Chemistry for Changing Times 12 th Edition Hill and Kolb Chapter 13 Air: The Breath of Life John...

Chemistry for Changing Times12th Edition

Hill and Kolb

Chapter 13Air:

The Breath of LifeJohn Singer

Earth’s Atmosphere: Division and Composition

The Earth’s atmosphere is divided into four regions:1. Troposphere: This layer is nearest Earth and contains

nearly all living things. The temperature decreases as altitude increases in the troposphere.

2. Stratosphere: This layer lies above the troposphere and contains the protective ozone layer. In this layer, temperature increases with increasing altitude.

3. Mesosphere: This layer lies above the stratosphere.4. Thermosphere: This layer lies above the mesosphere.

Chemistry of the Atmosphere

Nitrogen comprises about 78% of all gases in the atmosphere. All animals and most plants cannot use the nitrogen available in the atmosphere as N2 molecules. Organisms must first “fix” or use “fixed” nitrogen. Fixed means that the nitrogen atoms are combined with another element.

Chemistry of the AtmosphereLightning can fix nitrogen as follows:

N2 + O2 + energy (lightning) → 2 NO2 NO + O2 → 2 NO2

Nitrogen dioxide can then react with water, forming nitric acid.

3 NO2 + H2O → 2 HNO3 + NOThe nitric acid in rainfall contributes to available “fixed” nitrogen in the oceans and soil. Unfortunately, it also acidifies lakes and streams.

Nitrogen can also be fixed industrially using the Haber-Bosch process:

N2 + 3 H2 → 2 NH3

This process has allowed us to increase the productivity of soil for food production.

Certain plants (legumes) contain bacteria in their roots that are able to fix nitrogen.

The Nitrogen Cycle

Oxygen Cycle Oxygen makes

up 21% of Earth’s atmosphere. Oxygen is cycled as shown here.

In the stratosphere, oxygen molecules react to form ozone, which is capable of absorbing harmful ultraviolet radiation.

3 O2(g) + UV radiation → 2 O3(g)

Temperature InversionA temperature inversion occurs when cold air is trapped near Earth’s surface by a layer of warmer air. Polluted air can then be trapped near Earth’s surface.

Pollution Through the Ages

Wildfires, windblown dust, and volcanic action can all contribute to air pollution.

A Closed Ecosystem?

The earth is a closed ecosystem. What you see is what you get.

The Air Our Ancestors Breathed

Air pollution has always been with us.

Humans have always altered their environment.

Clearing of land and use of fire have always impacted the atmosphere.

Pollution Goes Global

A pollutant is any substance in the wrong place at the wrong time.

With increased urbanization and globalization, air pollution has become a global concern.

Air Pollution in China

As China industrializes its economy, its people are experiencing tremendous air pollution.

Industrial Smog

The term smog is a contraction of smoke and fog.

Air that has been polluted by industrial activity is called industrial smog.

Chemistry of Industrial Smog

Oxides of CarbonWhen coal (mostly carbon) is burned, carbon dioxide, carbon monoxide, and soot are produced:

C(s) + O2(g) → CO2(g)

2 C(s) + O2(g) → 2 CO(g)

Unburned carbon is soot.

Oxides of SulfurCoal containing sulfur produces sulfur dioxide:

S(s) + O2(g) → SO2(g)The sulfur dioxide is further oxidized to sulfur

trioxide:

2 SO2(g) + O2(g) → 2 SO3(g)Sulfur trioxide can then react with water, forming

sulfuric acid.

SO3(g)+ H2O (l) → H2SO4(l)

Particulate matter (PM) is the solid and liquid particles that are larger than individual molecules. Much of particulate matter consists of unburned minerals found in coal. Some PM remains in the combustion chamber as bottom ash, but much flies out the stack as fly ash.

The United States Environmental Protection Agency estimates that as many as 40,000 premature deaths occur each year due to PM.

Heath and Environmental Effects of Industrial Smog

HealthSulfuric acid and smaller particulates act synergistically to harm health. The alveoli of the lungs lose resiliency and this lung damage can lead to pulmonary emphysema characterized by shortness of breath.

EnvironmentalAcidic precipitation and smaller particulates can damage plants, including farm crops.

What to Do About Industrial Smog

Electrostatic precipitators induce electrostatic charges on particulates. The charged particulates are then attracted to the oppositely charged plate and deposited.

Bag filtration works like a giant vacuum cleaner. Flue gases are passed through a series of filters in a bag house, which removes particulates.

A cyclone separator works by cycling stack gases in a spiral motion. Heavier particulates hit the outer walls of the separator and deposit out of the gas stream.

Wet scrubbers remove particulates by passing the stack gases through water.

Sulfur dioxide can be reduced by either removing sulfur from coal before combustion or by adding limestone (CaCO3) to the coal.

CaCO3 + heat → CaO(s) + CO2(g)

CaO(s) + SO2(g) → CaSO3(s)

Automobile Emissions

Gasoline is a mixture of many hydrocarbons with carbon numbering from about 5 to 12.

Octane (C8H18) is a reasonable representative for gasoline. Octane undergoes complete combustion as follows:

2 C8H18(l) + O2 → 18 H2O(g) + 16 CO2(g)

Most internal combustion engines do not burn fuel to complete combustion.

Carbon MonoxideWhen not enough oxygen is available for complete combustion, carbon monoxide (CO) is produced. Many metric tons of CO are released into the atmosphere from automotive exhaust each year.

Carbon monoxide is a toxic, colorless, odorless, and tasteless gas.

Carbon Monoxide

Carbon monoxide bonds with the hemoglobin in blood. Many hundreds of people each year die from carbon monoxide poisoning.

Nitrogen Oxides

When nitrogen in the air combines with oxygen at the high temperatures within an automotive engine, nitrogen oxides are produced.

N2(g) + O2(g) → 2 NO(g)

Nitrogen monoxide can then oxidize to nitrogen dioxide.

2 NO(g) + O2(g) → 2 NO2(g)

Nitrogen Oxides

Nitrogen oxides: Together, nitrogen monoxide and nitrogen dioxide are known as NOx. These oxides react with water in the atmosphere to form nitrous and nitric acids. They lead to smog formation and are components of acid rain. Breathing high concentrations of NOx can lead to serious lung complications.

Automobile EmissionsVolatile organic compounds (VOCs) are major contributors to smog formation. They are produced by the evaporation of gasoline, unburned fuel in exhaust, paints, and consumer products. Most VOCs are hydrocarbons. Some are released from natural sources.

Alkenes can react with oxygen or ozone to form aldehydes.

Peroxyacetyl nitrate (PAN = CH3CO3NO2) can be produced by the reaction of certain hydrocarbons with oxygen and nitrogen dioxide. PAN, ozone, and aldehydes are responsible for many of the harmful effects of smog.

Photochemical SmogThe components of smog react with sunlight to form an amber haze known as photochemical smog.

Photochemical Smog

Development of Air Pollutants on a Typical Sunny Summer Day

Solutions to Photochemical Smog

Reducing the quantities of the pollutants entering the atmosphere is the answer to how to reduce photochemical smog. Improved design of gasoline storage and dispensing systems reduces the emissions of hydrocarbon VOCs. Catalytic converters reduce hydrocarbon and carbon monoxide emissions from automobiles.

Acid Rain

Acid rain is defined as precipitation having a pH of less than 5.6. Sulfur oxides and nitrogen oxides can react with water forming sulfuric and nitric acids. These are the major contributors to acid rain.

Acid Rain

Acid rain is destructive to both the natural and man-made environment.

Indoor Air Pollution

Indoor air pollution is a major health concern. The EPA estimates that pollutant levels of indoor air ranges from 2 to 100 times higher than the levels of outdoor air.

CO and NOx are released by gas kitchen stoves, cigarette smoke, and free-standing unvented kerosene heaters.

Mold will grow wherever there is moisture. Mold spores can exacerbate asthma, bronchitis, and other lung diseases.

Ozone is released from copy machines, electronic air cleaners, and other devices. Ozone is a respiratory tract irritant.

Cigarettes and Secondhand SmokeCigarette smoke has been shown to contain at least 40 different carcinogens. The EPA considers secondhand smoke to be a Class A carcinogen. Regular exposure to smoke and secondhand smoke has been shown to increase the risk of heart disease, lung cancer, miscarriage, and sudden infant death syndrome (SIDS).

Radon is a radioactive noble gas. It is colorless, odorless, and tasteless. Radon is released naturally from rock and soil. Radon decays by alpha emission.

Polonium-218 is a daughter isotope of radon. It deposits in lung tissue and continues to emit radiation.

Ozone: The Double-Edged Sword

Ozone (O3) is an allotrope of oxygen (O2).

Ozone in the troposphere is a hazardous, toxic substance. It contributes to smog and indoor air pollution.

Ozone in the stratosphere shields life on Earth from harmful ultraviolet radiation.

In the mesosphere, short wavelength ultraviolet radiation splits oxygen molecules into oxygen atoms.

Some of these reactive oxygen atoms diffuse to the stratosphere where they react with oxygen molecules to form ozone.

The ozone in the stratosphere can absorb longer wavelength ultraviolet radiation as follows:

O3(g) + UV radiation → O2(g) + O(g)

Chlorofluorocarbons (CFCs) have been shown to contribute to the destruction. At one time, CFCs were the propellants used in aerosol cans, foaming agents, and refrigerants.

Many countries have banned the use of CFCs.

Effective substitutes have been developed.

The Ozone Hole Over Antarctica

Carbon Dioxide and Climate Change

Greenhouse Effect

Carbon dioxide (CO2) is known as a greenhouse gas. CO2 and some other gases will allow solar energy to penetrate the atmosphere, but trap heat in (much like a greenhouse).

Human activity has contributed tremendous amounts of CO2 to the atmosphere in recent decades. There is much evidence to show that global warming is indeed occurring.

Carbon Dioxide and the Greenhouse Effect

Greenhouse Gases and Global Warming

Climate Change and Weather

As Earth’s climate changes, impacts on food production, flooding, and increases in infectious diseases are predicted.

Mitigation of Global Warming

Reducing the output of greenhouse gases has no easy fix. Combinations of emerging technologies, such as solar, nuclear, and wind, along with carbon sequestration, are potential answers.

Who Pollutes? Who Pays?

Who Pollutes? How Much?

Paying the Price

Air pollution costs us tens of billions of dollars each year. There is no cheap and easy fix.

Chemistry for Changing Times 12 th Edition Hill and Kolb Chapter 13 Air: The Breath of Life John...

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