There are many sources of pollution that can have adverse impacts on the quality and cleanliness of the air we breathe. A major source of these air pollutants is the exhaust from motor vehicles.
The chemicals present in the exhaust from cars and trucks, include carbon monoxide, lead, oxides of nitrogen, sulphur dioxide, aromatic hydrocarbons and tiny particles called particulates. Many of these pollutants can harm the health of humans and animals and have the potential to directly affect the respiratory and cardiovascular systems.
"Motor vehicles and other motorised machines like lawn mowers contributed by far the largest proportion (84%) of air pollution with approximately 72,000 tonnes made up of 12 different pollutants. By far the largest proportion of these emissions were criteria pollutants, nitrous oxides, sulfur dioxide and carbon monoxide, which made up 97% (69945 tonnes) of emissions." -Greenpeace Australia, Analysis of Victorian EPA National Pollutant Inventory Air Pollution trials, Dandenong Victoria 1995.
"The consumption of automotive fuels has increased markedly in the last decade. In the 1985 emissions survey Canberra used 218 million litres of petrol, diesel and LPG or 797 litres per person. Calculations based on 1993/94 excise data reveal the apparent consumption of 348 million litres or 1161 litres per person." - Barney Foran, "Ecological Footprints - Cars, transport and emissions" , Nature & Society Summer 1995
The ACT Health Department monitors priority pollutants at 6 monitoring stations in Canberra's urban environment. The pollutants include sulphur dioxide, carbon monoxide, oxides of nitrogen, suspended particulates, ozone and atmospheric lead. On the basis of these monitoring results and our current standards, the only priority pollutant exceeding the guideline is carbon monoxide. These breaches have occurred during winter at the Civic and Gowrie sites. Carbon monoxide is a serious air pollutant which is toxic to humans and affects the oxygen carrying capacity of our blood causing symptoms such as headache, tiredness and if the exposure is high enough, death. The carbon monoxide pollution results from the combined impact of motor vehicles and wood fires with the highest concentrations being detected on winter nights. Comparing Canberra's results to those of Sydney and Melbourne provides a reasonably positive picture of air pollution in Canberra particularly the significant decline in atmospheric lead levels since the early 1980s. Yet Canberra's ambient air monitoring has not included comprehensive sampling of pollutants such as 1,3,butadiene, xylene, polyaromatic hydrocarbons or formaldehyde. These pollutants are known as 'air toxics'.
In Canberra, regulatory authorities have just commenced assessing levels of benzene in air, (so far the only 'air toxic' analysed.) Preliminary sampling has indicated the levels of benzene are low compared with the larger capitals.
The potential impact on community health of the priority pollutants is clearly recognised by regulatory authorities across Australia, with the acknowledged health impacts ranging from lung damage to the exacerbation of asthma. Yet the possible impacts from exposure to other air toxics may be as or even more significant. Many of these air toxics are recognised as potential human carcinogens and immuno-suppressive agents. Already, preliminary human testing has indicated that the Australian population including children are carrying significant body burdens of these chemicals in their blood. While quite often the specific source of the chemicals cannot be clearly identified, the exhaust emissions from cars and trucks must be considered one prime source of these potent air poisons.
The results of the Department of Health air monitoring are available in published quarterly reports and in the ACT State of the Environment.
Enormous quantities of carbon dioxide are liberated into the atmosphere when fossil fuels are burnt. Although carbon dioxide is a colourless and odourless gas and usually not considered a pollutant as such, its build up in the atmosphere leads to major changes in climate. Carbon dioxide in the atmosphere acts like the walls of a greenhouse, trapping the energy from the sun and absorbing the heat. The more carbon dioxide there is, the greater the rise in temperature in both the atmosphere and on the earth's surface.
Carbon monoxide (CO) displaces oxygen in the blood which can lead to cardiovascular, neurological and behavioral effects. While carbon monoxide can also exacerbate existing heart conditions, continuous exposure, even to very low levels can affect the nervous and muscular function of the body. The toxic effects increase as the concentration and duration of exposure increase. The effects can range from mild headache (50 ppm and above) to severe headache (above 200 ppm); weakness, dizziness, nausea, fainting (above 400 ppm); increased heartbeat, irregular heartbeat (above 1200 ppm) to loss of consciousness and death (above 2000 ppm). Levels of 50 to 100 ppm are not uncommon in crowded large city centre streets during rush hour.
The two primary oxides of nitrogen involved in air pollution are nitric oxide and nitrogen dioxide. Nitrogen dioxide is produced by motor vehicles and other industrial sources. It is a reddish brown gas with a pungent smell. It can affect the respiratory system exacerbating asthma. The main health issues associated with NO2 are increased incidence of lower respiratory tract infections in children and increased airway responsiveness in asthmatics. In the atmosphere nitrogen oxides are changed into nitric acid which is washed out in rain and is a principle precursor of acid rain.
Sulphur dioxide is a colourless gas with a strong suffocating odour. It is produced by burning sulphurous fuels such as coal and oil and combines with moisture to form acid rain. SOx is responsible for ongoing damage to buildings. SO2 causes increased respiratory airway resistance and this is exacerbated by breathing through the mouth rather than the nose. The nasal mucous removes most sulphur dioxide. Asthmatics are more sensitive to SO2 than healthy subjects.
Lower atmosphere (tropospheric) ozone is formed by reactions of volatile organic hydrocarbons and nitrogen oxides, primarily from industrial sources. Ozone has a wide range of respiratory effects including decreases in athletic performance at levels as low as 0.12ppm in ambient air. High risk groups include athletes and asthmatics, and young adults seem to be more affected by O3 than older people. Health effects have been measured at 0.08ppm.
Particulate pollution is a mixture of solid particles and liquid droplets that vary in size, composition and origin. While particles of less than 10 microns (PM10) and above 2.5 microns (PM2.5) make up around 80% of TSP, it is the fine particles of less than 2.5 microns that are developing as the major health concern. These extremely small particles may penetrate the lung and remain there for long periods of time. The fine particulate matter attracts potentially potent chemicals to their surface and when inhaled can contain complex mixtures of chemical compounds. Acute exposure to airborne particles is associated with increasing mortality and morbidity. Asthma and bronchitis are associated with particulate matter in several studies. Levels as low as 150 ug/cu metre ambient air are associated with decreased peak respiratory flow.
Adolescent allergic asthmatics are more sensitive to sulphuric acid, and responses have been observed at levels as low as 70-100 ug/cu m. Healthy adults have few responses below 500 ug/cu m. Increased frequency of bronchitis and respiratory illness have been associated with particulate sulphate exposure in children. Atmospheric nitric acid has been associated with possible pulmonary responses in asthmatics.
Atmospheric lead is predominantly from motor vehicles but is also emitted from smelting and some industrial operations. Lead affects multiple organ systems and effects on childhood development and adult blood pressure are evident at or below 10 ug/dl in blood. There has been a significant reduction in ambient lead levels in the air of Canberra since the introduction of lead free petrol. .
Combinations of variable concentrations of air pollutants may have synergistic and additive effects.
Atmospheric toxics include a range of carcinogens, acute toxicants, reproductive, mutagenic, immunotoxic and neurotoxic compounds that target multiple organ sites in addition to the lung and respiratory tract. Carcinogens include particulates, benzopyrenes, benzene, chlorinated organics, dioxins, aromatic amines, arsenic, chromium, nickel, and many other individual compounds. Identifying the effects of individual toxics in atmospheric pollution may be beyond the scope of epidemiology. Extrapolation from animal models, in vitro tests and study and development of biomarkers of toxicity will be important. The top twenty air toxics in the U.S. have been identied as : Toluene, Ammonia, Acetone, Methanol, Carbon Disulfide, 1,1,1-Trichloroethane, Methyl Ethyl Ketone, Xylene (Mixed Isomers), Dichloromethane, Chlorine, Aluminum Oxide, Ethylene, Hydrochloric Acid, Freon 113, Trichloroethylene, N-Butyl Alcohol, Methyl Isobutyl Ketone, Benzene, Styrene, Chloroform.