Why third-hand smoke is dangerous – aerosol toxins easily find their way indoors

Cigarette smoke finds its way indoors in the form of aerosols attached to smokers, which means "non smoking" areas aren't really smoke free. If a person walks through a smoke cloud and enters a room, they are actually carrying it indoors.

Cigarette smoking has been banned in most indoor spaces around the world, including restaurants, offices and schools. This was done to protect non-smokers from the harmful effects of second-hand smoke –smoke inhaled by non-smokers in the vicinity of the smoke cloud. A new study by Drexel University has found that third-hand smoke is real and that chemical residues still find their way into buildings. In sealed off air-conditioned buildings, this could mean cigarette smoke simply finds its way indoors and gets circulated, reports a release by the University.

The study set out to find out just how easily toxic chemicals can spread through a building which is a smoke-free zone. Because of the way these chemicals travel through the air, the study has found that people are exposed to more of the dangerous chemicals than previously thought.

"While many public areas have restriction on smoking, including distance from doorways, non-smoking buildings and even full smoking bans on campus for some universities, these smoking limitations often only serve to protect non-smoking populations from exposure to second-hand smoke," said Michael Waring, PhD, an associate professor in Drexel's College of Engineering, and a co-author of the research.

"This study shows that third-hand smoke, which we are realizing can be harmful to health as with second-hand smoke, is much more difficult to avoid."

The study, funded by the National Science Foundation focused on indoor air quality, notes the report. It found a new pathway of exposure to what they call third-hand smoking.

"Aerosol particles are ubiquitous particles suspended in the air- they come from a variety of sources and are known to be detrimental to health," said Peter DeCarlo atmospheric chemist at Drexel.

"The fact that third-hand smoke can attach to them, like it would to the clothing or furniture of a smoker, means that the potentially toxic chemicals associated with third hand smoke are found in places we wouldn't have expected."

In one of the studies, researchers found that in an empty classroom where smoking was not allowed, they found 29 percent of the entire indoor aerosol mass had third-hand smoke particles. That raised concern about just how much smoke gets carried indoors in a non-ventilated room, say the researchers.

These particles are everywhere and can easily latch on to skin, hair, clothing, so smoke free environments are, in reality, not necessarily completely without the influence of smoke. They can also get concentrated in particles where chemicals are gaseous and exposed acidic, liquid aerosols, notes the release.

"In the summertime warm air with varying amounts of water content is brought into the building, mixed with recirculated air, and conditioned to cooler temperatures," they write. "This process leads to significant uptake of water by aerosol particles. This continuous summertime presence of aerosol water allows third-hand smoke chemicals to partition into the aerosol phase."

As to how exactly the aerosols get transported, the researchers point out to the HVAC systems found in most modern buildings. HVAC systems condition the aerosols to wet or dry states, write the researchers. They also disperse the air throughout the indoor space, in multiple rooms connected to the ducts.

The study was first published in the Journal Science Advances.