As wildfire smoke continued to cloak elements of the United States and Canada, some residents reported that they smelled a burning campfire. But different residents stated they smelled burning plastic and chemical compounds outdoors. What was inflicting the unusual scent?

Kang Sun, an assistant professor on the University at Buffalo learning the chemistry and physics of the Earth’s environment, stated that when timber, branches and leaves — also referred to as biomass — are burned in wildfires, they emit gases referred to as risky natural compounds.

And when these compounds are first emitted, some react rapidly and create that recognizable smoke scent sometimes related to a campfire.

But some compounds are steady sufficient to journey 1000’s of miles downwind to Michigan and upstate New York from the fires in Canada, Dr. Sun stated. Other molecular compounds are additionally shaped as byproducts of earlier chemical reactions.

Some of the molecules is likely to be inflicting the chemical, plastic scent that many individuals have reported just lately. When he opened a window in Buffalo on Wednesday himself, Dr. Sun stated, he additionally smelled the acrid, burning scent of plastics and synthetics, relatively than a campfire scent.

These longer-surviving compounds, corresponding to benzene and formaldehyde, are “certainly a health concern,” stated Michael Jerrett, a professor of environmental well being science on the U.C.L.A. Fielding School of Public Health.

Both benzene and formaldehyde are Group 1 carcinogens, which implies a panel of consultants on the W.H.O. has discovered enough proof that these compounds trigger most cancers. This might point out the persistent wildfire smoke might doubtlessly get extra poisonous as time goes on, Dr. Jerrett stated, including that there’s restricted analysis on the subject.

In the quick time period, the perfect factor individuals can do to remain protected is to stay inside as a lot as attainable, Dr. Jerrett stated. The compounds might not pose a well being concern until the smoke persists over an extended time frame, he stated.