March 24, 2022

expert reaction to a high air pollution warning being issued for London

The Mayor of London issued a high air pollution alert earlier this week.

Prof Bill Collins, Professor of Climate Processes, University of Reading, said:

“The poor air quality is due to a high pressure over NW Europe (including UK) that has been there for a few days. This is bringing us air from the near continent (poorest air quality is in the east). It has also given us stagnant conditions over England which means that our own pollution is trapped. The combination of near-continental and local pollution is what is giving us the high events.

“These weather conditions aren’t unusual at all. In 2020 the lack of cars during lockdown meant that weather conditions that we might have expected to cause poor air quality didn’t. The lesser lockdowns in 2021 will have had some effect, but probably not noticeably. It is more likely that the weather patterns just happened to be less conducive to air quality events in 2021.”

Prof Helen Dacre, Professor of Meteorology at the University of Reading, said:

“There are moderate to high pollution levels over the central, east and south-east of England.  These pollution levels are forecast to remain high tomorrow but to reduce over the weekend.

“There is large year-to-year variability in the number of high pollution episodes due to the range of meteorological conditions we experience in the UK.  Typically, the UK is influenced by south-westerlies which transports relatively clean air from the North Atlantic into the UK.  Relatively high wind speeds disperse any locally emitted pollution preventing it from accumulating and rain can also remove some pollutants from the atmosphere. However, it’s not uncommon for high pressure to dominate the UK weather.  The weather associated with high pressure conditions in the Spring are typically light winds, clear skies and reduced chance of rain.  If these high-pressure conditions persist, then the stagnant conditions and increased frequency of winds from the east can cause locally emitted pollution to accumulate and pollution emitted in Europe to be transported to the UK.  This leads to high pollution episodes such as we are currently experiencing.”

Dr Claire Ryder, Associate Professor and NERC Independent Research Fellow, University of Reading, said:

“In addition to local and European pollution building up in the atmosphere, we are also still experiencing Saharan dust over the UK, adding to the unpleasant cocktail of particles in the air. This dust was transported by strong winds over the Sahara last week, causing orange snow in the Pyrenees Mountains, red skies across Europe and blood rain in the UK. As high pressure moved in across the UK, satellite imagery shows that some of this dust has been recirculated and remains in the current stagnant atmosphere.

“High pollution episodes in the UK are usually associated with high pressure systems building over several days, when the pollution does not get ‘ventilated’ by strong winds or rained out. The January 2022 episode was the result of high pressure, and the lack of episodes during 2021 will have been down to the particular weather patterns experienced, including how the position of the jet stream drives our weather.”

https://www.london.gov.uk/press-releases/mayoral/mayor-of-london-issues-high-air-pollution-alert-0

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