These ultrafine particles also become major components of thirdhand smoke - the residue from tobacco smoke that persists long after a cigarette or cigar has been extinguished.

Another reason for including asthma on the list of potential health risks posed by secondhand tobacco smoke, especially for non-smokers, has been uncovered. Furthermore, the practice of using ozone to remove the smell of tobacco smoke from indoor environments, including hotel rooms and the interiors of vehicles, is probably a bad idea.

Mohamad Sleiman, a chemist with the Indoor Environment Department of Berkeley Lab’s Environmental Energy Technologies Division (EETD) who led this research, said: “Our study reveals that nicotine can react with ozone to form secondary organic aerosols that are less than 100 nanometers in diameter and become a source of thirdhand smoke.

“Because of their size and high surface area to volume ratio, ultrafine particles have the capacity to carry and deposit potentially harmful organic chemicals deep into the lower respiratory tract where they promote oxidative stress. It’s been well established by others that the elderly and the very young are at greatest risk.”

Co-authoring this paper with Mr Sleiman were Hugo Destaillats and Lara Gundel, also with EETD’s Indoor Environment Department, and Jared Smith, Chen-Lin Liu, Musahid Ahmed and Kevin Wilson with the Chemical Dynamics Group of Berkeley Lab’s Chemical Sciences Division.

This past February, a study, also spearheaded by Sleiman, Destaillats and Gundel, revealed the potential health hazards posed by thirdhand tobacco smoke which was shown to react with nitrous acid, a common indoor air pollutant, to produce dangerous carcinogens. Until now, however, in terms of forming ultrafine particles, there have been no studies on the reaction of nicotine with ozone.

Released as a vapor by the burning of tobacco, nicotine is a strong and persistent adsorbent onto indoor surfaces that is released back to indoor air for a period of months after smoking ceased. Ozone is a common urban pollutant that infiltrates from outdoor air through ventilation that has been linked to health problems, including asthma and respiratory ailments.

While the findings in this study support recommendations from the California EPA and the Air Resources Board that discourage the use of ozone-generating air purifiers, which among other applications, have been used for the removal of tobacco odors, the Berkeley Lab researchers caution that the levels of both ozone and nicotine in their study were at the high end of typical indoor conditions.

Mr Sleiman said: “In addition, we need to do further investigations to verify that the formation of ultrafine particles occurs under a range of real world conditions. However, given the high levels of nicotine measured indoors when smoking takes place regularly and the significant yield of ultrafine particles formation in our study, our findings suggest new link between asthma and exposure to secondhand and thirdhand smoke.”

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