London Air Quality - Pollution

“The air is definitely much healthier,” said Prof James Lee at York
University and the National Centre for Atmospheric Science, who
analysed the data. “[Tiny particles and NO2] are the two air
pollutants that have the biggest health impacts on people.”

“These are big changes – pollution levels are the equivalent at the
moment of a holiday, say an Easter Sunday,” he said. “And I think we
will see an even starker drop off when the weather changes.”

https://www.theguardian.com/environment/2020/mar/27/coronavirus-uk-lockdown-big-drop-air-pollution

People can hear birdsong in north London where before it was constant traffic noise.