Eco gas mixtures for the MRPC cosmic ray telescopes of the EEE project.

The Extreme Energy Events (EEE) experiment is designed to detect and study high-energy cosmic rays. The whole EEE network is composed of 61 gas filled muon telescopes based on Multigap Resistive Plate Chambers (MRPC). The use of a mixture with lower Global Warming Potential (GWP) is essential to abate Greenhouse Gas (GHG) emissions, in accordance with the project of ecological transition. After studying different eco-friendly gas mixtures suitable for the EEE detectors, an increasing number of detectors of the EEE array is presently being fluxed with a new ecological mixture made of $C_{3}H_{2}F_{4}$ with the addition of He or $CO_{2}$ which replaces the standard gas mixture (98% $C_{2}H_{2}F_{4}$ - 2% $SF_{6}$) used so far. Tests on performance and long-term data acquisition are ongoing on several EEE telescopes.