Tobacco smoke is bad for the environment, according to Italian experimenters who have compared the adverse environmental effects of cigarette smoke and diesel exhaust. The rise of environmental tobacco smoke (ETS) as the largest source of polluting particulates is a powerful argument against smoking to pitch at environmentally aware adolescents, they say.

Regular checks in a closed environment showed that particulates of 10 μm diameter (PM₁₀) were significantly more abundant from slowly burning cigarettes than from an idling ecodiesel engine (mean (SD) 343 (192) v 44 (9) μg/m³), after correcting for background amounts. This was also true for smaller particulates—PM_2.5 and PM₁. Peak PM₁₀ concentration for cigarettes was fifteen times the ambient outdoor concentration whereas the peak for the engine was only about twice as high. PM₁₀ concentration for ETS persisted at >300 μg/m³ up to an hour after the experiment started, way above the EU outdoor limit (40 μg/m³).

The tests were performed in a 60 m³ garage in a mountain region with high air quality. Particulate concentrations were measured before each test, and after either three consecutive cigarettes had been left burning for 30 minutes or a 2.0 l, 2002 model eco turbo diesel engine running on low sulphur fuel had been left idling for the same time.

The public is worried about particulates in air and increased risk of lung disease. ETS and fossil fuel emissions have similar compositions, but there is concern that air pollution indoors is much higher than that outdoors because of success in cutting vehicle emissions.