On the Synergy between Elemental Carbon and Inorganic Ions in the Determination of the Electrical Conductance Properties of Deposited Aerosols: Implications for Energy Applications

Abstract

The role of the elemental carbon (EC), in synergy with hygroscopic ionic species, was investigated to study the formation of electrical bridging phenomena once the aerosol deliquescence is achieved. Ambient aerosol samples were collected on hydrophobic surfaces in urban and rural sites in Northern Italy; their conductance was measured in an Aerosol Exposure Chamber (AEC) while varying the relative humidity. An electric signal was detected on 64% of the collected samples with conductance values (11.20 ± 7.43 μS) above the failure threshold (1 μS) of printed circuit boards. The ionic content was higher for non-electrically conductive samples (43.7 ± 5.6%) than for electrically conductive ones (37.1 ± 5.6%). Conversely, EC was two times higher for electrically conductive samples (26.4 ± 4.1 μg cm−2; 8.4 ± 1.7%) than for non-electrical ones (12.0 ± 4.1 μg cm−2; 5.2 ± 1.9%) suggesting that the synergy between the ionic and carbonaceous fractions is necessary to promote a bridging phenomenon. Synthetic aerosols (EC only, saline only, mixed saline and EC) were generated in laboratory and their conductance was measured in the AEC to verify the ambient results. Only in case of a contemporary presence of both EC and ionic components the bridging phenomenon occurred in keeping with the theoretical deliquescence values of each salt (R2 = 0.996).

On the Chemical Composition and Hygroscopicity of Aerosols Deposited on the Insulators of Italian Power Lines

“…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 π-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 Ferrero et al [2].…”

“…Transmission lines are used for the transmission of electric power and their continuous operation is essential for the reliability of the power grid. Electrical insulators are one of the most important elements of the electric power grid because of their role in the isolation of conductors from the tower and mechanical support for the electric line, affecting the reliability of transmission and distribution lines, which is clearly of huge importance in modern society [1,2]. Insulator performance, at any given time, is commonly affected by several factors: material, shape, degradation, and the properties of atmospheric pollution [3,4] deposited.…”

“…All the aforementioned processes affect both the amount and the chemical characteristics of the deposit onto an insulator; as a result, any deposit can be composed of internal mixing of soluble and non-soluble compounds (water-soluble ions, organic matter, black carbon, metals, dust, and crustal material) [2,9] caused by natural (e.g., sea spray and dust sources) or anthropogenic origins [11].…”

“…This phenomenon happens when soluble pollution species dissociate in ions, acquiring conductive characteristics. The consequence is a disruptive discharge over the insulator surface [2,17,18], which finally turns into line outages with possible not negligible financial consequences for the grid operator.…”

“…Conversely, a reduction in RH (starting from a value above DRH) leads to evaporation until the CRH is reached, promoting aerosol crystallization and bringing the aerosol to a dry state again. The aforementioned cycle is known as the hysteresis cycle of the aerosol [2], and a direct consequence of it is that in order to understand if an aerosol particle is "wet" or "dry" and the effect on the insulators, it is fundamentally important to know the RH history together with the DRH and CRH values.…”