the component, which is the part of the linear predictor ascribed to the related variable.