YOU can't see toxic air, but it's all around us. From smog hanging over cities to streets filled with car emissions, air pollution is one of the biggest environmental threats to our health, and it comes from lots of different man-made sources.
The World Health Organisation (WHO) estimates that over 70 per cent of towns and cities in the UK have unsafe levels of air pollution, while around 4.2 million premature deaths globally are linked to outdoor air pollution, which is associated with serious health issues like heart disease, stroke and lung cancer.
The most recent annual report published by Northern Ireland's Department of Agriculture, Environment and Rural Affairs stated that pollutants in some areas “continue to exceed air quality objectives”, with Stockman's Lane in west Belfast, Downpatrick and the "Limavady Dungiven" area highlighted for exceeding levels of nitrogen dioxide (NO2), a pollutant mostly associated in urban areas with vehicle exhaust.
:: What is air pollution?
In simple terms, an air pollutant is any substance in the air that could cause harm. Tiny pollutants that are too small for the naked eye to see can evade our body's defences when we breathe them in, damaging our lungs, heart and brain.
"Air pollution is made up of a number of things, such as gases and particles in the air," explains Vanessa Smith, senior cardiac nurse at the British Heart Foundation (bhf.org.uk).
She says there is a variety of pollutants in the air. "The ones we talk about the most in the UK include nitrogen oxides, sulphur dioxide, non-methane volatile organic compounds, ammonia and tiny particles known as 'particulate matter'."
Air pollution can disperse widely, so it's a myth that you can avoid it in the countryside, as you don't necessarily have to be at the centre of the source to be affected by it.
It can affect anyone of any economic background too – some of the UK's most expensive postcodes have the highest levels of air pollution.
"Pollution can come from natural sources such as pollen and soil, but it's often caused by emissions from vehicles, dust from the road, construction work or burning fossil fuels," explains Dr Kathryn Basford at UK-based online doctor Zava UK (zavamed.com).
Air pollution is bad for the environment too. It has close links to climate change, as burning fossil fuels such as coal and oil releases a variety of chemicals into the atmosphere, including greenhouse gas carbon dioxide.
:: Why is it bad for health?
On days when the air pollution is particularly bad, breathing it in can irritate the eyes, nose and throat, cause shortness of breath, make asthma symptoms worse and possibly affect the heart and cardiovascular system.
Being exposed to polluted air for longer periods can cause more serious health problems too.
"There is strong scientific and medical evidence that short and long-term exposure to air pollution can negatively impact on human health by increasing the risk of morbidity and mortality," says Dr Antonio Pena-Fernandez, a senior lecturer in biomedical and medical science at De Montfort University (dmu.ac.uk).
Pena-Fernandez says air pollution is now believed to be the leading cause of early death in the UK.
"Studies have found that people that breathe contaminated air can develop different conditions including cardiovascular and respiratory conditions, and enhance the likelihood of developing chronic diseases such as cancer, neurodegenerative diseases or diabetes," he says.
In the UK, Public Health England has attributed 28,000-36,000 deaths a year to long-term exposure to air pollution. And while anyone can be affected, children and the elderly are particularly vulnerable to air pollution issues.
:: How can you protect your health from air pollution?
Knowledge is key. It's important to regularly monitor the air pollution level around where you live and work, especially if you have asthma or a circulatory condition.
"The government's UK-AIR website (uk-air.defra.gov.uk – in Northern Ireland DAERA operates the website airqualityni.co.uk) has a daily pollution forecast, which tells you if air pollution levels in your postcode are low, moderate, high or very high," says Smith.
Smith adds that on high pollution days, it's a good idea to avoid spending long periods of time outdoors – especially areas such as busy roads with heavy traffic.
"When pollution is high, I'd advise people – and particularly those with lung conditions such as asthma – to avoid exercising outdoors, particularly in the evening when the pollution has had a chance to build up," agrees Basford.
"Keep windows and doors closed, and keep your car windows shut, especially if you're stuck in traffic. If you have asthma, carry an inhaler at all times and take an antihistamine if pollen levels are high.
"If you find you're using your reliever [blue] inhaler more than three times a week, you should speak to your GP or asthma nurse about whether you need to start a preventer inhaler, or increase the strength if you're already using one."
Pollution can make you more likely to react to your usual asthma trigger, such as house dust mites and pollen, so it's wise to invest in special hypoallergenic fabrics around the home, says Pena-Fernandez.
Air pollution is something that the government will aim to tackle over the next few decades, with the UK pledging to become carbon neutral by 2050.
On an individual level meanwhile, there are measures we can all take to help reduce our own carbon footprint and challenge the air pollution problem at the same time.
Opt for energy-efficient light bulbs, use electricity from environmentally friendly sources where possible and keep your vehicles properly tuned. Better yet, use public transport or try cycling or walking to work.
