Characterization of Saharan dust episodes over central Italy

Saharan dust episodes can be observed over Mediterranean region several times a year, affecting PM10 concentration. In particular, Italian peninsula can be affected by Saharan dust outbreaks, which can contribute to the exceedance of legal limit values for PM10 concentration. For this reason, it is mandatory to identify the quantitative amount of relevant mineral dust events. Several methods and techniques are been proposed to identify and quantify the amount of mineral dust to PM10 concentration, using both experimental techniques and numerical models. Numerical models can simulate the dynamic of long-range transport of mineral dust and the consequent deposition, while some specific analysis can quantify the effective amount of Saharan dust to the PM10 concentration. During the summer of 2014, the University of Florence conducted a specific field campaign, in the framework of PATOS project [2], allowing the assessment of the mineral dust contribute to the PM10 concentrations. This specific campaign provides daily measurements, on alternate days, for the whole period and hourly measurements for two weeks. The measurements are performed in two sites: one along the Tuscany coast (Livorno-La Pira) and the second at an hinterland site (Pistoia-Montale). The characterization of the main Saharan dust outbreaks affecting the Tuscany Region during the same period, has been conducted using the SPARTA model chain [1], developed by LaMMA Consortium, as designated by Tuscany Regional Government. SPARTA is based on the meteorological model WRF-ARW and on the chemical model CAMx, using CHIMERE boundary conditions. This modelling system is able to provide a three-dimensional description of the dynamic evolution of the dust episode. In such a way, it is possible to recognize, in a more efficient way with respect to using the back-trajectories or satellite images, the episodes involving the lower part of the atmosphere, near the soil, contributing to the increase of PM10 concentration. The joined use of numerical model and in-situ measurements provides a complete characterization of Saharan dust outbreaks, from meteorological, dynamical and quantification point of view. The comparison between simulations and measurements, during the studied period, reveals a good agreement, properly detecting high concentration episodes, both on hourly and daily base.