Settled very warm and sunny weather is forecast for the coming days with temperatures rising to high twenties. This is unusually warm for the time of year.
Back-trajectories show air arriving that will have passed over continental Europe including Paris which is also forecast to experience elevated ozone levels.
The expected import of pre-cursor pollutants plus the warm temperatures and sunshine mean ozone will likely rise through the day, and the 'Moderate*' threshold might be breached.
The time of year does reduce the likeliness of any 'High' levels being realised as the sun's strength and daylight hours are reduced at this time of year.
High Ozone has not been measured in September since the heat-wave summer of 2003.
Forecasts remain low for other pollutants
Source: Kings College, London Air.org
*Moderate levels mean that adults and children with lung problems, and adults with heart problems should reduce strenuous physical exertion, particularly outdoors, and particularly if they experience symptoms. People with asthma may find they need to use their reliever inhaler more often. Older people should also reduce physical exertion.