Chemistry and the Environment

Chemistry andthe Environment

Learning Objectives

a. The environment consists of the lithosphere, the atmosphere, and the hydrosphere.

b. The lithosphere serves as the source for raw materials and energy resources such as fossil fuels.

c. Depletion of traditional fuel sources is leading to the need for alternative/renewable fuels.

d. Solid waste disposal is a growing burden on the lithosphere.

Learning Objectives (cont)

e. The atmosphere is suffering from increased levels of pollutants.

f. Increasing atmospheric CO2 levels have been linked to global warming through an enhancement of the greenhouse effect.

g. The Earth’s sunscreen, the ozone layer, has been damaged by chlorofluorocarbons.

h. During the hydrologic cycle, rainwater can pick up many pollutants.

i. Acid rain can also result from the reaction of H2O with atmospheric SO3 and NO2.

Outline

• Overview of the Environment a. Lithosphere

1. The solid surface of the Earth

b. Atmosphere 1. The gaseous layer of air surrounding the Earth

c. Hydrosphere 1. The aqueous part of the Earth

Outline

• The Lithosphere a. Traditional Energy Resources

1. Traditional sources of energy have included biomass and fossil fuels.

2. More recently, nuclear power has become an option.

3. Supplies of fossil fuels and uranium are limited.

Evolution of fuel use

Composition andEnergy Content of Various Fuels

Global Reserves of Fuels

Carbon andHeat Content by Type of Coal

Coal mining oftenleaves environmental disaster in its wake

Therefining and separation process

Outline

• The Lithosphere (cont) b. Alternative Sources of Energy

1. Depletion of traditional sources of energy such as petroleum has led to the development of alternative sources of energy.

2. Renewable energy sources can be replenished on a short time scale; e.g., solar power and biomass.

3. Example: photovoltaic cells (PVCs), which convert solar energy into electricity.

Schematic ofa “pressurized water” type of nuclear reactor

Differenttypes of semiconductors

Photovoltaic Cells

Outline

• Lithosphere (cont) b. Alternative Energy Sources (cont)

4. Fuel cells generate electricity through an oxidation-reduction reaction for which the reactants are constantly supplied.

5. An example is the Proton Exchange Membrane (PEM) fuel cell based on the following reaction:

2 H2 + O2 2 H2O + energy

In a PEM fuelcell, H2 is split into H+ and electrons

Outline

• The Lithosphere (cont)c. Land Pollution

1. Solid waste disposal is a growing problem.

2. The Environmental Protection Agency (EPA) recommends that we “reduce, reuse, and recycle.”

Solid WasteGenerated by Americans in 2003

Composting

Municipal solidwaste recycling rates, 1960-2003

Source: EPA

RECYCLE!!!

The Atmosphere

The atmosphere is divided into five layers. It is thickest near the surface and thins out with height until it eventually merges with space.

1) The troposphere is the first layer above the surface and contains half of the Earth's atmosphere, which we breathe. Weather occurs in this layer. 2) Many jet aircraft fly in the stratosphere because it is very stable. Also, the ozone layer absorbs harmful rays from the Sun.

3) Meteors or rock fragments burn up in the mesosphere.4) The thermosphere is a layer with auroras. It is also where the space shuttle orbits. 5) The atmosphere merges into space in the extremely thin exosphere. This is the upper limit of our atmosphere.

Atmosphere, continued

Composition of Dry Air at Sea Level

Outline

• The Atmospherea. The Nitrogen Cycle

1. The atmosphere at sea level is comprised of 78% N2 and 21% O2.

2. The nitrogen cycle is the exchange of nitrogen atoms between the living and non-living parts of the environment.

3. During nitrogen fixation, atoms from atmospheric N2 are incorporated into biologically useful nitrogen-containing molecules.

The Nitrogen Cycle

Nitrogen-Fixation Reactions

Outline

• The Atmosphere (cont)b. Air Pollutants

1. Pollutants (chemicals in the wrong place at the wrong concentration) can occur naturally or from human activity.

2. EPA’s six major air pollutants are SO2, particulate matter (PM), CO, NOx, O3, and Pb.

3. Depending on atmospheric conditions, pollution can result in industrial smog or photochemical smog.

EPA’s Principal (Primary) Air Pollutants

Secondary pollutants are formed in the atmosphere through chemical and photochemical reactions from the primary pollutants examples include:

sulfuric acid H2SO4 - can cause respiratory problems nitrogen dioxide NO2 - gives air a brownish coloration ozone O3 - colorless gas, has a sweet smell, is an oxidizing agent, irritates the eyes

Photochemical Smog

Sunlight + emissions fromcars and power plants = photochemical smogN2 + O2 2NONO + O2 NO2 (a corrosive brown gas)

Created by forest fires and the combustion engine

4 NO2 + 2H2O + O2 4 HNO3 (nitric acid)

• requires clear, sunny skies• NOx + ROG + sunlight --> O3 + NO2 • ROG are reactive organic gases from unburned gasoline • NOx are oxides of nitrogen

LA. smog:

Review the Components of Photochemical Smog

Industrial Smog

The Source: Burning Coal

Thermal Inversion, in which a blanket of warm air above a low lying layer of cooler air traps pollutants (SO2, CO, NO2) near the ground.

Production of Sulfur compounds that arise from coal combustion originates with the release of sulfur within the coal as sulfur dioxide:

S + O2 SO2

Which is a choking gas in its own right, reacts further with atmospheric O2, which forms sulfur trioxide and combines with water vapor to form sulfuric acid (H2SO4)

2SO2 + O2 SO3 + H2O H2SO4

Contributes to acid rain

Thermal inversion occurs when a layer of warm air settles over a layer of cooler air that lies near the ground. The warm air holds down the cool air and prevents pollutants from rising and scattering.

A thermal inversioncaused air pollution in London in the 1950s

Air pollution at theGreat Smoky Mountains National Park

Strategies to Reduce Industrial Smog

Strategies to Reduce Photochemical Smog

Cut down on PM and sulfur compounds

Scrubbers that pass emission gases through water and filters that act like vacuum cleaners and remove sulfur compounds through a chemical treatment with limestone (CaCO3):

CaCO3(s) + SO2(g) CaSO3(s) + CO2(g)

Reduce the number of automobiles on the road

More efficient gasoline-dispensing systems to reduce the release of hydrocarbons into the atmosphere and catalytic converters to improve the efficiency of combustion, gas-electric hybrid vehicles, reduced tailpipe emissions, and fuel efficiency.

Declining mean blood lead levels for U.S. children age 5 and younger

Source: EPA

Thomas MidgleyJr. invented Chlorofluorocarbons

(CFCs) and tetraethyl lead

Credit: Kettering University

Outline

• The Atmosphere (cont)c. Global Climate Change (Global Warming)

1. The greenhouse effect is a warming of the Earth by a layer of gases that trap the sun’s energy.

2. Human activity appears to be causing an increase in the amount of atmospheric CO2.

3. Increased atmospheric CO2 appears to be enhancing the greenhouse effect, leading to an increase in average global temperatures.

CO2 levels arestill increasing in the atmosphere

Source: National Oceanic and Atmospheric Administration (NOAA).

The Earth'satmosphere acts like the glass in a

greenhouse

Rising global temperatures

Source: NASA

Aerosolscan block out solar radiation

Outline

• The Atmosphere (cont)d. Ozone Depletion

1. Ozone forms the Earth’s sunscreen.

2. Chlorofluorocarbons, formerly used as propellants and refrigerants, break down in the upper atmosphere to form free radicals that degrade the ozone layer.

CF2Cl2 + UV light CF2Cl + Cl•

Cl• + O3 ClO • + O2

ClO • + O Cl• + O2

Ozone holeover Antarctica, October 1979

Outline

• The Hydrospherea. Hydrologic Cycle

1. Movement of water between the atmosphere, the lithosphere, and the hydrosphere

2. During the hydrologic cycle, water may pick up many pollutants.

3. An example is acid rain (pH < 5.6), resulting from formation of H2SO4 and HNO3 when water reacts with atmospheric combustion products SO2 and NO2.

AverageDaily Water Use per American

Source: Data from the American Water Works Association.

Hydrologic Cycle

Hard-waterdeposits inside pipes and kettles

EPA'sPermissible Mineral Levels in Water

Ion-exchangecolumns for removing Ca2+ and Mg2+

Handheld water purifier

Removal of bothbiological and chemical

contaminants

Possible sources of contamination in the hydrologic cycle

Water pollution

Acid rain ismost severe in the Mid-Atlantic states

SO2 further reacts with atmospheric O2, which forms sulfur trioxide and combines with water vapor to form sulfuric acid (H2SO4)

2SO2 + O2 SO3 + H2O H2SO4

Acid rain is when the rain has a pH of 5.6 or lower due to the presence of atmospheric carbon dioxide, which reacts with water to form dissolved carbonic acid (H2CO3).

CO2 + H2O H2CO3

Acid Rain

The Effect of Acid Rain on calcium carbonate over time

Picture taken before acid rain at the Field Museum in Chicago in 1920

Picture taken after acid rain at the Field Museum in Chicago in 1990

Erosionincreases in the absence of vegetation

Credit: Alamy

A healthy lake (top)and one that is suffering from eutrophication

Eutrophication occurs when a body of water is rich in nutrients that lead to an explosion of vegetation and algae at the expense of other aquatic life.

Algae formed at the surface of the lake

An oiled birdafter the Exxon Valdez accident

Credit: AP/Wide World Photos

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