Innovative system maps air pollution at pavement level and in vehicles

Air pollution experienced by pedestrians at the pavement level and by drivers in their cars just feet away can now be mapped accurately with a new monitoring system using satellites hundreds of miles above the earth. The system, either carried on the back of a surveyor or mounted in a car, has been used both in Oxford and London to provided accurate maps of pollutants across urban areas.

Air quality is a concern not just for major cities like London but also for smaller towns and cities such as Oxford where the number of vehicles entering the city centre continues to increase. The Groundhog Air system developed by AEA Technology Environment advances pollution measurement science as it is able to measure variations in pollutants in different parts of an area, or even different sides of the same street.

The system is completely self-contained, consisting of an aerial and electronics for a global positioning system, auxiliary batteries, a data logger/interface and a mix of gas and particulate detectors chosen as appropriate to the study in hand. This enables accurate pollution maps to be instantly developed on computer. Currently, the system is equipped with a mini pac carbon, monoxide detector, a Transducer Research Inc nitrogen dioxide analyser and a “ppb-Rae” photo ionisation detector (PID). Positional data and readout from the gas detectors is passed to a Trimble TSC1 handheld computer. The system has a positional accuracy 0.2 metres horizontal and 0.6 metres vertical. The concentration of pollutants and position are measured every second. The data collected from the study is processed and presented using a geographical information system.

Test survey

In Oxford the backpack system has already demonstrated that effective monitoring of carbon monoxide, nitrogen dioxide and hydrocarbons (VOCs) at the pavement level is possible, all are related to respiratory problems. To test out the technology, an early morning survey of Oxford was conducted on foot.

Nitrogen dioxide (NO2) is formed at elevated levels following emissions of pollutants from vehicle exhausts. A colour coded map of NO2 levels in Oxford was produced and showed that, in the main, levels were low. Where higher levels were encountered, these were due to emissions from eg lorries loading or unloading or where busses were idling waiting for passengers. The lowest levels of NO2 were encountered in the semi-pedestrianised areas of the city centre.

Carbon monoxide (CO) tends to be produced by petrol driven cars rather than by diesels. Groundhog Air showed that levels were low. Elevated levels were encountered wherever queues of traffic formed at junctions and at bottlenecks. Higher levels were also observed close to a major car park possibly as a result of cold starting of engines.

Volatile organic carbon (VOCs) compounds can be emitted as unburned fuel from poorly maintained vehicles. Whereas some VOCs are emitted by idling or queuing vehicles, the highest levels observed were as a result of petrol vapour blown from a petrol station forecourt. Levels were slightly elevated near to a major car park again as a result of cold engine starts.

This work around Oxford shows the extra detail available to planners and decision makers from the rapid and accurate mapping of air quality at the pavement level. The technology is applicable to investigating a wide range of rapidly changing air quality situations. The data can be presented in a form that is clear, unbiased and easy to discuss with professional and lay people. In addition, the data has the following uses:

  • Monitoring of air quality action zones
  • Controlling the impact of temporary and permanent traffic measures
  • Exposure monitoring of the general public
  • Temporal and spatial effects – throughout the day and around town

    In-car exposure

    A study using the Groundhog Air system to monitor pollution levels inside a vehicle has revealed that city drivers are exposed to pollution levels up to three times higher than those experienced by pedestrians. A study by AEA Technology plc has revealed that levels of carbon monoxide, nitrogen dioxide and ultrafine-particulates are much higher inside vehicles. All three pollutants are thought to contribute to respiratory problems such as asthma.

    The Department of Environment, Transport and the Regions (DETR) commissioned AEA Technology to undertake the most comprehensive study of its kind so far carried out in the UK. The AEA Technology team took 180,000 readings inside a car during 15 days of commuter driving into the heart of London.

    Among its findings the study revealed that average levels of nitrogen dioxide inside the car were above the one hour mean UK Air Quality Strategy (AQS) objective for 2005. There were also found to be an average of 10 million ultrafine particles per cubic centimetre inside the car during motorway journeys in and out of London. There is currently no AQS target for particle number, but the general background level is around 10,000 particles/cc.

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