A study of PM2.5 and PM2.5-associated polycyclic aromatic hydrocarbons at an urban site in the Po valley (Bologna, Italy)

PM^sub 2.5^ and PAHs bound to PM^sub 2.5^ were investigated in downtown Bologna, from January to June 2003, in order to determine the burden of the fine fraction in the aerosol of a typical urban environment of the Po Valley, a critical area in Northern Italy in terms of atmospheric pollution. The sampling campaign was divided into three parts: a winter sub-campaign, an intermediate campaign where PM^sub 2.5^ and PM^sub 10^ were simultaneously sampled and which identified PM^sub 2.5^ as the major component of PM^sub 10^, and a summer sub-campaign. Critical concentrations of both PM^sub 2.5^ and PAHs were observed in winter time; for example, in January 2003 the mean value for the 24-h average PM^sub 2.5^ concentration was 58 μg/m^sup 3^, much higher than the annual arithmetic mean of 15 μg/m^sup 3^ established by the US ambient air quality standard (NAAQS). Correspondingly, the mean value for benzo[a]pyrene (BAP) in PM^sub 2.5^ was 1.79 ng/m^sup 3^, again higher than the annual mean of 1 ng/m^sup 3^, required by European regulations for BAP in PM^sub 10^. In summer time the BAP concentration considerably decreases to 0.10 ng/m^sup 3^ as the likely effect of photolysis and dilution on a higher boundary layer; PM^sub 2.5^ decreases too, but the mean concentration (22 μg/m^sup 3^) is still higher than the NAAQS value. Further analysis included TEM microscopy of collected particles and correlations between PM^sub 2.5^, PAHs and gases (benzene, O^sub 3^, CO, NO^sub 2^, SO^sub 2^). All these observations identified on-road mobile sources as the main source of emissions and, in general, of the poor air quality level in the city of Bologna.[PUBLICATION ABSTRACT]