Gaseous air pollution - Measurement principles

By its very nature, life is a process out of equilibrium. So, to maintain their structure, living beings must consume energy, and the result is that every living being feeds and excretes: it takes materials from the environment and discharges waste. By its very existence, life necessarily induces environmental disturbance. Man is no exception to the rule, and it is therefore pointless to imagine a society in which man does not modify the environment: from the moment we live, we accept to disturb it.

In fact, the challenge is to minimize the unfortunate consequences for human beings and avoid endangering the life forms that Nature has taken over a billion years to create.

Drawing on the definition given by the International Council of the French Language for the concept of nuisance, we would say that "pollution occurs when the environment contains substances that pose a significant risk to human health and well-being, or which may indirectly affect man through their repercussions on his natural, cultural or economic heritage".

Pollution is therefore defined by the nature of the substance concerned, the environment in which it may become harmful, and its effects on man and the environment. A given compound may be totally inert (or very beneficial) in one environment, but have very serious consequences in another. Chlorofluorohydrocarbons (CFCs), for example, are totally inert in the lower atmosphere, but can destroy ozone in the stratosphere; similarly, there would be no life outside the oceans without ozone in the stratosphere (protecting us from the Sun's distant UV rays, which can induce mutations and cancer), but this compound can be quite aggressive in the lower atmosphere; finally, carbon dioxide is essential for plant growth, but increasing its concentration in the atmosphere can lead to very harmful climatic changes in certain regions.

The field of air pollution measurement is therefore very vast, and we had to limit it. What's more, from a metrological point of view, sampling and measurement protocols are very different depending on whether we're looking at gaseous or particulate pollutants.

This series of articles [P 4 030] gives priority to :

• measurement of gaseous pollutants. Particulate pollution as such is not part of this field, but will be touched upon when dealing with organic pollutants at medium to low vapour pressure or adsorbed on the surface of mineral particles or soot;

• pollution on a local scale (the city and its surroundings). However,...