London is being hit by high air pollution levels today as temperatures rise. So, what's going on with our air and why is it bad news?
Q: Why are we experiencing this air pollution?
A: It is caused by a combination of factors. Local pollutants from sources such as traffic fumes are being trapped by the warm still weather conditions so they do not disperse, while a light south easterly breeze is bringing more pollutants from the continent. There is also a small amount of dust from the Sahara in the air.
Q: What is meant by "pollution"?
A: It relates to very fine particles, known as PM2.5, in the air which reduce visibility and make the air look hazy. They come primarily from vehicle exhausts and other fossil fuel burning activities such as power plants.
Q: Is it dangerous to health?
A: Yes. At high concentrations the particles can travel into the lungs and cause short term health effects such as irritation to eyes, nose, throat and lungs, sneezing, coughing and shortness of breath. They can also affect lung function and worsen conditions such as asthma and heart disease.
Q: What is the health advice for the pollution incident?
A: At high levels of air pollution, adults and children with lung problems, and adults with heart problems should reduce strenuous physical exertion, particularly outdoors, people with asthma may need to use their reliever inhaler more often and older people should reduce physical exertion. Anyone with symptoms such as sore eyes or throat or a cough should consider reducing activity, particularly outdoors.
At very high levels of air pollution vulnerable people should avoid strenuous physical activity, and people in general are advised to reduce physical exertion, particularly outdoors and if experiencing symptoms.
Q: But it is only lasting a short time - why does it matter?
A: Although spikes in air pollution such as this one tend to be short-lived and can often occur at this time of year, a range of pollutants including PM2.5, larger particles known as PM10 and nitrogen dioxide are having a significant effect on people's health.
Tens of thousands of people are estimated to be dying prematurely each year because of air pollution, with thousands dying early in London alone, while the costs to the NHS are estimated to run to tens of billions of pounds.
Q: What can be done to reduce the problem?
A: Measures can be taken to cut pollution from vehicles, for example through low-emission zones in cities which charge motorists for driving heavily polluting cars and lorries, promoting electric or hybrid vehicles and public transport, walking and cycling.
Other measures include reducing electricity generation from fossil fuel combustion plants, with more use of renewables.
The Government has been criticised for failing to do enough to tackle the problem, and a case brought by environmental lawyers ClientEarth against the Government over levels of air pollution that breach European Union rules is shortly to return to the Supreme Court.