Quantification of Saharan dust contribution to PM10 concentrations over Italy during 2003–2005

Italy is frequently affected by Saharan dust intrusions, which result in high PM10 concentrations in the atmosphere and can cause the exceedances of the PM10 daily limits (50 μg m−3) set by the European Union (EU/2008/50). The estimate of African dust contribution to PM10 concentrations is therefore a key issue in air quality assessment and policy formulation. This study presents a first identification of Saharan dust outbreaks as well as an estimate of the African dust contribution to PM10 concentrations during the period 2003–2005 over Italy. The identification of dust events has been carried out by looking at different sources of information such as monitoring network observations, satellite images, ground measurements of aerosol optical properties, dust model simulations and air mass backward trajectory analysis. The contribution of Saharan dust to PM10 monthly concentrations has been estimated at seven Italian locations. The results are both spatially (with station) and temporally (with month and year) variable, as a consequence of the variability of the meteorological conditions. However, excluding the contribution of severe dust events (21st February 2004, 25th–28th September 2003, 23rd–27th March 2005), the monthly contribution of dust varies approximately between 1 μg m−3 and 10 μg m−3 throughout year 2005 and between 1 μg m−3 and 8 μg m−3 throughout year 2003. In 2004 the dust concentration is lower than 2003 and 2005 (<5 μg m−3 at all sites). The reduction in the number of daily exceedances of the limit value (50 μg m−3) after subtraction of the dust contribution is also calculated at each station: it varies with station between 20% and 50% in 2005 and between 5% and 25% in 2003 and 2004.