LAQN Pollution Episodes

Pollution Notification released on 19/05/2024

Widespread Moderate Ozone Sunday 19th May to Monday 20th May 2024.

With the arrival of warmer summer weather, the second episode of widespread Moderate Ozone in 2024 occurred across London from Sunday 19th May to Monday 20th May. Over the two days, ground level ozone production was driven by rising temperatures and sunshine acting on local and continental precursor emissions such as Oxides of Nitrogen, Volatile Organic Compounds and Carbon Monoxide.
Moderate ozone was reached in London at six sites on Sunday 19th, four sites on Monday 20th May. There was strong sunshine and temperatures reached the mid 20s degrees Celsius. A very light breeze resulted in poor dispersion of local emissions which probably then played a significant role in increased ozone production. In addition, a continental air-feed on Sunday likely also contributed pollutants required for ozone production.
It is important to remember that ozone is an area wide pollutant, and whilst monitoring sites are relatively sparse compared to those monitoring other pollutants they represent the wider population exposure, so a single site may represent the ozone concentrations that hundreds of thousands of people have been exposed to. The National Daily Air Quality Index for Ozone is measured on a running 8 hour mean.
The episode finished with the arrival of a cooler and cleaner Atlantic air feed, with temperatures falling back to the mid to high teens and significantly increased cloud cover further inhibiting ozone production.
Erica Withers Duty Forecaster