Air pollution is invisible, but it’s in the air we breathe. In our towns and cities we rely on air quality monitors to tell us how polluted the air around us is. There are many different types of monitors - here we explore the pro’s and con’s of each kind, based on what we’ve learnt through the ‘Air We Share’ campaign.  

Air pollution monitoring in our cities 

Most air quality data comes from large static monitoring stations, funded and managed by Local Authorities. Monitoring air pollution was a obligation that came out of an 2008 EU Directive, which set legal limit values across Europe for a range of air pollutants including nitrogen dioxide gas and particulates (PM 10 and PM 2.5). 

The data captured is used in health research, which has linked areas of high pollution to wide ranging health issues, from reduced average life expectancy to the impact on child lung development.   

The monitors enable us to see how we’re doing against legal limits. The latest government figures show that limits for nitrogen dioxide are being breached at 37 out of 43 sites, resulting in legal challenges from Environmental Lawyers ClientEarth.  

But it’s not a perfect system. Reduced Local Authority funding has had an impact on the effectiveness and consistency of local monitoring. Outdated equipment is being used, and many areas no longer have dedicated air quality officers.  The list of DEFRA approved monitors hasn’t kept pace with the surge of new monitors that have landed on the market.  

These static monitors also reveal little about how much individuals are exposed as they move around the city. As public concern about the health impacts has grown, so has the demand for cost-effective portable monitors that give insight into people’s personal exposure. 

The rise of portable devices

According to Kings College London, the portable monitors market is a ‘wild west’. “For example it’s not currently possible to credibly measure No2 via portable monitors” says Andrew Grieve, Senior Air Quality Analyst. He explains that most No2 devices use 'Alphasense’ technology which rely on a chemical reaction. These experience high levels of interference, as the technology also reacts with other gases; ozone and carbon dioxide. Chemical reactions are also affected by heat fluctuations and humidity. 

Monitoring particulates via portable devices can be done in a more robust way. These use a lazor to count particles as they pass by. Some issues include the fact that monitors can only detect particles above 300 nano metres, meaning some of the finer particles are missed. Also readings include any particles suspended in the air including moisture, which can result in over-readings.   

The Air We Share – tracking black carbon 

We decided to use black carbon monitors to track the exposure of 10 Londoners as part of the Air We Share campaign. These monitors give a cleaner data set as they measure pollution that comes from combustion, which in an outdoor urban environment is mostly traffic. Levels of black carbon correlates with overall pollution levels, so readings provide a good indication of people’s exposure. However these devices cost a prohibitive £5k each. They also generate vast amounts of data, taking a reading every minute, which was incredibly time intensive to sift through.   

Monitoring can make the invisible visible and serve as a powerful engagement tool, but understanding the limitations and challenges of each type of monitor is essential. Investing in more data collection also must not be a distraction from taking action. 

Air pollution is a complex issue and the evidence-base and technology is fast evolving – if you have any questions about the monitoring, or have any research you can share with us, please get in touch. We’d love to hear from you.  

Find out more about the Air We Share and what you can do at