By the time it reaches the East Coast, a California smoke plume will have changed in a number of ways: Because it’s spent so much time aloft, the bigger particles have fallen out, but new particles will have formed. And because the cloud has spawned ozone, “it can be extremely impactful if you already have some health condition, let’s say asthma,” says Tarik Benmarhnia, a climate change epidemiologist at the UC San Diego’s Scripps institution of Oceanography and School of Medicine.
The solid stuff in wildfire smoke may also contain nasties. “Some particulate matter has more heavy metals than others,” says Mary Prunicki, director of air pollution and health research at Stanford University’s Sean N. Parker Center for Allergy Research. “Lead for example, or cadmium. There’s also other types of cancer-causing toxins. There’s things like PAHs—polyaromatic hydrocarbons,” which are found in fossil fuels. Keep in mind that when a wildfire