Could the humble street light be adding to air pollution? Yes it can, says Harald Stark from the University of Colorado at Boulder, US according to a story on the BBC website.

Talking at the American Geophysical Union meeting in San Francisco, Stark explained that artificial lights that shine throughout the night are destroying chemicals in the night sky that help to clean up the pollution caused in the day.

Chemicals such as NO3 radicals help to break down volatile organic compounds at night. But during the day these pollution controlling compounds are destroyed by sunlight. Stark carried out experiments in the lab and confirmed that artificial light also destroys NO3 radicals.

Using Los Angeles (LA), in the US as a case study, Stark measured the levels of light intensity over the city and the levels of NO3 radicals and other chemicals, using a research plane.

With the help of models of known atmospheric reactions, Stark concluded that artificial light could be destroying as much as 7 per cent of the chemicals needed to clean up pollution at night. This in turn would increase the chemicals that create smog by about 5 per cent every morning, he estimated.

The major types of lighting in LA are high-pressure sodium or metal halide lights. But changing the types of lights used would only have a limited effect, explained Stark.

Apparently red light doesn’t destroy NO3 radicals so perhaps that’s a solution to the problem – but maybe cities illuminated with red lights would give the wrong impression!

Mike Brown

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