Air pollution: your questions answered

Day 1: Do you know your NO2s from your PM2.5s? Do you know if you are at risk? Our guide to understanding air pollution will set you straight

Air pollution poses a bigger health risk to children, the elderly and those with respiratory illnesses. Pic: Sarah Glover-Smith

Information on air pollution is available to the public: local authorities publish yearly reports, and interactive maps created by Defra and London Air inform people on air pollution levels on a real-time basis. But what do all these numbers mean? What pollutants should you be wary of and why? This is everything you need to know about air pollution.

The pollutants

Pollutants such as carbon monoxide, nitrogen dioxide, particulates and ground-level ozone, are released into the atmosphere; causing air pollution. These pollutants are largely the result of human activity. Nitrogen dioxide (NO2) and particulate matters (PM) are mainly associated with road transport, a significant contributor to emissions and air pollution in the UK. “Because of these pollutants’ connection to road transport, local authorities mostly focus on PM and NO2 in their policies,” Dr Heather Walton, member of the Environmental Research Group at Imperial College London, explains.

Road transport is responsible for about 50% of total NO2 emissions. The closer you get to a major road, the higher NO2 levels will be. In large urban areas, levels can exceed permitted limits. Reducing NO2 levels is currently the UK’s biggest challenge relating to air pollution.

PM affect more people than any other pollutant. They originate from carbon emissions from engines, small bits of metal and rubber from engine wear, braking and dust from road surfaces. But it also occurs from material from the building industry, wind-blown dust, sea salt, pollen and soil particles. There are two important types of PMs; PM10 and PM2.5. Both cannot be seen with the naked eye, but PM2.5 is especially small and can settle in the airway and deep within the lungs. They can cause health problems such as lung damage and respiratory illness, and heart disease.

PM levels are not exceeding the UK’s legal limits, but these limits are much higher than the level from which exposure could affect your health. PM levels within the UK are still unhealthy, just not illegal.

What does this mean for your health?

Air pollution can have a negative impact on your health, depending on the levels of the pollutants and the period of time you’re exposed. “The most obvious is the effect on the lungs. They can provide some defence to it, but if there’s too much exposure to air pollution it can be damaging,” Walton says. But it’s not just your lungs: “What many people don’t know is that it also impacts the heart. We’re not exactly sure why yet, but there are several ideas. Some believe your heart rate can be affected by the way your immune system copes with lung damage caused by air pollution, and some think fine PMs can even make their way into the bloodstream.”

Some groups are more at risk than others: “Children are more vulnerable because they breathe in more air pollution relative to their body weight and they breathe faster. For the elderly, air pollution can worsen diseases they already have – especially lung conditions occurring in smokers. Your lung function also declines as you get older, so air pollution can affect you more at old age,” Walton explains. “People with pre-existing health conditions, such as asthma and other respiratory issues, are more at risk – regardless of their age. And there is a connection between air pollution and levels of deprivation. Generally, people who have less money to spend live closer to bigger roads – where air pollution levels are higher. So they’re exposed more.”

Long-term exposure to air pollution is more likely to cause health issues, but short-term exposure to extremely high levels can also be damaging. Both can cause or worsen symptoms of bronchitis, lung cancer, cardiovascular disease, heart disease and both chronic and acute respiratory diseases – such as asthma. “Some new data, which is still being debated, suggests there might be a connection between air pollution and dementia,” Walton adds.

When is exposure dangerous?

“It’s difficult to pinpoint one specific limit and say ‘from this point on air pollution will affect your health’, because it depends on the pollutants and effects will differ per person,” Walton says. The WHO has set guidelines for air pollution levels that only consider health effects but at the same time, they acknowledge that there is no safe level for exposure to PM2.5. The European Union used these guidelines to set their own legal limits, which the UK took over, based on the costs of measures necessary to reach these limits and how feasible they would be.

Because of these considerations, the limits the UK adapted for PM2.5 and PM10 are much higher than the WHO guideline limits, as you can see in the table below. This means that PM levels within the UK that are not exceeding the legal limits but are higher than the guidelines, are still unhealthy. This is why London mayor Sadiq Khan committed to the capital being in compliance with WHO guidelines in 2030.

For the different pollutants, both organisations have set annual average limits and hourly or daily average limits. The average level for a specific pollutant over a one year period should be lower than the annual average limit in the UK guidelines. If these exceed the limit, the levels are illegal. If the pollutant is in compliance with the UK limit, but exceeds the WHO guideline, it’s unhealthy.

Table: The UK’s legal limits and WHO guidelines for NO2 and PM

The hourly and daily limits are also averages, so it doesn’t mean that a pollutant cannot exceed that limit somewhere during that day, year, or within the hour, just that the average is in compliance with the legal limits. UK legislation allows for pollutants to exceed these limits a certain number of times within a year, depending on the pollutant. The NO2 hourly limit for example, is allowed to be exceeded up to 18 times per year. Pollution levels can thus be extremely high within a short time frame and damage your health, even when they meet annual average limits.

“The limit for NO2 is higher than it should be. Studies show health effects below that level, and the limit was set a long time ago”, Walton says. But the UK doesn’t even meet the current limits, with 75 per cent of urban areas still having illegally high levels of NO2.

Who does what?

National government sets these limits and targets and might put certain incentives in place that can help reach them. But regional and local authorities have a responsibility as well. “You need coordinated actions at all levels. Local authorities can allow vehicles with specific engine standards to particular places in their area, but they cannot set vehicle standards – that is done on an EU or national level”, Walton explains.

For that reason, all local authorities set up their own Air Pollution Action Plan in which they explain what measures they will take to reduce air pollution in their borough. Councils report back to the national government by publishing yearly reports of air pollution levels; identifying areas where levels are still exceeding the legal limit and require more attention in their future action plans. Local authorities can also create awareness by making sure information on air pollution reaches the people who need it most – those who are more at risk. 

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