###### Abstract
Despite the aforementioned growing attention on the complexity of aerosol particles, up to now, few works have focused their attention on the DRH and CRH of real ambient atmospheric particles, especially on their deposits onto surfaces such as insulators. In fact, the flashover voltage and the hysteresis cycle of the aerosol on the insulators are both influenced by the chemical composition of the deposit. The water-soluble fraction of aerosol particles (i.e., saline species) dissociates in ions when RH \(>\) DRH, acquiring conductive characteristics and increasing the risk of flashover conditions [17] during their water-soluble state; in this respect, a huge variety of water-soluble chemical compounds can influence the final conductivity on an insulator [25]. It has also been realized that the non-soluble part of the pollution also influences the flashover voltage under contaminated conditions [26]. Insoluble compounds of atmospheric aerosols consist of, for instance, dust, sand, clay, and water-insoluble organic material. Moreover, it has been demonstrated that even non-electrolyte substances can play a part in adverse phenomena connected to electrical contexts; on the one hand, they promote the adhesion of new particulate matter to the insulator surface, and on the other hand, they absorb the water vapor present in the surrounding air, increasing the possibility of humidification of the soluble salts present into the deposition layer. Among the non-electrolyte substances, black carbon (BC) could play a significant role. Black carbon represents carbonaceous particles deriving from combustion processes; it is composed of graphene layers with small contents of heteroatoms, especially oxygen and hydrogen; flame generated BC can be electrically conductive, even if the measured conductivity values (between \(10^{-6}\) and \(10^{-2}\)\(\Omega^{-1}\) cm\({}^{-1}\), depending on the sample density and the fuel used for its production) may be lower than those of pure graphite (between \(10^{-3}\) and \(10^{-1}\)\(\Omega^{-1}\) cm\({}^{-1}\), depending on the sample density). This is caused by the mainly disordered and amorphous structure of BC: in effect, unlike pure graphite that has just hybrid sp\({}^{2}\) C atoms and valence electrons in the remaining \(\pi\)-orbital, flame BC also contains some sp\({}^{3}\) bonds. BC could play a role in electrical bridging processes caused by aerosols deposition as recently demonstrated by [PERSON] et al. [2]. Based on the aforementioned evidence, the International Electrotechnical Commission (IEC) standardized the selection and dimensions of insulators to be used in high-voltage systems with respect to pollution through the IEC/TS 60815-1 [4] document of 2008 (currently under review). This first edition of IEC/TS 60815-1 cancels and replaces IEC/TR 60815 [27], which was issued as a technical report in 1986. Of course, the key to applying this standard properly is establishing the correct site pollution severity (SPS) before insulators are specified, and this document provides a guide for the assessment of SPS. If the site pollution is underestimated, the standard can lead to an under-dimensioning of the insulation design with a risk of frequent flashovers. It is important to highlight that there are many guides to help to assess the site pollution severity of any service environment even if they are not standardized solutions in the IEC. Such not standardized procedures have been used in countries such as Iran (by the Niroo Research Institute) [28] and China (by the State Grid and Southern China Power Grid) [29]. Another method of insulator pollution characterization [26] consists of the evaluation of the soluble deposit density through the evaluation of the equivalent salt deposit density (ESDD) and non-soluble deposit density (NSDD) [11]. Assessing electrically conductive deposits forms a fundamental part of these studies, and the selection of leakage distance based on measuring equivalent salt deposit density (ESDD) is well established.