Why monitor air quality? Well, to monitor is to know. Everything else is just more or less qualified guesses. International, national and local air quality targets and limits are also tied to monitoring results.
What is Air Quality?
How is air quality characterised? It is quite common to find air quality indexes, where the ranges are divided in sections indicating “good”, “fair”, “troublesome”, “alarming”, or similar. Different population groups might need to take different precautions based on the current value of the index.
What to Measure
An air quality index is not a direct measurement result, but typically a weighted value based on concentrations of a number of specific, characteristic air pollutants. Those pollutants are monitored by various types of gas analysers and/or particulate monitors. Examples of such pollutants are nitrogen dioxide (NO2), ozone (O3), and particulate matter (PM10 and/or PM2.5 particulate fractions). There is not a global standard for air quality index, but different countries and regions can compose their own indicators based on the local air pollution situation.
Where to Measure
Once you have established what to measure, the next question is where to measure. This is just as important as “what”, since the levels air pollution can vary widely between different locations. The location is often chosen to be representative for the worst case where people normally spend noticeable time. By example, it can be an intersection between two busy streets in a city centre. However, to just monitor in one location can be misleading, so there are usually also regulations or recommendations on the number of monitoring locations. The monitoring locations might also be changed due to city planning activities, new findings on pollution sources, or complaints from the public.
To achieve reliable and representative monitoring of air pollution which also can be the base for an air quality index, national or local authorities operate air quality monitoring networks. Such networks are based on monitoring stations where each station is equipped with gas analysers and particulate monitors, often with the ability to deliver pollutant concentration data in close-to real time.
It is not unusual to find networks consisting of 10 to 20 monitoring stations. Data from each station is transferred in real time to data centres where the quality of the data is checked and various data including real-time air quality indexes can be made available to the public and other stakeholders. The data is also used for subsequent analysis and as a tool for city planning and other activities that might improve the air quality.
The daily operation of an air quality monitoring network can be a challenge, but with the right equipment and well trained maintenance staff, it is still quite manageable.
Air quality indexes give important information to the public, and it can be a vital input for planning authorities to make the right decisions. Just make sure the index is based on trustworthy, continuous air quality monitoring!