The representative day

The work presents a daily trend of pollutant concentrations, referred to as the “representative day”, i.e. the day for which the overal sum of the mean-square differences between its concentration, averaged within each hour, and the concentrations for all other days at the same hour, is a minimum. The approach also allows the identification of the “least representative day” (the daily series that maximises the mean sum of squared residuals), which usually indicates an anomalous situation in pollutant dispersion, characterised by concentration maxima at the ground.