LAQN Pollution Episodes

Pollution Notification released on 02/04/2020

Particle pollution episodes are a regular feature of spring time over western Europe. They occur when the wind direction becomes easterly and air pollution builds up across the continent and the UK. Last week transport restrictions and the temporary closures of many businesses may have averted a widespread moderate or high air pollution episode.

From 25th to 27th March London and south east England experienced air widespread air pollution that reached three on the ten point UK Air Quality Index. A small number of monitoring sites reached index four, breaching the threshold for 'moderate'. The chemical signature of the particles that we did detect indicated that the dominant pollution sources were wood burning along with emissions from agriculture, transport and industry. A change in wind direction on Saturday 28th March resulted in a northerly flow and an immediate decrease in PM2.5 concentrations.

An additional consequence of the reduced emissions from traffic is that ozone concentrations were greater than we normally experience at this time of year. Ozone is a secondary pollutant, it is produced by reactions of other pollutants in the atmosphere, and locally it is scavenged (reduced) by exhaust emissions. As a result 'moderate' ozone was measured at a small number of sites in Sussex, Kent, Surrey and London on Thursday 26th and Friday 27th. It is important to remember that ozone is regional pollutant, and although monitoring sites are sparsely distributed, compared with those monitoring nitrogen dioxide, they represent the large population exposure.

Timothy Baker and Gary Fuller.

Further information and discussion of this episode may be found in a short article by Gary Fuller for the Guardian Newspaper

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