Atmospheric aerosol modal structure in the urban and rural area of Bologna, Italy

Aerosol particles have been recognised as a potential adverse factor for human health [WHO, 2002; Oberdoster, 2005]. While many of the health related evidence has been based on PM10, specific questions have arisen: which particular aerosol types might be responsible and how the exposure risk for the population may be reduced in a cost-efficient way. Specific sub-groups in the environment aerosol suspected to cause adverse health effects are: carbonaceous, metal, ionic aerosol and ultrafine particles (diameter < 100 nm). A current trend in air quality monitoring is to define the measurement techniques and thus identify the abundance (and later the possible health effects) of these aerosol sub-fractions. An effective and widespread method to observe atmospheric aerosol is to evaluate particles mode distribution. Whity (1978) popularised the tri-modal scheme including the coarse, the accumulation and the “nuclei” (i.e. Aitken) mode. In rural sites (not affected from direct sources) these models reflect the age and the life-time of the particles, while in urban sites, the schemes can reveal the proximity and/or activity of anthropogenic sources. The knowledge about the spatio-temporal behaviour of aerosol modes could greatly simplify the description of aerosol related processes and effects, and also particles exposure assessment. While PM mass concentrations appear to be less variable in time and space, this is not true for total or ultrafine particles number concentration. In this work, it is shown the spatial variations of sub-μm particles size distributions in urban and rural area of Bologna.