The air pollution emitted by cigarettes is 10 times greater than diesel car exhaust, suggests a controlled experiment, reported in Tobacco Control.

Environmental tobacco smoke produces fine particulate matter, which is the most dangerous element of air pollution for health. Levels indoors can far exceed those outdoors, because new engine models and lead free fuels have cut the levels of particulate matter emissions from car exhausts, say the authors.

The controlled experiment was carried out in a private garage in a small mountain town in northern Italy. The town enjoys very low levels of particulate matter air pollution

A turbo diesel 2 litre engine was started and left idling for 30 minutes in the garage, with the doors closed, after which the doors were left open for four hours. The car was fuelled with low sulphur fuel.

Three filter cigarettes were then lit up sequentially, and left smouldering for a further 30 minutes. The nicotine and tar content of each cigarette was 1 mg and 11.2 mg, respectively.

A portable analyser took readings every two minutes during the experiments.

Combined particulate levels in the first hour after the engine had been started measured 88 ug/m3. Those recorded in the first hour after the cigarettes had been lit measured 830 ug/m3: 10 times greater.

The diesel engine exhaust doubled the particulate matter levels found outdoors at its peak; the environmental tobacco smoke particulate matter reached levels 15 times those measured outdoors.