Hamilton has dropped to fourth worst air in the province, according to ratings from Ontario's Ministry of the Environment.

Hamilton’s air quality was the worst in Ontario Monday morning but by noon was better than Parry Sound, Dorset and west Toronto.

The three Hamilton areas where air quality is measured -- downtown, the mountain and the west end — were not improving over earlier in the day but Parry Sound, Dorset and west Toronto were getting worse.

Air quality is expected to improve later today with a forecast for rain.

"The rain will scrub and cool the air," said Dave Phillips, Environment Canada’s senior climatologist.

"And the rest of the week is looking pretty good."

A smog advisory has been in effect since Saturday afternoon.

Smog advisories are issued when air quality is poor because of ground-level ozone and particulate matter.

Phillips told CBC Hamilton that wind is pushing chemicals from places like the Ohio Valley in the United States in Hamilton’s direction.

With lots of sun, "we have the right ingredients to cook the chemicals," Phillips said.

Local factors, like being close to a highway, contribute too, said Phillips. On Monday morning, the wind in Hamilton was only 6 km per hour, no where near strong enough to blow any pollutants out of the city.

"This adds to the poor air quality," he said.

Phillips said there have been seven smog days in southern Ontario 2012. Hamilton sees an average of five smog days a year, he said.

Brenda Ferguson, director of corporate affairs and communications for Today's Family Early Learning and Child Care, is trying to keep her students indoors today. "It's unfortunate and it's something that will probably be prevalent over the summer," she said.

Ian Wright, Hamilton EMS commander, is expecting more calls because of the smog and heat.

"We do typically see calls related to respiratory problems increase," he said.

Wright recommends staying indoors or planning a stop inside during your trips.

The good news is Hamilton will see some temporary releif from Monday's 30 degree heat and smog. Phillips said a thunderstorm is expected in Hamilton Monday night.

"The rain will scrub and cool the air," he said. "And the rest of the week is looking pretty good."