Performance of the new eco-friendly gas mixtures for the MRPC muon telescopes of the EEE Project.

The Extreme Energy Events Project is a large network of 60 telescopes, devoted to study the muon component in the Extensive Air Showers. The EEE telescopes are distributed over Italy, mainly located in high-school buildings where teachers and students are involved in an educational and scientific program. Each telescope consists of three Multi-gap Resistive Plate Chambers which operate in avalanche mode by using so far, a gas mixture containing $C_{2}H_{2}F_{4}$ and $SF_{6}$ . These are fluorinated gases with a high Global Warming Potential, and first studies for new suistanable gas mixtures were performed already in 2018. At present, in compliance to the regulation of European Union and in line with its educational goals, the EEE Collaboration decided to completely phase out these greenhouse gases, starting a R&D campaign to test eco-friendly mixtures. Taking into account the binary gas system and the bias voltage provided by the MRPC power supply, the most promising mixtures have proved to be HFO-based with $CO_{2}$ and He. Some EEE telescopes have been taking data for months with the new mixtures to test both performance and stability. The most recent results of the campaign will be presented.