LAQN Pollution Episodes

Pollution Notification released on 14/04/2020

From Wednesday 8th April through to the end of Friday 10th April, London and south east England experienced widespread air pollution with a large number of monitoring sites breaching the threshold for 'Moderate' PM10 and PM2.5 particulate.

This episode was driven by air recirculating at low altitudes over the near continent and the Channel and resulted in a sustained import of particulate pollution.

The chemical signature of the particles detected indicates that the dominant pollution sources were a combination of emissions from agriculture, transport and industry.

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. The current transport restrictions and the temporary closures of many businesses may have helped to avert a widespread ‘high’ PM10 and PM2.5 particulate episode.

Only Stanford-Le-hope in Thurrock reached High (index level 8) on Thursday 9th for PM2.5, other sites on the networks peaked at Moderate.

An additional consequence of the reduced emissions from traffic is that ozone concentrations are higher and longer lived than we normally experience at this time of year.

Last week’s Ozone episode lasted for five days, from Wednesday 8th April through to the end of Sunday 12th April.

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 number of sites, both urban and rural.

It is important to remember that ozone is a regional pollutant, and although monitoring sites are sparsely distributed, compared with those monitoring nitrogen dioxide, they represent the large population exposure.

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