The hot and humid weather prompted Environment Canada to issue a special air quality statement for parts of southwestern Ontario on the weekend.
The weather agency issued the alert on Sunday morning for Windsor-Essex, Chatham-Kent, London-Middlesex, as well as Oxford and Elgin counties.
The advisory was lifted late Sunday night.
Higher levels of air pollution were expected throughout the day Sunday and into Monday.
The national weather agency said the hot and sunny conditions were expected to cause deteriorating air quality and increased levels of ground ozone.
People with lung diseases, heart or breathing problems, diabetes, children and seniors are especially at risk and may experience more serious impacts.
The agency suggests that anyone experiencing symptoms like coughing, throat irritation, shortness of breath or headaches, consider reducing or rescheduling strenuous outdoor activities until the air quality statement is lifted.
