The dependent variable, Poll, denotes the level of pollution concentration (see Section 3 for details), Fragments is the variable of interest. Sources is a vector of variables controlling for the sources of the pollutant, it may comprise variables relative to: population, transportation, manufacturing and agriculture (cf. Moreover, model (1) includes land cover controls (LandCover) which are of interest to test and geo-meteorological variables (GeoMeteo) which may impact the level concentration (Elminir, 2005, Kerrie et al.,