The recently resigned US Environmental Protection Agency Administrator, Scott Pruitt managed to fire a parting shot on his last day in office by cementing a  massive loophole for the dirtiest and most polluting trucks in US roads and allowed manufacturers to make even more glider kits.

It was Pruitt’s final knock to clean air after President Trump asked him resign on Thursday last week as the torrent of scandal that engulfed his administration finally came to a conclusion.

“Pruitt didn’t want to leave his post and was described as being devastated that he had to resign … ,” according to  Bloomberg reporter Jennifer Dlouhy.

Andrew Wheeler, a former lobbyist for industries including coal, will take Pruitt’s role as the as acting director of  the US EPA.

Pruitt’s last policy decision benefits a small slice of the truck industry, including one large dealer in that hosted a campaign event for President Donald Trump during his election process.

The loophole, which the Obama administration took steps to close, involves glider kits. Gliders are brand new trucks sold without a driveline including the  engine or transmission.

This type of truck was created so that  truck dealers could couldsell trucks powered by salvage parts from older trucks or parts from those damaged in accidents that do not have what they believe to be complex and expensive pollution equipment.

Older engines don’t use technologies such as SCR (selective catalytic reduction) to reduce NOx emissions. Some truck buyers aren’t fans of the these pollution control systems citing added cost, complexity and reduced fuel economy.

As a result a cottage industry quickly sprang up to take advantage of a loophole that enabled these ‘Glider trucks’ to use older ‘dirty’ powertrains and to pitch their virtues to buyers.

“This process creates a reliable, more fuel efficient truck that requires less maintenance, yields less downtime and has the safety features and amenities owners have come to expect in trucks on the road today,” according to the largest glider truck manufacturer in the United States, Fitzgerald Glider Kits.

Glider kit truck production has surged from 1,000 trucks in 2010 to more than 10,000 in 2015 and is on track to increase further.

However the EPA’s tests show that new glider trucks can emit upward of 55 times the amount of pollution that trucks using current generation pollution controls do.

Though they make up just a tiny fraction of the overall US truck fleet, the EPA estimated that if current trends hold, gliders would account for half of all nitrogen oxide pollution from trucks by 2030.

Community health groups in the US  including the American Lung Assoiciation describe the glider trucks as “super polluting.”

Under the Obama administration, the EPA moved to throttle the loophole and limit the number of glider trucks produced each year to just 300 and estimated that the rule’s requirement that gliders use modern engines by this year 2018, would have prevented between 350 and 1,600 premature deaths over the lifetime of the vehicles.

However left unchecked, refurbished trucks would emit more per year than all vehicles affected by the Volkswagen ‘Diesel-Gate’ emissions-cheating scandal would have emitted by 2025 according to an analysis by the nonprofit Union of Concerned Scientists.

The cap was supposed to take effect this year.

“Our goose was cooked until President Trump and Pruitt came to town,” wrote Tommy Fitzgerald Sr., CEO of Fitzgerald Glider Kits.

Fitzgerald met with Donald Trump when he was campaigning for president in 2016. Pruitt subsequently met with Fitzgerald after taking office.

Pruitt’s EPA soon began working to undo the Obama-era policy.

To justify keeping the loophole open, the EPA cited a study by Tennessee Tech University which happened  to be funded by Fitzgerald.

The study showed that the pollution from glider trucks is on par with that from completely new trucks.

The university has since disavowed the study with the interim dean of Tennessee Tech’s engineering department Darrell Hoy calling the key finding a “farfetched, scientifically implausible claim.” He also noted in a memo that raising the alarm about the study could be “professional suicide” since Fitzgerald funds some facilities at the school. The university is now conducting an investigation.

However shady science was not enough to stop Pruitt. The EPA announced last Friday that it would not enforce the 300-truck cap through to the end of 2019.

“The Agency is exercising its enforcement discretion in 2018 and 2019,” Molly Block, an agency spokeswoman said in a statement last Friday, meaning that it is notifying glider manufacturers that even though the limit legally remains in place, the companies can effectively ignore it.

The statement said the agency is also considering formally delaying the 300-unit cap until December 2019 — by which point it hopes to have permanently repealed the cap.

That means the most-polluting trucks in America may see a resurgence and Pruitt’s toxic legacy will endure at least for now.