Vehicles Pollution Essay

The automobiles play an important role in the transport system. With an increase in population and living standard, the transport vehicles as well as car population is increasing day by day. In addition to this there is steep increase in the number of two wheelers during the last two decades. All these are increasing exhaust pollution and particularly in metros as density of these vehicles in metros are very high. The main pollutants contributed by I.C. engines are CO, NOX unburned hydro-carbons (HC) and other particulate emissions. Other sources such as Electric power stations industrial and domestic fuel consumers also add pollution like NOX, SO2 and particulate matters. In addition to this, all fuel burning systems emit CO2in large quantities and this is more concerned with the Green House Effect which is going to decide the health of earth. Lot of efforts are made to reduce the air pollution from petrol and diesel engines and regulations for emission limits are also imposed in USA and in a few cities of India. An extensive analysis of energy usage and pollution shows that alternative power systems are still a long way behind the conventional ones. Further developments in petrol and diesel engines, combined with improvements in the vehicles, will make fuel consumption reduction of 40% or more in the future cars. This, in turn, will reduce the CO2 emissions, a gas which is responsible for greenhouse effect.


Page Number

Chapter 1 Introduction

Chapter 2 Environmental Pollution from Internal Combustion Engine Vehicles.

2.1 Pollutants

2.2 Sources

2.3 Health Hazards

Chapter 3 Formation of Pollutants and Their Estimation.

3.1 Internal Combustion Engines.

3.2 Formation of Pollutants.

Chapter 4 Emission Control Methods

4.1 Exhaust Gas After-Treatment

4.2 Three-Way Catalytic Converter

4.3 Exhaust Gas Recirculation (EGR)

4.4 Variable Compression Ratio (VCR)

Chapter 5 Conclusions


Report on plagiarism


Figure 1: Percentage of Emission

Figure 2: Air Pollution by a Car.

Figure 3: Three-Way Catalytic Converter.

Figure 4: EGR System with One-Stage Cooling.

Figure 5: Schematic Representation of a High-Speed Passenger Car EGR/Intake Throttle System.



Internal combustion (IC) engines are used in a variety of stationary applications ranging from power generation to inert gas production. Both spark ignition and compression ignition engines can be found. Depending on the application, stationary IC engines range in size from relatively small (~50 hp) for agricultural irrigation purposes to thousands of horsepower for power generation. Often when used for power generation, several large engines will be used in parallel to meet the load requirements. A variety of fuels can be used for IC engines including diesel and gasoline among others. The actual fuel used depends on the owners/operators preference but can be application dependent as well.

The operation of IC engines results in the emission of hydrocarbons (NMHC or VOC), carbon monoxide (CO), nitrogen oxides (NOx), and particulate matter (PM). The actual concentration of these criteria pollutants varies from engine to engine, mode of operation, and is strongly related to the type of fuel used.

Various emission control technologies exist for IC engines which can afford substantial reductions in all four criteria pollutants listed above. However depending on whether the engine is being run rich, lean, or stoichiometrically and the emission control technology used, the targeted emissions vary as do the levels of control. For example, an oxidation catalyst can be used to control NMHC, CO, and PM emissions from diesel engines which inherently operate in a lean environment, whereas selective catalytic reduction (SCR) could be used to additionally control NOx emissions. More recently, lean-NOx catalysts have been demonstrated to provide greater than a 80 percent reduction in NOx emissions from a stationary diesel engine, while providing significant CO, NMHC, and PM control as well.

PM emissions from stationary diesel engines are more of a concern than those for IC engines using other fuels. Several emission control technologies exist for diesel engine PM control. Oxidation or lean-NOx catalyst can be used to not only reduce the gaseous emissions associated with the use of diesel engines but further provide significant PM control. Likewise, diesel particulate filter systems can be used to achieve up to and greater than 90 percent PM control while in some instances, also providing reductions in the gaseous emissions. Additionally, special ceramic coatings applied to the combustion zone surfaces of the piston crown, valve faces, and head have shown the ability to significantly reduce NOx and PM emissions in diesel engines. These ceramic coatings can be used by themselves or combined with an oxidation catalyst to give even greater reduction of PM. Ceramic engine coatings change the combustion characteristics such that less dry, carbon soot, is produced. Also, when combined with an oxidation catalyst, ceramic coatings allow retarding of the engine to reduce NOx, whilen CO and particulates are maintained at low levels.

In the case of gaseous fuels, ceramic coatings have shown the ability to allow the user to operate their engines with timing significantly advanced generating higher power levels. Also, wider ranges of fuel composition and ambient air temperature fluctuations are tolerated without the deleterious effects of pre-combustion. Tests are currently underway to evaluate the effects of the coatings on specific emissions from gaseous fueled engines.

Emission control technology for stationary IC engines is currently available and can be used to provide substantial reductions in the CO, NMHC, NOx, and PM emissions from these sources in a cost-effective manner.



Emissions from mobile sources constitute a major negative anthropogenic influence on the environment. In 1997, they were roughly 30, 4, and 67 per cent of the generated in the USA CO2, CH4, and N2O. Total emissions of nitrogen oxides (NOx) from mobile sources represented 49 per cent of national emissions, while CO, NMVOC and SO2 emissions contributed approximately 81, 40 and 7 per cent, respectively. Emissions of particulate matter in the USA for the same year are reported as particulate matter smaller than 10 microns (PM10) – 2.569 Gg and total particulate matter (PT) – 5.489

Table 1 illustrates the relative participation of major vehicles groups to the total air pollution from mobile sources in the US in 1997. The above data show that even in countries, leading in pollution control and efficiency, vehicles with ICE contribute a significant portion to air pollution. The contribution of the particular vehicle types can also be seen. Leaded gasoline was banned in the US in 1995. Still, one source cited more than 1270 tons of lead emissions from vehicles in that country in 1994. Brazil and Japan eliminated leaded gasoline in the 1980s. The first European country, which prohibited leaded gasoline (in 1993), was Austria. Most of the countries in Central and Eastern

Fuel/Vehicle type

Air Pollutants


NO x




Gasoline Highway, Gg 44 225 4629 4528 211 191

Passenger Cars, % 55.1 56.1 54.5 47.4 56.0

Light Duty Trucks, % 37.6 37.2 39.4 43.1 41.9

Heavy Duty Vehicles, % 6.9 6.5 5.4 7.6 2.1

Motorcycles, % 0.4 0.2 0.7 1.9 +

Diesel Highway, Gg 1 368 1 753 217 12 7

Passenger Cars, % 2.0 1.8 5.1 + +

Light Duty Trucks, % 0.7 0.6 2.3 + +

Heavy Duty Vehicles, % 97.3 97.6 92.6 91.7 100

Non Highway, Gg 15 201 4 137 2 205 20 9

Ships and Boats, % 11.2 6.6 21.2 15.0 11.1

Locomotives, % 0.7 20.8 2.0 10.0 11.1

Farm Equipment, % 2.0 23.2 5.3 30.0 11.1

Construction Equipment,

% 7.1 27.2 9.9 5.0 +

Aircraft a, % 6.0 3.9 7.8 35.0 66.7

Other b , % 73.0 18.3 53.8 5.0 +

Total, Gg 60 794 10 519 6 949 242 207


 Sulfur oxides

 Nitrogen oxides

 Carbon monoxide

 Carbon dioxide

 Particulate matter



 Anthropogenic sources

 Natural sources


 Cardiopulmonary disease linked to breathing fine particle air pollution

 Pneumonia related deaths

 Heart attacks

 Asthma



The relative proportions of the major pollutants in exhaust emissions depend mainly on the specific organization and parameters of the ignition and combustion processes in the ICE. Fuels are usually matched to engines although the full utilization of the advantages of some alternative fuels requires modification of the engine or the development of a new type of engine.



ICE may be classified by different criteria. For instance, -according to fuel type, to power, to ignition type and so on. An appropriate classification from the point of view of combustion chemistry and air pollution will divide them into two major groups. The first group includes engines in which combustion is performed periodically in a chamber of changing volume (i. e. reciprocating piston engines). In the second group combustion takes place continuously (steady flow) in a chamber of constant volume.

The first group may be further divided into spark ignition (SI) and compression ignition (CI) engines, although there are engines combining both principles. SI engines may be classified as two stroke and four stroke engines, CI engines –as direct and indirect injection engines.

The second group includes the jet engines, which may use a gas turbine, liquid fuel, air as oxidation agent and a turbo compressor (aircraft jet engines), and the rocket jet engines, which have chemical agents as fuels and oxidizers.

Another useful distinction between internal combustion engines is the fact that only in SI engines the fuel is evaporated and mixed with the oxidizing agent before the ignition takes place. In other designs, the fuel is sprayed in the combustion chamber, in the form of drops of different size.

Modern SI engines used in passenger and freight vehicles are four-stroke, although two-stroke passenger cars are still running in some European countries. Two-stroke engines have the important advantages of lower weight and cost per unit of power output. They are widely used in small motorcycles, as outboard motors and other small power equipment.

The main pollutants from four-stroke gasoline engines are hydrocarbons, CO and nitrogen oxides. They are contained in exhaust emissions, but hydrocarbons are contributed both with the exhaust, and with the evaporative emissions. Particulate matter is usually negligible and is produced mainly from oil components brought in the combustion chamber by the piston. Sulfur oxides are typically low and for some time were not considered a problem.

New regulations restrict drastically sulfur in gasoline, because of reconsidering its influence on catalysts. Two-stroke engines emit 20 to 50 per cent of their fuel unburned in the exhaust, but also a considerable amount of oil, which is a component of the air-fuel mixture by design.

Air pollution from them is higher and includes a considerable amount of particulate matter. Two-stroke engine designs with advanced fuel injection, lubrication and combustion systems are being developed. They are expected to achieve lower emissions and higher fuel efficiency, while keeping their traditional other advantages.

In direct injection CI engines, the fuel is sprayed directly into compressed heated air. It evaporates, and ignites. These engines are typical for medium and larger vehicles. They provide higher power output and better efficiency than engines with indirect ignition, but are noisier. For passenger cars, indirect injection engines are more common, because of lower noise and high performance characteristics. Ignition takes place in a pre-chamber, often by a glow spark, and combustion then spreads into the main chamber. Direct ignition engines with improved noise and efficiency controls are being introduced lately in passenger vehicles as well.

Diesel engines can be also classified as naturally aspired, supercharged or turbo charged, depending on the organization of the airflow and its pressure before spraying the fuel. If properly controlled, emissions from turbo charged engines are smaller than from the other two types. Compared to the typical gasoline SI engines, both light and heavy duty diesel engines have considerably higher compression ratios and better fuel efficiency, which leads to lower CO and hydrocarbon emissions. Light duty vehicles emit also less nitrogen oxides than comparable gasoline engines, but nitrogen oxides from heavy-duty diesel engines are higher. Particulate matter and the poly-cyclic carcinogenic hydrocarbons adsorbed on it are eight to ten times as much as in gasoline counterparts and pose a serious problem or diesel engines. They also emit a considerable amount of sulfur compounds due to the presence of more sulfur still allowed in diesel, than in gasoline fuels. Stratified charge engines are a hybrid between typical gasoline and diesel engines. Indirect injection engines relyon spark for ignition of fuel rich mixture. They utilize non-uniform fuel distribution to improve turbulence mixing,and more efficiently avoid fuel rich zones in which the amount of the fuel is more than the stoichiometric extent. Direct injection engines use a high-pressure injector to create a swirl tangential motion of the fuel towards the spark plug. Stratified charge engines have high fuel efficiency, but use fuels with volatility closer to gasoline, and their emission performance is not very impressive.

Rotary car and motorcycle engines have a triangular rotor, which replaces the piston. They are smaller, lighter and simpler, but their CO and hydrocarbon emissions are higher than from conventional engines, while the NOx emissions are the same. Stirling engines are capable of higher fuel efficiency and lower emissions, but are impractical for common automotive use, because of high cost, poor transient response and power to weight ratio. Gas turbine engines are widely used in aircraft, high speed trains, marine vessels and stationary applications, and have been tested without a great success in road vehicles. They use jet fuel, which in volatility is intermediate between gasoline and diesel fuels.

The combustion environment and emissions from aircraft gas turbines vary widely with load. At low loads, temperature and NOx emissions are low, but CO and hydrocarbon emissions are higher. At high loads, CO and hydrocarbon emissions are low, but temperatures and NOx emissions are high. Soot is also formed at high loads, because of the imperfect mixing and fuel rich zones. The rapid quenching of combustion products in gas turbines promotes the emission of significant quantities of NO2, which might be comparable to those of nitric oxide, NO. As a whole, the emissions from gas turbine engines per power output are smaller than from the other engines.

Rocket internal combustion engines may use petroleum fractions, alcohols, ammonia, hydrazin, liquid hydrogen, etc. as fuels. The oxidation agents include nitric acid, tetranitromethane, hydrogen peroxide, liquid oxygen, etc. The emissions from rockets, especially those formed from nitrogen compounds are highly toxic.


Chemical elements under ideal reaction conditions should burn to the corresponding oxides, so CO2 and water are the most likely products to be expected from oxidation of hydrocarbons. However, conditions in engineering applications of combustion reactions are not ideal. The stoichiometric quantity of air needed to burn completely 1 g of gasoline is roughly considered to be around 14.7 g, approximately eleven grams of this being nitrogen. If the air quantity is higher than the stoichiometric proportion the flames are called “lean”, if it is lower – “rich”. In a real combustion chamber flames may be both, depending on the particular chamber type. Other important factors include flame temperatures, gas residence time at high temperatures and combustion chamber turbulence. None of these factors is at its most favorable values throughout the whole chamber space. The fuels are in fact mixtures of compounds with different molecular masses, volatility, diffusion coefficients, etc. Under the non-ideal conditions in the chamber, they undergo pyrolysis and oxidation pyrolysis, prior to reaching the flame propagation zone. The mode of ignition of the fuel, and the intermediate products through which it passes in combustion reactions are very important for the type and the relative quantity of pollutants formed.



Modification of current IC engine design and development of effective after-treatment systems are required to fulfill the requirements of the future emission norms. Emissions from IC engines have already been controlled to a certain extent by precise fuel metering, quality of air supply, better fuel-air mixing, using homogeneous mixtures, lower combustion temperatures, precise ignition timing, and fully computerized engine management. These techniques are just sufficient to meet the current emission regulations. However, better technologies are needed to meet future severe emission norms. Along with these, quality of fuel plays an important role in reducing emissions and enhancing performance of IC engines.


Exhaust gas after-treatment system is usually used to chemically treat the exhaust gases produced from IC engines. Hazardous exhaust gases like CO, HC, and NOx are chemically treated with oxidization and reduction processes, outside the engine before letting it to the atmosphere.


The three-way catalytic converter is used to reduce NOx along with the oxidization of CO and HC. Oxidation and reduction are simultaneously possible only when the engine runs using near stoichiometric mixture. The converter consists of a ceramic matrix or corrugated metal,bundled with a wash coat to provide a large surface area for chemical reactions. The wash coat is composed of actual catalyst materials, which consist of noble metals like platinum (Pt), rhodium (Rh) and palladium (Pd). Pt and Rh are used as reduction catalyst, while Pt and Pd are used as oxidization catalyst (Twigg,2011).Normally three-way catalytic converters achieved good conversion rates (~ 80%) and have a long service life in range of 400oCto 800oC temperature.


They are in effective at exhaust gas temperatures below 250oC, and will be destroyed at exhaust gas temperatures above 1000oC.Leadand lead compounds reduce the effectiveness of catalysts,so this technology works better with the introduction of unleaded gasoline (Vora, 2000). Three-way catalytic converters are suitable for gasoline engines which normally run with near stoichiometric mixture. Diesel engines always run on an overall lean mixture, hence benefit of NOx reduction by this catalyst is very less.


In internal combustion engines, exhaust gas recirculation (EGR) is a nitrogen oxide (NOx) emissions reduction technique used in petrol/gasoline and diesel engines. EGR works by recirculating a portion of an engine’s exhaust gas back to the engine cylinders. This dilutes the O2 in the incoming air stream and provides gases inert to combustion to act as absorbents of combustion heat to reduce peak in-cylinder temperatures. NOx is produced in a narrow band of high cylinder temperatures and pressures.


In a gasoline engine, this inert exhaust displaces the amount of combustible matter in the cylinder. In a diesel engine, the exhaust gas replaces some of the excess oxygen in the pre-combustion mixture. Because NOx forms primarily when a mixture of nitrogen and oxygen is subjected to high temperature, the lower combustion chamber temperatures caused by EGR reduces the amount of NOx the combustion generates (though at some loss of engine efficiency).Gasses re-introduced from EGR systems will also contain near equilibrium concentrations of NOx and CO; the small fraction initially within the combustion chamber inhibits the total net production of these and other pollutants when sampled on a time average. Most modern engines now require exhaust gas recirculation to meet emissions standards.

The exhaust gas, added to the fuel, oxygen, and combustion products, increases the specific heat capacity of the cylinder contents, which lowers the adiabatic flame temperature.

In a typical automotive spark-ignited (SI) engine, 5% to 15% of the exhaust gas is routed back to the intake as EGR. The maximum quantity is limited by the need of the mixture to sustain a continuous flame front during the combustion event; excessive EGR in poorly set up applications can cause misfires and partial burns. Although EGR does measurably slow combustion, this can largely be compensated for by advancing spark timing. The impact of EGR on engine efficiency largely depends on the specific engine design, and sometimes leads to a compromise between efficiency and NOx emissions. A properly operating EGR can theoretically increase the efficiency of gasoline engines via several mechanisms:

• Reduced throttling losses: – The addition of inert exhaust gas into the intake system means that for a given power output, the throttle plate must be opened further, resulting in increased inlet manifold pressure and reduced throttling losses.

• Reduced heat rejection: – Lowered peak combustion temperatures not only reduce NOx formation, it also reduces the loss of thermal energy to combustion chamber surfaces, leaving more available for conversion to mechanical work during the expansion stroke.

• Reduced chemical dissociation: – The lower peak temperatures result in more of the released energy remaining as sensible energy near TDC (Top Dead-Center), rather than being bound up (early in the expansion stroke) in the dissociation of combustion products. This effect is minor compared to the first two.

EGR is typically not employed at high loads because it would reduce peak power output. This is because it reduces the intake charge density. EGR is also omitted at idle (low-speed, zero load) because it would cause unstable combustion, resulting in rough idle. The EGR valve also cools the exhaust valves and makes them last far longer (a very important benefit under light cruise conditions).

Since the EGR system recirculates a portion of exhaust gases, over time the valve can become clogged with carbon deposits that prevent it from operating properly. Clogged EGR valves can sometimes be cleaned, but replacement is necessary if the valve is faulty.


In modern diesel engines, the EGR gas is cooled with a heat exchanger to allow the introduction of a greater mass of recirculated gas. Unlike SI engines, diesels are not limited by the need for a contiguous flamefront; furthermore, since diesels always operate with excess air, they benefit from EGR rates as high as 50% (at idle, when there is otherwise a large excess of air) in controlling NOx emissions. Exhaust recirculated back into the cylinder can increase engine wear as carbon particulate wash past the rings and into the oil.

Since diesel engines are unthrottled, EGR does not lower throttling losses in the way that it does for SI engines. Exhaust gas—largely carbon dioxide and water vapor—has a higher specific heat than air, so it still serves to lower peak combustion temperatures. However, adding EGR to a diesel reduces the specific heat ratio of the combustion gases in the power stroke. This reduces the amount of power that can be extracted by the piston. EGR also tends to reduce the amount of fuel burned in the power stroke. This is evident by the increase in particulate emissions that corresponds to an increase in EGR.

Particulate matter (mainly carbon) that is not burned in the power stroke is wasted energy. Stricter regulations on particulate matter (PM) call for further emission controls to be introduced to compensate for the PM emissions increase caused by EGR. The most common is a diesel particulate filter in the exhaust system which cleans the exhaust but causes a constant minor reduction in fuel efficiency due to the back pressure created. The nitrogen dioxide component of NOx emissions is the primary oxidizer of the soot caught in the DPF at normal operating temperatures. This process is known as passive regeneration. Increasing EGR rates cause passive regeneration to be less effective at managing the PM loading in the DPF. This necessitates periodic active regeneration of the DPF by burning diesel fuel in the oxidation catalyst in order to significantly increase exhaust gas temperatures through the DPF to the point where PM is quickly burned by the residual oxygen in the exhaust.

By feeding the lower oxygen exhaust gas into the intake, diesel EGR systems lower combustion temperature, reducing emissions of NOx. This makes combustion less efficient, compromising economy and power. The normally “dry” intake system of a diesel engine is now subject to fouling from soot, unburned fuel and oil in the EGR bleed, which has little effect on airflow. However, when combined with oil vapor from a PCV system, can cause buildup of sticky tar in the intake manifold and valves. It can also cause problems with components such as swirl flaps, where fitted. Diesel EGR also increases soot production, though this was masked in the US by the simultaneous introduction of diesel particulate filters. EGR systems can also add abrasive contaminants and increase engine oil acidity, which in turn can reduce engine longevity.

Though engine manufacturers have refused to release details of the effect of EGR on fuel economy, the EPA regulations of 2002 that led to the introduction of cooled EGR were associated with a 3% drop in engine efficiency, bucking a trend of a .5% a year increase.


Variable compression ratio is a technology to adjust the compression ratio of an internal combustion engine while the engine is in operation. This is done to increase fuel efficiency while under varying loads. Higher loads require lower ratios to be more efficient and vice versa. Variable compression engines allow for the volume above the piston at ‘Top dead centre’ to be changed. For automotive use this needs to be done dynamically in response to the load and driving demands.

Higher compression ratio (CR) is always desired to get better thermal efficiency but it increases NOx emissions. Research works were carried out to optimize CR and effective CR according to load on engine so as to get better overall efficiency as well as low engine-out NOx.

Christensen et al. (1999) did experiments with variable compression ratio engine to demonstrate the multi fuel capability of HCCI engine. Secondary piston was placed in the cylinder head to achieve VCR from 10 to 28 by replacing one of the exhaust valves. They used different kind of fuel mixtures (mixture of iso-octane and n-heptane as well as gasoline and diesel) for experimental purpose. All tests were carried out with an equivalence ratio of 0.33. Test results showed that pure n-heptane (diesel) and iso-octane (gasoline) required a CR of about 11 and 22 respectively to get auto-ignition at TDC. Because of the poor atomization and vaporization of diesel fuel at low CR and at low inlet temperature (below 90oC), combustion quality became very poor. For all operating conditions, NOx emissions observed were very low, while soot was generated only with diesel fuel. Studies had shown that thermal efficiency was increased with increased CR but combustion efficiency was decreased leading to a minor variation in gross indicated efficiency. Higher amount of charge might be trapped in crevice volume which reduces the combustion efficiency with increased CR.

In general, compression ratio was varied either by having a secondary piston or by adopting variable valve timing. Late intake valve closure reduced the effective CR and hence reduced the peak temperature leading to reduced NOx. However, HC and CO were increased at lower CR.



Compared to gasoline engines, carbon dioxide, carbon monoxide and hydrocarbons produced in diesel engines are much lower. The issue of simultaneous control of NOx and PM becomes more complex in diesel engines. Both after-treatment and in-cylinder technologies to reduce emissions in CI engines have been reviewed. It is understood that various technologies to reduce emissions can just meet the present emission regulations. Better in-cylinder and/or after-treatment technologies have to be developed to meet future stringent emission norms.

EGR seems to be a simple and most effective way of reducing NOx emissions, but suitable measures need to be taken to reduce soot. There is a need to modify the EGR system along with some in-cylinder solutions viz. various injection techniques, charge conditions, late intake valve closing to improve the combustion phenomena and to reduce the emissions However, achieving wider operating range and controlling HC and CO emissions are the major challenges with this technique. An optimized combination of all in-cylinder solutions is required to overcome these issues.


1) Wikipedia-the free encyclopedia.

2) Internal Combustion Engines: V. Ganesan.

3) Bolshakov, G. F. (1987). 209 pp., Physicochemical Fundamentals of the Application of Fuels and Oils, Nauka, Novosibirsk, USSR (in Russian).[Covering theoretic and practical aspects concerning all engines and fuels.]

4) Flagan, R. C. and Seinfeld, J. H. (1988), Fundamentals of Air Pollution Engineering, 542 pp., Prentice Hall, New Jersey, USA [Engineering fundamentals concerning combustion processes and pollution control technologies].


6) Handbook of Air Pollution from Internal Combustion Engines: Pollutant formation and Control (1998), 663 pp., Ed. E. Sher, Academic Press, Boston, London, 1998. [Latest handbook, on pollution ICE].


Air Pollution Essay

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Air pollution concentrations have been rapidly increasing in the major urban areas of Brazil caused mainly by the increasing use of vehicles. Policies to control car emissions in Brazil have relied basically on mandatory emission standards and subsidies for specific cleaner technology resulting in substantial decrease of car emission rates. Nevertheless, taxes on car sales, differentiated by vehicles' size and fuel, have also influenced car emission patterns. This paper analyses the compliance trend of the Brazilian fleet with environmental standards between 1992 and 1997. We find that larger automobiles had the fastest compliance schedule while popular models adjusted very slowly. Also gasoline-fuelled models had a faster adjustment pattern than ethanol cars. Additionally, we analyse the current relationship between pollution emissions and car characteristics in order to
orient policy formulation. We find a positive relationship between emissions rates and horse power, concluding that although the current value-added sale car tax is not environmental harmful, a tax differentiating clean from dirty models, within each tax bracket, could create substantial incentives for emission control in the future.

Urban air pollution is a serious environmental problem in developed as well as in most
developing countries. In the case of Brazil, air pollution concentrations have been rapidly
increasing in the major urban areas over the last decades. As elsewhere, this expansion has
been caused mainly by the increasing use of vehicles. Today, emissions from vehicles are the
major source of air pollution in Brazil's largest cities. In 1997 in São Paulo, for example,
private cars were responsible for approximately 75% of carbon monoxide (CO), 73% of
hydrocarbons (HC), 23% of nitrogen oxides (NOx) and 10% particulate matter (PM)

Costs associated with high air pollution concentrations in large cities are known to be
important. Human health costs predominate, and range from eye irritations to respiratory
problems and increasing cancer rates, all of which induce direct and indirect costs to society2.

They also estimate the health costs associated with concentration levels in
excess of air pollution standards, finding a loss of approximately US$ 700 million per year in
the early 1990s.

Even when consumers can perceive individual emission damage, they are unable to reduce
alone the aggregate social emission costs. Consequently, their preferences will usually not
consider fuel and car cleanliness. In the presence of this negative externality, environmental
regulation is required.

If we were able to measure emissions by individual cars, the first best incentive option for car
emission control would be the imposition of a Pigovian tax on each source according to its
marginal contribution to air pollution damages.

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This would allow flexibility for car owners in
the choice of emission reduction strategies. However, such first best approaches can incur
high administrative cost. As put by Innes (1996), even if tamper-resistant emissionmeasurement
from tailpipes were available at reasonable costs, such devices do not detect
important non-tailpipe pollution and, therefore, high costly reliable periodic car monitoring
would be required. Consequently, the application of car emission control policies would have
to reckon on regimes which do not require direct emission monitoring.
When emission output measurements are difficult, the economic literature on MBIs proposes
instead that regulators may apply first best taxes on the use of inputs and products which are
related to emissions. For car emissions, fuel and automobile taxes are good candidates for
this option. Fullerton and West (1999 - hereafter FW), have derived a set of fuel and car
optimal taxes which are able to mimic, at least in theory, the unavailable tax on emissions. In
order to derive a closed form solution, FW consider emissions per gallon (EPG) and miles
per gallon (MPG) only to depend on si, the size of the car. Under these specific technological
conditions, FW propose a closed form solution for a fuel tax (tg) differing according to
characteristics of the vehicle at the pump.
The owner of car model i, would pay a tax given by
)( ) ( i i gi s MPG s EPM t : =
where :, represents the marginal social cost of a unit of emissions and EPG and MPG
represent car features. More generally, we could specify such a tax to be a function of other
car characteristics which are likely to affect EPG and MPG, as well as emission features of
different fuel types.
Admitting regulators know the mileage consumption and useful life of each car model i
owned by consumer j, an equivalent car sale tax would consist of the present value of the
above fuel tax. This car tax could be, instead, applied periodically for licensing purposes, and
its value would be set by monitored mileage at that period.
Both fuel and car taxes would make consumers perceive the emission-increasing cost of extra
mileage consumption and recognise the emission-reducing benefits of fuel cleanness and
economy as well as car pollution abatement devices.
Note that under this approach regulators must know the marginal social cost of a unit of
emissions ( :). Moreover, this parameter will be location-specific since marginal damages are
dependant on total pollution charges and the environment assimilative capacity which, in
turn, varies according to atmospheric variables (e.g., wind speed, temperature, humidity, etc).
Suppose, however, that regulators know : and location-specific taxes can be applied.
Although the fuel tax is simpler than the equivalent car tax, it would still require car features
to be identifiable at the gas station. Again such an approach is likely to generate high
administrative costs in order to be feasible and reliable. Therefore, if we cannot mimic the
first best solution with alternative taxation schemes, we would have to rely on second best
market instruments. The ideal second best mechanism should create price incentives for

consumers to drive fewer miles and, at the same time, buy cleaner cars. While the former
decision is related to fuel use, the latter works through car price differentiation3.
A car tax based on the estimation of a vehicle's annual emission is proposed by Eskeland
(1994) and Sevigny (1998). Emission rates per mile would be estimated based on car
characteristics, and miles travelled could be measured by the change in the vehicle's
odometer in a given year4. What makes this proposal different from the first best alternative
proposed by FW is the lack of knowledge on each specific car's EPM. While FW's model
assumes that it is possible to estimate individual EPM for all car models in order to charge an
emission gas tax at the fuel pump, Sevigny (1998) only expects to be able to derive average
EPM figures. Again, implementation may prove to be costly for the case of odometer
measurement procedures.
An alternative constrained optimal regulation is proposed by Innes (1996). A combination of
taxes on gasoline and automobiles could be combined with a government fuel content
standard. The fuel tax would be independent of individual automobiles, but the car tax would
depend on auto characteristics (eg, power, size, style), fuel economy and abatement features.
Since mileage demand is highly correlated with automobile features, the automobile tax
would also affect miles driven. Moreover, additional incentives could be created. In a
dynamic setting, a car sale tax could be partially returned to consumers as incentive for
scrapping older models according to the abbreviation of the car's useful life5.
For the previous mechanism, a subsidy for pollution control equipment is relatively simple to
define since control equipment such as catalytic converters and filters are directly observable.
The same applies for fuel, insofar as that emissions will rise more or less proportionately with
fuel consumption for a given vehicle and given driving conditions6. On the other hand, a tax
on car characteristics requires a periodic identification of the relationship between car
characteristics and emissions.
In general, market based instruments are difficult to implement and regulators wishing to
apply them would have to combine tax schemes with technological and emission standards.
This approach does not maximise social welfare by setting optimal levels of pollution.
Rather, the aim is to use pricing mechanisms to increase cost-effectiveness in achieving a
certain standard compliance regarded as desirable7. That is, once environmental goals are
defined, economic instruments can reduce the social costs of achieving them. The rationale is
rather simple. Since users face different marginal control cost schedules, pollution taxes
varying directly with users' pollution levels will make users adopt control levels up to the
point where pollution control costs are equal, at the margin, to non-compliance tax costs.
Taxes are set at certain level which will make the maximised individual decisions, in
aggregate, to meet the desirable standards. Society will first start to control from the leastcost
users which will reduce total control cost. In this case, individual emission standards are
3 See Johnstone and Karousakis (1998) for a review.
4 This tax would take the form of Annual tax =, VMT cEPM bEPM aEPM * ) ( 3 2 1 + + where EPM is the emission
per mile, VMT is the vehicle mile traveled and a, b, c are tax rates set to induce the desired level of abatement
for each pollutant.
5 Road fees, varying with air pollution concentration levels and car's characteristics, are also regarded as
possible second best options, although they may induce longer travel distances to avoid charges.
6 See Seroa da Motta and Mendes (1996) for an analysis of fuel taxation in Brazil.
7 Desirable here may mean either one standard politically acceptable or targeted at one specific damage. In the
case of urban pollution, human health damages are usually targeted.
CREED Working Paper Series No 29 4
dropped out and regulators become only concerned with ambient standards which reflect total
Instead of setting prices, regulators may distribute pollution permits to users, as a share of the
desired total emission targets and allow these permits to be traded among users. This
mechanism creates incentives for achieving the same marginal cost equalising outcome given
the competitive structure of the prices emerging from the permit market transactions.
Apart from cost-effectiveness benefits, such economic instruments can generate revenue. In
the case of pricing mechanisms, note that users with non-compliance will face the respective
tax costs and thereby generate a tax revenue. In the case of tradable permits, they can be
distributed through auctioning mechanisms8.
Car emission control policy in Brazil is basically defined on mandatory emission standards.
Since 1988 the Brazilian governmental authorities have implemented a regulatory mechanism
called The Vehicle Air Pollution Control Programme (PROCONVE), establishing maximum
pollution emission standards (in grams per kilometer) for new vehicles entering the market.
The program has been very successful in reducing emissions per kilometer for new car
models. Nevertheless, as with any command and control approach, it is inflexible and
increases the costs of reducing pollution.
This paper analyses the evolution of average emissions in the Brazilian fleet between 1992
and 1997 (the final compliance date). Together with environmental policy, car tax structures
have been differentiated by car characteristics such as size and fuel use, in order to
accommodate sectoral policy aims. Therefore, government initiatives have affected the car
market and consequently the emission pattern of new automobiles. We try to relate these
sectoral policies with the average emission compliance trends comparing the average
emission changes across car sizes and fuel types. Additionally, we analyse the present
relationship between pollution emissions and car characteristics in order to orient current
policy formulation. Our analysis is based on emission data recorded from laboratory tests
undertaken by the São Paulo Environmental Agency (CETESB) which electronically
measures emissions of HC, CO and NOx for each car model along with the model's
The rest of this paper is structured as follows: the next section presents the Brazilian
regulatory framework for car pollution control and the car tax structure. This is followed by a
description of our database and model characteristics. Section 4 presents the econometric
results; concluding remarks and policy recommendations are discussed in the final section.
8 Cost-effectiveness of permits does not depend on permit auctioning. Freely distributed permits have different
equity effects, although they are equally cost-effective if transactions costs are assumed not constrained.

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