Chapter 3 The Chemistry of Global Warming

Sections 3.4 & 3.8-end

Chapter 3; The Chemistry of Global Warming

1. Global Warming and the Enhanced Greenhouse Effect

2. Carbon Dioxide Concentrations & Average Global Temperature

3. Carbon Dioxide Cycle

4. Molecular Structure (3-D) Shape

5. Why Some Gases are Greenhouse Gases; while other are not

Chapter 3; The Chemistry of Global Warming

6. Other Greenhouse Gases and Global Warming Potential (GWP)

7. Molar Mass and Mass Percent

8. Possible Effects of Global Warming

9. Global Warming vs. Ozone Hole

10.Quantitative Aspects

Gases

Greenhouse Gases

• Carbon dioxide; CO2

• Water; H2O

• CFC’s

• Nitrous Oxide; N2O

• Methane; CH4

NOT Greenhouse Gases

• Nitrogen; N2

• Oxygen; O2

• Argon; Ar

Different Types of Electromagnetic Radiation Do Different “Things” to Molecule

Vibrations of Molecules

• Bond Stretching • Molecule Bending

It takes less energy to bend a molecule than stretch a bond.

Vibrations of CO2 Molecule

Symmetric Stretch Assymmetric Stretch

Bending motion Bending motion

For a bending or stretching motion to absorb IR radiation; it must change the dipole moment of the molecule

+ --

Symmetric Stretch;IR Inactive

Antisymmetric Stretch;IR Active

+ -- - + -

Electronegativity- Measure of an atom’s attraction for the electrons it

shares in a covalent bond.

Infrared Spectrum of CO2

Infrared Spectrum of Water (H2O) Vapor

Greenhouse Gas Requirements

• Minimum of 2 atoms needed for stretching bonds– Two atoms must be different in order for

vibration to change the dipole moment of molecule

• Minimum of 3 atoms needed to bend a molecule

Why Argon, Ar, Can Not Be a Greenhouse Gas

1. Argon is in atomic form. Thus, there is no bond to another atom. So it can’t absorb IR to stretch a bond it doesn’t have.

2. Argon can’t absorb IR to bend a molecule since a minimum of 3 atoms is needed and it has only 1 atom.

Global Warming Potential – Represents the Relative Contribution a

Molecule Has in Global Warming

1. How Long a Molecule in the Troposphere/ Is There a Way to Remove Molecule From Troposphere?

2. Does the Molecule Absorb in the Window Region?

3. Amount of Molecule in the Troposphere

Global Warming Potential (GWP)

Substance GWP Tropospheric Abundance (%)

CO2 1 0.0375

CH4 23 0.0018

N2O 296 0.00031

H2O 0.1 variable

O3 2000 0.000004

CCl3F 21000 0.000000028

CCl2F2 25000 0.000000026

IR Spectrum of CO2 and H2O Overlapped Leaves “Window” Region when Neither Absorbs IR Energy

Window

Increasing the GWP of a Greenhouse Gas

• When a different greenhouse gas absorbs in the window region of the IR spectrum; it will have a higher GWP

• *Biggest Effect

• The higher the tropospheric abundance; higher GWP

• The higher the lifetime of the molecule; higher GWP

Methane; CH4

Natural Sources (~40%)

• Component of Natural Gas

• Decayed vegetable matter in wetlands

Man-made Sources

• Oil wells• Landfills• Rice paddies• Cattle and sheep• Frozen methane

hydrate cages

Frozen Methane Hydrate Cages

Methane Absorbs at the Edge of Window Region of IR Spectrum

Methane Absorbs at the Edge of Window Region of IR Spectrum

Nitrous Oxide, N2O; “Laughing Gas”

Manmade Sources• Dental/medical Use• Fertilizers• Burning

Biomass/catalytic converters

• Production of nylon and nitric acid

• Absorbs in the Window Region of IR Spectrum

Nitrous Oxide, N2O, Absorbs in the Window Region of the IR Spectrum

Nitrous Oxide Absorbs in the Window Region of IR Spectrum

Gas Human Cont. to Global Warming

1896 Conc;

ppb

1996 Conc;

ppb

2000Conc;

ppb

CO2 55 % 290,000 360,000 370,000

CFC’s 25 % 0 3 7

CH4 15 % 900 1700 1800

N2O, O3 5 % 285 310 315

Human Contribution of Different Greenhouse Gases to Global Warming

Feedback

• Positive; Amplifies/reinforces ongoing trend

• Negative; Diminish/reverse trend to maintain status quo

Possible Impacts of Global Warming

• Sea Levels• Forests• Biodiversity• Food Production• Water• Weather• Health

Climate Change and Sea Level

Early Warning Signs of Global Warminghttp://www.climatehotmap.org/

FINGERPRINTS: Direct manifestations of a widespread and long-term trend toward warmer global temperatures

http://www.climatehotmap.org/

• Heat waves and periods of unusually warm weather

• Ocean warming, sea-level rise and coastal flooding

• Glaciers melting

• Arctic and Antarctic warming

Glacier National ParkAll but 37 of 150 glaciers in the park

have melted since 1850.

Glacier National Park1957 1998

Global Climate Change

Melting

permafrost

HARBINGERS: Events that foreshadow the types of impacts likely to become more frequent and

widespread with continued warming.

• Spreading disease• Earlier spring arrival• Plant and animal range shifts and

population changes• Coral reef bleaching• Downpours, heavy snowfalls, and

flooding • Droughts and fires

Coral Bleaching

Possible Consequences of Global WarmingHighly Plausible

•Global Av Surface Warming•Global Avg. Precipitation Increase•Reduction in Sea Ice•Surface Winter Warming at High Altitudes

Plausible •Global Sea Level Rise•More Summer Mid-altitude Drying•High Latitude Precipitation Increase

Highly Uncertain

•Local Details of Climate Change•Regional Distribution of Precipitation•Regional Vegetation Changes•Increase in Tropical Storm Intensity/Frequency

Ways an Individual Can Help Reduce Global Warming

• Reduce use of fossil fuels; car pool, use mass transit, walk, bike

• Use energy efficient appliances and light bulbs

• Plant trees (Cool house with shade trees)

• Use solar energy to heat household as much as possible

Fig.03.p158

A major point of disagreement of the Kyoto Protocol isthat developing countries do not have to cut emissions as much as developed countries.

Greenhouse gas emissions are expected to increase faster in developing rather than developed countries

Global Warming vs. Ozone Depletion

Global Warming Ozone Depletion

Possible Consequences:

Altered climate and agricultural productivity

Increased sea level

Increased skin cancer, damage to phytoplankton

Possible Responses:

Use less fossil fuel and less deforestation

Eliminate use of CFC’s

Global Warming vs. Ozone Depletion

Global Warming Ozone Depletion

Region of the Atmosphere:

Mostly troposhere Stratosphere

Major Substances Involved:

CO2, CH4, N2O O3, O2, CFC

Radiation Involved:

Infrared radiation vibrates molecule & remit energy to Earth

UV Radiation breaks apart O2 and O3 & is filtered in process

Global Warming vs. Ozone Depletion

Global Warming Ozone Depletion

Nature of Problem:

More greenhouse gases increase avg global temp

Less ozone conc increases UV exposure

Source of Problem:

CO2 released from burning fossil fuels & deforestation

CH4 from agriculture

CFC’s (from refrigerants, solvents, foaming agents)form Cl free radical that destroys ozone

Determining the Amount of CO2 Produced by Burning Gasoline or Coal

1. Look at balanced chemical equation to determine the ratio of CO2 produced for burning each fuel.

Determining the Amount of CO2 Produced by Burning Gasoline or Coal

2. Determine the molar mass of fuel and CO2 to set up appropriate ratio.

Molar Mass (Carbon dioxide, CO2) = molar mass C + 2 (molar mass O)

Molar Mass coal 2 = molar mass C

Ratio = (molar mass CO2/ molar mass C)

Determining the Amount of CO2 Produced by Burning Gasoline or Coal

3. Convert amount of fuel to grams and use ratio to calculate mass of CO2 produced.