Air pollution is likely to rise significantly this weekend because of the warm, still weather and heavy holiday road traffic – leading the Government to issue a "summer smog" warning.
People with breathing difficulties and parents of children with asthma are being especially urged to take precautions. Experts believe that levels of ozone and ultra-fine particles in the air that irritate the respiratory system are likely to rise with the daytime temperatures. A high-pressure system over England and Wales, combined with ample sunshine, is likely to bring the warm and still conditions over much of the country that can lead to a "high-pollution episode", said a spokesman for the Department for the Environment.
Sunlight reacting with the gases released by car exhausts can generate ground-level ozone and fine particles called PM10s, which can irritate the lungs when inhaled, especially in people with pre-existing respiratory conditions.
"Some people are more sensitive to ozone than others and may begin to notice an effect on their breathing," said a spokesman for the department. "People with asthma... if affected, can use their 'reliever' inhaler."
The Department for the Environment urges the public to take "sensible precautions" such as avoiding taking exercise in the afternoon when ozone levels are highest, and to avoid making short car journeys to reduce the formation of ozone.
The department must issue "smog alerts" when the first of the year's occurrences of ozone and PM10s is expected. In the past 10 years, it has issued eight such smog alerts, but only one of them was earlier than this year's.
Temperatures in the South-east are due to reach 27C tomorrow. Heathrow was one of the hottest places in Europe yesterday with temperatures rising to 25.8C, while Tuesday was the hottest day of the year so far.
Health officials around the country reported many thousands of cases of sunburn caused by the surprise heatwave. NHS Bournemouth and Poole issued a health alert, warning people to protect themselves from the sun and avoid prolonged exposure. A spokeswoman for the Trust said hospitals, GPs and walk-in centres had experienced "higher than normal incidences of sunburn, exhaustion and dehydration" in the past week.
Bridget Sampson, deputy director of medicines at NHS Cornwall and Isles of Scilly, said she was concerned about the number of people who had been seeking treatment for cases of sunburn and dehydration. She added that warnings of smog might "fool some people into thinking they won't get burned when they will".
She added: "With elevated levels of ozone over the weekend, we are concerned about people with asthma and other respiratory conditions; they're the people who need to be most careful over the next few days."
Out-of-hours GP services have also reported a spike in calls related to skin conditions in the past week. Judith Wright, the director of public health at NHS West Sussex, said: "It is concerning that this early in the year people are calling for NHS help for sunburn. Everyone loves good weather, and it's fantastic to be outdoors, but people need to realise that the sun can be powerful no matter what time of year it is and what the weather conditions are."
The lack of traditional April showers has also led to fears that parts of the country are running out of water, with reservoirs and rivers reaching worryingly low levels. The Environment Agency has reported a 13 per cent drop in average rainfall over the last three months. Flows in some rivers are lower than expected for the time of year, particularly in the South-west, Central and Eastern England, where some areas have received just 66 per cent of their expected rainfall.
Terry Marsh of the Centre for Ecology and Hydrology said: "Water resources held up well in March. That said, the recent, exceptionally dry six- to seven-week spell, following a moderate rainfall deficiency since the autumn of 2009, has come at a pivotal time for water resources. A dry April could lead to a significant deterioration in the resources outlook."
The Met Office reported that England and Wales have had their driest March for more than 50 years. The UK average rainfall total for the month was 39.1 mm, just 41 per cent of the normal monthly average.
Meanwhile, an estimated 10 million people took to the roads yesterday in an early start to the bank holiday, but congested roads meant delays to journeys, with traffic on the M25 around London moving at speeds of under 20mph.
Bank Holiday heatwave
The Met Office has forecast four days of glorious sunshine. With the mercury set to hit 25C, it is likely to be one of the hottest Easter weekends since records began a century ago.
Today temperatures in London and the South-east are due to reach 24C, although some isolated showers are forecast for the afternoon. However the sunshine will return tomorrow, with temperatures of 25C in London and the South-east and into the Midlands, while northern counties will see the mercury touch 23C. Scotland and Wales are also set to bask in the unseasonably warm weather, with temperatures heading to highs of 19C and 22C respectively. Again, isolated showers are predicted.
Sunday sees a slight dip, though the North and parts of Wales will see the mercury reaching 22C, while the South will see temperatures of 24C. Average temperatures for Scotland will be cooler, about 16C. On Easter Monday, central and south-eastern areas are set to bask in 22C sunshine. The Midlands and Northern England will see temperatures in the high teens.
Rebekah Sherwin, from the Met Office, said: "It is really unseasonably warm at the moment as we normally expect to see maximum temperatures of between 14 and 15C in April."