BEIJING -- A new study published in the scientific journal Building and Environment reveals a persistent and evolving threat to indoor air quality known as "thirdhand smoke."

While the risks of secondhand smoke are well understood, this study, led by researchers from the Institute of Atmospheric Physics (IAP) at the Chinese Academy of Sciences, provides the first real-time analysis of how thirdhand smoke lingers and chemically transforms in our homes long after active smoking has ceased.

Thirdhand smoke is the toxic residue from tobacco smoke that adheres to surfaces such as walls, furniture, carpets and curtains. Unlike secondhand smoke, which is inhaled directly from the air, this contamination can embed itself in indoor environments.

The study demonstrates that it is not an inert stain but a dynamic source of pollution, continuously re-emitting particles and gases back into the air and undergoing chemical changes over time.

Using advanced air monitoring technology, the team tracked the release of both fine particles and gases from contaminated surfaces. They found a critical difference between the two types of smoke. Secondhand smoke particles disperse relatively quickly, but thirdhand smoke maintains a stable, low-level presence in indoor air for extended periods.

Furthermore, the chemical composition of the emitted particles evolves, becoming increasingly nitrogen-rich over time, suggesting the formation of more harmful compounds.

The research also identifies how household materials influence this prolonged contamination. Porous materials like wool carpets and fabric upholstery act as deep reservoirs, absorbing tobacco-related chemicals and then slowly releasing them back into the air. This process makes thirdhand smoke highly resistant to simple ventilation, allowing contamination to persist for hours or even days after a single smoking event.

This study provides crucial scientific evidence for public health guidelines, underscoring the need to incorporate thirdhand smoke into tobacco control policies and indoor air quality standards, said Sun Yele, a professor at the IAP.

It also establishes new chemical markers to detect this lingering and often overlooked form of contamination, highlighting a significant and enduring challenge in ensuring healthy indoor environments, he added.