Characteristics of Pollutants from Car Exhaust and suggested solution:

Characteristics of Pollutants from Car Exhaust and suggested solution:

The internal combustion engine is an engine in which the combustion of fuel and an oxidizer (typically air) occurs, and generates gases at high temperature and pressure, which are permitted to expand to perform useful work. Internal combustion engines are most commonly used in automobiles such as trucks, cars, motorcycles etc.; in a wide variety of aircraft and locomotives; running of various equipments, and they appear mostly in the form of turbines where a very high power is required, such as in jet aircraft, helicopters, and large ships.

Motor fuel, by which almost all internal combustion engine runs, is obtained from crude oil. Its major constituents are the elements carbon (C), hydrogen (H), oxygen (O) and nitrogen (N), along with some amounts of sulfur (S). In other words, motor fuel contains hydrocarbons and organic compounds containing nitrogen and sulfur. When these are burned in air the products are water (H2O), carbon dioxide (CO2), carbon monoxide (CO) and oxides of nitrogen (NOx). Nitrogen gas in the atmosphere may also react with oxygen at the high temperatures in the combustion chamber to form oxides.

Characteristics of Pollutants from Car Exhaust:

a. Carbon dioxide (CO2) - This gas is naturally present in the atmosphere at low concentration (approximately 0.035%). It absorbs infrared energy and is thus a greenhouse gas, a contributor to global warming. Concentrations of CO2 in the earth's atmosphere appear to be increasing. This is a great concern as it has a substantial effect on the climate. The internal combustion engine contributes to the increased concentrations of CO2 in the atmosphere.

b. Carbon monoxide (CO) - The main source of CO in cities is the internal combustion engine, where it is produced by incomplete combustion. Anthropogenic sources account for approximately 6% of the 0.1 ppm concentration of CO in the earth's atmosphere globally. In an urban area, the concentration can be much higher. CO is highly toxic. It binds to haemoglobin more strongly than oxygen does, thus reducing the capacity of the haemoglobin to carry oxygen to the cells of the body. CO also has the nasty habit of sticking to haemoglobin and not coming off. This means that a fairly small amount of it can do a lot of damage. However, CO can be oxidized to the far less harmful CO2, if there is enough O₂ available. At higher air-fuel ratios the level of CO emission goes down. CO can also be oxidized to CO2 in a catalytic converter.

c. Oxides of nitrogen (NOx) - While some nitrogen may be present in the fuel, most oxides of nitrogen are produced when elemental nitrogen (N2) in the air is broken down and oxidized at high temperatures (approximately at 700 degree Celsius or greater) and pressures within the internal combustion engine. Nitrogen monoxide (NO) is produced in higher concentration than nitrogen dioxide (NO2) but the two species are in any case inter-convertible by means of photochemical interactions. Other oxides of nitrogen, such as N₂O₄, may occur; but chances are rare. NO and NO₂ are toxic species. Oxides of nitrogen also play a major role in the formation of photochemical smog.

d. Hydrocarbons (HC) - Hydrocarbon fuel, sometime, passes through the process unconsumed and is expelled into the atmosphere along with other exhaust fumes. Fuel close to the wall of the combustion chamber may be quenched by the relative coolness of that area and not be burned. Also, if the engine is poorly designed or is not in proper working order the proportion of unburned fuel rises. Some hydrocarbon fuels are also released to the atmosphere by direct evaporation from fuel tanks. It may be noted; hydrocarbons can be dangerous to human health and are also part of the makeup and cause of photochemical smog.

e. Benzene and its derivatives (C6H6) - Benzene is, of course, a hydrocarbon, but is sufficiently different from straight-chain hydrocarbons. The six carbons (C) in benzene form a regular hexagon, with one hydrogen (H) attached to each carbon and sticking out. All 12 atoms lie on one plane. This structure of benzene is quite stable — stable enough for a large proportion of the benzene in fuel to pass unchanged through the combustion process. There is quite a lot of benzene in fuel. It acts as an anti-knock agent, making cars run more smoothly. Since the abolition of lead additives as anti-knock agents, the levels of benzene and benzene-related compounds (modified form where one or more hydrogen have been removed to form a phenyl ring and other things have been attached in their places) in car fuel have increased. Benzene (C6H6), and also many of its derivatives such as toluene (PhCH3) and phenol (PhOH), is carcinogenic (the level of toxicity varies). Benzene vapors are therefore quite dangerous. It has been suggested that benzene is more dangerous to filling station attendants than to the general public in the streets as the concentration of benzene will be higher in the raw fuel than in the combustion products.

f. Sulfur dioxide (SO2) - Fossil fuels are derived from once-living organisms. Some sulfur occurs in protein and will still be present in the fuel. Under combustion this sulfur reacts with oxygen to form sulfur di- and trioxide. Sulfur dioxide emission does occur from cars. SO2 and SO3 are acidic pollutants which dissolve in moisture in the atmosphere to form sulfurous and sulfuric acids (H2SO3 and H2SO4), which are components of 'acid rain'. These corrode metal surfaces and weather limestone buildings.

Acid rain also mobilizes toxic aluminum ions in the soil, washing them out into streams and ponds. This causes sticky mucus to accumulate in the gills of fish and eventually kills them. Trees and other plants which absorb aluminum ions will be damaged. In humans, sulfur dioxide irritates the eyes, the mucous membranes and the respiratory tract, along with the skin in general. SO2 also has the effect of slowing down the movements of the cilia (the hairs in the trachea which act to prevent dust entering into lungs), thus exacerbating the irritation caused by allowing more pollutant to access the respiratory system.

g. Particles micro-particulate, 10 microns (Particulate matters – PM10) - These are ultra-fine particles which are less than one-hundredth of a millimeter across. Thus they are too small to settle or be dispersed by rain. These particles absorb acidic gases which are also present in exhaust fumes and, when inhaled, penetrate into the microscopic air sacs of the lungs (alveoli). Scavenging white blood cells are overwhelmed by these particles, and release a stream of chemicals that trigger an inflammatory reaction in the lungs, and increase the stickiness of red blood cells, thus increasing the likelihood of blood clots. The main victims of this type of pollution are the elderly, smokers, and those suffering from chest complaints, heart conditions and asthma. It is considered that PM10s may be the most important and dangerous component of vehicle pollution. These particles can drift for miles, and accumulate inside buildings. The major source of PM10s in urban air is motor vehicles, particularly diesel engines.

h. Photochemical Smog - Reactive pollutant hydrocarbons in the presence of NOx and under certain atmospheric conditions can produce a brown haze known as photochemical smog. It is formed by photochemical reactions (that is, reactions catalyzed by light) between NOx and hydrocarbons (HC). Photochemical smog is most common on windless sunny days when the ingredients are not dispersed and there is plenty of light energy available to power the reaction. Photochemical smog is characterized by the presence of particulate matter (which creates a sort of haze), oxidants such as ozone, and noxious organic species such as aldehydes.

Suggested Solutions to the vehicle exhaust problems:

(i) Catalytic Converters - Most modern cars contain catalytic converters. In these, exhaust fumes and added air pass over a catalyst where they are broken down to less harmful products.

(ii) Drive less.

(iii) Use cleaner engines – Use cars that are designed to be more fuel-efficient and less pollutant.

(iv) Drive hybrid vehicles - Whether a hybrid engine is more environmentally sound than a normal engine depends on how the car is used. For city stop-start driving, they're usually better.

(v) Keep your car in good working order

(vi) Use smaller cars.

(vii) Drive intelligently - The way a car is driven can have a huge effect on its fuel-consumption and hence on its effect on the environment.

Adverse Impacts of Road Traffic exhaust on Human Health and Mitigation measures:

Adverse Impacts of Road Traffic exhaust on Human Health and Mitigation measures:

Automotive vehicle engines produce a number of air pollutants that pose risks to human health. Road vehicles such as cars, buses and trucks are a source of air pollution. When their engines burn fuels (gasoline or diesel), they produce large amounts of chemicals that are emitted in engine exhaust. In addition, some of the gasoline used by engines vaporizes into the air without having burned, and this also creates pollution.

A. Recent study shows that those who reside near major highways had worse indoor air pollution than those in more rural settings, with respect to PAHs (polycyclic aromatic hydrocarbons), a class of compounds that contain known cancer-causing toxins.

Although, stringent regulations on engine performance and fuel formulation have brought about a decline in the amount of air pollution produced by individual vehicles, but due to increase in number of vehicles the air pollution level in urban areas have not come down. Automobile exhaust remains a major source of pollution and the pollutants cause local changes in the air quality, which affect the human health adversely.

B. This causes us great concern on health front of public, especially, children who pose risk to various hazards. Children exposed to high levels of air pollution during their initial years of life run a greater risk of developing asthma, pollen allergies, and impaired respiratory function.

Another group of people those are greatly affected due to vehicular exhaust are traffic personnel - men and women. It has also been reported in many countries that, due to high exposure to toxic fumes of vehicular exhaust among traffic personnel, induced impaired reproductive system observed.

C. The following is a summary of the main pollutants produced by road traffic and the way they may affect our health:

Nitrogen oxides: These are created when vehicle engines burn nitrogen that is present in the air and nitrogen compounds found in fossil fuels. Nitrogen oxides can irritate airways, especially your lungs.

Carbon monoxide: This gas is produced by incomplete combustion of gasoline and diesel fuel. All engine exhaust contains a certain amount of carbon monoxide, but the amount will increase if your vehicle engine is poorly maintained. Carbon monoxide decreases the ability of your blood to carry oxygen.

Volatile organic compounds (VOCs): These are a large family of carbon-containing compounds that evaporate easily. Engine exhaust contains a number of different VOCs. Some of them, such as benzene and 1,3-butadiene, are cancer-causing agents, although the risk at current levels in the environment is small.

Fine particulate matter: These tiny particles contain many substances, including metals, acids, carbon, and polycyclic aromatic hydrocarbons. Some of these particles are emitted in vehicle exhaust, while others are formed in the atmosphere through chemical reactions between the various pollutants found in exhaust. Particulates are known to aggravate symptoms in individuals who already suffer from respiratory or cardiovascular diseases.

Ground-level ozone: This is not emitted directly by vehicle engines, but is formed by chemical reactions between nitrogen oxides and VOCs. These reactions are stimulated by sunlight, and this is why concentrations of ground-level ozone are higher during the summer months. Ground-level ozone irritates airways and can trigger reactions in people who have asthma (Ground-level ozone should not be confused with the ozone layer in the stratosphere, which provides protection from the sun's ultraviolet rays.).

The air pollution from road traffic causes two types of effects on health:

Acute Effects: These effects occur rapidly (in a few hours or days) following exposure to high levels of pollutants. In certain cases, air pollution may worsen symptoms for people with existing heart and lung conditions. Scientific research carried out in some countries has shown that the number of deaths and hospitalizations related to respiratory and cardiac conditions increases when the levels of ground-level ozone or fine particulate matter increase.

Chronic Effects: These occur over time following extended exposures (months or years). Scientific studies in Europe have shown that children living in areas with higher traffic density have more respiratory symptoms than other children.

In general, traffic exhaust pollutants are a major source of air pollution especially in urban areas, and are a major source of greenhouse gas emissions as well. Vehicles run on conventional or diesel engines. Although diesel engines are more efficient, they emit more fine particles than conventional engines. According to many, diesel exhaust is responsible for 70 percent of the cancer risk that the average urban population faces from breathing toxic air pollutants.

Potential health effects from being exposed to traffic-exhaust pollutants include respiratory illnesses (including asthma), cardiovascular disease, adverse reproductive outcomes, cancer, and shortening of the life span.

D. We can help to minimize risks by taking steps to reduce traffic-related air pollution. (a) Whenever possible, use public transit, bicycle or walk instead of using your vehicle. (b) Take fuel efficiency into account when you buy a vehicle. (c) Turn off the engine of your car when you stop for more than 10 seconds, unless you are in traffic or at an intersection. (d) Keep your vehicles well maintained. (e) In addition, you can take steps to help minimize your risk of health effects from traffic-related air pollution, such as,

(i) Pay attention to air quality forecasts in your community, and tailor your activities accordingly.

(ii) Avoid or reduce strenuous outdoor activities when air pollution levels are high, especially in the afternoon during summer months when ground-level ozone reaches its peak.

(iii) Choose indoor activities instead.

(iv) Avoid or reduce exercising near areas where traffic is heavy, especially during rush hour.

(v) If you have a problem of heart or lung, consult health care professional about additional ways to protect your health when air pollution levels are high.

E. Governments can encourage the reduction of vehicular use by:

a. Promoting Voluntary abstention,

b. Increase Public Transit - diversify options and limit access to existing roads.

c. Separate commercial and private traffic to increase efficient use of roads,

d. Stop building car-oriented roads and highways,

e. Replace 30% of the existing roads designed for cars with a variety of transportation options,

f. In cities, build more walking paths, bicycle routes and paths for small electric vehicles, g. Reduce commuting - link residence and business activities by rezoning and rebuilding cities,

h. Reward car-pools and car-sharing plans,

i. Redefine road use by defining access privileges - no longer a right,

j. Road Tolls and increased gasoline and vehicle registration taxes,

k. Base car license fees on fuel consumption in the previous year. Use exponential fee rate increase for high fuel consumption individuals,

l. Provide generous development grants and tax incentives for all non-polluting transportation alternatives.