23 April 2001: The car - and the motorist - are blamed for congestion and pollution. But few think about the impact motoring can have on those who drive. And how gridlock and poor traffic management play major roles in increasing the exposure to pollution on an individual basis.
Scientific evidence suggests road users - of all kinds - are exposed to higher levels of air pollution than the background data might suggest. Furthermore, this evidence indicates how varied the level of exposure can be depending on whether you are driving, cycling or walking.
Just for the records, so you can refer back to them, the main pollutants applicable to motoring are what they call volatile organic compounds (VOCs, including benzene and other hydrocarbons), carbon monoxide (CO), nitrogen dioxide (NO2) and respirable particulates (PM10).
Of these, benzene and CO are primary by-products of the combustion of petrol, and particulates emanate mainly from diesel combustion . NO2 is mainly a secondary pollutant, formed when nitric oxide (NO), another primary by-product of the internal combustion engine, is oxidised in air.
Dozens of studies have been conducted in the recent past on how road users are affected and there is an overwhelming amount of consensus between them.
The research strongly indicates that:
# Cars offer little or no protection against pollutants created by vehicle traffic.
# Road users can be exposed to significantly high levels of pollutants simply because they are travelling in what the experts call the 'tunnel' of pollution.
Indeed studies from Britain, continental Europe and the US agree that levels of car pollutants such as benzene (and other hydrocarbons), carbon monoxide, and nitrogen dioxide can be much higher in and around the car are far higher than those in the air around 50-100 metres from the vehicle.
Most of the studies indicate that drivers and passengers in motor vehicles are exposed to higher levels of the main pollutants than pedestrians and cyclists .
Larger public transport vehicles do not appear to have as much an impact on their drivers as cars, but can still affect pedestrians and others. Images of belching buses spring immediately to mind and raise the question of just how serious the Government is on emissions when public transport can be so polluting.
Cyclists are potentially subject to higher exposure and the reason is obvious. They tend to use more energy to propel their vehicle and therefore breathe more often, so they take in more of the 'polluted' air. Contrary to popular belief, pedestrians generally experience the lowest exposures of any road users. The extraordinary thing is that some studies have have failed to detect any marked improvement in levels of in-vehicle pollution despite the introduction of catalytic converters.
But like all statistics and studies there are as many to contradict as agree and there are several studies which indicate that there has been a downward trend since 'cats' became more widespread, especially for VOCs.
Some data from the US, where the majority of vehicles now use catalytic converters, do suggest some improvement. It is too early to draw firm conclusions on the likely impact of catalytic converters in Europe, but it is possible that catalysts alone are not sufficient to solve the problems caused by motor vehicle emissions, the experts say. It is also stating the obvious, even if it took several studies to confirm it, that congested, slow moving traffic is a major contributor to higher levels of VOCs and CO in cars.
Other serious contributors to the problem are older cars and faulty exhaust systems.
Typical urban rush-hour conditions tend to produce the highest in-car concentrations of these pollutants. Yet the levels of nitrogen oxides inside the car, on the other hand, seem to be worse during motorway driving, and levels of NO2 in particular seem to rise later in the day.
Interestingly, in most studies the level of ventilation did not significantly alter the concentration of pollutants inside the car although conditions tended to be worse with the heater or ventilation on and sometimes better (for VOCs) with air conditioning. While open air car parks have relatively low levels of pollution, enclosed car parks appear to retain the pollution caused by vehicles, and high levels have been recorded. That is not surprising considering the volume of traffic and poor ventilation in many of these. It does not stop them charging large amounts per hour to park your car.
Vehicle filling stations also expose drivers to high levels of VOCs unless sophisticated vapour-recovery systems are fitted, the experts says. We can only hope that, in the long term, the new car test will help lower the level of emissions and help to keep cars in better tune and emitting fewer noxious materials.
In the meantime we should be aware that even in our cars we are subject to the side-effects of emissions and realise just how many implications gridlock and our appalling traffic management system have for our health.
In future when we talk about traffic congestion and how we deal with it we should remember that we are part of the environment and sitting in city traffic is neither good for our mental or physical health. FCC
