Mediterranean dust outbreaks: meteorological patterns and weather types

Long range transport of desert dust may be responsible of high PM10 concentration events frequently recorded over wide areas in remote regions with respect to the dust origin sites. Over the Mediterranean basin several of such events are recorded each year, that may contribute to the exceedance of legal limit values for PM10 concentration. For this reason the quantitative estimation of the desert dust episodes is very relevant. Such events are the result of a sequence of dynamical mechanisms, beginning in desertic areas where uplift mechanisms raise from the surface relevant amounts of dust and lift them high in the troposphere. These are followed by a long range transport due the strong winds frequently present at that altitude, and terminate over remote regions with the onset of dust deposition. As a result a sound study of such events requires the suitable combination of synoptic modelling resources, for the high altitude long range transport, and detailed models to characterize the peculiar dynamics in the deposition areas. Observed air quality data can be used to complete the analysis and confirm numerical modelling results. In the present study, several dust outbreak events are picked out from a five years (2018-2022) dataset of dust concentration estimates from the large scale CHIMERE model, provided by PrevAir. The study is focussed on the area of Central Italy. The availability of observed PM10 data from two background measuring stations of Tuscany Region Air Quality monitoring network allowed to check and confirm the real occurrence of the dust outbreaks. Moreover the availability at Consorzio LaMMA of a recently implemented Weather Types classification has been exploited to relate the studied episodes with the relative meteorological patterns both at the synoptic and at the local level. As from the widespread evidence in literature, most of the dust outbreaks in the Mediteranean basin have their sources in the Sahara Desert area, but a minority set of these events originates in remote areas farther east from Europe. This study has been performed also in the perspective of an operational application, for implementing a dust outbreak warning system, based on the real-time recognisance of each meteorological configuration and its eventual tracing to one of the Weather Types identified as strongly correlate with relevant dust transport. A correct implementation of such an operational warning system could require an adhoc specific Weather Types classification, that will be the subject of further developments this study.