Paris has taken a huge step forward in achieving its goal of cleaning up its entire bus fleet by 2025 in a grand effort to curb air pollution. The current bus fleet is mostly made up of old diesel buses, but that’ll change soon after Paris’ public transport operator announced it has ordered up to 800 new electric buses for the capital city. The price tag for 800 buses? Up to 400 million euros ($450 million), making it the biggest bus purchase of its kind in Europe. Even with this latest order, however, it will be a major task to transform the city’s full fleet of 4,700 buses into zero-emission vehicles. Something interesting to take away from the size of this order is the perspective it gives to what’s going on across the globe. A recent order of just 20 electric buses will give the University of Georgia one of the largest electric bus fleets in the U.S. On the other side of the ledger, Paris’ 800 e-bus order pales in comparison to the 16,000+ strong fully electric bus fleet of Shenzhen, China.