BBC reveals a dirty secret about our sooty cities – the grunge doesn’t trap air pollution – it creates it:
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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On a tower above the city they set up two large shelves filled with beads of window glass.
Both sets of beads received the same air flow – and got thoroughly grimy – but only one was in the sun.