Uber drivers in London will be required to use either hybrid or fully electric vehicles by 2020; today, just under half of London Uber drivers have cars that fit the bill. By 2025, 100% of the company’s cars in London must be fully electric or plug-in hybrids, which generally don’t switch to gasoline until the battery dies after about 40 miles, according to The Guardian. The city’s customers will pay a surcharge to help cover the cost.

Uber will give financial assistance of up to 5,000 pounds (about $6,600) to its 40,000 licensed drivers in London to switch to a hybrid or fully electric car. The car-hailing company will fund the financial assistance in part, but is also adding a 35p surcharge on all London trips beginning in October.

The company says it is focusing first on London because the city has a particularly severe problem with pollution and toxic gases from vehicles.

Uber is also hoping to lure more customers from London’s population who own older cars. Drivers of cars built before 2005 will be given a voucher of 1,500 pounds (nearly $2,000) to use Uber instead of hopping into their own, dirtier vehicles

A 2015 study conducted by researchers of Kings College London found that dirty air in the city causes nearly 9,500 deaths a year.