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From monitoring stations to microsensors – air and health

From the NILU Annual Report 2016: New technology brings new opportunities. So why haven’t we discarded those large monitoring stations and started using microsensors yet?

Along Norway’s roads and streets stand two different types of air quality monitoring stations. The traffic oriented stations measure pollution from traffic, and thus stand close to the road.

Urban background stations, on the other hand, must be able to capture total air pollution from various sources (traffic, heating, urban industries, natural sources, etc.), so they are found in parks or other open spaces.

Montering av AQMesh-sensorer på målestasjonen i Kirkeveien
Scientists from NILU and the Technion Israel Institute of Technology evaluated 24 low cost AQMesh sensors in 2015. These sensors were mounted on top of the traffic oriented monitoring station in Kirkeveien (above), so that the scientists could compare measurements from the AQMesh sensors to air quality measurements from the monitoring station at the same location. Photo: NILU

Strict routines, high quality

Such monitoring stations house sensitive instruments that record very accurate data in near real-time. Thus, they are also expensive to install and operate.

– Currently, there is no alternative to these monitoring stations, says Kjersti Tørnkvist. She is Director of NILU’s Department of Monitoring and Instrumentation Technology, and thus also strongly involved in the National Reference Laboratory for Air Quality.

– We are required to monitor air quality as described in the European Air Quality Directive (2008/50/EC) and in the EU Commission Directive 2015/1480 and the Norwegian Pollution Control Act Chapter 7. Together this constitutes a very detailed regulatory framework for both what to measure, how, where and how often.

All European countries monitor air quality according to the same directives. This means they use the same reference methods and the same operating and calibration routines to ensure high quality data and low uncertainty. It also means that you can compare air quality data from cities across Europe – Tromsø with Berlin, Bergen with Barcelona.

Monitoring air quality to assess health risks

Tørnkvist is often asked why traffic oriented stations are placed next to roads, rather than in gardens or parks where people spend time outdoors.

– The location is related to what we call limit values for pollution, rules for how much pollution is allowed over a given period. These values are based on two things: what level of contamination we know can be hazardous to health, and how far away from the source of pollutants the monitoring stations are.

For instance, the limit value for NO2 is max. 200 micrograms NO2 per cubic meter of air (μg/m3) per hour. It is allowed to exceed this limit value for 18 hours a year, but the nineteenth hour past 200 μg/m3 breaks the law.

That the permitted limit value is as high as 200 micrograms is because traffic orientated stations are situated close to the source of pollution – that is, road traffic. Had the directive stated that the measurement stations were to be placed further away from the cars, the limit would have been lowered to make up for the increased distance.

– Health is the reason we monitor the air, says Tørnkvist. – The purpose is to provide authorities with real data about how the air quality actually is. This information is further used by scientists and managing authorities to develop measures that provide us with cleaner air and better health.

Limited micro-information


During recent years, microsensors have appeared on the market. Concerned citizens and other actors have begun purchasing these low cost air quality sensors to measure air quality where they live and work.

– We understand very well that people are engaged, says senior scientist Núria Castell from NILU’s Department for Urban Environment and Industry, – and we appreciate that. At the same time, it is important to orient yourself in the market.

Castell has participated in several evaluations of various types of microsensors. She believes it is important that both private citizens and others are aware that these sensors are still in the development phase.

– Most microsensors for air quality monitoring available today are so unstable that we would not advise to use them in contexts that require high data quality and reliability, she explains.

– For instance health related or regulatory monitoring.

Engage yourself!

Currently, there are no EU directives, other regulations or independent quality assurance for microsensors, as for the stationary monitoring stations used in Norway today. Thus, it is difficult to be sure that data quality from microsensors is good enough. This must be taken into account when selecting surveillance solutions to help protect the health of citizens.

– It is necessary to establish a quality check framework for microsensors to be calibrated against reference stations, explains Castell.

– Another challenge to be solved is how different weather conditions affect microsensors, for instance, when measurements are affected by changes in temperature and relative humidity.

– For now, data from microsensors must be quality assured by experts in order to be useful. We believe that the future of air quality measurement by microsensors is very promising, but for now we do not recommend using them as a basis for making health related decisions.

– Nevertheless, with proper calibration and quality control, some of the sensors on the market provide data sufficiently reliable to determine whether the air quality is good, moderate or highly polluted. What this means is that that citizens can use these microsensors to get an overall opinion of the air quality where they live, she concludes.

Montering av AQMesh-sensorer på målestasjonen i Kirkeveien
Mounting of AQMesh sensors at the monitoring station in Kirkeveien. Photo: NILU

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