© Stephen Giardina / AlamyAvoid the green ones.
When those fireworks light up the sky on New Year's Eve, be careful not to breathe in too much smoke. A study of the fallout from a New Year display in Austria shows for the first time that the fireworks can aggravate respiratory conditions like asthma because they shoot out harmful aerosols.

Georg Steinhauser and his colleagues at Vienna University of Technology analysed fallen snow before and after a display in the village of Saalbach. Fireworks often contain metal salts to give them colour, such as barium for green flashes and strontium for red. The researchers wanted to find out whether any traces remained, clinging to snowflakes. If they did, it would mean the particles were present in the smoke from the fireworks and could be breathed in by spectators.

"We found huge amounts of barium in the snow," says Steinhauser (Atmospheric Environment, DOI: link). Concentrations were typically 500 times higher than in snow samples taken from the same sites before the display. Barium poisoning is known to constrict the airways, so inhaling it could aggravate asthma symptoms, says Steinhauser.

Fireworks have been linked to breathing difficulties before. A study during the Indian Diwali festival, of which firecrackers are a key part, showed that asthma cases rose by 12 per cent, and some spectators without asthma even had attacks of bronchitis.

The team are now developing fireworks that are free of both barium and perchlorate oxidant, which supplies the oxygen for the pyrotechnic combustion. Perchlorate can contaminate water supplies, impair thyroid function and harm fetuses.

In the meantime, Steinhauser says people can still watch displays - as long as they try not to inhale.