Air quality measurements at NPL: Providing support to government and environmental research.

While NPL's primary role is to provide highly accurate techniques to underpin requirements for measurements made elsewhere, there are areas where NPL also has long experience of the practical aspects of the measurements. This allows direct links between the national standards and 'real' measurements, with benefits both for those who use the measurements and for the continued relevance of NPL's work.

Air Quality measurements are one such area. Air Quality refers to the levels of pollutants in air that are relevant to human health or ecosystems. The most important pollutants have changed over recent decades. Historically, coal burning in towns led to high levels of sulphur dioxide (and particles – see below), but this pollutant is now only a localised problem. The most important gaseous pollutants for human health effects are currently ozone and nitrogen dioxide. These are difficult both to control and predict because they are not directly emitted into the atmosphere, but form there through reactions between other gases. Hydrocarbon species, including benzene, for example, play a critical role in ozone production.

The pages linked through the Air Quality site describe activities and services relating to field measurements of pollutants for regulatory purposes (excluding particles), both by automatic and manual methods, occupational exposure, and related work. For example, real time measurements of ozone, sulphur dioxide and nitrogen dioxide in the air in Teddington have been made since 1996.

Airborne Particles are important, complicated and difficult to measure. They have the largest effect on human health of all air pollutants in Europe; they have a large but poorly-quantified effect on climate change; and both of these factors are highly relevant to the current interest in the manufacture of nanoparticles for industrial purposes. Airborne particles in outdoor air are a varied and changing mixture of natural particles (such as dust and sea salt), man-made particles (such as carbon-rich particles from engine exhaust) and particles formed within the atmosphere by reactions between gases (such as ammonia and nitrogen dioxide, which form ammonium nitrate). They vary in size from a few nanometres to tens of micrometres. Many different techniques are used to measure them, and techniques intended to measure the same property, such as the total mass of particles in a given volume of air, can give very different results.

The pages linked through the Airborne Particles site describe work in characterising particles by their mass (such as PM₁₀ and PM_2.5), by their number and size distribution, and by their composition.

For further information on environmental measurements at NPL, please contact us.