Weather advisories warning of poor air quality and dense fog in the Edmonton region Monday are no longer in effect.

A special air-quality statement due to high pollution levels was issued around 4 a.m. Monday for Edmonton, St. Albert, Fort Saskatchewan, Vegreville, Redwater and Smoky Lake.

As of 10:30 a.m., the air-quality advisory had been lifted.

Environment Canada said "stagnant winter weather" caused an atmospheric inversion, trapping pollution and contributing to a dense fog during the morning commute.

An atmospheric inversion happens when the air becomes warmer as the altitude increases and can trap pollution below.

Imperial Oil said the Strathcona Refinery had greater than normal levels of flaring on Sunday due to an operational issue with one of the refinery units. However, the company said the incident had no impact on air quality in the Edmonton region.

"Taking it offline to repair resulted in greater than normal flaring and smoke throughout the day [Sunday] into the early evening, which is a standard safety procedure," said Keri Scobie, a spokesperson for Imperial.

The issue was resolved around 10:30 p.m. Sunday, the company said.

"We also worked with Alberta Environment [Sunday] and were able to determine that the air quality issues in Edmonton [Sunday] were unrelated to the flaring," the company said in a statement. "Monitoring data indicated that the refinery issue did not impact air quality levels."

Meanwhile on Monday, an extensive area of fog developed around Edmonton and Lloydminster and drivers were urged to use caution during the morning commute. The fog advisory was lifted around 10 a.m.