Residents may notice darker than normal emissions from Imperial Oil.
The company said it is in the process of restarting units at the Sarnia site following planned maintenance activity that began in early September.
In a Community Notification alert, Imperial said it does not expect emissions from the refinery to exceed government guidelines, and the Ministry of Environment, Conservation and Parks has been notified.
"Testing during similar past events indicates emissions have not exceeded health related air quality standards during those occurrences," said Public and Government Affairs Manager Kristina Zimmer in the alert. "Personnel are working to return the site to normal operations."
As units begin coming back online this week and next week, there will also be periods of intermittent elevated flaring and noise.
The scheduled maintenance 2023 turnaround allowed for repairs and upgrades to equipment to keep the site running safely and efficiently.
An additional 1,200 contractors were on site during the shutdown.
