In the three-year period from 2015 to 2017, the past knowledge and modeling experience of RSE was applied in the studies of surface contamination of high voltage overhead power line insulators and allowed for the preliminary update of the insulators maximum pollution severity map. The preliminary map, which replaced the previous one by ENEL, provided the necessary indications to start a two-year (2016-2018) measurement campaign carried out in collaboration with Terna aimed at the characterization of the pollution levels to which insulators are subjected in the Italian territory. On the basis of this map, 206 sampling sites were identified to install an equal number of supports with sets of ‘cap and pin’ insulators made of tempered glass with normal profile and 5 ‘cap and pin’ tempered glass insulator sets with anti-salt profile, for a total of 211 sets of sample insulators.

The activity covered by this report aimed to analyze the measurements taken in collaboration with Terna in order to validate and update the preliminary mapping of the severity levels of the Italian territory produced in 2015 and subsequently obtain a stable version of a precise mapping based on the observed data. In particular, ESDD and NSDD measurements of the samples taken in eight measurement campaigns were analyzed, both as they were and reprocessed with an algorithm for the reconstruction of the maximum levels of deposition starting from measured ESDD and NSDD values and based on different precipitation thresholds. This previously developed algorithm was further updated in this year of activity. The update mainly concerned the change of precipitation thresholds and the selection of the meteorological station necessary for its application.

The results showed that the regions most subject to salt pollution are Sardinia, especially its western coast, the south-west area of Sicily, the southern coast of Calabria and the eastern coast of Puglia.

The most evident finding of the application of the algorithm was the increase in the ESDD and NSDD values after the precipitation thresholds were changed. The algorithm therefore allowed us to redefine the measurements on the sample insulators in order to link them with the maximum contamination values of the Italian territory, thus making them directly comparable with the preliminary mapping.

The comparisons show a certain alignment between the two distributions in the northern areas and in Sicily. In both cases, the most problematic areas are in Sardinia, where the pollution severity degree is ‘very heavy’, in southern Puglia and along the Campania and Calabria coasts. A heavy pollution is even observed in the Caserta hinterland due to the overlapping of urban and marine pollutants.

However, the comparisons highlight how in the remaining areas of Italy the 2015 mapping tends to show lower values than those reconstructed by the algorithm starting from the observed data.

The activity also involved a preliminary experimental phase relating to the speciation of the ionic fraction contained in 65 samples of atmospheric particulate matter deposited on the insulators. The experimental activity was part of a collaborative project with the Department of Environmental and Earth Sciences (DISAT) of the Università degli Studi di Milano Bicocca (UNIMIB). The comparison highlights an excellent linear correlation between the chemical analysis of inorganic ions and the electrical conductivity measurements with clear territorial differentiations. The highest values of the equivalent concentrations are associated with insular and coastal regions. Knowledge of the chemical composition of the deposit will allow for a deeper understanding of the phenomenon, with particular reference to the characterization of the types of sources that cause the contaminant deposit.