بنام خدا عباس بهرامی عضو هیات علمی گروه بهداشت حرفه ای . دانشکده بهداشت دانشگاه علوم پزشکی کاشان

خدا بنامبهرامی عباس

بهداشت . دانشکده ای حرفه بهداشت گروه علمی هیات عضوکاشان پزشکی علوم دانشگاه

[email protected]

جلسه پایان در میرود انتظار: باشد قادر دانشجو

نام- 1 را هوا طبیعی ترکیب اجزایببرد

کند- 2 بیان را هوا آلودگی تعریف

آلودگیها- 3 انتشار بر موثر عواملدهد شرح را

4. ببرد- نام را هوا آلودگی منابع

توضیح- 5 هوارا های آالینده انواعدهد.

According to the World Health Organization (WHO), about 2 million premature deaths are caused each year due to air pollution in cities across the world .

A recent study has revealed that exposure to fine particle matter in polluted air increases the risk of hospitalization due to respiratory and cardiovascular diseases

The Atmosphere

•78 percent nitrogen

•21 percent oxygen

•0.09 percent Argon

•Carbon Dioxide 0.03 percent

•Trace elements 0.07 percent–Methane, ozone, hydrogen sulfide, carbon

monoxide, etc...

•Water vapor can range from 0 to 4%

Air Pollution

Definition: The addition of harmful substances to the atmosphere resulting in damage to the environment, human health, and quality of life. Just one of many forms of pollution, air pollution occurs inside homes, schools, and offices; in cities; across continents; and globally. Ambient (outdoor) air pollution is the focus of this presentation.

Stratospheric Ozone

1 atm 101 kPa

(From: Introduction to Environmental Engineering G. Masters, 2nd and 3rd eds.)

Causes of Air Pollution

Car ExhaustThe exhaust that comes out of the tail pipe of a car contains carbon monoxide, an odorless, colorless gas, and Nitrogen Oxide. These gases are produced as the car burns gasoline.

Coal PlantsThese plants let off small, airborne particles. These particles are known as soot. Sulfur Dioxides are also gases given off by these plants.

Factorie

sFactories

emit tons of harmful

chemicals into

atmosphere on a daily

basis. Ammonia

gases is just one emitted from these factories.

OzoneChemicals found in paint and hair spray create hazardous pollutants with highly toxic effects. These pollutants form the ground level ozone.

Home

با تشکر

از توجه شما

عباس بهرامی

Air Pollution IAir Pollution I

بر- 2 هوا های آالینده اثراتاموال و گیاه ، حیوان ، انسان

. دهد توضیح را

را- 3 هوا آلودگی استاندارد. دهد شرح

را- 4 هوا آلودگی شاخصهای. ببرد نام

: باشد قادر دانشجو جلسه پایان در میرود انتظارهوا- 1 آلودگی از ناشی تاریخی حوادث

An active adult inhales 10,000 to 20,000 liters of An active adult inhales 10,000 to 20,000 liters of air each day, or 7 to 14 liters every minuteair each day, or 7 to 14 liters every minute . .

Types of Air PollutionTypes of Air Pollution

Primary air pollutantsPrimary air pollutants:: harmful chemicals that enter directly harmful chemicals that enter directly into the atmosphere.into the atmosphere.

Secondary air pollutantsSecondary air pollutants:: harmful chemicals that form from harmful chemicals that form from other substances in the atmosphereother substances in the atmosphere.

Examples of Catastrophic Air Examples of Catastrophic Air PollutionPollution

19111911 in London - 1150 died from the effects of coal smoke. in London - 1150 died from the effects of coal smoke. Author of the report coined the word Author of the report coined the word smogsmog for the mix of for the mix of smoke and fog that hung over London.smoke and fog that hung over London.

19521952 in London - 4000 died from smog. in London - 4000 died from smog.

1948 1948 in Donora, Penn. Town of in Donora, Penn. Town of 14,000 people - 20 died and 6000 14,000 people - 20 died and 6000 were ill from smog from the were ill from smog from the community's steel mill, zinc smelter,community's steel mill, zinc smelter,and sulfuric acid plant.and sulfuric acid plant.

19631963 in New York City - 300 people died from air pollution. in New York City - 300 people died from air pollution.

London London Smog 1952Smog 1952

London Smog 1952London Smog 1952

In 13th century London - laws In 13th century London - laws against burning outside against burning outside because London was already because London was already heavily polluted since the heavily polluted since the middle agesmiddle ages

London London Smog 1952Smog 1952

A Brief History

•1930s-60s: severe air pollution episodes: Meuse Valley, Belgium, Donora, Pennsylvania, London, U.K.

•1960s-70s: introduction of clean air legislation•1970s-80s: significant reduction in ambient

concentrations of many pollutants•1980s, early 1990s: studies demonstrating adverse

effects even at lower levels of exposure•Mid to late 1990s: large number of studies replicated

findings worldwide•Late 1990s-present: evaluation of nuances of

associations observed in epidemiological studies, effects of specific sources, biological mechanisms, long term

effects

Local and Regional Pollution

•Pollution sources tend to be concentrated in cities.

•In the weather phenomenon known as thermal inversion, a layer of cooler air is trapped near the ground by a layer of warmer air above. Normal air mixing is greatly diminished and pollutants remain trapped in the lower layer.

•Smog is intense local pollution usually trapped by a thermal inversion.

This cloud of smog was typical of the skyline hovering over Los Angeles in the 1940s and 1950s.

تاريخي حوادث و تاريخچههوا آلودگي

ميوزبلژيك) دره حادثهدسامبر اول روز وارونگي 1930در وجود علت به

اسيد صنايع، از خروجي آالينده هاي تراكم و هواروي تهيه و سازي شيشه و 60سولفوريك، نفرانسان

. حالت البته شدند تلف گوسفند و گاو زيادي تعدادحدود و 5وارونگي مرگ بيشتر و كشيده طول روز

گزارش دسامبر پنجم و چهارم روزهاي در ميرها . غلظت است تا SO2شده فوق، روز هاي طي هوا

38. است بوده ميليون در قسمت

Severe Air Pollution Episodes

In 1948 in the steel-mill town of Donora, Pennsylvania, intense local smog killed 19 people.

In 1952 in London over 3,000 people died in one of the notorious smog events known as London Fogs; in 1962 another 700 Londoners died in a similar event.

Donora, PA at noon on Oct. 29, 1948

Deadly smog envelops the town.

آمريكا ـ پنسيلوانيا دونورابرفراز 1948اكتبر 31از پايدار حالت

آالينده ها وتراكم گرديد مستقر دونورا شهرمي شوند ناشي فوالد صنايع از عمدتا كه

بيماري جمعيت 6000باعث از هزار 12نفر. شدند بستري هم تعدادي كه شد شهر نفري

نشده مشخص حادثه اين در مير ها و مرگاست.

Denora, Pennsylvania 29 Oct 1948

لندن ) اسماگ ) دود ـ 1952دسامبر 9تا 5مه

آلودگي ناگوار حوادث معروفترين از لندنحدود روز ها آن طي كه است 4000هوا

هوا آلودگي علت به مير و مرگ اضافه نفر . كه نيز حادثه اين در است شده گزارشعلت به سولفورو انيدريد و ذرات تراكم

بود، يافته افزايش هوا وارونگي پديده . است شده شناخته ميرها و مرگ مسئولمشابه حوادث ساير و فوق موارد كليه درريوي بيماران مسن، افراد قربانيان بيشتر

. اند بوده خردسال اطفال و

Summer 2004 ICARTT Campaign(International Consortium for Atmospheric Research on Transport and Transformations)

http://www.al.noaa.gov/ICARTT/

http://www.epa.gov/airnow//health-prof/EPA_poster-final_lo-res.pdf

Health Effects of Air Pollution :Key Findings I

Know more about short term effects:•More people die and are admitted to hospital for heart and

lung problems on days with elevated levels of air pollution•These effects are the “tip of the iceberg” relative to other,

milder effects•A variety of biological mechanisms have been identified for

these effects•Effects found at levels previously thought to be safe•Effects observed using widely varying study designs: large

scale population studies to controlled laboratory studies in humans/ animals

“Tip of the Iceberg”

Adverse health effects that could be avoided every year by meeting the US EPA's daily maximum ozone standard (80 ppb 8-hr) in New York. Figure sections not drawn to scale. From Thurston 1997.

Health Effects of Exposure to Ozone and PM2.5

• coughing• nose and throat irritation• chest pain• reduced lung function• increased susceptibility to respiratory illness•aggravation of asthma •children and people with chronic

lung disease are particularly at risk

• increased risk of cardiac arrest and premature death

• aggravation of asthma• respiratory related hospital

visits • reduced lung function and

chronic bronchitis• work and school absences• children and people with

chronic lung disease are particularly at risk

Ozone PM2.5

Factors which “cause” asthma (asthma prevalence)Hereditary

Exposure to contaminantsCigarette smokeObeistyHeigeneAir Pollution?

Factors which provoke asthma (asthma attack)Cigarette SmokeBiological - Pollen, MoldEmotional StressIndoor Air QualityWeather / Outdoor Air Quality

Effects of Air Pollution on PlantsEffects of Air Pollution on Plants

Air pollution commonly leads to oxidation damage of Air pollution commonly leads to oxidation damage of both crop plants and wild species.both crop plants and wild species.

Effects of Air Pollution on PlantsEffects of Air Pollution on Plants

Air pollution weakens plants by damaging their Air pollution weakens plants by damaging their leaves, limiting the nutrients available to them, or leaves, limiting the nutrients available to them, or exposing them to toxic substances slowly released exposing them to toxic substances slowly released from the soil. Quite often, injury or death of plants is from the soil. Quite often, injury or death of plants is a result of these a result of these effects of acid rain effects of acid rain in combination with in combination with one or more one or more additional threats.additional threats.

Welfare Effects of Air Pollution

Effects of Pollution on BuildingsEffects of Pollution on BuildingsFor limestone, the acidic water reacts with the calcium to For limestone, the acidic water reacts with the calcium to form calcium sulfate:form calcium sulfate:

CaCOCaCO33 + H + H

22SOSO44 CaSO CaSO

44 + 2H + 2H++ + CO + CO33

2-2-

The calcium sulfate is soluble so it is easily washed away The calcium sulfate is soluble so it is easily washed away during the next rain storm.during the next rain storm.

Statue carved in 1702 Statue carved in 1702 photographed in 1908 photographed in 1908 (left) and 1969 (right).(left) and 1969 (right).

Criteria Air Pollutants: Ozone

•Unpleasant appearance in urban cities

photochemical smog

•Deterioration of synthetic rubber, textiles, paints

Gates Corporationhttp://www.gates.com/brochure.cfm?brochure=2833&location_id=3369

US EPA in How Stuff Works Website, http://science.howstuffworks.com/ozone-pollution.htm

National Ambient Air Quality Standards

Pollutant Primary Stds. Averaging Times Secondary Stds.

9 ppm )10 mg/m3(

8-hour1 None Carbon Monoxide

35 ppm )40 mg/m3(

1-hour1 None

Lead 1.5 µg/m3 Quarterly Average Same as Primary

Nitrogen Dioxide 0.053 ppm )100 µg/m3(

Annual )Arithmetic Mean(

Same as Primary

50 µg/m3 Annual2 )Arith. Mean(

Same as Primary

Particulate Matter )PM10(

150 ug/m3 24-hour1

15.0 µg/m3 Annual3 )Arith. Mean(

Same as Primary

Particulate Matter )PM2.5(

65 ug/m3 24-hour4

Ozone 0.08 ppm 8-hour5 Same as Primary

0.03 ppm Annual )Arith. Mean( -------

0.14 ppm 24-hour1 -------

Sulfur Oxides

------- 3-hour1 0.5 ppm )1300 ug/m3(

1 Not to be exceeded more than once per year.

2 To attain this standard, the 3-year average of the weighted annual mean PM10 concentration at each monitor within an area must not exceed 50 ug/m3.

3 To attain this standard, the 3-year average of the weighted annual mean PM2.5 concentrations from single or multiple community-oriented monitors must not exceed 15.0 ug/m3.

4 To attain this standard, the 3-year average of the 98th percentile of 24-hour concentrations at each population-oriented monitor within an area must not exceed 65 ug/m3.

5 To attain this standard, the 3-year average of the fourth-highest daily maximum 8-hour average ozone concentrations measured at each monitor within an area over each year must not exceed 0.08 ppm.

I ndex Value

PSI Descriptor

General

Health

Effects

Cautionary Statements

Up to 50 Good None for the general population.

None required.

50 to 100 Moderate Few or none for the general population.

None required.

100 to 200

Unhealthful Mild aggravation of symptoms among susceptible people, with irritation symptoms in the healthy population.

Persons with existing heart or respiratory ailments should reduce physical exertion and outdoor activity. General population should reduce vigorous outdoor activity.

200 to 300

Very Unhealthful

Significant aggravation of symptoms and decreased exercise tolerance in persons with heart or lung disease; widespread symptoms in the healthy population.

Elderly and persons with existing heart or lung disease should stay indoors and reduce physical activity. General population should avoid vigorous outdoor activity.

Over 300 Hazardous Early onset of certain diseases in addition to significant aggravation of symptoms and

Elderly and persons with existing diseases should stay indoors and avoid physical exertion.

Major Pollutants•Hydrocarbons and Volatile Organic

Compounds: Gasoline, paint, solvents, cleaning solutions.

•Carbon Monoxide: Carbon Monoxide - highly poisonous gas … attaches to hemoglobin

and won’t let go.•Nitrogen oxides - contribute to photochemical

smog. Catalytic converters are designed to break this down.

Major Pollutants

•Photochemical smog - ozone and hydrocarbons producing peroxyacetylnitrate.

•Sulfur oxides - Poisonous gas to both plants and animals

•Lead and other heavy metals•Photochemical oxidants - Toxic to plants and

animals. Ozone is a “pollutant out of place .”

جلسه پایان در میرود انتظارباشد قادر :دانشجو

مواد- 1 به مربوط هوا كننده پاك دستگاههاي. ببرد نام را ثابت منابع در اي ذره

را- 2 وزني دهنده رسوب دستگاه كار اساس. دهد توضيح

3. دهد- شرح را سيكلون دستگاه كار اساس4. كند- بيان را فيلتر كار نحوهالكترو- 5 دهنده رسوب كاركرد كار سازو

. دهد توضيخ را استاتيك

Why Air Pollution Control?

Quality of Life

This is what you would have lived with in Saint Louis in

1940.

Quality of Life

This is Saint Louis today, a different kind of air pollution.

Yesterday

Low Pollution/High Visibility

High Pollution/Low Visibility

Two Types of Air Pollution

Particulate (Visible)

Gaseous

Three Types Of Control

MechanicalChemicalBiological

Particulates

Regulated Particles10 microns or less diameter

Human hair averages 25 microns25 microns is 1/1000 inch

Example Sources OfParticulate Pollution

Wood ProcessingRock QuarriesCoal Power Plants

Particulate Control(Mechanical)

CycloneFabric Filter (Baghouse)ScrubberElectrostatic Precipitator

Cyclone

Most CommonCheapestMost Adaptable

Cyclone Operating Principle

“Dirty” Air Enters The Side.

The Air Swirls Around The

Cylinder And Velocity Is Reduced.

Particulate Falls Out Of The Air To The Bottom Cone And Out.

Multiple Cyclones(Multi clone)

Smaller Particles Need LowerAir Flow Rate To Separate.

Multiple Cyclones Allow Lower Air Flow Rate, Capture Particles to 2 microns

Fabric Filter(Baghouse)

Same Principle As Home Vacuum Cleaner

Air Can Be Blown Through Or Pulled Through

Bag Material Varies According To Exhaust Character

Baghouse

About Baghouses

Efficiency Up To 97%+

(Cyclone Efficiency 70-90%)

Can Capture Smaller Particles Than A CycloneMore Complex, Cost More To Maintain Than Cyclones

Electrostatic Precipitator(ESP)

High Efficiency Able to Handle Large Air Flow

RatesOr Can Be Very Small (Smoke

Eaters In Bars and Restaurants)

How An ESP Operates

Electrostatic Precipitator Drawing

PrincipleHigh-Voltage Charges WiresGases Are IonizedParticles Become ChargedCollection Plates (Opposite Charge) Attract ParticlesRapper Knocks Plates So That The Collected Dust Layer Falls Into Hoppers

میرود انتظار جلسه پایان در: بتوانند دانشجویان

نام- 1 را تر های شوینده انواعببرند.

و- 2 گازها کنترل روشهایتوضیح را ثابت منابع در بخارات

دهند.

را- 3 بیولوژیکی کنترل روشهای. دهند شرح

ScrubbersGas Contacts A Liquid StreamParticles Are Entrained In The

LiquidMay Also Be A Chemical

ReactionExample: Limestone Slurry With

Coal Power Plant Flue Gas

Tower Scrubber

Types Of Scrubber

Tray Tower ScrubbersImpingement TraySieve TrayPacked Bed ScrubbersCylinder Filled with Media

Which Promotes Gas-Liquid Contact

Types Of ScrubberFiber Bed Scrubber

Vertical Mesh Pads Of Interlaced Fibers Promote Gas-

Liquid ContactSpray Tower Scrubber

Nozzles Spray Liquid Across the Inlet Gas Flow Path

Gaseous Pollutant Control

Pollutants Of Interest

Volatile Organic Compounds (VOC)

Nitrogen Oxides (NOx)Sulfur Oxides (SOx)

Example Sources OfGaseous Pollutants

Surface Coating ProcessesPrintingCombustion (Boilers)Dry CleaningBakeries

Mechanical ControlFor Burners, Air/Fuel Ratio

Control, Called Low-NOx Burners.

For Dry Cleaners And Similar Processes Using Solvent In

Closed Vessels, Refrigerated Condensers.

Chemical Control

Flue Gas ControlSolvent Destruction

Flue Gas Control

To Reduce Emissions of NOx From Burners:

Break NOx Into O2 And N2 With A Catalyst.

Same Process As In Autombiles.

Flue Gas SOx ControlSOx Forms Sulfuric Acid With Moisture In Air Producing Acid Rain.

Remove From Flue Gas By Chemical Reaction With Limestone

Thermal Oxidizers

For VOC Control

Also Called Afterburners

Two Types Of Oxidizer

Catalytic

Non-Catalytic

Thermal Oxidizer(Non-Catalytic)

Catalytic Thermal Oxidizer

Biological MethodUses Naturally Occurring

Bacteria (Bugs) To Break Down VOC

“Bugs” Grow On Moist Media And Dirty Gas Is Passed

Through. Bugs Digest The VOC .Result Is CO2 And H2O

A Bio Filter For VOC Removal

?Questions?

میرود انتظار جلسه پایان در: بتوانند دانشجویان

هوا- 1 آلودگی متحرک منابع انواع. ببرد نام را

و- 2 گازها کنترل روشهایتوضیح را متحرک منابع در بخارات

دهند.

در- 3 ای ذره مواد کنترل روشهایدهند توضیح را متحرک منابع

What are catalysts?Simply put, catalysts are

substances which, when added to a reaction, increase the rate of

reaction by providing an alternate reaction

pathway with a lower activation energy (Ea).

They do this by promoting proper

orientation between reacting particles.

In biochemistry, catalysts are known as

enzymes .

Catalytic ConvertersOne common

application for catalysts is for catalytic

converters.Catalytic converters are

found in automobiles.Their role is to reduce

to emissions of harmful gases (CO, VOC’s, NOx)

that are the result of the combustion of fuel

in vehicle engines.

Specifics of Catalytic Converters

Most modern cars are equipped with three-way

catalytic converters. "Three-way" refers to the

three regulated emissions it helps to reduce -- carbon monoxide, VOCs and NOx

molecules .The converter uses two

different types of catalysts, a reduction catalyst and an oxidization catalyst.

Both types consist of a honeycomb-shaped ceramic

structure coated with a metal catalyst, usually

platinum, rhodium and/or palladium .

A: Reduction CatalystB: Oxidation CatalystC: Honeycomb Ceramic Structure

Step 1: The Reduction Catalyst

The reduction catalyst is the first stage of the catalytic converter .

It uses platinum and rhodium to help reduce the NOx emissions. When an NO or NO2 molecule

contacts the catalyst, the catalyst rips the nitrogen atom out of the molecule and holds on

to it, freeing the oxygen in the form of O2 .The nitrogen atoms bond with other nitrogen

atoms that are also stuck to the catalyst, forming N2.

The equation for this is as follows:2 NO => N2 + O2 or 2 NO2 => N2 + 2 O2

Step 2: The Oxidization Catalyst

The oxidation catalyst is the second stage of the catalytic converter .

It reduces the unburned hydrocarbons and carbon monoxide by burning (oxidizing) them

over a platinum and palladium catalyst .This catalyst aids the reaction of the CO and

hydrocarbons with the remaining oxygen in the exhaust gas .

The equation for this process is as follows:2 CO + O2 => 2 CO2

Once this process is complete, most of the harmful substances have been broken down

into harmless ones such as N2, O2, and CO2.

Catalysts in IndustryOf course, reducing vehicle

emissions is not the only area in which catalysts can

prove useful. The petrochemical industry

also makes great use of them in various processes .

One of these processes, called catalytic cracking, is

detailed below. Catalytic cracking is the name given to the breaking up of large

hydrocarbon molecules into smaller, more useful

pieces.

Catalytic Cracking: Part 1:Hydrocarbons are the result of the fractional distillation of

gas oil from crude oil (petroleum). These fractions are obtained from the distillation process as liquids, but are re-

vaporised before cracking.The hydrocarbons are mixed with a very fine catalyst

powder. These days, the catalysts are zeolites (complex alumniosilicates).

In the past, the catalyst used was aluminum oxide and silicon dioxide, however, these are much less efficient than

the modern zeolite.The whole mixture (hydrocarbons and zeolites) is blown

through a reaction chamber at a temperature of about 500 C. The catalyst is recovered afterwards, and the cracked

mixture is further separated by cooling and fractional distillation.

CATALYTIC CONVERTERS

•Catalytic converters remove harmful gases from car exhausts.

•It consists of a honeycomb of ceramic with metals such as platinum,palladium and rhodium coated on the honeycomb

•It removes up to 90% of the harmful gases

CONox

C8H18

CO2

N2

H2O

Catalytic converter

EQUATIONS FOR REACTIONS IN THE CATALYTIC CONVERTER

CO + NO CO2 + N2222

C8H18 + NO CO2 + N2 + H2O25 8 12 1/2 9

EXAMPLES OF POISONING OF CATALYSTS

Leaded petrol cannot be used in cars fitted with a catalytic converter since lead strongly absorbs onto the surface of the catalyst

Cannot use copper or nickel in a catalytic converter on a car instead of the expensive platinum or Rhodium. REASON :- Any SO2 present in the exhaust fumes (trace amounts ) would poison the catalyst

Once the catalytic converter has become inactive it cannot be regenerated

Control of exhaust for unburned HC and CO involves :

fuel modifications minimizing pollutants from the combustion

chamber - better engineering of motors oxidation of pollutants outside the

combustion chamber - either by normal combustion, or by catalytic oxidation.

Requires pumping of air to the exhaust stream .

To lower NOx, two systems are used :exhaust gas recirculation sends part of

the exhaust stream back into the intake manifold which reduces the combustion

temperature and decreases NOx production (tolerated when ``power'' is

not required) ;a second catalytic converter can be used

in series with the HC/CO converter to decompose NOx to O and N .

ENVE 4003

MOBILE SOURCES

Types of emissions, control technologies and trends, inspection and maintenance programs .

Motor VehiclesInternal combustion (IC) engines

Spark ignition (SI) - gasoline, propane, natural gas, ethanol

4-stroke vs 2-stroke

Compression ignition (CI) - diesel, biodiesel

Figure 13.1 de NeversSchematic of piston and cylinder in

IC engine

Figure 18.2 Cooper & AlleySchematic of four stroke IC engine

Figure A3.1.5 Faiz, Weaver & Walsh

Two stroke motorcycle engine

Figure A3.2.1 Faiz, Weaver & Walsh

Diesel combustion

stages

MOTOR VEHICLE EMISSIONS

Regulated (criteria pollutants):

CO, NOx, NMHC, PMNon-regulated:

Individual (speciated) HCs carbonyl compounds (alcohols,

aldehydes, ketones)Air toxics, e.g. benzene, toluene,

ethylbenzene, 1,3,butadiene, formaldehyde, acetaldehyde

CO2 (i.e. fuel economy)

Table 13.1 de Nevers

Contribution of motor vehicles to U.S. national emissions

MOTOR VEHICLE EMISSIONS

Exhaust (tailpipe) (CO, NOx, VOC, PM)Evaporative (VOC)

RestingDiurnal heat buildHot soak

RunningRefuelling

COMBUSTION IN IC ENGINESAir/Fuel ratio, mass of air per mass of fuel, ~15Normalized A/F ratio ,

= (A/F) actual / (A/F) stoichiometric

Equivalence ratio :

= (A/F)stoichiometric / (A/F) actual

1 for gasoline engines most of the time , > 1 (fuel rich) during high power demand and start

< 1 (fuel lean) for diesel most of the time ,ignition - combustion - extinction

sequence repeated 102 ~ 103 times a minute; unsteady combustion

Figure (13.2) de Nevers

Emissions and fuel

consumption vs lambda

Figure 10.16 (7.5) de Nevers

Effect of air-fuel ratio and quality

of mixing on composition of

combustion gases

Table 13.3 de NeversEquivalence or A/F ratios

POLLUTANT FORMATION MECHANISMS - SI ENGINES

HC

Rich Fuel/Air mixture, “oxygen deficit”

Flame quenching at walls, crevices, “quench zone”CO

Rich Fuel/Air mixture, “oxygen deficit”

“incomplete reaction”, even with sufficient oxygenNO, Thermal ;

T compression ~ 600 F

T combustion ~ 3600 F

Short times but high peak temperatures

DIESEL COMBUSTION CHARACTERISTICS

Only air is compressed during compression stroke, reaching 700-900 C

Fuel is injected into hot air just before top of compression stroke

A fuel-air mixture forms around the periphery of the fuel jet and ignites after an ignition delay. This

premixed combustion phase accounts for only a fraction of the fuel and causes a pressure peak

The remainder of the fuel burns under mixing controlled combustion causing a more gradual

pressure increase, and then decline with expansion

DIESEL NOx FORMATION CHARACTERISTICS

Most NOx formed during the high T and P premixed combustion phase

NOx formation can be reduced effectively by reducing flame temperature:

delay combustion into the expansion phasecool the air charge going into the cylinderexhaust gas recirculation (EGR)

PARAMETERS AFFECTING DIESEL

PM AND HC EMISSIONSAir/Fuel ratio, generally lean overall, to allow for

complete combustion within limited time available for mixing

Minimum = 1.5 for smoke point, smoke increases dramatically below this limit

Rate of air-fuel mixing, can be enhanced by imparting a swirl to the injected fuel

fuel injection timingcompression ratiotemperature and composition of charge in the

cylinder

DIESEL VISIBLE SMOKE

Black smoke : from sootWhite, blue or gray smoke: condensed

hydrocarbon droplets in the exhaustBlue or gray generally due to vaporized

lubricantWhite due to cold startSulfur in the fuel forms sulfuric acid which is

later sampled as PM

Table 13.5 de NeversComparison of gasoline and diesel

engines

VEHICLE EMISSION CONTROL

Control technology is aimed at reducing the second term: fuels, engines, vehicles etc .

Urban and transportation planning addresses the first term: housing density, location,

transportation infrastructurethe second term is relatively insensitive to the

number of passengers in the vehicleIncreasing vehicle occupancy helps reduce

emissions: mass transit, car pooling etc.

Emissions km travelled emissions km( )( / )

CONTROL TECHNOLOGY - SI

Air/Fuel ratio. CO and HC emissions increase as mixture gets richer in fuel (start and high

power conditions), NOx emissions peak near stoichiometric ratio

Fuel metering systems: carburetors and fuel injectors (throttle body TBI, multi-port PFI,

simultaneous or sequential)Electronic Control Systems adjust the air/fuel

ratio based on the signal from an oxygen sensor in the exhaust

EXHAUST GAS RECIRCULATION (EGR) - SI AND CI ENGINES

Dilutes Air/Fuel mixture with exhaust gases thereby reducing peak combustion

temperatures and NOx formationThere are limits to how lean an air-fuel-exhaust

gas mixture can be for ignitionIgnition systems (spark plugs etc.) and

combustion chambers can be designed to improve performance with these lean mixtures

EXHAUST AFTERTREATMENT SI ENGINES

Air injection - thermal oxidation of residual CO and HC with excess air introduced after the

engine into the exhaust system, very temperature sensitive: Minumum 600 C for HC,

700 C for COCatalytic convertors can achieve conversion at

lower temperatures ~ 350 COxidation (two-way) catalyst - for HC and COOxidation-reduction (three-way) catalyst (TWC)

for HC, CO, and NOx according to:

NO + CO + HC Pt - Rh

N + CO + H O2 2 2

CATALYTIC CONVERTORS SI ENGINES

Pellet and monolith typesRequire near stoichiometric combustion for

effective conversion of all three pollutants, CO and HC conversion efficieny drop for rich

mixtures, NOx conversion efficiency drops for lean mixtures

Exhaust gas oxygen sensor (Zirconia, ZrO2 based) essential to keeping the Air/fuel ratio in

window of optimum conversion efficiency for all three

TWC picture from ICT-Umicore CD

EVAPORATIVE EMISSION CONTROL SI ENGINES

Blowby and Crankcase emissions - fuel and partial combustion product molecules pass by the piston into the crankcase - recycled back to air intake manifold by Positive Crankcase

Ventilation (PCV)Charcoal canister for capturing fuel tank,

carburetor and miscellanous evaporative emissions. Adsorption during hot-soak, diurnal

heat build (breathing), refuelling periods, desorption into the air intake during engine

operation (regeneration)

CONTROL TECHNOLOGY - CI

PM and NOx more important in diesel exhaust than CO and HC, relative to gasoline exhaust

A general trade-off between PM and NOx exists although reductions in absolute levels of both

emissions have been achievedEmissions more strongly dependent on engine

design - most emission reductions so far have been achieved through combustion

modifications rather than exhaust aftertreatment in contrast to gasoline engine

emissions

DIESEL PM FORMATION CHARACTERISTICS

Particulate Matter forms in fuel rich zones primarily during the mixing controlled combustion phase

mostly an aggregate chain carbon core (soot)

adsorbed hydrocarbons (aliphatic and polyaromatic): soluble organic fraction (SOF)

significant fraction of SOF may come from lubricating oil

Most of the PM formed during combustion is subsequently burned during the expansion stroke, the unburned part forms the

emissions

Sulfur in the fuel forms sulfuric acid which is later sampled as PM

DIESEL EXHAUST AFTERTREATMENT

Flow through oxidation catalyst (two-way catalytic convertor) for reduction of CO and VOC (80%), and PM SOF (20-30%), does not

retain PM

Trap oxidizer (Diesel particulate filter), reduce PM by 95%, filter + oxidation (regeneration) functions

active and passive regeneration types

Passive regeneration: catalyst coated onto trap or added to fuel bring regeneration temperature down to 400-450 C which can be

achieved in diesel exhaust

Active regeneration monitors PM build-up on the trap and triggers regeneration by diesel fuel burning, electric heating, catalyst

injection

DPF from ICT-Umicore CD

DPF detail from M.Walsh

EXHAUST EMISSION MEASUREMENT

Simulated driving conditionsMass Emission rates in g/km for light duty

vehicles (LDV) on a chassis dynamometer Mass Emission rates in g/kWh for heavy

duty (HD, diesel) engines on an engine dynamometer

Actual driving conditions“On-board” measurement systemsTunnel studiesRemote sensing, g/L of fuel burned

EVAPORATIVE EMISSION MEASUREMENT

SHED Test, Sealed Housing Evaporative Determination

Carbon canisters attached to various points on vehicle to adsorb HC vapors

DRIVING OR OPERATING CYCLES

Actual vs SynthesizedTransient, steady state, multi-modeModal analysis:

AccelerationCruiseDecelerationIdle

EMISSION FACTORS

Amount of pollutant emitted per unit activity:g/km, (distance travelled)g/kWh, (mechanical energy delivered)g/L, (quantity of fuel burned)

For a single vehicle with given engine and emission control technology, the factors that influence the

emission factor are: speed, acceleration/deceleration, trip length, ambient temperature

Vehicles with similar size, engine, and emission technology may be expected to show similar

emission behaviour

EMISSION FACTORS AND EMISSION MODELLING

Regulated emissions from new vehicles vs emissions from in-use vehicles

Emissions surveillance program to test emissions from thousands of in-use vehicles at different ages in the U.S .

Emission modelling from motor vehicles involves the consideration of different types of vehicles and their

driving conditions to arrive at a grand total

Emissions km travelled emissions km( )( / )

INSPECTION AND MAINTENANCE PROGRAMS

Field studies suggest that more than 50% of motor vehicle pollution may come from less than 10% of vehicles which

have poorly maintained or malfunctioning emission control devices

Inspection and maintenance (I/M) programs aimed at identifying such gross-emitter vehicles and ensuring the

repair of their emission control systems are becoming more important in the face of reduced emission regulations for

new vehicles

Remote sensing of CO, HC, and NOx, along with CO2 offers both I/M and fuel-based emission inventory advantages

I/M PROGRAMSEmission control technology for LDGV very effective;

90--95% reduction compared with no controls

Emission control system performance deteriorates with vehicle age but only gradually

Emissions from a small fraction of vehicles with malfunctioning control systems erode the benefits of emission reductions from a large number of vehicles

I/M programs aim to maintain control system efficiency for the entire fleet, over the useful life of vehicles

I/M PROGRAMS

Objectives:Identify and repair vehicles with maladjustments or

control system malfunctionsDiscourage willful tampering with control systems

Modes:Periodic checks of all vehiclesIdentification and repair of high emitting vehicles ,Identification and exemption of low emitting vehicles,

“clean screening”

I/M PROCEDURESSI Engines

Exhaust concentrations measurement; CO, HC, NOxNo load, idle/2500 rpm

Loaded dynamometer testsASM, Acceleration simulation mode

(AMS2525, 25 mph, 25% maximum FTP acceleration)

IM240, first 240 seconds of FTP (Federal Test Procedure)

Visual inspection of control system componentsPressure/purge tests for evaporative emission control systems

CI EnginesBosch method for smoke: pull measured amount of exhaust through

filter paper, check light transmission of filterOpacity meter: check light attenuation directly across exhaust path

under “snap acceleration” conditions

I/M PROGRAMS

Institutional setting:Centralized - inspectionDecentralized - test and repair

FrequencyVehicle age at first test, 1-4 yearsSubsequent tests every 1-2 years

CostsProgram operating costsRepair costs

Cost/benefit ratioImprovement in ambient air quality vs I/M costs

I/M PROGRAMS - COMPLEMENTS

Remote sensingClean screening, high emitter profiling

On-board diagnostics (OBD)Sensing and monitoring devices to detect malfunctions

Light indicatorStored computer codes for malfunctioning

components:catalystoxygen sensorengine misfireevaporative system integrity

Pb, S, and Transportation fuels

Pb used to be added to gasoline (tetra-ethyl lead TEL) as an octane enhancer.

Phased out in most countries and being phased out in others:

permanent poisoning of TWC – using leaded gasoline in a vehicle with TWC once is sufficient to

make the TWC useless Neuro-toxic health effects on children

Pb, S, and Transportation fuels

S is a natural component of crude oil. Can be removed effectively by hydrodesulfurization .

Adverse (though reversible) effect on efficiency of TWC and DPF. Low sulfur fuel increases efficiency of modern TWC and makes it possible to use advanced

diesel exhaust after-treatment like DPFcontribution to PM emissions as sulfatecontribution to gaseous Sox emissions

Current trends: coming down to 15 ppm (ULSD ultra low sulfur diesel), from 300-500

ppm.

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