Keen to learn more about air pollution? Read our interview with Dr Ben Barratt, senior lecturer in Air Quality Science at King’s College London.

We asked Ben some of the most frequently asked questions about air pollution:

1. What is air pollution made up from?

Air pollution comes from a range of sources, including some nearby, like vehicles, other sources throughout the city, and some further afield. The proportion of pollution that reaches us from each source depends on the weather, the location, the time of day, and a number of other factors. Wherever you are, you’ll breathe in some of this pollution.

The main pollutants are carbon monoxide, nitrogen dioxide, ground level ozone, particulates, sulphur dioxide, hydrocarbons and lead. Each one comes from a different source, has different effects on our health, and different chemical behaviours, which is why it’s hard to understand and control air pollution.

2. When are you most likely to be affected by air pollution?

Air pollution concentrations depend on the emissions level and how the emissions are dispersed in the air. A combination of still air (low dispersal) and the morning rush hour (high emissions) mean the highest pollution levels are often in the morning. There’s often a second smaller, more spread out peak in the late afternoon and evening too when people are travelling home.

Air pollution is different on different days, it’s usually lower at the weekend than on weekdays. Another important factor is ground-level ozone concentrations, which normally peak in the mid to late afternoon in summertime.

3. How can I get warnings when there are periods of high pollution? 

Air pollution forecasts and alerts are available for the whole of the UK from Defra.

Sign up to get daily pollution forecasts for London here or to just receive alerts on high pollution days click here.

You can also get warnings on your iPhone by subscribing to the ‘At-risk’ group in this app, which will help you plan the best route through London to minimise air pollution exposure.

4. What should I do on a high pollution day? 

Just go about your day as normal. If you walk to work, stay away from busy roads with lots of traffic. If you normally drive to work, try to leave your car at home to not add to the problem and you can also try working from home.

If you’re in an 'At-risk' group it’s best to follow government guidance and avoid taking part in any energetic outdoor activities. And make sure you have your medication to hand if you have asthma. On days when pollution is very high, it’s a good idea to discourage children from taking part in strenuous outdoor activities too. But it’s important to stress that such high pollution only happens for a few days every year, so outdoor exercise should be the norm.

5. Can we solve inner city air pollution by planting more trees? 

Some studies have suggested that planting trees on highly polluted streets can significantly reduce pollution. But there isn’t much evidence that it works and some other studies say it doesn’t help at all. Even if it does make a difference, the effect of ‘greening’ is very small relative to the size of the problem and in certain circumstances it might actually make things worse.

Trees planted on the roadside can limit how far pollutants disperse away from the road. Yet certain plants emit a high level of volatile organic compounds during the summer months that contribute toward ozone generation – a form of pollution.

Planting more trees can be popular because it’s easier than legislating against those creating the pollution. There are many other benefits of greening the environment but the potential impacts on urban air quality have been overstated and I don’t believe it’s the solution.

6. How dangerous is walking/cycling on busy roads in London? 

Evidence shows that cyclists are actually often exposed to less air pollution than people travelling by car, taxi or bus.

This video compares the pollution levels commuters are exposed to when they use different modes of transport to get about. You might be surprised by the results … (spoiler alert – the driver experiences the most pollution)

7. Do air masks actually work? 

Many commercially-available masks don’t reduce exposure to tiny exhaust particles much. And it’s small particles that cause the issues. Larger particles are generally filtered in the nose and throat anyway and don’t cause problems.

Particles that come from road traffic include carbon emissions from engines, small bits of metal and rubber from engine wear and braking, and dust from road surfaces. Pollutants also include material from building and industry, and wind-blown dust, sea salt, pollens and soil particles.

People often associate air pollution particles with smoky engines but the majority of particles that can get into the airway are too small for us to see, so they can exist in air that seems clean.

Particles smaller than about 10 micrometres (PM10) and particles smaller than 2.5 micrometres (PM2.5) can settle in the airway and deep in the lungs, where they cause health problems. Even the best masks won’t filter out these small particles unless they fit very snugly.

8. Which groups of people are most affected by air pollution? 

Everyone can be affected by air pollution but it has the most impact on young children, the elderly, and people with existing lung or heart conditions.

9. Does turning my engine off actually make a difference? 

Yes it does! King's College London worked with Global Action Plan and the Cross River Partnership to measure the impact of ‘no-idling days’.

On designated ‘clean air action days’, teams of trained volunteers approached drivers of parked vehicles at various locations across London and asked them to switch off their engines. Hundreds of drivers were engaged and the project reached almost 4 million people online during the two days of action.

The results showed that turning off engines had the most impact where pollution was highest and where the no-idling action was focused. In those places, air pollution peak concentrations were reduced by as much as 20-30%.

If you’d like to find out more you can read the full report here.

10. How can I monitor air pollution near me? 

There are a few low-cost sensors on the market but monitoring air pollution can be a complicated and expensive task and there isn’t a sensor that we fully endorse. Another problem is that many sensors being advertised are still being developed and aren’t publicly available.

If you do want to give it a go you could try one of these:

The Dylos is the most established sensor (and it’s also the most expensive). The Cleanspace Tag monitors carbon monoxide, which is a good tracer for combustion emissions. It’s also cheap and easy to use but will not necessarily pick up more subtle changes in pollution levels that more expensive equipment can. The other sensors monitor PM2.5 particles.

If you’d like to monitor air pollution in your community you could get involved with Mapping For Change. They help local community groups carry out diffusion tube monitoring to check exposure levels.

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