Wildfires have taken over from industry as a major source of a group of cancer-causing chemical toxins in the air, Environment Canada says. The first national assessment of polycyclic aromatic compounds in more than 25 years has found that air has improved around aluminum and steel plants. But wildfires and vehicles have stepped in to keep average concentrations at about the same level that they were in the 1990s, says federal researcher Elisabeth Galarneau. … “The largest (remaining) source by far is the natural emissions from forest fires,” she says. The levels are still high enough in many places across the country to exceed health guidelines …Research has found that climate change contributes to bigger, hotter fires by drying out forests and extending the fire season. Other increased sources of the chemicals are increased vehicle emissions as well as residential wood-burning. The contributions of those sources vary widely from place to place.