Fire and health officials began issuing warnings about wildfire smoke several weeks earlier than normal this year. With almost the entire U.S. West in drought, signs already pointed to a long, dangerous fire season ahead. Smoke is now turning the sky hazy across a large swath of the country as dozens of large fires burn, and a lot of people are wondering what’s in the air they’re breathing. As an environmental toxicologist, I study the effects of wildfire smoke and how they differ from other sources of air pollution. We know that breathing wildfire smoke can be harmful. Less clear is what the worsening wildfire landscape will mean for public health in the future, but research is raising red flags. In parts of the West, wildfire smoke now makes up nearly half the air pollution measured annually. A new study by the California Air Resources Board found another threat: high …