Roads and junctions have been blocked in four main areas of central London due to a climate change protest by Extinction Rebellion. The affected areas are: Waterloo Bridge, Marble Arch, Oxford Circus and Parliament Square. The air quality effects have been analysed up to Wednesday 17th April, the latest full day of the protests.

Hourly nitrogen dioxide concentrations from sites on the London Air Quality Network (LAQN) were compared for the days when the protests were taking place, from Monday 15th to Wednesday 17th April, to the concentrations on these days of the week when the when the protests were not taking place. The measurements used for non protest days were taken from March, April and May to reduce the effect of seasonal variations in air pollution. Only measurements since 2016 were included to reduce the impact of any long term changes, whilst still including sufficient data to make a comparison.

At the Northbank BID site on the Strand, close to the north end of Waterloo Bridge, a small reduction in hourly nitrogen dioxide concentrations was noted for much of the day during the protests. Although the Strand is not itself blocked traffic was visually observed to be lighter than normal, although Easter school holidays may have contributed to this. Over the full day, nitrogen dioxide concentrations during the protest were about 91% of usual concentrations.

At the Westminster – Oxford Street site, near Selfridges, a larger reduction in nitrogen dioxide concentrations was seen. Roads are blocked at Oxford Circus and Marble Arch. The section of Oxford Street next to the monitoring sites is not blocked but access is likely to be reduced. Over the full day, nitrogen dioxide concentrations during the protest were about 18% lower than usual concentrations at this location. The reduction in hourly pollution concentrations was as much as 45% in the mid afternoon.

The analysis was repeated for locations in areas neighbouring those affected by the protests. Some commentators have suggested that an increase in congestion and queuing traffic, or increased traffic in areas surrounding the protests may increase pollution concentrations in these areas. At Bee Midtown BID’s site in Holborn, to the north of Waterloo Bridge, there was very little change in nitrogen dioxide concentrations. Concentrations during the protest were around 98% of the usual concentrations. At Marylebone Road, to the north of Oxford Street which could be used as an alternative route for traffic there was a reduction in nitrogen dioxide concentrations during the protest. Concentrations were around 80% of usual concentrations on these weekdays. At Euston Road, nitrogen dioxide concentrations were around 5% higher during the time when the protests took place.

Away from Central London, the difference in nitrogen dioxide concentrations between the period when the protests are taking place and usual concentrations was variable. A location by the North Circular had approximately 11% higher nitrogen dioxide concentrations during the protest, a location in Greenwich had around 54% higher concentrations during the protest and a location in Sutton had around 4% lower concentrations. A site in Havering, well away from Central London and outside the North Circular had concentrations around 1% higher than usual. It is not possible to directly attribute or exclude any of these changes as being due to the protest. It is important to note that the protests are taking place at a time when traffic is in London is often reduced as it is during the school Easter holidays. Therefore, reductions in pollution could also be expected for this reason. Conversely, a major pollution episode is taking place across London which would be expected to increase particulate pollution concentrations. This analysis has focused on changes in nitrogen dioxide concentrations, for which the main source in Central London is road traffic. Similar results would not be seen for particulate matter due to a pollution episode in progress, which includes local and imported pollution - Further details.

In summary, the measurements show some evidence of a reduction in nitrogen dioxide concentrations close to locations where roads are closed. None of the monitoring sites are in locations where traffic is completely blocked and reductions in nitrogen dioxide concentrations would be likely to be much larger where no traffic is able to pass at all as has been seen during other road closures. There is little evidence of any significant increase in nitrogen dioxide concentrations in areas neighbouring those where the protests are taking place. The difference in concentrations well away from the affected areas is inconsistent and reflects possible increases in pollution due to meteorological conditions, offset by the possible decreases in concentrations due to lighter traffic in the school Easter holidays.