A haze permeates the air over Parliament Hill in Ottawa on Monday, along with the smell of smoke. (Emily Chung/CBC)

The air quality in Ottawa has significantly improved after the city spent much of the day covered in a dull haze due to smoke drifting in from forest fires in central and northern Quebec.

The city was under a smog advisory Monday and residents with breathing difficulties and heart conditions were told to avoid strenuous outdoor activities.

Air quality index readings reached levels over 100 in the late morning, according to Ontario's Ministry of the Environment. Any level over 50 is considered "poor" air quality.

But by late afternoon, the level had dipped below 50, which is considered "moderate."

Ottawa Public Health had said it expected air quality to improve later in the day as wind direction changed.

The strong smell of wood smoke in Ottawa Monday morning prompted firefighters to deploy trucks to conduct a search throughout the greater Ottawa area.

However, they received no reports of fires, spokesman Marc Messier said in a statement.

More than 50 forest fires are burning in Quebec, including eight that remain out of control, according to Quebec's public safety agency.

Forest fires in the Trois-Rivières area have been causing similar conditions throughout eastern Ontario and western Quebec including Montreal, Messier added in a statement. Trois-Rivières is about 260 kilometres northeast of Ottawa.

Ontario's Ministry of the Environment also indicated that the easterly flow of polluted air from forest fires in Quebec was the cause of the high smog levels that prompted a smog advisory for several eastern Ontario regions Monday, including:

• Brockville-Leeds and Grenville.
• Ottawa.
• Cornwall-Morrisburg.
• Prescott and Russell.
• Renfrew-Pembroke-Barry's Bay.
• Smiths Falls-Lanark-Sharbot Lake.

Health warnings

Ottawa residents canvassed by CBC News Monday said the smell of smoke in the air was very noticeable and distinctive, but they were surprised to hear it could be coming from so far away.

Ottawa Public Health warned that wood smoke can irritate the lungs, eyes, nose and throat and can cause coughing, wheezing and difficulty breathing. The agency issued a public service announcement advising residents, especially seniors, children and people with breathing difficulties or heart and lung conditions, to avoid strenuous outdoor activities.

Rosa Holmes, a spokeswoman for the Ottawa Lung Association, advised local residents to stay indoors Monday, as carbon monoxide from the smoke could aggravate respiratory problems such as asthma.

"We don't want people to panic," she said, "but if they don't need to be outside, it would be better to be inside with the air conditioners on."