Taking a taxi could increase your exposure to pollution

Researchers have discovered that your level of exposure to pollution can vary according to what method of transport you use, with travelling by taxis resulting in the highest levels of exposure and walking the least.

Research published in the journal Atmospheric Environment, describes how the team from Imperial College London and the Health and Safety Laboratory, Buxton, measured and visualised exposure to pollution levels, while using a variety of different transport methods for travelling across London.

The researchers looked at five modes of transport, including walking, cycling, car, taxi and bus, and measured levels of exposure to ultrafine particles when travelling on them using a newly developed system that uses in combination an ultrafine particle counter and video recorder.

Ultrafine particles are less than 100 nanometres in diameter and mainly traffic related. Their small size and large surface area means it is possible to inhale large quantities which makes them particularly dangerous.

The visualisation system allows video images of individuals' activities to be played back alongside the ultrafine particle concentrations they are exposed to. As a result, most activities and behaviours that cause high exposures can be visibly identified, such as being trapped on traffic islands and waiting in congested traffic.

On average, while travelling in a taxi, passengers were exposed to over 100,000 ultrafine particles counts per cubic centimetre (pt/cm3), travelling in a bus resulted in exposure to just under 100,000 pt/cm3, travelling in car caused exposure to 40,000 pt/cm3, cycling was around 8,000 pt/cm3, and walking was just under 5,000 pt/cm3.

Surbjit Kaur, from Imperial College London, and first author of the paper, said: "It was a real surprise to find the extent to which walking resulted in the lowest exposure. The higher exposure from travelling in taxis may come from actually sitting in the vehicle while being stuck in traffic where you are directly in the path of the pollutant source. Also the fact that taxis are probably on the road for much longer than your average car could cause an accumulation of ultrafine particles."

Dr Mark Nieuwenhuijsen, from Imperial College London, added: "The particular strength of the system is the visual aspect. The new monitoring and visualisation system is an effective environmental risk communication tool that can be used to identify, visualise and avoid hotspots of pollution. "

The study was carried out as part of the DAPPLE (Dispersion of Air Pollution & Penetration into the Local Environment) project, which looks to provide a better understanding of the physical processes affecting street and neighbourhood scale flows of air, traffic and people, and their corresponding interactions with the dispersion of pollutants. The project consortium includes the University of Bristol, the University of Cambridge, Imperial College London, University of Leeds, University of Reading and the University of Surrey.