Smog happens when air pollution levels are higher than usual. This can cause breathing problems for some people, so find out how you can protect your health.
Certain weather conditions can result in smog. At any time of year, in the summer or winter, still weather without much wind can lead to a build-up of harmful substances in the air (known as pollutants).
Pollutants include nitrogen dioxide, particulate matter (tiny solid particles in the air) and ozone. The main sources of air pollution include traffic and industrial sources, such as factories. Ozone is formed when sunlight reacts with substances in the air close to the ground. These substances come from a range of sources, including petrol and other fuels.
Who is at risk from the effects of smog?
Most people won’t notice any problems when there is smog, but people who have heart conditions and/or lung diseases – including asthma – might notice their symptoms get worse. This is especially true for older people.
If you are affected, alter your treatment the way you normally do when your symptoms get worse. For example, if you have asthma you can use your ‘reliever inhaler’. You should talk to your doctor if this doesn’t work.
Avoid any strenuous outdoor activity if you have noticed that your breathing is affected on hot, sunny days. This reduces your exposure to ozone.
Air pollution updates
You can find updates on air pollution at Defra’s UK air information resource pages and from Defra’s freephone helpline on 0800 55 66 77. The helpline also offers health advice.
The Health Protection Agency also has information about smog and air pollution.
Air pollution is described as low, moderate, high or very high. Find out more about these air pollution health bandings.
The Committee on the Medical Effects of Air Pollution (COMEAP) has more information about air pollution.