NEW YORK (CBSNewYork) – What is the mysterious odor that’s lingering at L train stations and where is it coming from?

That’s what MTA officials, transit workers and riders want to know.

“When are we going to get help for this?” said Greenpoint resident Yael Gottlieb.

There have been days of head throbbing, stomach churning fume effects for some riders and MTA workers.

Late Thursday afternoon, the MTA said third party contractor Environmental Planning and Management, Inc. tested air in four Brooklyn sections, and found volatile organic compounds are at 0.0 parts per million, meaning nothing detectable.

WEB EXTRA: Read the environmental report (.pdf)

Try telling that to some regular L train riders smelling it all week, like Craig Grigg.

“They’re saying it’s not harmful, but if it’s an organic smell, I don’t see how it’s not harmful,” Grigg said.

“Many of our members are experiencing exhaustion and sickness due to this condition along with our ridership,” said Lynwood Whichard of Transport Workers Union Local 100.

TWU leaders say more and better testing must be done.

MTA worker Crystal, who works the Bedford Station booth and preferes we not give out her last name, says she’s not satisfied.

“I smelled. I did smell this morning at about 5:30,” she told CBS2’s Dave Carlin. “When the fumes do come in we report it… hopefully they’ll resolve the issue.”

Riders told Carlin the stops where they notice the odor most are Bedford Avenue, Lorimer Street, Graham Avenue and Grand Street. They say once the smell gets inside the train it’s with them for the entirety of the route.

Some people are taking buses and finding other ways to get away from the smelly L.

“I ride a skateboard, so I’ve been doing that… to avoid that situation,” Paris Howard said.

Station agents could be seen wearing masks Wednesday, and riders posted about sore throats and headaches on Twitter. The transportation workers union, Local 100, says at least four workers have been hospitalized this week due to the fumes.

Many say it does not inspire confidence knowing platform workers are limiting their exposure or to see photos of MTA workers wearing masks, but Lenox Hill emergency room doctor Robert Glatter says it makes sense that people do that if they work long shifts with prolonged exposure to any irritating fuel-like smell.

“Have a mask, and that would help to reduce the exposure,” Dr. Glatter said. “Repeated exposure is not a good idea and we need to get to the bottom of this.”

The most maddening part? No one can say for certain yet what the smell actually is.

The MTA has said the smell is coming from non-flammable heating oil, found near the Graham Avenue station in Williamsburg.

“We don’t really totally know what it is, but it appears to be some kind of oil that seeped up through the ground. It’s not clear exactly where it came from,” MTA Chief Safety Officer Patrick Warren said Wednesday. “It is absolutely safe for passengers and our workers to be down there.”

L train service was temporarily suspended Tuesday after commuters started complaining about a smell like oil or gas. The Graham Ave. stop had to be evacuated because of the unsettling smell.

The MTA determined the odor has nothing to do with the ongoing L train project.

The MTA has put heavy-duty fans in place to help circulate air away from the stations and continues to monitor the air quality.

The agency encourages anyone with health concerns to see their doctor.