Air Quality Monitoring
Dr Melanie Williams Group Leader, Environmental Measurements, National Physical Laboratory
Climate change, pollution and air quality have become a part of modern life. There are definitive links between pollutants and adverse effects on human health as well as on environmental sustainability. We need to ensure that the quantity of these pollutants in the air does not go above levels where they become dangerous to our health or to the environment.
This is an issue that concerns the government, business and the public. Governments need to meet set regulations which limit the levels of pollutants in the air, and businesses, councils and communities need to ensure they don’t exceed these levels.
Furthermore, having a clear understanding of the presence of certain toxins and pollutants underpins environmental and health research and supports modelling of future impact. This provides an infrastructure which can quickly respond to changes, such as the specification of new pollutants or events which lead to sudden increases in harmful emissions.
Underpinning this is the need for accurate measurement. This is critical to understanding the levels of man-made and naturally occurring pollutants, and is essential to developing strategies to mitigate short- and long-term impacts. It provides the basis for setting the limits and the ability to enforce them.
In the UK, the government has established several Air Quality Networks, through the Department of Food and Environmental Affairs (Defra) that are organised into networks that target a particular pollutant, using a particular measurement method. This information informs government policy, validates emission reductions, and provides warnings if pollutants reach dangerous levels.
How does NPL help? The National Physical Laboratory (NPL) is the UK’s National Measurement Institute and as such has developed considerable expertise in the measurement of airbourne particles which affect air quality.
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 considerable experience of the practical aspects of the measurements.
Air quality measurements are one such area. NPL's expertise has been called upon to play leading roles in
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the World Meteorological Organisation (WMO), and the European Air Quality Reference Laboratories (AQUILA). We are entrusted by Defra, the Environment Agency and NERC to lead UK monitoring networks as well as the provision of traceable measurements for climate change models.
These measurement projects include detecting gases such as ozone, water-vapour, airborne particles from 1 nm to 10 mm in size, and VOCs (volatile organic compounds - chemical compounds with significant vapor pressures that can be dangerous to health and the environment, eg 'smog').
Air quality surveys are applicable to many industrial and air quality applications, including: groundwater and soil contamination assessment, tanker loading emissions monitoring, detection of leaks from storage facilities and vehicle emissions.
Accurate monitoring of air quality is also vitally important for regulatory purposes and industrial impact assessment. Ambient air quality surveys at NPL include characterising industrial emissions in accordance with UK and EC legislation, monitoring roadside and urban air quality, validating pollution abatement measures and supporting corporate environmental policies.
The science behind air quality Airborne particles are complicated and difficult to measure. They have the most serious effect on human health of all air pollutants. The also have a significant but poorly-quantified effect on climate change. 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.
NPL have been closely involved with the development of standard methods for measuring airbourne particles, which are generally classed in two groups, PM10 (particles of 10 micrometers in diameter or less) and PM2.5 (particles less than 2.5 micrometers in diameter).
A range of techniques are available for measuring airbourne particles. The reference method involves weighing filters before and after they are exposed to the air being sampled.
Some common automatic methods of measurement include Tapered Element Oscillating Microbalances (TEOM), which measure the increasing mass of a filter
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