TORONTO -- Environment Canada is expanding its smog advisories to cover much of southern Ontario as the long weekend looks to be a steamy one.
   The weather agency says that with high humidity added in, the region from Sarnia to Ottawa will bake in temperatures hovering near 40 C.
   The agency says the hot and sunny conditions, along with southerly winds, are causing elevated smog levels across southern and parts of eastern and central Ontario.
   The smog advisory now covers from Windsor in the south to Kingston in the eastern region, and from the Niagara area to Grey-Bruce.
   Temperatures are expected to drop Sunday as cold winds blow in from the north.
   Smog -- a complex mixture of air pollutants sometimes visible as a brownish-yellow haze -- is harmful to the lungs and heart and can reduce lung function even in healthy people.