How Air Quality is Measured

Air quality is simply the concentration of pollutants and particles in the atmosphere and there are a variety of ways to measure it.  Many people are familiar with the air quality indexes produced by countries to indicate when air pollution might be a problem for vulnerable groups. 

In the United States the air quality index is production by the Environment Protection Agency (EPA) and in Canada by Meteorological Service of Canada. (MSC)  Like most other countries they only measure five major pollutants: ground-level ozone, particulates, sulphur dioxide, carbon monoxide and nitrogen dioxide. 

The air quality measurements necessary to produce these indexes are taken in different ways.  Methods are chosen based on cost and accuracy and are divided into passive and active.  Active methods suck up a portion of air to be analysed.  Passive methods simply allow the air to flow into the monitoring device and filter what is being measured.  

Passive air quality monitoring is this most economical method and utilses a wide range of devices.  Some examples are diffusion tubes, partisol monitors, and the brilliantly named ‘dust frisbees’. 

Diffusion tubes monitor polluting chemicals such as nitrogen dioxide.  They are extremely simple devices which are hung up for a set period of time while the air flows through them.  Pollutants are absorbed in a small pad which is later analysed. 

There are other simple passive monitoring devices used to measure particulate pollution, dust and pollen.  

Partisol monitors filter the air and are used for particulate pollution.  This is also known as particle pollution, and you might be more familiar with it as soot.  It is one of the main indicators of air quality.  Dust frisbees are used to measure how much dust is in the atmosphere.  Excessive dust can cause lung problems. 

Pollen counts are not an indication of air quality as such but provide information of importance to people with allergies.  They are usually taken with the aid of a sticky device.  The pollen grains adhering to the monitoring equipment are then counted.

Active methods differ only in that a sample of air is pumped up and the sample analysed rather than the impurities filtered out.

The pollutants or particles collected are then either analysed on the spot or, more commonly, the sample is taken to a laboratory for analysis.  The data collected provides an idea of the air quality in an area.  It is often used in conjunction with computer modelling to make predictions and identify potential trouble spots.

These readings and predications are extremely useful.  The public finds out how good the air quality is in their area and make decisions accordingly.  This is especially important to those in vulnerable groups such as people with respiratory or heart problems.  It can also be used to make decisions on reducing pollution by identifying where it is, or is likely to be, worst.

Air pollution can be a serious problem in modern cities and is linked to a range of health problems.  The pollutants emitted from the burning of fossil fuels are not something it is advisable to breathe in.  Dust and pollen might be natural but when their concentration is high they too are damaging.  Measuring the air quality gives an indication of what, if any, action is needed.  This could be advising asthmatics to stay indoors, fitting filters on chimneys, or taking action to reduce the number of cars in use.

Further information.  There is a huge amount of information about measuring air quality online.  These sites provide easy to understand introductions: