Lecture 17AIR POLLUTION

HRh

Ahh Fresh Clean Air

Air Pollution Any undesirable changes in air that adversely affect the health, survival, or activities of humans or other organisms

Primary air pollutants emitted directly into the atmosphere

Primary pollutants that account for nearly all air pollution problems are carbon monoxide, particulates, hydrocarbons, nitrogen oxides, and sulfur oxides

Secondary pollutants

Produced through reactions between primary pollutants and normal atmospheric compounds, e.g. ozone, peroxy-acyl nitrate (PAN), photochemical smog, sulfur trioxide, acid rain

Tehran Air Pollution

Polluted Air/ Mexico City

Sources of Air PollutionStationary sources are those that have a fixed location Emit most of the particulate matter, sulfur oxides, nitrogen oxides, hydrocarbons, and carbon oxidesInclude point sources, fugitive sources, and area sources

Point sources are stationary sources that emit air pollutants from one or more controllable sites, e.g., smokestacks of power plants

Fugitive sources generate air pollutants from open areas exposed to wind processes, such as dirt roads, construction sites, farmlands, surface mines, etc

Area sources are locations from which air pollutants are emitted from a well-defined area having several sources, e.g., agricultural areas sprayed with herbicides and pesticides

Mobile sources are emitters of air pollutants that move from place to place while yielding emissions, include automobiles, trucks, buses, aircraft, ships, trains

Sources of Air Pollution

Combustion of fossil fuels release significant quantities of nitrogen oxides, carbon oxides, particulate matter, and hydrocarbons

Each year over a billion tons of these pollutants enter the atmosphere from human-related processes

About half is carbon monoxide

Power plant Smokestacks

Tank farm

Smokestacks from (N) power plant

Factory chimneys, Cologne, Germany

Mobile Source

Natural Sources of Air Pollution

Volcanoes discharge ash, acid mist, and H2S

Natural forest fires Trees and bushes emit millions of tons of volatile organic

compounds (terpenes & propenes), pollen, spores, virus, bacteria in the air cause wide spread suffering from allergies and airborne infections

Dust storm

Various chemicals used in buildings Both inside and outside pollutants create a high risk for the

human health

General Effects of Air Pollutants

Affects many aspects of environment: Visually aesthetic resources, vegetation, animals, soil, water quality, structures, and human health

Affect visual resourcesAffect visual resources

by discoloring atmosphere, by discoloring atmosphere, reducing visual range,reducing visual range,

atmospheric clarity, etcatmospheric clarity, etc

Effects on vegetationEffects on vegetation Damage to leaf tissue, needles, Damage to leaf tissue, needles, or fruit or fruit Suppression of growth Suppression of growth Increased susceptibility to a Increased susceptibility to a variety of diseases variety of diseases Disruption of reproductive Disruption of reproductive processesprocesses

General Effects of Air Pollutants

Effects on human health Toxic poisoning causing

cancer Eye irritation Irritation of respiratory system Increased susceptibility to

viral infections Causing pneumonia &

bronchitis Heart disease Aggravation of chronic

diseases, such as asthma

Effect on vertebrate animals Impairment of respiratory

system Damage to eye, teeth bones Increased susceptibility to

disease, pests Decreased availability of food

sources Decreased ability to reproduce

Effects on Soil & WaterDegrades soil and water quality; may become toxic from the deposition of various pollutantsEffects on structures include discoloration, erosion, and decomposition of building materials

Potential for Urban Air Pollution Q The potential for air pollution in urban areas is determined by the

following factors: Population density The rate of emission of pollutants per unit area The distance downwind that a mass of air may move through an

urban area Temperature inversion The average speed of the wind The height to which pollutants may be thoroughly mixed in the

lower atmosphere Stronger the wind and the higher the mixing layer, the lower the

pollution Hills, mountains, tall buildings Rain helps clean the air pollutants

Acid rain

Pure rainfall has a pH (a numeric value to describe the strength of an acid) of about 5.6

Acid rain is defined as the precipitation in which the pH is below 5.6

(Acid rain is rain consisting of water droplets that are unusually acidic because of atmospheric pollution - most notably the excessive amounts of sulfur and nitrogen released by cars and industrial processes)

Acidic deposition occurs in two ways: wet and dry Wet deposition refers to acidic rain, fog, and snow Dry deposition : In areas where the weather is dry, the acid

chemicals may become incorporated into dust or smoke and fall to the ground through dry deposition, sticking to the ground, buildings, homes, cars, and trees

Dry deposited gases and particles can be washed from these surfaces by rainstorms

Acid rain

Causes (Q) Acid deposition can occur via natural sources like

volcanoes but it is mainly caused by the release of sulfur dioxide and nitrogen oxide during fossil fuel combustion

When these gases are discharged into the atmosphere they react with the water, oxygen, and other gases already present there to form sulfuric acid and nitric acid

About 70% of the acidity of acid rain is due to sulfur oxides emissions

30% is due to nitrogen oxides emissions These acids may travel long distances with prevailing

winds to be deposited as acid precipitation

Emission from power plant in New Mexico contained excessive amounts of SO2

Acid rain

Harmful effects on Terrestrial ecosystems

1. Damages leaves and needles

2. Decrease ability of trees to tolerate cold

3. Weakened trees either are killed or become susceptible to diseases

5. Causes leaching of basic essential elements

6. Causes dissolution of Fe, Al, Mn from minerals

Can cause human respiratory diseases such as bronchitis and asthma

Aquatic ecosystemsAquatic ecosystems 1.1. Loss of essentially all fish Loss of essentially all fish

populations populations below a pH below a pH of 4.5of 4.5

2.2. Dissolution and release of Dissolution and release of aluminum ions (aluminum ions (AlAl3+3+) from ) from minerals can kill many minerals can kill many kinds of fishkinds of fish

3. Accumulation in fish of 3. Accumulation in fish of heavy metals pose health heavy metals pose health hazards to humans, hazards to humans, mammals, and birdsmammals, and birds

Consequences of acid rain

Fish kill

Solution to Acid Rain Problem

Liming periodically, though not satisfactory over a

long period Also expensive & requires continuing effort Long-term practical solution is to ensure that the

production of acid-forming components in the

atmosphere is minimized Best strategy Increasing energy efficiency and conservation

measures that result in burning less coal Alternative energy sources Pollution abatement technology to lower the emission

Solution to Acid Rain Problem

The only way to fight acid rain is by curbing the release of the pollutants that cause it

This means burning fewer fossil fuels But even if acid rain could be stopped today, it would still take

many years for its harmful effects to disappear Individuals can also help prevent acid rain by conserving

energy The less electricity people use in their homes, the fewer

chemicals power plants will emit Vehicles are also major fossil fuel users, so emissions can be

reduced by using public transportation, carpooling, biking, or simply walking wherever possible

Smog Air pollution that is localized in urban areas, where it reduces visibility Formation of smog depends on local climate, topography, population density, industry, fuels used in industry, heating, and transportation

Two types

Photochemical smog (brown air) Solar radiation is important Directly related to automobile use Involve both N- oxides & HCs

Sulfurous smog (gray air/ Industrial smog )

Produced primarily by burning coal or oil at large

power plants

Affects human health and comfort Damage to materials Affects atmosphere Toxic to plants

Smog over California

Looking from the Hollywood hills, air pollution is visible in downtown Los Angeles

Smog in Cairo

Smog over a city

Pollution Control

Most reasonable strategies are to reduce, collect, capture, or retain the pollutants before they enter the atmosphere

The reduction of emissions via energy efficiency and conservation measures is the preferred strategy

Particulates emitted from fugitive, point, or area stationary sources are much easier to control than released from mobile sources

Settling chambers or collectors are may be used to control emissions of coarse particulates from power plants and industrial sites

Particulates from fugitive sources (waste pile) must be controlled on-site so that the wind does not blow them into the atmosphere

Pollution Control

Control of pollutants such as carbon monoxide, nitrogen oxides, and hydrocarbons in urban areas is best achieved through control measures for automobiles

Control of nitrogen oxides from automobile is accomplished by recirculating exhaust gas

Carbon monoxide and hydrocarbons from automobile is reduced by using catalytic converter which converts carbon monoxide to carbon dioxide, hydrocarbons to carbon dioxide and water by passing exhaust gases over a catalyst

Sulfur dioxide emission can be reduced by abatement measures performed before, during, or after combustion

End of SlidesThank You