chapter 24: air pollution

Chapter 24: Air Pollution

A Brief History of Air Pollution

• The atmosphere has long been a sink for waste disposal.

• Long history of recognition of the existence of atmospheric pollutants– Natural photochemical smog recognized in

1550– Acid rain first described in 17th century– Word smog introduced in 1905

• Mixture of smoke and fog

A Brief History of Air Pollution

• Two events sparked research on air pollution and regulations to control air quality.– Donora fog in 1948– London smog event in 1952– Both cause by pollutants being trapped by

weather events. Both killed numerous people.– Could happen again in cities like Beijing or

Mexico City

Stationary Source of Air Pollution

• Stationary sources are those that have a relatively fixed location. – Point sources emit pollutants from one or more

controllable sites.– Fugitive sources generate air pollutants from

open areas exposed to wind processes. – Area sources are well defined areas within

which are several sources of air pollutants.

Point source

Fugitive source

Mobile Source of Air Pollution

• Mobile source of air pollutants move from place to place while emitting pollutants.– Automobiles, trucks, buses, aircraft, ships, and

trains.

General Effects of Air Pollution

• Affects many aspects of our environment– Visual qualities– Vegetation– Animals– Soil – Water quality– Natural and artificial structures– Human health


• Significant factor in human death rate for many large cities– Athens, Greece- # of deaths higher on bad air

quality days– Hungary- 1 in 17 deaths contributed to air

pollution– US- 300,000 deaths/year, health cost $50 billion– China- health cost $50 - $100 billion


• Affect human health in several ways– Toxic poisoning, cancer, birth defects, eye

irritation, and irritation of respiratory system.– Increased susceptibility to viral infections,

causing pneumonia and bronchitis.– Increased susceptibility to heart disease.– Aggravation of chronic diseases, such as

asthma and emphysema.


• Many air pollutants have synergistic effects– Do greater damage to the lungs than a

combination of the two pollutants would be expected to do based on their separate effects.

Air Pollutants

• 200 air pollutants recognized and assessed by US EP and listed in Clean Water Act– Six called critical pollutants

Primary and Secondary Pollutants

• Major air pollutants occur either in gaseous forms or as particulate matter.

• Classified as primary or secondary– Primary pollutants- emitted directly into the air– Secondary pollutants- produced through

reactions between primary pollutants and normal atmospheric compounds.

Primary and Secondary Pollutants

• In addition to human sources, our atmosphere contains many pollutants of natural origin.– Release of sulfur dioxide from volcanic eruptions.

– Release of hydrogen sulfide from geysers and hot springs and from biological decay in bogs and marshes.

– Release of ozone in the lower atmosphere as a result of unstable meteorological conditions.

– Emission of a variety of particles from wildfires and

– windstorms.

– Natural hydrocarbon seeps.

Criteria Pollutants

• There are six criteria pollutants– Sulfur dioxide– Nitrogen oxides– Carbon monoxide– Ozone– Particulates– Lead

Sulfur Dioxide

• SO2

– Colorless odorless gas

– Once emitted can be converted to sulfateSO4

– Removed from atmosphere by wet or dry deposition

– Major human sources; coal power plants, industrial processes

Sulfur Dioxide

• Adverse effects depend on dose and concentration present– Injury or death to animals and plants– Corrosion of paint and metals– Important precursor to acid rain

Nitrogen Oxides

• Occur in many forms in the atmosphere but largely emitted in two forms:– Nitric oxide- NO– Nitrogen dioxide- NO2

• A yellow-brown to reddish-brown gas• May be converted to NO3

2-

– Both subject to emissions regulation and contribute to smog

– NO2 major contributor to acid rain

Nitrogen Oxides

• Nearly all NO2 emitted from human sources

– Automobiles and power plants that burn fossil fuels

• Environmental effects– Irritate eyes and mucous membranes– Suppress plant growth

• However when convert to nitrate may promote plant growth

Carbon Monoxide

• CO is a colorless, odorless gas– Even at low concentrations is extremely toxic

to humans• Binds to hemoglobin in blood.

– 90% of CO in atmosphere comes from natural sources

– 10% comes from fires, cars, and incomplete burning of organic compounds

Ozone and Other Photochemical Oxidants

• Photochemical oxidants result from atmospheric interactions of nitrogen dioxide and sunlight.– Most common is ozone- O3

– Colorless gas w/ slightly sweet odor– Very active chemically, oxidizes or burns

• Beneficial in the upper atmosphere

Ozone and Other Photochemical Oxidants

• Because ozone is a secondary pollutant it is difficult to regulate.– Health standards often exceeded in urban areas

• Effects include– Kills leaf tissue at high concentration– Damage eyes and respiratory system– Even young, healthy people may have

breathing difficulty on polluted days

Particulate Matter

• PM10 is made up of particles less than 10μm in diameter– Present everywhere but high concentrations

and/or specific types dangerous– Much particulate matter easily visible as

smoke, soot, or dust– Includes airborne asbestos and heavy metals

Particulate Matter

• Of particular concern are very fine pollutants– PM 2.5- less than 2.5 μm in diameter– Easily inhaled into the lungs, then absorbed

into the bloodstream– Ultrafine particles- <0.18 μm released by

automobiles.• Related to heart disease

Particulate Matter

• When measured often referred to as total suspended particles (TSPs)– Tend to be highest in large cities in developing

countries

Particulate Matter

• Recent studies estimate that 2 to 9% of human mortality in cites is associated w/ PM– Linked to both lung cancer and bronchitis– Especially hazardous to elderly and those w/

asthma

• Dust can be deposited on plants– Interferes w/ absorption of CO2 and O2 and

transpiration

Particulate Matter

• Block sunlight and may cause climate change.

• Global dimming– Gradual reduction in the solar energy that

reaches the surface of Earth– Cools the atmosphere– Lessens global warming

Lead

• Lead is constituent of auto batteries and used to be added to gasoline.– Lead in gas emitted into air w/ exhaust– Spread widely around world in soils and water

along roadways– Once in soil can enter the food chain– Lead now removed from gas in US, CAN, EU

• 98% reduction in emissions since 1970s

Air Toxics

• Among pollutants that are known or suspected to cause cancer or other serious health problems.– Associated w/ long-term and short-term

exposures– Gases, metals, and organic chemicals that are

emitted in relatively small volumes– Cause respiratory, neurological, reproductive,

or immune diseases

Air Toxics

• Standards have been set for more than 150 air toxics– E.g. hydrogen sulfide, hydrogen fluoride,

chlorine gases, benzene, methanol, ammonia– EPA estimates that the average risk for cancer

from exposure to air toxics is about 1 in 21,000

Hydrogen sulfide

• Highly toxic corrosive gas easily identified by its rotten egg odor.

• Produced from – Natural sources such as geysers, swamps, and bogs – Human sources such as industrial plants that produce

petroleum or that smelt metals.

• Effects of hydrogen sulfide include – Functional damage to plants – Health problems ranging from toxicity to death for

humans and other animals.

Hydrogen Fluoride

• Extremely toxic gaseous pollutant • Released by some industrial activities

– Such as production of aluminum, coal gasification, and burning of coal in power plants.

• Even a small concentration (as low as 1 ppb) of HF may cause problems for plants and animals.– Potentially dangerous to grazing animals because

forage plants can become toxic when exposed to this gas.

Methyl Isocyanate

• An ingredient of a common pesticide– known in the United States as Sevin.

• Colorless gas • Causes severe irritation (burns on contact) to eyes,

nose, throat, and lungs. – Breathing the gas in concentrations of only a few ppm

causes violent coughing, swelling of the lungs, bleeding, and death.

– Less exposure can cause a variety of problems, including loss of sight.

Volatile Organic Compounds

• Variety of organic compounds used as solvents in industrial processes – Dry cleaning, degreasing, and graphic arts.

• Hydrocarbons– Comprise one group of VOCs. – Thousands of hydrocarbon compounds exist,

including natural gas, or methane (CH4); butane (C4H10); and propane (C3H8).

Volatile Organic Compounds

• Some VOCs react w/ sunlight to produce photochemical smog

• Globally 15% of hydrocarbons emissions are anthropogenic– In the US 50%– Primary human source automobiles

Benzene

• Additive in gasoline and an important industrial solvent.

• Produced when gasoline and coal undergo incomplete combustion.– Also component of cigarette smoke– Major environmental source on and off road

vehicles

Arcolein

• A volatile hydrocarbon that is extremely irritating to nose, eyes, and respiratory system.

• Produced from– Manufacturing processes that involve

combustion of petroleum fuels– Component of cigarette smoke

Variability of Air Pollution

• Problems vary in different regions of the country and the world.– LA pollution mainly from mobile sources– Ohio and Great Lakes point sources

• Also varies w/ time of year– Smog a problem in summer when there is lots

of sunshine– Particulates a problem in dry months

Las Vegas: Particulates

• Particulates a problem in arid regions– Where little vegetation is present and wind can

easily pick up and transport fine dust.– Brown haze over Las Vegas partly due to

naturally occurring PM 10 – 60% of the dust comes from new construction

sites, dirt roads, and vacant land.

Haze From Afar

• Air quality concerns are not restricted to urban areas.– North slope of AK has an air pollution problem

that originates from sources in EE and Eurasia.– Transported by the jet stream.– Significant as we try to understand global air

pollution.

Urban Air Pollution

• Whether air pollution develops depends on topography and meteorological conditions– Determine the rate at which pollutants are

transported away and converted to harmless compounds.

Influences of Meteorology and Topography

• Meteorological conditions determine whether air pollution is a nuisance or major health problem.

• Primary adverse effect– Damage to green plants and aggravation of

chronic disease– Usually low-level over long period of time– However major disaster have occurred


• In the lower atmosphere, restricted circulation associated w/ inversion layers may lead to pollution events.

• Atmospheric inversion-– Occurs when warmer air is found above cooler

air

Occurs primarily in summer and fall.

Occurs when cloud cover associated w/ stagnant air


• Cities situated in a valley or topographic bowl are more susceptible to smog problems than cities in open plains.

• Surrounding mountains and inversions prevent pollutants from being transported by wind or weather systems.– E.g. Los Angeles

Potential for Urban Air Pollution

• Determined by the following factors:– 1. The rate of emission of pollutants per unit

area.– 2. The downwind distance that a mass of air

moves through an urban area.– 3. The average speed of the wind.– 4. The elevation to which potential pollutants

can be thoroughly mixed by naturally moving air in the lower atmosphere.

Potential for Urban Air Pollution

• Concentration of pollutants in the air is directly proportional to the first two factors.– As either emission rate or down wind travel

distance increase, so will the concentration of pollutants

• City air pollution decreases w/ increases in third and forth factors.– The stronger the wind and the higher the

mixing layer, the lower the pollution.

Smog

• Term first used in 1905 as mixture of smoke and fog that produced unhealthy air.

• Two major types– Photochemical smog (LA type smog or brown

air)– Sulfurous smog (London type smog, gray air,

or industrial smog)

Smog

• Photochemical smog reaction involves sunlight, nitric oxides and VOCs– Directly related to automobile use

• Sulfurous smog is produced by the burning of coal or oil at large power plants.

Future Trends for Urban Areas

• The optimistic view – Air quality will continue to improve – Because we know so much about the sources of air

pollution and have developed effective ways to reduce it.

• The pessimistic view – In spite of this knowledge, population pressures and

economics will dictate what happens in many parts of the world,

– The result will be poorer air quality in many locations.

Future Trends for Urban Areas; The United States

• LA is a good area to look at for strategies for pollution abatement.

• Air quality plan involving the entire urban region includes the following features:– Strategies to discourage automobile use and reduce the

number of cars.– Stricter emission controls for automobiles.– A requirement for a certain number of zero-pollutant

automobiles (electric cars) and hybrid cars with fuel cell and gasoline engines.


– A requirement for more gasoline to be reformulated to burn cleaner.

– Improvements in public transportation and incentives for people to use it.

– Mandatory carpooling.– Increased controls on industrial and household

activities known to contribute to air pollution.


• Have focused on LA because the air quality is so poor for a significant portion of the year.

• However, many large and not so large US cities have poor air quality– 30 days per year of unhealthy air resulting from

ozone pollution.

Future Trends for Urban Areas; Developing Countries

• Less developed countries w/ growing populations are susceptible to air pollution– Don’t have the financial base necessary to fight air

pollution

• E.g. Mexico City– 25 million people

– 50,000 buses, millions of cars, LPG leaks

– In a natural basin w/ mountains surrounding it

– Perfect situation for severe air pollution problem

Future Trends for Urban Areas; Developing Countries

• Attempts to reduce air pollution– Shutting down oil refinery– Ordering industrial plants to relocate

• Air pollution however will continue to be a problem if unable to control vehicle use and LPG leaks.

Pollution Control

• The most reasonable strategies for control have been to reduce, collect, capture, or retain the pollutants before they enter the atmosphere.– Reduction of emissions through energy

efficiency and conservation measures is preferred.

Pollution Control: Particulates

• Particulates emitted from fugitive, point or area stationary sources are much easier to control.

• Point and area sources can be controlled by– Settling chambers or collectors which cause

particulates to settle out

• Fugitive sources– Protecting open areas, controlling dust,

reducing effects of wind

Pollution Control: Automobiles

• Control of pollutants such as carbon monoxide, nitrogen oxides, and hydrocarbons is best achieved through pollution control for automobiles.– Nitrogen oxides controlled by recirculating

exhaust gas– CO and hydrocarbons reduced by catalytic

converter

Pollution Control: Automobiles

• Automobile emission regulations plan in US has not been effective– Pollutants may be low when car is new– But many people do not maintain them properly– Suggested that effluent fees replace emission

controls– Other strategies reduce the number or type of

cars

Pollution Control: Sulfur Dioxide

• Can be reduced through abatement measures performed before, during, or after combustion.

• Cleaner coal technology available but makes fuel more expensive.

• Switch to low-sulfur coal– But transportation is an issue


• Washing it to remove sulfur– Iron sulfide settles out– Ineffective for removing organic sulfur

• Coal gasification– Converts coal to gas in order to remove sulfur– Gas obtained is clean


• Emissions from power plants can be reduced by removing the oxides from the gases in the stack– Scrubbing (flue gas desulfurization)– Occurs after coal is burned– Gases treated w/ a slurry of lime or limestone– Reacts to form calcium sulfite– Can then be process into building materials

Clean Air Act Amendments of 1990

• Comprehensive regulations enacted by the U.S. Congress that address acid rain, toxic emissions, ozone depletion, and automobile exhaust.

• Buying and selling of sulfur dioxide emissions

• One step back occurred in 2003 when the president and EPA allowed companies to upgrade w/o new pollution controls.

Clean Air Act Amendments of 1990

• Also calls for control of

• Nitrogen dioxides– Reduced by 10 million tons

• Toxins– Especially those causing cancer

• Ozone depletion in the stratosphere– End production of all CFCs

Ambient Air Quality Standards

• Important because they are tied to emission standards that attempt to control air pollution.

• Tougher standards set for ozone and PM 2.5– When challenged in court justices help that the

EPA’s responsibility is to consider benefits to health not financial costs.

Air Quality Index

• AQI is used to describe air pollution on a given day.

• AQI is determined from measurements of the concentration of five major pollutants:– Particulate matter, sulfur dioxide, carbon

monoxide, ozone, and nitrogen dioxide.

Air Quality Index

• An AQI value of greater than 100 is unhealthy.• Air pollution alert is issued if the AQI exceeds

200. • Air pollution warning is issued if the AQI exceeds

300, hazardous to all people. • If the AQI exceeds 400, an air pollution

emergency is declared, and people are requested to remain indoors and minimize physical exertion.

Cost of Air Pollution Control

• Cost for incremental control in fossil fuel-burning may be a few hundred dollars per additional ton of particulates removed.

• For aluminum plant, may be several thousand per ton.

• Also, a point is reached at which the cost of incremental control is very high in relation to additions benefits.

Cost of Air Pollution Control

• Economic analysis of air pollution includes many variables, some of which are hard to quantify. We do know the following:– W/ increasing air pollution controls, the capital cost for

technology to control air pollution increases.– As the controls for air pollution increase, the loss from

pollution damages decreases.– The total cost of air pollution is the cost of pollution

control plus the environmental damages of the pollution.

Ozone Depletion

• Ozone (O3)

– Triatomic form of oxygen in which three atoms of oxygen are bonded.

– Strong oxidant and chemically reacts with many materials in the atmosphere.

– In the lower atmosphere, ozone is a pollutant.– Highest concentration of ozone in the

stratosphere

Ultraviolet Radiation and Ozone

• Ozone layer in the stratosphere called the ozone shield– Absorbs most of the potentially hazardous ultraviolet

radiation from the sun.

• Ultraviolet radiation consists of wavelengths between 0.1 and 0.4 μm – Ultraviolet A (UVA)

– Ultraviolet B (UVB)

– Ultraviolet C (UVC).


• Ultraviolet C (UVC) – Shortest wavelength and most energetic of the types of

ultraviolet radiation.

– Sufficient energy to break down diatomic oxygen (O2) into two oxygen atoms.

– Each of these oxygen atoms may combine with an O2 molecule to create ozone.

• UVC strongly absorbed in the stratosphere, and negligible amounts reach the Earth’s surface.


• Ultraviolet A (UVA) – Longest wavelength– Least energy of the three types of ultraviolet

radiation. – UVA can cause some damage to living cells– Not affected by stratospheric ozone, and is

transmitted to the Earth’s surface


• Ultraviolet B (UVB)– Energetic and strongly absorbed by

stratospheric ozone– Ozone is the only known gas that absorbs UVB. – Depletion of ozone in the stratosphere results in

an increase in the UVB that reaches the surface of the Earth.


• Approximately 99% of all ultraviolet solar radiation (all UVC and most UVB) is absorbed by the ozone layer. – Natural service function– Protects us from the potentially harmful effects

of ultraviolet radiation.

Measurement of Stratospheric Ozone

• First measured in 1920s using Dobson ultraviolet spectrometer.– Dobson unit (DU)- 1DU = 1 ppb O3

– Now have measurements from all over the world for 30 years

• Ground based measurements first identified ozone depletion over the Antarctic.– Concentrations have been decreasing since the mid-

1970s– “Ozone hole”

Ozone Depletion and CFCs

• Hypothesis that ozone in the stratosphere is being depleted by CFCs– First suggested in 1974 by Molina and

Rowland.– Based on physical and chemical properties of

CFCs and knowledge about atmospheric conditions.

– Vigorously debated by scientists, companies producing CFCs, and other interested parties.


• The major features of the hypothesis:– CFCs emitted in the lower atmosphere are extremely

stable. Unreactive in the and therefore have a very long residence time (about 100 years).

– CFCs eventually wander upward and enter the stratosphere.

– Once above the stratospheric ozone, they may be destroyed by UV radiation, releasing chlorine, a highly reactive atom.


– The chlorine released then depletes the ozone.– Depletion increases the amount of UVB

radiation that reaches Earth’s surface.– UVB is a cause of human skin cancers and is

also thought to be harmful to the human immune system.

Emissions and Uses of Ozone Depleting Chemicals

• CFCs have been used– As aerosol propellants in spray cans– Working gas in refrigeration and AC– Production of Styrofoam

• No longer used in spray cans but use has increased in refrigerants.

Simplified Stratospheric Chlorine Chemistry

• CFCs are – transparent to sunlight,– essentially insoluble– Non-reactive in the oxygen-rich lower atmosphere

• When CFCs reach the stratosphere, reactions do occur.

• UVC splits up the CFC releasing chlorine, the following two reactions can take place:Cl + O3 → ClO + O2

ClO + O → Cl + O2

Simplified Stratospheric Chlorine Chemistry

• This series of reactions is what is known as a catalytic chain reaction.– Chlorine is not removed– Reappears in the second reaction– Repeated over and over

• Process considerably more complex• Chain can be interrupted and Cl stored in

other reactions

The Antarctic Ozone Hole

• Since 1958 ozone depletion has been observed in the Antarctic every Oct.– Thickness decreasing and geographic area

increasing

Polar Stratospheric Clouds

• Form during the polar winter (polar night)– Antarctic air mass isolated from the rest of the

atmosphere– Air circulates about the pole in Antarctic polar

vortex.– Forms as the isolated air mass cools, condenses,

and descends.


• Type I polar stratospheric clouds – When air mass reach a temp between 195 K

and 190 K, small sulfuric acid particles are frozen and serve as seed particles for nitric acid (HNO3).

• Type II polar stratospheric clouds – If temperatures drop below 190 K water vapor

condenses around Type I cloud particles


• During the formation nearly all the nitrogen oxides held in clouds– Facilitates ozone depleting reactions– When spring comes and sun returns it breaks

apart Cl2

– Chlorine can not be sequestered to form chlorine nitrate, one of its carbon sinks.

An Arctic Ozone Hole?

• Polar vortex also forms over the North Pole – Weaker and does not last as long as Antarctic– Ozone depletion does occur at the NP– Major concern is ozone-deficient air moving

southward over population centers.

Tropical and Midlatitude Ozone Depletion

• Evidence suggests an increase in ozone depletion at midlatitudes over areas including the US and Europe.

• We know the most about ozone depletion in polar regions (particularly Antarctica), but depletion of ozone is a global concern.

The Future of Ozone Depletion

• If the manufacture, use, and emission of all ozone-depleting chemicals were to stop today, the problem would not go away, – millions of metric tons of those chemicals are

now in the lower atmosphere, working their way up to the stratosphere.

• Several CFCs have atmospheric lifetimes of 75 to 140 years.

Environmental Effects

• Several serious potential environmental effects– Damage to food chain on land and in oceans

(loss of primary production )– Damage to human health (skin cancers,

cataracts, and suppression of immune system)• UV Index measure of UV radiation on a given day

Environmental Effects

• Reduce the risk of skin cancer and other skin damage from UV exposure by:– Limit exposure to the sun between the hours of 10

A.M.and 4 P.M. – When possible, remain in the shade.– Use a sunscreen with an SPF of at least 30. – Wear a wide-brimmed hat and, where possible, tightly

woven full-length clothing.– Wear UV-protective sunglasses.– Avoid tanning salons and sunlamps.– Consult the UV Index before going out

Management Issues

• The Montreal Protocol– Outlined a plan for the eventual reduction of

global emissions of CFCs to 50% of 1986 emissions

– Elimination of the production of CFCs by 1999– Assessment of the protocol suggest that CFCs

will return to pre-1980 levels by 2050

Management Issues

• Substitutes for CFCs– hydrofluorocarbons (HFCs) and

• Do not contain chlorine. However, fluorine atoms participate in reactions similar to those of chlorine but approximately 1,000 times less efficient in those reactions

– hydrochlorofluorocarbons (HCFCs). • Contain an atom of hydrogen in place of a chlorine

atom. Can be broken down in the lower atmosphere. However, cause ozone depletion if they do reach the stratosphere before being broken down.

Management Issues

• Short-term Adaptation to Ozone Depletion– Given the nature of problem and the atmospheric

lifetimes of the chemicals that produce the depletion

– people will be learning to live with higher levels of exposure to ultraviolet radiation.

• In the long term, achievement of sustainability w/ respect to stratospheric ozone will require management of human-produced ozone-depleting chemicals.

chapter 24: air pollution

Documents

sources of air pollutants

air pollutionus

secondaryprimary pollutants

airsecondary pollutants

bad air quality dayshungary

pollutants of natural

human sources

fugitive sources