The Ontario government has approved a rail link between Union Station and Pearson International airport.

The plan, worth $875 million is meant to ease congestion for the five million people who go to the airport every year.

But 18 conditions stipulated by the Ministry of the Environment could set the plan back. The trains must use clean technology that is still in development.

The technology would reduce tiny particles in pollution -- which can be harmful to health -- by 90 per cent versus regular engines using low-sulphur fuel. The technology is known as the Tier 4 emissions standard, which is set by the U.S. Environmental Protection Agency.

Environment Minister John Gerretsen said he believes the technology should be complete by 2015.

"It's all about getting cars off the road and getting people into transit," he told reporters on Tuesday.

Some opponents of the rail link are demanding an electrified train service as they fear the effects of diesel emissions on the air quality of their neighbourhoods if hundreds of trains per day are passing through the Georgetown corridor.

Gerretsen said electrification is too expensive, but said he's told Metrolinx about its as-yet-completed electrification study, "Whatever comes out of that electrification study, I expect them to implement it -- particularly within this particular corridor."

With files from The Canadian Press