Face masks at the ready – a musty smog has been crawling its way over Sussex in recent days.

In scenes closer to Beijing than the south coast, air pollution levels have been so high that public health warnings have been issued.

The fog is a concoction of traffic fumes trapped near the ground, combined with dirty air blown from the continent and a small amount of Saharan dust.

Asthma sufferers, people with heart problems and the elderly have been advised to ‘reduce physical exertion’ – particularly while outdoors.

The advice also extends to thousands of people set to run the Brighton Marathon tomorrow.

Rob Galloway, marathon medical director, urged runners to proceed with caution as they do last minute training.

He said: “We advise those training to refrain from training outdoors if they experience a cough, sore throat or sore eyes.

“Anyone training with a respiratory condition, such as asthma, should have refrained from training outdoors yesterday when pollution was highest.

“Predictions are that the air quality will have improved greatly by the weekend.”

The Department for Environment, Food and Rural Affairs (Defra) yesterday warned air pollution could reach “very high levels” in south east England.

Fresher, cleaner air from the Atlantic was expected to arrive today, although pollution levels will remain moderate for many areas over the weekend.

Dr Sotiris Vardoulakis, head of the air pollution group at Public Health England’s centre for environmental hazards, said: “While most people will not be affected by short term peaks in air pollution, some individuals, particularly those with existing heart or lung conditions, may experience increased symptoms.”

Although the pollution and fog are not all entirely down to traffic congestion, green campaigners say that pollution is a killer.

Brenda Pollack, of Friends of the Earth, said: “Air pollution kills tens of thousands of people prematurely in the UK every year, and puts extra pressure on our overstretched NHS.

“Ministers must protect our health by acting urgently on the main cause of air pollution, which is too much dirty traffic.

“Plans for new roads will make things worse. We need to see less traffic and more walking, cycling and public transport use.”

Keith Taylor, Green MEP for South East England, added: “Whoever forms the next Government, one of the first things they must do is to urgently address this crisis that seems to be getting worse.”

How has it come about?

As well as dust from the Sahara, the high levels of pollution in Sussex are made up of various substances including ammonia, sulphur dioxide and nitrogen dioxide. All chemicals primarily come from vehicle exhausts.

In addition, a calm south easterly wind is bringing in polluted air from France, which is combining with our own home-grown pollution.

Paris in particular is one of the most air-polluted cities in the world.

With the fine, settled weather conditions in the UK, the pollution becomes trapped over the country and causes above average levels.

With warm weather arriving this week, doctors have also reported seeing hay-fever sufferers experiencing symptoms.

While the pollen levels are moderate for much of the south and low for the rest of the UK according to the Met Office, many people are already suffering from hay-fever symptoms.

Met Office meteorologist Charles Powell said recent good weather may be a “shock to the system” after uncharacteristically warm temperatures.

Today’s temperatures are expected to be around 14C (57F) or 15C (59F) across the UK, providing some cooler air for spectators and competitors in the Grand National and the Boat Race.

Brighton and Hove’s noxious problems

Brighton is no stranger to air pollution, with some areas recording almost three times the legal limits of toxic gas nitrogen dioxide (NO2) in recent years.

Around North Street, east of the Clock Tower, levels were recorded at an average of 114.3 micrograms of NO2 per cubic metre in 2013.

The EU standard is just 40mg per cubic metre. Diesel buses and taxis are blamed for the road’s pollution.

The Lewes Road Vogue Gyratory and the Elm Grove Junction also recorded a yearly average of 67.4 and 63.9 respectively – 50% higher than the legal limit. St James’s Street has also breached EU standards, despite being a bus and taxi only route.

Brighton and Hove has similar nitrogen dioxide to small historic cities such as York, Oxford and Cambridge, with poor air quality dominated by near ground level emissions and local transport sources.

To tackle the problem, a low emission zone was introduced in central Brighton earlier this year.

Some buses have had their exhaust systems modified to meet European standards while bus drivers have to switch off their engines if stationary for more than a minute. The zone covers Castle Square, North Street and parts of Western Road.

Councillor Ian Davey, lead member for transport at the city council, said: “Poor air quality as a result of transport emissions has been a stubborn problem for more than 20 years.

“Positive joint working with bus and taxi operators has led to external funding and a strong commitment to a low emission zone for Brighton and Hove."

Lib Dem MEP for South East England, Catherine Bearder, is negotiating new EU limits on air pollution.

She said: “We cannot ignore this problem any longer. We urgently need strict Europe-wide limits to force governments to improve air quality.

“People deserve to go outside and enjoy the good weather without having to worry about health.”

Dr Kirsty Smallbone, Brighton University principal lecturer in geography, writes:

Air pollution causes 50,000 premature deaths in the UK every year (PHE 2014).

Pollution levels in most city and town centres in Sussex will be close to or exceeding standards set by the UK Government to protect our health. We are currently experiencing an ‘air pollution episode’.

The sunny weather and light south-easterly winds have let Saharan dust plus pollution from northern Europe contribute to local traffic pollution and cause concentrations of particulate matter and nitrogen dioxide to high levels. When air pollution levels are high, people who are fit and well should consider reducing their outdoor physical activity if they experience sore eyes or throat, or a cough. So if you are getting in shape for the Brighton Marathon, it’s a good idea to delay your training run until Sunday morning, when pollution levels will be low. People with heart/lung conditions like asthma, emphysema and COPD, children and the elderly are at risk of suffering adverse effects of air pollution. During high air pollution events these people should avoid or reduce physical activity outdoors, especially if they experience symptoms. They may also be affected at moderate levels of air pollution so it’s a good idea to check out the air quality health advice on the Defra website or go to www.cleanerairbetterhealth.eu/en/ to find out more. The University of Brighton, funded by EU INTERREG IVB are installing cutting-edge monitoring equipment to help us understand and predict these episodes in the future and look at the effects of this pollution on the people of the city.

Obviously this is an extreme event that we have been experiencing over the last few days, but air pollution is a problem all year round.

Public Health England has calculated that every year in Brighton and Hove, there are 115 premature deaths related to air pollution and 1,333 life years lost (life expectancy is reduced). The Government are attempting to reduce air pollution by introducing strict measures to control traffic emissions but we need to change too. We can walk or cycle on short journeys (which has the added benefit of increasing life expectancy and burning off those Easter egg calories!).

We can use the bus or the train and we can turn off electronic devices when not in use. All of this helps to reduce air pollution levels on a day-to-day basis and will help to make our town a better place to breathe.