Sun and city dirt trigger smog

Sunny days have been found to trigger the release of potentially harmful smog from grime which coats buildings, statues, and other outdoor surfaces in city areas.

In the past, it had been thought that, once the airborne pollution which was emitted from cars and factories settled onto the various surfaces, it was absorbed into the grime there and became inactive and was no longer harmful.

Scientists have now discovered that, when exposed to sunlight, the grime releases “smog-forming” nitrogen oxide compounds.