How can we know when the air we are breathing is harmful?
In response to public concern, small, relatively inexpensive air pollution sensors are coming on to the market. But tests show that they can be inaccurate. Is there an alternative?
Sunday 9 October 2016 21.30 BST
If only we could see the air pollution around us we could identify the culprits and avoid exposure. From an early age we are taught not to drink dirty water or eat mouldy food but we have less opportunity to avoid harmful air.
In a re-run of autumn 2010, this September’s warm weather caused unusually late summertime smog. Air pollution over most of England reached six on the UK government’s ten point scale. These incidents go largely un-noticed but they have a health impact; 10 days of high particle pollution in spring 2014 caused an estimated 600 extra deaths.
Start-up businesses are now selling small sensors so that we can measure the air pollution around us. These cost hundreds of pounds rather than the tens of thousands required for instruments in official networks, but do they work? Many people measure the temperature in their garden where a precision of one or two degrees is fine, but an inaccurate pollution sensor could falsely reassure or alarm. Tests by Allister Lewis and Peter Edwards at the University of York found small nitrogen dioxide sensors that mostly measured carbon dioxide, and in tests on 20 ozone sensors there was a difference of six times between the highest and lowest results.
One alternative is real-time pollution mapping. This is provided by the air quality networks in London and Paris so that you can see the hotspots on your phone and avoid them. Instead of driving along a main road, walking or cycling along a quiet street or through the park significantly reduces your air pollution exposure.