Automobile Emissions

Pollution from automobile emissions has become over the past few decades an issue of great concern. With a growing number of motor vehicles on our roads great concern has been attributed to the effects of these emissions to our health and to the environment. Several of the gases emitted, which when present in certain concentrations in our atmosphere can be toxic, therefor these ultimate concentrations must never be achieved. Strict legislation as well as sophisticated control technology has been implemented in the automotive industry in order to limit the pollution caused. These aspects of automotive pollution shall be further discussed in this paper.

KEYWORDS: Pollution, Car Pollution, Automotive emissions, Emission gases, Catalysts

The relationship between air pollution and automobile exhaust emissions has been established largely due to studies done in California. At first the problem was believed to be a combination of smoke and fog, which was similar to problems faced in London since the middle ages. In Los Angeles the severity of air pollution has caused vegetation damage, eye and throat irritation, a decrease in visibility as well as several other effects.

Automobile and truck exhausts contain substances which can adversely affect human health when exposed to concentrations above ambient level. Emissions from automobiles usually consist of carbon monoxides, oxides from sulfur and nitrogen, unburned hydrocarbons, smog, and particulate matter, which includes smoke. Pollutant concentration and time of exposure are the two main factors which affect human health.

Air emissions from automobiles can also have an overall effect on the environmental quality in several ways. Emissions from nitrogen oxides (NOx) can contribute to the acid deposition problem, combinations of NOx and hydrocarbons can help produce ozone and photochemical oxidants and lastly pollutants from automobiles and ozone formation can contribute to the ambient air pollution problem in urban areas.

As a result of increasing concern about the role of the motor vehicle in contributing to these health and environmental problems as well as the possibility of these problems to increase due to a growing number of cars worldwide, strict legislation has caused engine emission control technology to quickly develop. As legislations become more severe, emission control technology is constantly changed or modified in order to meet the new requirements and reduce the emissions produced.

This report shall focus on the health effects that automotive emissions such as gases and particulates may have as well as discuss the control of these emissions via legislation and technology. The technology discussed is primarily the present technology implemented to control automotive emissions, namely catalysts.

2. HEALTH EFFECTS OF AUTOMOTIVE EMISSIONS

Carbon monoxide (CO) is found in high levels in the exhausts of diesel and petrol powered automobiles. CO is a colorless and odorless gas and can be toxic at certain levels. The effects of carbon monoxide is felt when inhaled, it enters the blood stream and binds to hemoglobin (which the CO has a higher affinity than oxygen by 240 to 1). The resulting compound formed is carboxlhemoglobin. The blood is then unable to supply oxygen to the cells. And depending the level of exposure, death may be the ultimate consequence.

The formation of carboxlhemoglobin lowers the available hemoglobin. Normal individuals will not feel any effects until 5% to 10% of hemoglobin is transformed. As carboxlhemoglobin increases, symptoms such as headaches, visual disturbances, nausea and vomiting and coma may occur. Death may occur if levels of carboxlhemoglobin reach the vicinity of 70%.

Usually levels of carbon monoxide are low except in enclosed areas. On average most carboxlhemoglobin levels are under 5%. Since low level exposure to carbon monoxide is not well understood, it is believed that it might contribute to cardiovascular disease. The heaviest exposures to motorist occur in heavy (stop and go) traffic.

When considering the effects of carbon monoxide, it is usually easily overlooked. Barometric pressure has a direct influence of the amount of oxygen available in the body (especially if there is a drop). But in general people who live in high altitudes have higher levels of hemoglobin in their bodies (hence compensates for lower levels of oxygen). For cities at high elevations with pollution problems such as Mexico the same CO concentrations at sea level may have no effect to the population but may have impact with those with health problems.

There are several species of nitrogen oxides. But for our discussion we will consider N2O since the others have relatively no toxic effects. Nitric oxide is produced in the greatest quantity during combustion. It has no direct effects on health because it has a tendency to rapidly disappear into the atmosphere. In the atmosphere in the presence of sunlight and other reactive hydrocarbons is transformed into N2O and other photochemical oxidants. Nitrogendioxide (a brownish gas) is a visible component of smog, which directly affects human health. The following figure illustrates this cycle Figure 1.

Long term studies were done on animals to determine the overall effects of nitrogendioxide. There were changes observed such as ciliary loss in upper respiratory tract in rats and mice, emphysematous changes in dogs, and edema in squirrel monkeys. Also scientists observed that NO reduces resistance to bacterial and viral infections. Research on humans, based on exposure levels of 4-5 ppm. Researchers noticed an increase in expiratory flow resistance. High occupational exposure has lead researchers to record exposure levels of unto 250 ppm. In some cases weeks apart, there were rapid onset of fever, chills and difficulty breathing. But there were no definite effects of nitrogen dioxide at ambient levels.

These volatile organic compounds (VOCs) make up the lower boiling fractions of fuels and lubricants, and partially combusted fuels. These VOCs are emitted during refueling, leakage in the engine, and tailpipe.

VOCs are complex compounds of aliphatics, olefins, aldehydes, hetones and aromatics. Many these compounds are known to be potentially hazardous to human health. But in general these compounds are found in such low quantities there are no fears of having direct effects on human health. Rather these compounds have a direct effect on photochemical smog.

Prolonged exposure to benzene especially in the respiratory tract or cutaneous contact can result in aplastic anemia or acute myelogenous