Variation of atmospheric emissions within the road transport sector in Italy between 1990 and 2016.

The concentration of road transport emissions impacts on air quality, is responsible for climate change and increases the average temperatures. The aim of this study was to analyze the trends of atmospheric emissions within the road transport sector in Italy between 1990 and 2016. A principal component analysis (PCA) was carried out to investigate the pollutants that showed similar trends over time. The Kendall's rank correlation coefficient was studied to establish the statistically dependent variables. Finally, a joinpoint regression analysis was performed to evaluate the time-trends of pollutants' emissions. The Pearson's correlation coefficients were positive for all pollutants except for CO2, that demonstrated an inverse relationship with CH4 (-0.07), NOx (-0.089) and NMVOC (-0.128); NO2 demonstrated inverse relationship with all other pollutants. According to the main component analysis, most pollutants were assimilable in their behavior, except for NO2, CO2 and N2O. The joinpoint analysis describes a general decrease of emissions over time with exception of N2O, NO2 and CO2, that showed different trends. This study shows that road traffic-related emissions in Italy, between 1990 and 2016, recorded significant reductions for most of the recorded pollutants. However, CO2 and N2O maintained a stable trend while NO2 showed an increasing trend.