A taxi could increase your exposure to pollution

Your exposure to pollution varies according to the transport you use. Travelling by taxis results 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 using a different modes of transport across London.

Ultra fine particles are less than 100 nanometers in diameter and mainly traffic-related, present in traffic-dense areas. Their small size and large surface area make it possible to inhale them in large quantities, which makes them particularly hazardous.

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

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

On an average, taxi passengers were exposed to over 100,000 ultra fine particles counts per cubic centimeter (pt/cm3), bus passengers to just under 100,000 pt/cm3, travelling in car caused exposure to 40,000 pt/cm3, cycling was around 80,000 pt/cm3, and walking was just under 50,000 pt/cm3.

Surbjit Kaur from Imperial College London, the first author of the study, 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 ultra fine particles."

The study was carried out as part of the DAPPLE (Dispersion of Air Pollution & Penetration into the Local Environment) project, which endeavors 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.