PM2.5 in the Po valley: patterns, long term trends and their influence on air quality

Po Valley is one the largest European region with remarkably high concentration level of atmospheric pollutants, both for particulate and gaseous compounds. In the last decade stringent regulations on air quality standards and on anthropogenic emissions have been set by the European Commission, leading to the latest 2008/50/CE, which requires a monitoring plan also for PM2.5, used as an indicator of population exposure to atmospheric particulates. These regulations lead to an overall improvement on air quality across Europe, including PM10 in the Po valley (Bigi and Ghermandi, 2014). Due to the different nature of PM2.5 and its large fraction of secondary aerosols, patterns and trends of PM2.5 exhibit large difference to PM10 features, therefore the latest air quality regulations may represent a hard challenge for municipalities and environmental agencies. Daily gravimetric equivalent PM2.5 concentration at 44 sites over the Po valley (either in urban or rural background conditions) has been analysed. Long term trends on deseasonalized monthly means have been estimated by Generalised Least Squares. These results have been compared with trends on annual quantiles. Changes, over the sampling period, in frequency distribution of PM2.5 in each month have also been estimated. For each site, impact of primary anthropogenic particulate emissions has been qualitatively estimated by testing PM2.5 series for a significant weekly periodicity using three different metrics. The former compares the median among time series of PM2.5 anomalies of weekdays, the second consists in the weekend effect magnitude. The latter used frequency domain analysis in order to test whether estimated spectral density at 1/7 day-1 frequency is significantly higher than the spectral density of a red noise series. Finally a cluster analysis on the dataset has been performed, showing a geographical pattern for PM2.5 concentration across the valley. This study provides a reliable tool to asses the impact of the current and previous emission control policies across the Po valley