The complex of refining and chemical companies is called Chemical Valley and located south of downtown Sarnia . The city have the highest level of particulates air pollution of any Canadian city because of its reliance on the petrochemical industry . About 60 percent of the particulate matter , however , come from the neighboring United States . Lake Huron is cooler than the air in summer and warmer than the air in winter ; therefore , it moderate Sarnia 's humid continental climate , which make temperature extremes of hot and cold very rare . In the winter , Sarnia experiences lake @-@ effect snow because Arctic air blow across the warmer waters of Lake Huron and condense to form snow squalls once over land .