Not only black lungs: Carpets retain a stubborn grip on smoke pollutants

Science and Health

It isn’t only their smokers’ lungs that get filthy from tar, nicotine, and about 70 other toxins known to cause cancer. In rooms where smoking has taken place regularly, tobacco’s imprint lingers on indoor surfaces – even long after regular smoking has stopped. 

The leftover residues, known as “third-hand smoke,” can be a long-term source of indoor pollutants. New research from a team led by the Lawrence Berkeley National Laboratory (Berkeley Lab) of the US Department of Energy (DOE) focuses on carpets and rugs as an especially potent and hard-to-clean reservoir of tobacco contaminants.

When third-hand smoke settles into surfaces, it doesn’t stay there. Chemicals re-enter the air, sometimes transforming into new types of contaminants. Carpeting is a major sink for third-hand smoke. In this study, the researchers evaluated the effects of ozonation, a common cleaning method, on smoke-exposed carpets. 

The study, just published in the journal Environmental Science and Technology under the title Remediation of Thirdhand Tobacco Smoke with Ozone: Probing Deep Reservoirs in Carpets, examined smoke-contaminated aged carpets that had been retrieved from homes in the San Diego area, as well as new carpet exposed to fresh smoke in the lab.

What is the role of ozonation? 

The team found that while ozonation partially removed a group of compounds named polycyclic aromatic hydrocarbons from both aged and fresh carpet samples, it was quite ineffective at removing deeply embedded nicotine because the fibers and other chemical constituents in the material serve as a chemical shield.

They evaluated the samples in a room-size environmental chamber, with additional tests carried out at the Molecular Foundry, a DOE Office of Science user facility.

The research highlights carpets as a common and important reservoir and source of contaminants from thirdhand smoke. “Because it doesn’t reach deeply into materials, ozone has a limited ability to ‘clean’ permanently,” said Berkeley Lab researcher Dr. Xiaochen Tang, the study’s lead author. “In the case of carpet, the best solution is to stop smoking and replace it with a new one.”

Ozone generators release ozone gas so that it can react with harmful compounds and remove them from the air and from surfaces. But the generator also creates a burst of contaminants when running, the previous study showed, pointing to the need for ventilation and a waiting period before people can re-enter a space after ozonation. 

Berkeley Lab senior scientist and engineer Hugo Destaillats noted that ozonation has been used as a remediation method for years because it is good at removing odors – but that can create a false sense of efficacy. “Ozone generators are also used to remediate fire damage and mold, but they have limitations, as we saw in this study,” he explained.

“The lack of a detectable smell doesn’t mean that all of the contaminants we are concerned about have been eliminated.” The steps in the research will evaluate the role of other indoor reservoirs such as drywall and upholstery.