Ideally, the measurement of pollutant concentrations outdoors (ambient air) should reflect public exposure but this is not always possible as air quality monitoring stations sample from a single fixed point. It is important that monitoring stations are placed in areas where high pollution is likely such as close to busy main roads and large industrial sources to record the ‘worst case scenario’.
The National Air Quality objectives are expressed in a variety of ways depending on the pollutant being measured; 1 hour, 8 hour, daily and annual averages. To calculate the various averages data is collected by automatic air quality monitoring stations which sample and analyse air 24 hours a day, this is known as ‘continuous monitoring’. Continuous monitoring equipment is both expensive to install and maintain but provide invaluable information. Find your nearest continuous monitoring station on the London Air website.
Each pollutant is measured in a different way: