Air quality 101
PM, NOx and all that
Hello again! For our second blog post we thought we would do a bit of an Air Quality 101: what is air quality all about? Do you know your nitrogen dioxide from your particulate matter? How are they measured? And what are the effects of poor air quality on the body?
What is air quality?
When we talk about air quality, we are usually talking about a few different pollutants that are present in the air. These include nitrogen dioxide (NO2, which is mainly produced by road traffic and energy production), ozone (when ozone is present at altitude it screens ultraviolet light from the sun which is beneficial, but at ground level it is toxic), and particulates. Particulates can be anything really: soot from car exhausts, wood burning fires, or even from tyres as they roll over tarmac. DEFRA has a good explainer. Particulates are categorised by their size: if you hear "PM2.5" or "PM10" mentioned, this refers to particles less than 2.5 microns or less than 10 microns (a micron is a thousandth of a millimetre). If the levels of these pollutants are high (we'll come onto levels and what high means later on), then this will have a negative effect on your health.
How high is too high?
As these substances can be bad for our health, the World Health Organisation (WHO) and the government set a range of guidelines and legal limits to help control them. You might often hear that there is no safe amount of air pollution. But the WHO does have guidelines that for PM2.5 the annual average should not exceed 5 micrograms per cubic metre, and there should be no more than 3-4 days a year that exceed 15 migrograms per cubic metre. Similar WHO guidelines exist for PM10, NO2 and other pollutants: this website has a good explainer.
The UK government has recently passed legislation which also tightens up UK legal limits: for instance for PM2.5, no more than 10 micrograms per cubic metre across a year. However, this has been criticised for being short of the WHO guidelines. In a future blog, we'll look at how different London boroughs approach the range of targets and guidelines.
How is air quality measured?
The air quality monitor that is being installed as part of the Breathe London initiative measures two key pollutants: PM2.5 particulates and NO2. Particulates are measured by shining a laser beam across a stream of air: by looking at the amount of scattered light, you can measure the number and size of particulates in the air. Measuring NO2 is done using an electrochemical cell: NO2 reacts with an electrolyte (a solution containing chemicals) and produces an electrical current. The current is proportional to the concentration of NO2, so by measuring the current you can measure the level of NO2 in the air. If you're interested in knowing more details about the units, have a look at the manufacturer's website.
The Breathe London Community Programme aims to provide sixty fully funded Breathe London Nodes to community groups and organisations across London. At the moment we're one of 40 Community Programme groups that are a part of the wider Breathe London project. All data produced by the sensors is public and freely available on the Breathe London website. You can access and download these data at any time and use them for your own projects at your own discretion.
Effects on our health
A shocking statistic: the Office for Health Improvement and Disparities has estimated that around 6% of deaths of over 30s can be linked to air pollution. Older people and those with lung and heart disease are particularly at risk. There is also a growing body of evidence on effects on active adults and their exposure when running or cycling. Breathing poor quality air has been shown to increase the risk of heart disease, lung cancer, strokes and asthma.
Children are particularly vulnerable to air pollution as they breathe faster and deeper and are closer to car exhausts. It's worth remembering that even small changes can lower our and our children's exposure. Estimates show that pollution is 2-4 times higher inside a car than outside, so active travel helps both you, your family and others around you. If you can't avoid busy roads then even walking a few metres away from the fumes, away from the kerbside, reduces your exposure (and is safer).
We’ve got a location agreed for our monitoring node so we’ll be bringing you up-to-date local data very soon. We also hope to bring lots of advice and experience from the wider Breathe London network. Stay in touch and stay healthy!