With almost a year’s worth of diesel emissions tests under their belts, Weber-Morgan health officials say they’re surprised by the results.
As of November, 18.8 percent of diesel vehicles inspected as part of new registration requirements have failed their emissions tests. That’s nearly one out of every five of the 10,038 vehicles tested since the program began in January.
“We were kind of thinking it would be in the 10 percent (failure) ballpark when running the numbers and looking at other counties,” said Scott Braeden, air quality program manager for the Weber-Morgan Health Department. “I think it justifies the hard work we all put into implementing the program.”
A total of 1,890 diesel vehicles failed their emissions tests, the health department reported.
Braeden said he also was surprised that 736 — just over 7 percent — of the failures were due to deliberate tampering.
Truck owners typically tamper with emissions to alter performance and to “roll coal,” blowing black clouds of smoke. Deleting or disabling emissions controls is a violation of the federal Clean Air Act.
“Those are most likely the gross polluters out there driving around without emissions controls,” Braeden said. “If we can get those in compliance, it will make a noticeable impact on our air quality.”
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By comparison, the emissions test failure rate for gas-powered vehicles in the county is 4.6 percent for 1996 and newer models, and 10.2 percent for 1995 and older models.
According to the Utah Tax Commission, 166,438 vehicles registered in Weber County are hybrid, flexible or gasoline fueled, while 12,799 are diesel-powered.
Diesel and gas models from 2012, 2014 or 2016 won’t have emissions inspections in 2017 but will have mandatory tests in 2018.
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Implementing a diesel emissions program was a contentious issue for the Weber-Morgan Board of Health through much of 2015 and most of 2016. The idea was first floated by the board’s Air Quality Advisory Committee, which the board dissolved last spring.
Health board members questioned the science presented about diesel emissions and whether improvements to air quality would outweigh the burden of a testing program on diesel vehicle owners.
“Our premise was correct,” said Iain Hueton, a member of the former air quality committee who pushed for a diesel emissions program. “All the more reason we should be doubling down on it, in the sense that emissions per (failed) diesel vehicles are so much higher … than for a gas vehicle.”
According to information presented to the board by the Division of Air Quality last year, Weber County’s diesels release 44 percent of on-road NOx emissions despite only comprising 13 percent of the fleet.
Those NOx compounds form particulate pollution and contribute to inversion smog. Unlike gas-powered vehicles, diesels also directly emit particulate pollution.
While DAQ officials can’t model or predict the exact air quality impacts of bringing Weber County’s failing diesels into compliance, Joe Thomas with the Mobile Sources and Transportation Program said emissions tests do make a difference.
“It takes a lot of these small controls for the pendulum to start moving,” he said. “One of the benefits of an emissions inspection program, a regulated program, is it changes peoples’ behavior.”
They might deter people from tampering with emissions controls or convince drivers to fix their cars with the “check engine” light comes on, he said.
“Diesel owners in Weber County are going to be much more in tune with clean air requirements,” Thomas said.
Looking forward, Weber-Morgan health officials are looking at other small steps to drive down air pollution.
This spring, they’ll be partnering with Davis County’s health department and Weber State University on a program that swaps gas-powered lawnmowers for electric ones. They’re also working with other Wasatch Front counties to create a statewide hotline to report smoking vehicles.
Weber-Morgan Health Department Director Brian Bennion said they’re still mulling emissions from heavy trucks, too, which currently aren’t regulated.
“I think that’s always on the table,” he said. “We know vehicles still (create) 50 percent of emissions. It’s really important they’re maintained, running as clean as they can.”