As forecast, the hot sunny weather - along with pollutant emissions from the continent and locally - has contributed to high concentrations of ground level ozone since Friday over most of England and Wales, including London. The summer smog is expected to continue over parts of the England and Wales until Tuesday.
Over the weekend high ozone levels were recorded in London, Birmingham, Manchester, Newcastle, Brighton, Leicester, Portsmouth, Swansea, Midlands, north-east, north-west, south-east and south-west England, East Anglia and South Wales.
For today (Monday), ozone concentrations are predicted to be high in England and South Wales, moderate or low in Scotland and Northern Ireland.
For tomorrow (Tuesday), ozone concentrations will possibly remain high in England where there are no thunderstorms, moderate in Wales, Northern Ireland and some parts of Scotland, low in northern Scotland
For Wednesday, ozone concentrations will reduce to moderate and low across the UK as forecast back-trajectories become westerly and temperatures decline.
Particulate matter (PM10) concentrations are likely to be moderate near busy roads in London and southern areas of the UK.
Despite the recent high levels of ozone, peak levels are generally decreasing in the UK due to tighter emission standards for road vehicles and comprehensive controls on industrial processes and domestic sources.
Highest ever recorded levels of ozone in the UK were in the hot summer of 1976 when levels exceeded 250ppb at Harwell in Oxfordshire.
Some people are more sensitive to ozone than others and may begin to notice an effect on their breathing. Avoiding exercise outdoors in the afternoon can reduce exposure to ozone. People with asthma are not necessarily more sensitive but, if affected, can use their 'reliever' inhaler. For further information on action to take during hot weather please see the Heat Wave plan (www.dh.gov.uk).
Ground level ozone is formed when sunlight acts on nitrogen dioxide and other atmospheric substances close to the ground. The pollutants that cause ground level ozone come from a range of sources, including petrol and other fuels.
Regular updates on levels of particulate matter (PM10), sulphur dioxide, nitrogen dioxide, ozone and carbon monoxide are available
on: TELETEXT (page 156), and the Internet www.airquality.co.uk (Air Quality Archive), which also offers health advice to those who may be particularly sensitive to air pollution.