There are many more potential health effects of air pollution from road transport. For example, the reaction of pollutants with natural sensitizers may also possibly underlie an increase in the incidence of other allergies, such as hay fever. Some pollutants, such as ozone and nitrogen dioxide may also increase our susceptibility to infection. Carbon monoxide can aggravate angina. Diesel and petrol exhaust fumes are considered respectively to be ‘probably’ and ‘possibly’ cancer
causing. Car exhausts certainly provide the bulk of most peoples exposure to numerous toxic substances including 1,3-butadiene, benzene, formaldehyde and polyaromatic hydrocarbons, all of which are known or probable cancer causing substances.