Car Emissions Pollute the Environment Essay Example

and reduce emissions. This report will focus on the health effects of automotive emissions, including gases and particulates, as well as discuss how legislation and technology are used to control these emissions. The primary technology examined will be catalysts, which are implemented for controlling automotive emissions.

Health Effects Of Automotive Emissions
Gaseous Emissions Effects

Carbon Monoxide
Carbon monoxide (CO) is present in high levels in the exhausts of diesel and petrol powered automobiles.

Carbon monoxide (CO) is an odorless and colorless gas that can be dangerous at certain levels. When inhaled, it enters the bloodstream and binds with hemoglobin to form carboxlhemoglobin. This compound has a higher affinity for CO than oxygen, which impairs the blood's ability to efficiently deliver oxygen to cells. The severity of these effects depends on the level of exposure, and in severe cases, it can be fatal.

The presence of carboxlhemoglobin decreases the available amount of hemoglobin. Typically, individuals without health issues will not experience symptoms until 5% to 10% of their hemoglobin is transformed into carboxlhemoglobin. However, as carboxlhemoglobin levels rise, symptoms like headaches, visual disturbances, nausea and vomiting, and even coma may manifest. If carboxlhemoglobin reaches approximately 70%, it can lead to fatality. Generally, carbon monoxide levels tend to be low unless in enclosed spaces.

Carboxlhemoglobin levels are usually less than 5%. The effects of low level exposure to carbon monoxide on cardiovascular disease are not well known. Motorists experience the highest exposures in heavy traffic, especially in stop and go situations. The importance of carbon monoxide's effects can be easily ignored. Barometric pressure can directly impact the body's oxygen availability, especially if it decreases.

Despite the fact that individuals living at high altitudes typically have

increased hemoglobin levels to compensate for lower oxygen levels, cities situated at higher elevations such as Mexico may be less susceptible to the effects of CO concentrations in comparison to coastal regions, thanks to their heightened hemoglobin levels. Nevertheless, it is important to recognize that these concentrations can still have an impact on people with preexisting health conditions.

Nitrogen Oxides

Out of the various kinds of nitrogen oxides, our focus will be on N2O in this discussion because it has fewer toxic effects when compared to other species.

Although nitric oxide is primarily found during combustion, its effect on health is minimal because it quickly disperses into the atmosphere. However, when nitric oxide combines with sunlight and reactive hydrocarbons in the atmosphere, it converts to N2O and other photochemical oxidants. Nitrogendioxide, a visible gas that looks brownish in color, plays a major part in smog creation and has a direct impact on human health.

The diagram below, Figure 1, depicts the cycle mentioned. Long term research on animals was conducted to analyze the global impacts of nitrogendioxide. Various alterations were observed including ciliary loss in the upper respiratory tract of rats and mice, emphysematous changes in dogs, and edema in squirrel monkeys. In addition, scientists noticed that NO decreases resistance to bacterial and viral infections. Studies on humans, considering exposure levels of 4-5 ppm, revealed an elevation in expiratory flow resistance.

According to researchers, high occupational exposure has resulted in recorded exposure levels of up to 250 ppm. In some cases, individuals experienced fever, chills, and difficulty breathing at different times several weeks apart. However, no definitive effects of nitrogen dioxide were observed at ambient levels.

Volatile Organic Compounds

Also referred to

as VOCs, these compounds consist of the lower boiling fractions of fuels and lubricants, along with partially combusted fuels.

There are different kinds of volatile organic compounds (VOCs) that are emitted into the air. These VOCs come from refueling, engine leakage, and the tailpipe. They consist of aliphatics, olefins, aldehydes, ketones, and aromatics. Although some of these substances can be harmful to human health, they usually occur in such small quantities that there is no immediate worry about their direct negative effects on human well-being.

These compounds have a direct impact on photochemical smog. Benzene can lead to aplastic anemia or acute myelogenous leukemia, particularly with prolonged exposure through the respiratory tract or skin contact. Furthermore, it affects the bone marrow and reduces the circulation of erythrocytes, platelets, and leukocytes.

Benzene-related leukemia is a common condition among workers who have been exposed to it for more than four decades.

Effects of Aromatics:

Modern fuels contain high levels of aromatics, which contribute to the increased release of benzene. The amount of aromatics in fuels directly affects the overall increase in benzene emissions. For each 1% rise in aromatics, there is a corresponding 4% increase in benzene emissions. Moreover, the presence of non-benzene aromatics in fuels leads to an elevation of benzene emissions from vehicle exhaust.

Effects of Hydrocarbons:

Inhaling large concentrations of aliphatic hydrocarbons can be harmful as they may depress the central nervous system, resulting in dizziness and lack of coordination.

Low level exposures are typically regarded as having minimal impact on the human body, but they do play a significant role in the formation of photochemical smog.

Effects of Alcohol

The challenge lies in incorporating methanol and ethanol as fuel additives to reduce emissions.

These additives have high volatility and contribute to an increase in overall VOC levels. Furthermore, the use of methanol as an additive can lead to emissions of formaldehyde.

Formaldehyde is responsible for two types of smog: one caused by inadequate coal combustion and the other caused by vehicle emissions. The first type of smog is formed when sulfur dioxide and smoke from coal combustion combine with fog. The second type, known as photochemical smog, occurs when oxidizing pollutants released from vehicles react with specific hydrocarbons and nitrogen oxides in the atmosphere under sunlight.

Various harmful effects on the human body can result from photochemical smog, including eye irritation, potential respiratory issues, reduced visibility, and damage to plants. During severe smog episodes, ozone levels can reach hazardous levels, posing health risks for humans. Several studies have examined the impact of ozone on animals and humans. For instance, when rats and mice are exposed to 6 ppm of ozone over a four-hour period, their mortality rate is around 50%. Additionally, even lower concentrations of ozone at approximately 1 ppm can cause permanent harm to the respiratory tracts of small animals.

While the short-term effects of ozone exposure on humans have been studied, the long-term effects are still unknown. However, findings from animal research suggest that humans may develop a level of tolerance to low levels of ozone, similar to the immediate impacts.

Recent studies have indicated that asthma sufferers experience similar effects to individuals without asthma when exposed to ozone, regardless of light exercise. However, when engaging in intense physical activity, irritation was observed at a concentration of 0.12 ppm. This effect at high exercise levels was found to be

influenced by the concentration of ozone, ventilation rate, and duration of exposure.

Particulate Emissions

Due to the construction of high compression ratio automobiles, particularly those manufactured in the United States, these vehicles required high-octane gasoline (typically 90-100 octane) for optimal performance. Achieving such levels either involved the use of tetraethyl lead or other organometallic compounds or increasing the aromatic content of the gasoline. However, with growing environmental consciousness, advanced nations have significantly reduced or eliminated lead from gasoline products. The removal of lead was also essential for the proper functioning of cars equipped with catalysts. The elimination of lead's effects was crucial in gasoline-powered vehicles.

Excessive lead levels have detrimental effects on human health, resulting in neurotic, renal, and reproductive problems. Even at lower exposure levels, lead can induce hyperactivity, hearing impairments, decreased cognitive abilities, and diminished nerve functioning. Moreover, research has demonstrated that reducing lead emissions leads to decreased blood lead levels in humans when measured.

Diesel Emissions

Diesel-powered vehicles resemble petrol-powered vehicles but generate elevated levels of particulate emissions. These particulate emissions are known to be carcinogenic as mentioned earlier. Rats exposed to high concentrations of diesel particulates exhibit lung inflammation, accumulation of soot and the development of chronic lung disease.

Lung tumors increased at high concentrations, but were not found at low levels. Manganese is a metal-containing anti-lock additive known as Methylcyclopentadienyl manganese tricarbon (MMT). It has been used in petrol cars since the phase out of leaded fuels to increase compression. The concentration of MMT in petrol fuels is very low.

Emission Control

Excessive exposure to high levels of manganese, particularly in occupational settings, does not significantly contribute to the increase in manganese emissions. However, it can cause a

condition called maganism. Maganism is characterized by psychotic behavior like hallucinations, delusions, and compulsions. Additionally, it can lead to a condition similar to Parkinson's disease and may even result in death.

Exhaust Emissions Control Legislation

In the 1600s, legislation was initially implemented in America to regulate emissions from motor vehicles. These regulations have since been modified to include more stringent requirements for emissions. A significant milestone occurred with the amendment made to the United States Clean Air Act in 1970 which mandated a reduction of 90% in carbon monoxide, hydrocarbon, and nitrogen oxide emissions.

Figure 3.1 illustrates the percentage of pollutants produced by car emissions. Back in 1989, cars were responsible for emitting a total of 1000 tons of pollution. The regulations introduced in the amendment of 1970 posed significant challenges during that period as the available engine technology was unable to meet them. However, technological advancements have now made it possible to fulfill these requirements. Nonetheless, more stringent standards are continuously being proposed to further enhance emissions control. Despite recent modifications and controls leading to substantial improvements in fuel efficiency, power output, and emissions reduction, no engine has been able to comply with current American standards while maintaining satisfactory performance, power output, and fuel efficiency without incorporating catalytic units within the exhaust system.

The Use of Catalysts for Emission Control The use of catalysts in emission control has been a long-established practice. Its purpose is to convert carbon monoxide, hydrocarbons, and nitrogen oxides into less harmful compounds such as nitrogen, water, and carbon dioxide. However, the chemical and petroleum industry faced challenges when it came to controlling motor vehicle emissions due to rapid changes in exhaust gas temperature,

volume, and composition that were previously unknown. Additionally, there were specific requirements for controlling emissions like ammonia, hydrogen sulfide, and nitrous oxide which could result from secondary catalytic reactions. Moreover, the catalyst system needed to maintain its performance under extreme conditions including high temperature excursions up to 1000°C and exposure to trace amounts of lead and phosphorous - both being catalyst poisons. Since 1975 when catalysts were implemented on American cars, different engine/catalyst systems have been utilized based on the oxidation and reduction reactions involved in removing carbon monoxide, hydrocarbons,and nitrogen oxides along with the operating characteristics of the preferred catalyst.

The Concept of Oxidation Catalyst for Carbon Monoxide/Hydrocarbon Control

When it comes to controlling carbon monoxide and hydrocarbon emissions without focusing on nitrogen oxide, such as in the European "Euronorms" standards, oxidation catalysts are utilized. This system has two main features: the use of a secondary air supply to ensure oxidizing conditions at all engine loads and the implementation of exhaust gas recirculation (EGR) to limit nitrogen oxide emissions. Initially implemented in America to meet interim emission standards, this Oxidation Catalyst System is likely to be adopted in Europe to comply with similar requirements for medium and smaller engine vehicles (engines less than 2 liters).

Dual Bed and Threeway Catalyst Concepts for Nitrogen Oxide Reduction

To address the challenges posed by EGR and meet stricter nitrogen oxide standards, catalysts capable of reducing nitrogen oxide emissions are essential. Initially, a dual catalyst bed was used due to the difficulty in controlling air/fuel ratios precisely within a single catalyst unit. The engine was tuned slightly rich of the stoichiometric ratio

to ensure reducing conditions in the first catalyst bed, where nitrogen oxides were reacted.

Secondary air is injected into the exhaust stream before the second catalyst bed (oxidation bed) to remove carbon monoxide and hydrocarbons. Advances in engine control and catalyst technology have led to the replacement of the dual bed system with a single three-way catalyst unit, which can remove 90% of hydrocarbons, carbon monoxide, and nitrogen oxides. This system includes an electronically controlled air/fuel management system that uses an oxygen sensor to monitor and control exhaust gas combustion. These systems are now commonly found in American, Japanese, and similar emission standard-adhering cars.

Lean Burn Catalyst Systems

Operating engines with air/fuel ratios of 20:1 can reduce nitrogen emissions and improve fuel economy. However, current engine technology requires adjustments to achieve nitrogen emissions compliance with US legislation.

An enhanced cycle with higher speeds and accelerations has been introduced to assess emissions in different driving conditions, such as urban and highway driving. To achieve higher speeds, more engine power is needed, which means reducing the air/fuel ratio in lean burn systems. However, this leads to increased nitrogen oxide emissions, exceeding current engine standards. Therefore, it is important for catalysts used in lean burn engines to not only oxidize hydrocarbons but also reduce nitrogen oxide emissions when the engine requires more power.

Diesel Exhaust Emission Control

Although Diesel engines emit lower levels of carbon monoxide and hydrocarbons and have better fuel efficiency compared to gasoline vehicles, particulate emissions are still a concern.

The EPA established standards to limit particulate emissions, including carbon particulates and aromatic hydrocarbons, produced during the combustion process. These emissions can be collected on a filter and removed through oxidation,

allowing the filter to regenerate and remain effective for the vehicle's lifetime. However, oxidation of particulates occurs only at temperatures above 600°C in the exhaust system when the engine is running at full power. To address this issue, catalysts are introduced into the filter to lower the oxidation temperature to around 300°C. Nitrogen oxide emissions primarily result from the reaction between oxygen and nitrogen during fuel combustion in both spark-ignition gasoline engines and compression diesel engines. Leanburn operation in gasoline engines provides a partial solution to the problem but is limited by hydrocarbon emissions as it approaches the non-flammability limit for spark ignition. While diesel engines do not face this limitation, they are constrained by high particulate emissions.

Using a catalyst to ignite the air/fuel mixture can solve the problem mentioned above by overcoming the limits of gasoline and diesel engines. This allows the engine to operate with a compression ratio of 12 to 1, optimizing combustion efficiency and mechanical energy, thus improving fuel economy. In a catalytic engine, fuel is injected into the combustion chamber just before combustion is needed during the engine operating cycle. The fuel is then mixed with the existing air in the cylinder and passed through the catalyst, where heat is released. Due to the presence of a catalyst, oxidation can occur at lower temperatures and with very lean mixtures.

The combustion process in engines can be optimized to run unthrottled and lean, resulting in complete fuel oxidation and good fuel economy. Additionally, the air/fuel ratio strongly influences the formation of nitrogen oxides and carbon monoxide in the combustion chamber, so lean operation helps reduce emissions of these pollutants in the

exhaust. By using a catalyst, hydrocarbons can be oxidized at lower temperatures, further decreasing emissions.

In conclusion,

the implementation of emissions reduction regulations in the United States in 1970 has led to catalyst technology playing a significant role in preserving air quality.

With the implementation of similar standards in other nations, catalyst systems are now primarily utilized in the automobile industry. However, it is important to acknowledge that the internal combustion engine is nearing its limit in terms of emission technology. To achieve significant reductions in carbon dioxide, hydrocarbon, and nitrogen oxide emissions, an alternative energy source will eventually be necessary to fuel vehicles. Ongoing advancements are being made in the utilization of "clean fuels" such as reformulated gasoline, diesel fuel, methanol, and natural gas in advanced engine design. Nevertheless, it is anticipated that strict environmental regulations will necessitate a completely novel power source. Automotive manufacturers are actively working towards replacing the current power source in automobiles.

Electric powered cars, solar powered cars and vehicles which utilize multiple power sources simultaneously (hybrid) are all being extensively researched. While the emission standards for cars set by the 1970 Clean Air Act Amendments were considered sufficient at the time, air quality has not significantly improved as projected due to the increasing car population in industrialized countries. By considering the potential negative effects on human health and wellbeing mentioned earlier, it can be concluded that in order to eventually "clean" our atmosphere, a power source with zero emissions will eventually need to be implemented in our primary mode of transportation, the automobile.

Bibliography

1. K.C. Taylor, Chem Tech., London, New York: Chapman and Hall, 1990; pp 525-60.

Ibid., pages 45-54