City grime ‘breathes back out’ polluting nitrogen gases – BBC News

City grime ‘breathes back out’ polluting nitrogen gases – BBC News.Scientists say the grime which clings to urban surfaces “breathes out” nitrogen gases when hit by sunlight.

The dark muck was known to absorb such gases from the air, but it appears the nitrogen does not stay locked away.

In rooftop experiments in Germany, the researchers tracked the content of grime in both sunshine and shade.

They say sunlit grime releases nitrogen in two forms: the toxic pollutant nitrogen dioxide (NO2), plus nitrous acid – a key driver of smog formation.

The findings, presented at a conference of the American Chemical Society in Boston, were welcomed by pollution experts – and may explain a “missing” source of smog-producing gas in the skies of London.

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