A fuel-like smell that some have likened to turpentine or lighter fluid wafted over Orange County on Thursday evening, August 16.

Police departments, many in the beach cities, received several calls from residents asking where the aroma was coming from.

No one seems to know.

Patrick Chandler, a representative for the South Coast Air Quality Management District, said the agency received calls from residents of Costa Mesa, Huntington Beach, Newport Beach, Anaheim Hills and Orange, saying they “smelled a chemical odor.”

“This isn’t the first time we’ve had a complaint about odors traveling the western side of O.C.,” Chandler said.

AQMD has dispatched inspectors to investigate the source of the odor.

The odor prompted discussions among Orange County residents on social media who voiced concerns and theories:

Offshore drilling to bug spraying.

But Orange County Mosquito and Vector Control representatives said Friday that the chemicals they use are water-based and odorless.

The agency did spray for mosquitoes on Wednesday and Thursday in several Orange County cities after recently detecting that some of them carried West Nile virus.

“(Spraying) has become pretty routine in the areas where we see a lot of mosquitoes,” spokeswoman Mary-Joy Coburn said. “We’ve been doing a lot of spraying during the summer, and there’s been no odor.”

Capt. Chris Coates of the Costa Mesa Fire Department said that agency received hundreds of smell-related calls.

We have received several calls reporting an area chemical smell. Reports are that several cities are experiencing similar conditions. Fire crews responded to investigate and the source is unfounded. We recommend closing windows & doors. — Costa Mesa FD (@CMFD_PIO) August 17, 2018

The city of Huntington Beach also shared that it was aware of the smell. Some agencies advised that residents contact the Air Quality Management District at 1-800-288-7664.

People who experience abnormal medical symptoms should call 911, firefighters said.

We have received many reports of a strong odor traveling through the city. The smell has traveled throughout many OC cities. We have made notifications to the proper authorities for follow up. At this time we do not know where the odor is originating from. — Huntington Beach FD (@HBFD_PIO) August 17, 2018