Atmospheric Pollution

Module 46

Major Air Pollutants and Their Sources

After reading this module, you should be able to

• identify and describe the major air pollutants.

• describe the sources of air pollution.

Air Pollution is a global system

• Air pollution The introduction of chemicals,

particulate matter, or microorganisms into the

atmosphere at concentrations high enough to

harm plants, animals, and materials such as

buildings, or to alter ecosystems.

• The air pollution system has many inputs and

outputs.

Classifying Pollutants

Sulfur dioxide (S02):

• A corrosive gas that comes primarily from

combustion of fuels such as coal and oil.

• A respiratory irritant and can adversely affect

plant tissue.

• Also released in large quantities during volcanic

eruptions and in much smaller quantities, during

forest fires.

Classifying Pollutants

Nitrogen Oxides (NOx):

• Motor vehicles and stationary fossil fuel combustion

are the primary anthropogenic sources of nitrogen

oxides.

• Respiratory irritant, increases susceptibility to

respiratory infection.

• An ozone precursor, leads to formation of

photochemical smog.

• Converts to nitric acid in atmosphere, which is harmful

to aquatic life and some vegetation.

• Contributes to over-fertilizing terrestrial and aquatic

systems.

Classifying Pollutants

Carbon Oxides:

• Carbon monoxide (CO) is a common emission in

vehicle exhaust and most other combustion

processes.

• CO can be a significant component of air pollution in

urban areas.

• Carbon dioxide (CO2) released by burning fossil fuels

has led to its becoming a major pollutant.

• CO2 recently exceeded a concentration of 400 parts

per million in the atmosphere and appears to be

steadily increasing each year.

Classifying Pollutants

• Particulate matter (PM) Solid or liquid particles suspended

in air. Also known as Particulates; The sources of particulate matter and

its effect. Particulate matter can be natural or anthropogenic. Particulate matter in the atmosphere ranges considerably in size and can absorb or scatter light, which creates a haze and reduces the light that reaches the surface of Earth.

Classifying Pollutants

• Haze Reduced visibility.

• Photochemical oxidant A class of air pollutants formed as a

result of sunlight acting on compounds such as nitrogen oxides.

• Ozone (O3) A secondary pollutant made up of three oxygen

atoms bound together.

• Smog A type of air pollution that is a mixture of oxidants and

particulate matter.

• Photochemical smog Smog that is dominated by oxidants

such as ozone. Also known as Los Angeles–type Smog; Brown

smog.

• Sulfurous smog Smog dominated by sulfur dioxide and

sulfate compounds. Also known as London-type smog; Gray

smog; Industrial smog.

Classifying Pollutants

Lead:

• A gasoline additive, also found in oil, coal, and

old paint.

• Impairs central nervous system.

• At low concentrations, can have measurable

effects on learning and ability to concentrate.

Classifying Pollutants

• Volatile organic compound (VOC) An organic

compound that evaporates at typical

atmospheric temperatures.

• Formed by evaporation of fuels, solvents,

paints, and improper combustion of fuels such

as gasoline.

• A precursor to ozone formation.

c methane

Primary and Secondary Pollutants

• Primary pollutant A polluting compound that

comes directly out of a smokestack, exhaust

pipe, or natural emission source.

• Examples include CO, CO2, SO2, NOx, and

most suspended particulate matter.

Primary and Secondary Pollutants

• Secondary pollutant A primary pollutant that

has undergone transformation in the presence

of sunlight, water, oxygen, or other compounds.

• Examples include O3, sulfate, and nitrate.

Primary and Secondary Pollutants

Primary and secondary air pollutants. The transformation from

primary to secondary pollutant requires a number of factors

including sunlight, water (clouds), and the appropriate temperature.These factors facilitate chemical reactions that can lead to the formation of harmful substances such as ozone and particulate matter, which pose significant risks to human health and the environment.

Air pollution comes from both natural

and human sources

• Natural emissions of pollution include

volcanoes, lightning, forest fires, and plants,

both living and dead, all release compounds

that can be classified as pollutants.

• Anthropogenic sources include on-road

vehicles, power plants, industrial processes,

waste disposal (incinerator).

Human

Anthropogenic Emissions

• In the United States, emissions from human activity

are monitored, regulated, and in many cases

controlled.

• Some anthropogenic sources are on-road vehicles,

power plants, industrial processes, and incineration.

• The Clean Air Act and its various amendments require

that EPA establish standards to control pollutants that

are harmful to “human health and welfare”.

• Through the National Ambient Air Quality Standards

(NAAQS) the EPA periodically specifies concentration

limits for each air pollutant.

Anthropogenic Emissions, cont’d

Emission sources of criteria air

pollutants for the United States.

Recent EPA data show that on-road

vehicles, categorized as

“transportation,” are the largest

source of (a)carbon monoxide and

(b)nitrogen oxides.

Anthropogenic Emissions

Emission sources of criteria air

pollutants for the United States.

The major source of

(c) anthropogenic sulfur dioxide is

the generation of electricity,

primarily from coal. Among the

sources of (d) particulate matter are

road dust, industrial processes,

electricity generation, and natural

and human-made fires.

Anthropogenic Emissions

Criteria and other air pollutant

trends. Trends in the criteria air

pollutants in the United States

between 1990 and 2010. All

criteria air pollutants have

decreased during this time

period. The decrease for lead is

the greatest.

Module 47

Photochemical Smog and Acid Rain

After reading this module, you should be able to

• explain how photochemical smog forms and why it

is still a problem in the United States.

• describe how acid deposition forms and why it has

improved in the United States and become worse

elsewhere.

Photochemical smog remains an

environmental problem in the United

States

• The formation of this photochemical smog is

complex and still not well understood.

• A number of pollutants are involved and they

undergo a series of complex transformations in

the atmosphere.

The Chemistry of Ozone and

Photochemical Smog Formation

Tropospheric ozone and photochemical

smog formation. (a) In the absence of VOCs,

ozone will form during the daylight hours.

(b) After sunset, the ozone will break down. (c)

In the presence of VOCs, ozone will form

during the daylight hours. The VOCs combine

with nitrogen oxides to form photochemical

oxidants, which reduce the amount of ozone

that will break down later and contribute to

prolonged periods of photochemical smog.

Thermal Inversions

• Thermal inversion A situation in which a relatively

warm layer of air at mid-altitude covers a layer of cold,

dense air below.

• Inversion layer The layer of warm air that traps

emissions in a thermal inversion.

• The warm inversion layer traps emissions that then

accumulate beneath it.

• Thermal inversions that create pollution events are

particularly common in some cities, where high

concentration of vehicles exhaust and industrial

emissions are easily trapped by the inversion layer.

Thermal Inversions

A thermal inversion. (a)

Under normal conditions,

where temperatures

decrease with increasing

altitude, emissions rise

into the atmosphere. (b)

When a mid-altitude,

relatively warm inversion

layer blankets a cooler

layer, emissions are

trapped and accumulate.

Acid deposition has improved in the

United States

• Acid deposition occurs when nitrogen oxides

and sulfur oxides are released into the

atmosphere and combine with atmospheric

oxygen and water. These form the secondary

pollutants nitric acid and sulfuric acid.

• The secondary pollutants further break down

into nitrate and sulfate, and hydrogen ions (H+)

which cause the acid in acid deposition.

• Acid deposition has been reduced in the United

States as a result of lower sulfur dioxide and

nitrogen oxide emissions.

Acid

How Acid Deposition Forms and

Travels

Formation of acid deposition. The primary pollutants sulfur dioxide and nitrogen

oxides are precursors to acid deposition. After transformation to the secondary

pollutants—sulfuric and nitric acid— dissociation occurs in the presence of water.

The resulting ions—hydrogen, sulfate, and nitrate—cause the adverse ecosystem

effects of acid deposition.

Effects of Acid Deposition

Acid deposition has many harmful effects:

• Lowering the pH of lake water

• Decreasing species diversity of aquatic organisms

• Mobilizing metals that are found in soils and releasing

them into surface waters

• Damaging statues, monuments, and buildings

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Module 48

Pollution Control Measures

After reading this module, you should be able to

• explain strategies and techniques for controlling

sulfur dioxide, nitrogen oxides, and particulate

matter.

• describe innovative pollution control measures.

Pollution control includes prevention,

technology, and innovation

Ways to address air pollution:

• Avoid emissions in the first place.

• Use cleaner fuel.

• Increase efficiency.

• Control pollutants after combustion.

Pollution control includes prevention,

technology, and innovation

Ways of controlling emissions:

• Remove sulfur dioxide from coal by fluidized

bed combustion.

• Install catalytic converters on cars.

• Use baghouse filters.

• Use electrostatic precipitators.

• Install scrubbers on smokestacks.

I

Control of Particulate Matter

The scrubber. In this air

pollution control device, particles

are “scrubbed” from the exhaust

stream by water droplets. A

water-particle “sludge” is

collected and processed for

disposal.

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Around the world people are

implementing innovative pollution

control measures

Municipalities have tried a number of strategies:

• Reduce gasoline spilled at the pump, restrict

evaporation of dry-cleaning fluids, and the use

of lighter fluid.

• Reduce use of wood-burning stoves and

fireplaces.

• Limit automobiles to every other day use or

charge user fees for roads during heavy

commute times.

Module 49

Stratospheric Ozone Depletion

After reading this module, you should be able to

• explain the benefits of stratospheric ozone and

how it forms.

• describe the depletion of stratospheric ozone.

• explain efforts to reduce ozone depletion.

UVB C

Stratospheric ozone is beneficial to

life on Earth

• The stratospheric ozone layer exists roughly 45-

60 kilometers above Earth.

• Ozone has the ability to absorb ultraviolet

radiation and protect life on Earth.

• The ultraviolet (UV) spectrum is made up of

three increasingly energetic ranges: UV-A UV-B,

and UV-C.

O

Formation of Stratospheric Ozone

• UV-C radiation breaks the molecular bond holding an

oxygen molecule together:

O2 + UV-C → O + O

• A free oxygen atom (O) produced in the first reaction

encounters an oxygen molecule, and they form ozone.

O + O2 → O3

• Both UV-B and UV-C radiation can break a bond in

this new ozone molecule:

O3 + UV-B or UV-C → O2 + O

Breakdown of Stratospheric Ozone

• When chlorine is present (from CFCs), it can

attach to an oxygen atom in an ozone molecule

to form chlorine monoxide (ClO) and O2:

O3 + Cl → ClO + O2

• The chlorine monoxide molecule reacts with a

free oxygen atom, which pulls the oxygen from

the ClO to produce free chlorine again:

ClO + O → Cl + O2

d

Breakdown of Stratospheric Ozone

• A single chlorine atom can catalyze the

breakdown of as many as 100,000 ozone

molecules until finally one chlorine atom finds

another and the process is stopped.

• In the process, the ozone molecules are no

longer available to absorb incoming UV-B

radiation.

• As a result, the UV-B radiation can reach

Earth’s surface and cause harm to biological

organisms.

Depletion of the Ozone Layer

Stratospheric ozone concentration. This data for one area of

Switzerland shows a generally decreasing trend from

1970 to 2011.

Module 50

Indoor Air Pollution

After reading this module you should be able

to

• explain how indoor air pollution differs in

developing and developed countries.

• describe the major indoor air pollutants and the

risks associated with them.

D

Indoor air pollution is a significant

hazard in developing and developed

countries

• Worldwide, approximately 4 million deaths each

year are attributable to indoor air pollution.

• Ninety percent of these deaths are in

developing countries.

• More than 50 percent are children.

E

2

Indoor Air Pollution in Developed

Countries

Some sources of indoor

air pollution in the

developed world.

A typical home in the

United States may contain

a variety of chemical

compounds that could,

under certain

circumstances, be

considered indoor air

pollutants.

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Most indoor air pollutants differ from

outdoor air pollutants

Indoor air pollutants include:

• Carbon monoxide from malfunctioning heating

equipment.

• Asbestos A long thin fibrous silicate mineral with

insulating properties, which can cause cancer when

inhaled; formerly used as insulation in buildings.

• Radon that seeps into homes through cracks in the

foundation, groundwater, or rocks.

• VOCs used in furniture, paint, and building materials.

Radon

Potential radon exposure in the United States. Depending on the

underlying bedrock and soils, the potential for exposure to radon exists in

houses in certain parts of the United States.

VOCs in Home Products

Reasons for sick building syndrome:

• Inadequate or faulty ventilation

• Chemical contamination from indoor sources

• Chemical contamination from outdoor sources

• Biological contamination from outside or inside