Trends and variability of atmospheric PM2.5 and PM10−2.5 concentration in the Po Valley, Italy
Atmospheric Chemistry and Physics Discussions
The Po Valley is one of the largest European regions 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, including also for PM<sub>2.5</sub> and its main components since 2008. These regulations lead to an overall improvement on air quality across Europe, including the Po valley and specifically
... nd specifically PM<sub>10</sub>, as shown in a previous study by Bigi and Ghermandi (2014). In order to assess the trend and variability in PM<sub>2.5</sub> in the Po valley and its role in the decrease in PM<sub>10</sub>, we analysed daily gravimetric equivalent concentration of PM<sub>2.5</sub> and of PM<sub>10&minus;2.5</sub> at 44 and 15 sites respectively across the Po valley. For both PM sizes, the trend in deseasonalized monthly means, annual quantiles and in monthly frequency distribution has been estimated: these showed a significant decreasing trend at several sites for both size fractions and mostly occurring in winter. All series have been tested for a significant weekly periodicity (a proxy to estimate the impact of primary anthropogenic emissions), yielding positive results for summer PM<sub>2.5</sub> and for summer and winter PM<sub>10&minus;2.5</sub>. Hierarchical cluster analysis showed moderate variability in PM<sub>2.5</sub> across the valley, with 2 to 3 main clusters, dividing the area in Western, Eastern and Southern/Apennines foothill sectors. The trend in atmospheric concentration was compared with the time series of local emissions, vehicular fleet details and fuel sales, suggesting that the decrease in PM<sub>2.5</sub> and in PM<sub>10</sub> originates from a drop both in primary and in precursors of Secondary Inorganic Aerosols emissions, largely ascribed to vehicular traffic. Potentially, the increase in biomass burning emissions in winter and the modest decrease in NH<sub>3</sub> weaken an otherwise even larger drop in atmospheric concentrations.