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1、NATURE AND TYPE OF POLLUTION FROM AUTOMOBILES AND STRATEGIES FOR ITS CONTROL Dr. G. C. Kisku, Scientist Industrial Toxicology Research Centre, Environmental Monitoring Division M. G. Marg, Post Box No. 80, Lucknow-226001, U. P. E- mail : kiskugc1@ INTRODUCTION Deterioration of ai

2、r quality is a major environmental problem in many large urban centers in both developed and developing countries. Although urban air quality in developed countries has been controlled to some extent during the past two decades, in most of the developing countries it is worsening and becoming a ma

3、jor threat to the health and welfare of people and the environment. In our modern society, quality of life is greatly measured by the amount of consumption of electricity or by the use of car. Electricity generation and operation of vehicles mostly use fossil fuel. As these fuels are burnt, hug

4、e quantity of lethal chemicals and poisonous particulate matter are released as a part of emission into the surrounding atmosphere due to incomplete combustion causing serious air pollution, affecting public health. The contribution of motor vehicles to air pollution was first recognized by Prof.

5、Hazen Smit who discovered that the two invisible vehicular emissions namely hydrocarbons and oxides of nitrogen were responsible for the famous Los Angeles ‘photochemical smog’. These gases interact with one another and other components of the atmosphere to generate several harmful compounds viz.

6、carcinogens. The auto exhaust also affects our valuable cultural heritage, historical places/ monuments/ architecture and the environment. The number of vehicles in India has increased from 1.86 million in 1971 to 32 million in 1996 and about 53 million in 2000. Meteorological and topographical c

7、onditions affect dispersion and transport of these pollutants in ambient air. AUTOMOTIVE ENGINE TYPES Spark-ignition and Diesel engines are the two most common engines. Other types of engines are Rotary (Wankel) Engines, Gas-Turbine (Brayton) Engines, Steam (Rankine) Engines, Stirling) Eng

8、ines, Electric and Hybrid Vehicles. Spark-ignition gasoline engines have either a 2-Stroke (the cycle is completed in 2-strokes of the piston) or 4-Stroke design (the cycle is completed in 4-strokes, Suction ?Compression ?Expansion or Power and ? Exhaust Strokes of the piston). 2-stroke eng

9、ines are cheaper, lighter and can produce greater power output per unit of displacement, so they are widely used in motorcycles, scooters and mopeds and small power equipment. It emits 20-50% of their fuel unburned in the exhaust, resulting in high emissions and poor fuel economy. All gasoline engin

10、es currently used in automobiles and larger vehicles use the 4-Stroke design. Advanced 2-Stroke engines under development would achieve lower emissions and fuel consumption than 4-Stroke engines. TYPES OF FUELS Pollutant emissions from motor vehicles are determined by the vehicle’s engin

11、e type and the fuel it uses. Ideal fuel must have certain physical, chemical and combustion properties, such as high energy density, good combustion qualities, high thermal stability, low deposit forming tendencies, compatibility with engine hardware, good fire safety, low toxicity, low pollution, e

12、asy transferability and on-board vehicle storage. Commonly use fuels are gasoline and diesel. Gasoline is a mixture of hydrocarbon compounds which have been distilled from petroleum. Sulfur is a constituent in oil; low sulfur oil is in great demand as a fuel because the SO2 emission is reduced.

13、 Low sulfur oil is called “Sweet”. Alternative fuels considered for vehicular use are natural gas (in compressed or liquefied form, Natural gas contains the lighter aliphatic compounds, largely methane, CH4. A typical gas would be 80-90% CH4 , 5 to 10 % ethane and the rest other compounds), liq

14、uefied petroleum gas (LPG), methanol (made from natural gas, coal or biomass), ethanol (made from grain or sugar) vegetable oils, hydrogen, synthetic liquid fuels derived from the hydrogenation of coal and various blends such as gasohol. POLLUTANTS EMISSIONS FROM MOTOR VEHICLES Emission from

15、vehicles especially automobiles contribute significantly two third of air pollution in the urban area. Main sources of emission from automobiles are : i). Evaporative Emissions- are HC vapors lost constantly and directly to the atmosphere due to volatile nature of petrol, mainly from the fue

16、l line’s, fuel tank and carburetor depending upon fuel composition, engine operating temperature and ambient temperature. Losses from the carburetor, called Hot Soak Emissions, occur when a hot engine is stopped. It should be noted that out of total emissions, which are much more in case of petrol

17、than diesel, 20-32% of the total emissions are due to evaporation losses, of which the HCs happen to be the chief constituents. ii). Crankcase Emission (also called running loss emissions) – are unburnt or partially burned fuel components that, under pressure, escape from the combustion chamber,

18、 pass the pistons and enter the crankcase. This mixture is called blow-by. The main constituent of blow-by emission is HCs. If uncontrolled, it may constitute 13–25% of total emissions. Since, diesel engines compress only air, blow-by contain very low levels of pollutants. iii). Exhaust Emiss

19、ion- Automotive exhaust is the major source constituting about 60% of the total emission. Automobile exhaust consists wide range of pollutants from simple to carcinogenic substances such as (1) Hydrocarbons (Unburnt), (2) Carbon monoxide, (3) Oxides of nitrogen (NOx), (4) Lead oxides, (5) Particulat

20、e matters e.g. lead, carbon, alkaline earth compounds, iron oxide, tar, oil, mist (6) Traces of aldehydes, esters, ethers, sulphur dioxide, peroxides, ketones benzene (C6H6), 1, 3 butadine, Poly Aromatic Hydrocarbons (PAH), metal dust, asbestos fibre, dioxin, furon, ammonia, organic acids , chloro

21、fluorocarbons (CFCs) etc. . Hydrocarbons and CO appear in the exhaust gas products of incomplete combustion. Oxides of nitrogen result from the reaction of nitrogen and oxygen contained in the combustion air at high temperature prevailing during combustion. Further, many of these primary pollut

22、ants react with each other to form secondary pollutants. Chief among these are HC, CO, NOx when mixed with atmospheric water vapors in presence of sunlight form ozone and variety of complex organic gases and resultant particulates known as Photochemical Smog (Sharma, and Agnihotri, 1992). The wo

23、rst smog disaster occurred during December 4-9, 1952 in London. The smog filled the Thames valley to a width of 20 miles and extended to a greater distance along the valley in each direction. The depth of the smoke and fog layer varied between about 150 – 400 ft. high landmarks and hilltops protrudi

24、ng into haze above this layer. About 4000 people died in smog-affected area. Most of the fatalities occurring among the population from age 45 and upward (Wilkins 1954 and Logan, 1953). Jelinkova and Branis, 2001 also reported the case of mortality happened during winter smog episodes, 1982, 1985, 1

25、987 and 1993 in the Czech Republic A comparative sulfur content in diesel fuel in different countries and pollution arise from different parts of the automobiles are given in Table-1 and Table-2. Table 1: Maximum Permitted Sulphur Content in Automotive Diesel Fuel. E.C

26、. Countries % Mass U.K. 0.3 France 0.3 Germany 0.2 Italy 0.3 Others Canada 0.5 Japan 0.5 Switzerland 0.2 South Korea 1.0 USA 0.5 India 0.5 Table 2 : Automobile Parts and Pollution Problems associated with Them. Parts Problem

27、s Battery Contains lead and HCl. Bumper Wastes include cyanide, chromium and other heavy metals. Brake shoes Contains asbestos. Engine Waste per tone of castings, 0.3 tones mainly slag’s with some toxic contaminants. Exhaust Contain several air pollutants, 20% NO2, 23% Hydrocarbons and 4

28、5% CO. Seat Textiles Wastes include dyes, acids, solvents, greases and waxes. Gasoline Tank Serves as a source of benzene and hydrocarbons emissions during fuelling. Plastic Components Toxic chemicals used in the production include vinyl chloride, formaldehyde, phenols and several solvents.

29、 Tyres Toxic chemicals used in the production include amines, thiurams, nitrosamines and solvents. The composition of automotive and diesel exhausts is characterized by greater amounts of carbon monoxide and hydrocarbons than that of emissions from other fuel burning processes. Factors for autom

30、otive and diesel exhaust emission, in pounds per 1,000 gallons of fuel consumed (Giever,1972), are given in Table-3. Table 3: Emission Factors for Gasoline Engines and Diesel Engines (lb/1000 gal of Fuel) Sl. No. Pollutants Gasoline Engines Diesel Engines 1 Particulates 11 110 2 O

31、xides of Sulfur 9 40 3 Oxides of Nitrogen 113 222 4 Carbon monoxide 2910 60 5 Hydrocarbons 524 180 6 Aldehydes 4 10 7 Organic acids 4 31 8 Ammonia 2 ----- 9 Benzo(a) pyrene 0.3 g/1000 gal 0.4 g/1000 gal Emissions from Gasoline Vehicles Gasoline- powered engines are

32、 of two types – 4 strokes and 2 strokes. The exhaust consists of CO, HC, NOx, SO2 and partial oxides of aldehydes, besides particulate matter, lead salts account for the larger chunk of all pollution from gasoline-run vehicles. The 2 stroke engine require 2 T oil for lubrication of engine. Since t

33、he burning quality of mineral based lubricating oil is very poor, major fraction either remain unburned or burns partially and comes out through exhaust and responsible for smoke and SPM emissions. S.N. Source Amount of Emissions (%) 4-stroke 2-stroke 1 Crankcase blowby 20 - 2 Evaporati

34、ve Emissions 20 3 3 Exhaust Emissions 60 97 Emissions from Diesel Vehicles Due to low volatility, evaporative emissions are non-significant. Though the concentration of CO and unburnt HC in the diesel exhaust are rather low, they are compensated by high concentration of NOx. There are smok

35、e particles and oxygenated HC, including aldehydes and odour-producing compounds. AIR POLLUTANTS FROM MOTOR VEHICLES The major pollutants emitted from gasoline fueled vehicles are CO, HC, NOx and Pb while pollutants from diesel-fueled vehicles are particulate matter (including smoke), NOX, SO2,

36、 PAH. Carbon monoxide (CO)- Colorless and odorless gas, slightly denser than air. Residence time and turbulence in the combustion chamber, flame temperature and excess O2 affect CO formation. Conversion of CO to CO2 in the atmosphere is slow and takes 2 to 5 months. In developing countries the t

37、ransport sector account for 53% of CO emissions and the residential and commercial sectors, 46%. Hydrocarbon Compounds (HC)- Compounds consisting of carbon and hydrogen and include a variety of other volatile organic compounds (VOCs). Most HCs are not directly harmful to health at concentrations

38、found in the ambient air. Through chemical reactions in the troposphere, however they play an important role in forming NO2 and O3 which are health and environmental hazards. Among the various HC, methane (CH4) does not participate in these reactions. Remaining HC, non methane hydrocarbons (NMHC) ar

39、e reactive in forming secondary air pollutants. NMHC are photo chemically reactive. Benzene and Polyaromatic Hydrocarbons (PAH)- Motor vehicles emit toxic HC including benzene, aldehydes and polyaromatic hydrocarbons (PAH). About 85 to 90% benzene emissions come from exhaust and the remainder com

40、es directly from gasoline evaporation and through distribution losses. Toluene and xylene HC compounds are present in the gasoline whereas aldehydes, 1, 3 butadiene are not present in gasoline, diesel fuel, ethanol or methanol but are present in their exhaust emissions as partial combustion produc

41、ts. PAH are emitted at a higher rate in exhaust of diesel-fueled vehicles than gasoline –fueled vehicles. Nitrogen oxides (NOX)- includes nitric oxide (NO), nitrous oxide ( N2O), nitrogen dioxide (NO2), dinitrogen trioxide (N2O3) and nitrogen pentoxide (N2O5). NO and NO2 collectively represe

42、nted as NOX, are the main nitrogen oxides emitted by vehicles. About 90% of these emissions are in the form of NO. NO is produced in the vehicle engine by combustion of nitrogen at high temperatures. NO2 formed by oxidation of NO, has a redish brown color and pungent odor. In the atmosphere, NO

43、2 involved in a series of reactions in the presence of UV radiation that produce photochemical smog, reducing visibility. It may also reacts with moisture to form nitric acid (HNO3) aerosols. In the lower atmosphere (troposphere), NO2 forms O3 by reacting with HC. In the upper atmosphere, it react

44、s with chlorine monoxide to form chlorine nitrates. In developing countries, the transport sector accounts for 49% of NOX emissions and the power sector, 25%; the industrial sector, 11%; the residential and commercial sectors, 10% and other sources 5%. Sulfur dioxide (SO2)- is a stable, nonflamma

45、ble, nonexplosive, colorless gas. In the atmosphere, SOX may be converted to sulfur trioxide (SO3) by reacting with O2. SO2 and SO3 react with moisture in air to form sulfurous (H2SO3) and sulfuric (H2SO4) acids may precipitate to earth as acid rain. Sulfates may also be produced through reaction of

46、 these sulfur compounds with metals present in particulate matter. Ozone (O3)- in the lower (troposphere) layer, ground level ozone (GLO) is formed by the reaction of VOCs and NOX with ambient O2 in the presence of sunlight and high temperatures. GLO is a major constituent of smog in urban area

47、s and motor vehicles are the main emission source of its precursors. The reactions that form GLO also produce small quantities of other organic and inorganic compounds such as peroxyacetyl nitrate (PAN) and nitric acid. GLO concentrations depend on the absolute and relative concentrations of its pr

48、ecursors and the intensity of solar radiation, which exhibits diurnal and seasonal variations. Thermal inversions increase GLO concentrations. Particulate matter (PM)- consists of fine solids and liquid droplets other than pure water that are dispersed in air. Total suspended particulates are p

49、articles with an aerodynamic diameter of >70 mm. PM with an aerodynamic diameter of 3 10 mm known as suspended inhalable particulate matter/ Respirable Suspended Particulate Matter (RSPM) or PM10, remains in the atmosphere for longer periods because of its low settling velocity. PM10 can penetrat

50、e deeply into the respiratory tract and cause respiratory illness in humans. PM with an aerodynamic diameter of 2.5-10 mm or less is defined as fine particles (PM2.5), while the larger PM is called coarse particles. Nearly all PM emitted by motor vehicles consists of fine particles and a large frac

51、tion of these particles has an aerodynamic diameter less than 1mm. PM2.5 can also be formed in the atmosphere as aerosols from chemical reactions that involve gases such as SO2, NOX and VOC. Sulfates, which are commonly generated by conversion from primary sulfur emissions, make up the largest

52、fraction of PM2.5 by mass. PM2.5 can also form as a result of solidification of volatile metals salts as crystals following cooling of hot exhaust gases from vehicles in ambient air. Gasoline fueled vehicles have lower PM emission rates than diesel–fueled vehicles. PM emissions from gasoline fueled

53、vehicles result from unburned lubricating oil and ash-forming fuel and oil additives. PM emitted by diesel-fueled vehicles consists of soot formed during combustion, heavy HC condensed or adsorbed on the soot and sulfates. These emissions contain PAH. With the advancement of emission control measur

54、es in engines, however, the contribution of soot has been reduced considerably. Black smoke, associated with the soot portion of PM emitted by diesel-fueled vehicles, is caused by O2 deficiency during the full combustion or expansion phase. Blue, gray and white smoke are caused by the condensed

55、 HC in the exhaust of diesel-fueled vehicles. Blue or gray smoke- results from vaporized lubricating oil and white smoke occurs during engine start-up in cold weather. Diesel fuel additives such as Ba, Ca and Mg reduce smoke emissions but increase PM sulfate emissions. These additives may also in

56、crease PAH emissions. Dioxins- Cu based additives can reduce PM emissions but may catalyze the reaction between HC and trace amounts of chlorides in diesel fuel to form dioxins which are emitted in the exhaust. Chlorofluorocarbons (CFCs)- The source of CFC emissions from motor vehicles is the

57、freon gases used in air conditioners. CFC emitted into the atmosphere rise to the stratosphere layer within 10 years and are estimated to remain there for 400 years. CFC molecules struck by UV radiation release chlorine atoms, which destroy O3 by forming chlorine monoxide. Furthermore, when a fr

58、ee O2 atom reacts with a chlorine molecule, an O2 molecule is formed and a chlorine atom is released to destroy more O3. Carbon dioxide (CO2)- is a green house gas associated with global worming, results mainly from increased combustion of fossil fuels including motor vehicle fuels. MODE OF V

59、EHICLE OPERATION AND EMISSION RATES The vehicle operation is divisible into 4 modes or driving cycles : (i) Idle /Start Mode - when the engine of vehicle has been started. It is yet stationary. At this stage there is high level of HC and CO and very low level of NOX, (ii) Acceleration- the emis

60、sion of HC and CO come down with rise in NOX levels, (iii) Cruise/Steady Mode-steady speed produces relatively low concentration of HC and CO but high concentration of NOX and (iv) Deceleration (a) free and while (b) applying brake- slow speed contributes to more pollutants. CONTROL TECHNOLOGY F

61、OR GASOLINE–FUELED VEHICLES (SPARK-IGNITION ENGINES) Emissions from spark-ignition engines can be reduced through changes in engine design, combustion conditions and catalytic aftertreatment. Some of the engine and combustion variables that affect emissions are the air-fuel ratio, ignition timin

62、g, turbulence in the combustion chamber and exhaust gas re circulation. Of these, the most important is the air-fuel ratio. Air-Fuel Ratio For a fuel quality, concentrations of many of these pollutants are influenced by such factors as the air-fuel ratio in the cylinder at the time of combust

63、ion, ignition timing, combustion chamber geometry, engine parameters (e.g. speed, load and engines temperatures) and use of emission control devices. Vehicles with electronic fuel injection engines maintain an air-fuel ratio of about 14.7 : 1 (i.e. burning of 1 lb of fuel about 14.7 lbs of air is n

64、eeded, which is the stoichiometric/ ideal ratio for the air-gasoline mixture) to achieve complete combustion. Lean mixture (Higher Ratios) produces less HC & CO emissions while Rich mixture (Lower Ratios) produces more CO & HC and low values of NOx emissions from unburned or partially burned fuel

65、. The air/fuel ratio is adjusted taking into consideration the emission and efficiency of an engine. It is seen that most of the gasoline operated engines are adjusted within the air/fuel ratio of 12:16. The air/fuel ratio and ignition timing are readily adjustable, both in design specifications an

66、d field tune up adjustments. Evaporative Emissions and Control Diurnal and Hot soak emissions have been controlled by venting the fuel tank to the atmosphere through a canister of activated carbon. The volatile nature of gasoline can be minimised by keeping gasoline Reid Vapor Pressure of 10 psi. Gasoline with an RVP of 11 psi will produce about twice the evaporative emissions of gasoline with an RVP of 8.7 psi. Crankcase Emissions and Control Crankcase emission