A study on atmospheric aerosol particles size distribution in several sites in Lombardia region by an optical particle counter

In Lombardia, a project (Particolato fine in Lombardia – PARFIL – 2004÷2006) aiming at the chemical and physical characterisation of atmospheric aerosol related with pollution sources is in progress. Sixteen measurement sites with different topography and urbanization are continuously monitored as for PM10/PM2.5/PM1 mass concentration and chemical composition. Moreover, particle number concentration was assessed at five sites (2 urban, 1 rural, 1 pre-alpine and 1 alpine) using an Optical Particle Counter (OPC) working on 15 classes over the size range 0.3–30 µm. In each site both winter and summer campaigns were performed. In order to investigate similarities in the behaviour of different sized particles, cluster analysis was applied on the dimensional classes. The autocorrelation function was determined on the clusters to estimate particles residence times and/or response time to variation of the system on local scale. Number concentration series were also analysed in relation to main meteorological parameters as air temperature and humidity, atmospheric pressure, wind speed and direction, rainfall and Pasquill categories. The results of the study highlight the role played by local sources for the coarse fraction, while meteorological conditions, seasonal changes and pollution emissions on the Po valley have a significant influence on the sub-micron sized particles