Fine and coarse fractions in the description of the atmospheric aerosol behavior

From the health stand point atmospheric Particulate Matter (PM) is regulated on mass basis through PM10 and PM2.5 conventions by the Directive 2008/50/EC. The Directive recognizes the negative impact on human health due to fine PM (PM2.5) and points out how the approach to be pursued should aim at a general reduction of PM2.5 concentrations in urban background. The Directive prescribes that Member States shall take the measures necessary to guarantee the fulfillment of such limit. Setting up a policy of particulate matter (PM) reduction necessarily involves a good level of knowledge of what components sum up to yield PM10 measurements. As reported in literature (Almeida et al., 2005) the fine mode of PM is dominated by both primary anthropogenic pollution from combustion processes and gas-particle partitioning, while the coarse mode is mainly related to wind erosion, mineral dust emission and long-range transport from desert area (natural events). In particular, episodes of coarse dust transport from Sahel towards Europe across the Atlantic Ocean occur in February and March, whereas from Sahara over the Mediterranean basin in summer. PM10 daily - average ponderal values are inadequate to investigate the occurrence of fine / coarse episodes and consequently do not give significant information on its source apportionment. The separation of coarse and fine fractions and their chemical characterization (Avino et al., 2002; Avino et al., 2006; Movassaghi et al., 2008; Avino et al., 2008) do not satisfactorily describe atmospheric PM pollution if data averaging times greatly exceed the time scale of the dynamic of the boundary layer (about one hour time scale). For this reason an integrated approach using average PM10 and PM2.5 mass concentration data and time resolved size spectrum analysis was developed and applied to analyze an intense episode of PM pollution occurred in Rome in the period 2005 - 2012.