While Extinction Rebellion blocked roads in London, the capital was awash with particle pollution, causing the mayor to issue alerts on bus stops.

But this poor air had nothing to do with the protests, quite the opposite. Analysis by King’s College London found air pollution improved close to the protest locations. This was especially clear on Oxford Street, without the constant flow of buses and taxis, but was also seen at Aldwych, close to Waterloo Bridge.

There was no sign of deteriorations on the surrounding roads, which might be partially explained by lighter traffic because of the Easter holidays.

The pollution alerts were part of the all-too-familiar rhythm of spring, when exhaust from traffic, emissions from industry chimneys and ammonia from fertilised fields combines to form particle pollution that drifts over western Europe.

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Unusually, this covered all of the UK and prompted the Irish Environmental Protection Agency to issue warnings for the east of the country.

Easter Monday brought a surprising additional pulse of particle pollution across Kent and Essex into London. Chemical analysis showed this was mainly due to wood burning.

By following wind patterns backwards across Belgium and into southern Germany the particle pollution was attributed to fires lit to mark Easter each year.

• This article was amended on 10 July 2019 to give a more accurate assessment of the source of Easter bonfire pollution, because an earlier version wrongly suggested that Easter bonfires were a tradition in Belgium.