Automobile Emissions Essay Research Paper ABSTRACTPollution from — страница 2

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. 2.1.2 Nitrogen Oxides 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. Figure1 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. 2.1.3 Volatile Organic Compounds 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. 2.1.3.1 Effects of Benzene Prolonged exposure to benzene especially in the respiratory tract or cutaneous contact can result in aplastic anemia or acute myelogenous leukemia. Bone marrow is also affected. When the bone marrow is affected it decreases circulation in the erythrocyte, platelets and leukocytes. Benzene related leukemia usually affects workers exposed to it for periods of forty years. 2.1.3.2 Effects

of Aromatics Aromatics have been added in modern day fuels which contain high levels of benzene. The total benzene emission increase is directly proportional to the amount of aromatics found in fuels. For about every 1% of aromatics there is 4% of benzene. It was also found that the amount of non-benzene aromatics in fuels also results in a n increase in tailpipe emissions of benzene. 2.1.3.3 Effects of Hydro Carbons Aliphatic hydrocarbons upon inhalation may be harmful, because in high concentrations, they depress the central nervous system causing dizziness and incoordination. It is generally accepted that low level exposures have no or little effects on the human body. But they do play an important role in photochemical smog. 2.1.3.4 Effects of Alcohol With the additions of

methanol and ethanol as fuel additives was implemented to reducing emissions. But the problem is that these additives are very volatile hence they will contribute to the overall VOC load. The problem with additives such as methanol tends to emit formaldehyde. And formaldehyde is a carcinogen and a key component to photochemical smog. 2.2 PHOHEMICAL SMOG There are two types of smog. The first, which has been known for a long time, is when there is an incomplete combustion of coal. This phenomena produces sulfur dioxide and smoke and in combination with fog forms smog. The second type is when automobiles exhaust produces oxidative pollutants, which leads to photochemical smog. Photochemical smog results from the atmospheric reaction between certain hydrocarbons and oxides of