Chapter 20

Atmosphere

Climate

Ozone

Layers of the Atmosphere

• Troposphere (lowest layer)

---------Tropopause• Stratosphere --------- Stratopause• Mesosphere --------- Mesopause• Thermosphere (highest

layer @100 km)

Composition of the troposphere

• 78% N2

• 20% O2

• Less than 2%• H2O vapor (.01%-4%)

• Argon gas (1%)• CO2 (0.04%)

• Trace gases

Structure & Temp of Atmosphere

• Look at Fig. 20-2 and Table 20-1• Troposphere = lowest layer; tropics 10 miles

(16km); higher altitudes 5 miles (8km)• Water vapor & clouds• Greenhouse gases• Colder w/ altitude (generally)• Pollutants reach top w/in a few days

Structure & Temp of Atmosphere cont.

• Tropopause ---- separate Troposphere from stratosphere

• Stratosphere

- temp increases w/ altitude 40 miles

- contains the ozone shield

- Ozone absorbs UV radiation from the sun &

filters the rays

- No precipitation

Global warming

• Global warming occurs when humans contribute too much of these greenhouse gases leading to a small (1-3 degree C) but significant rise in the global average temperature.

• Analogy – Car on a sunny day

The greenhouse effect is natural and important to keep the earth warm enough for

life to exist

Build up of Greenhouse gases:

CO2

• Fossil Fuel use• Deforestation

Methane (CH4)

• Microbial fermentation (Landfill)• Coal and oil deposits• Natural gas pipelines• Cows (manure)

• Methane is the second most important green house gas (next to CO2)

Nitrous OxidesBiomass burning

Chemical fertilizers

Fossil Fuel Burning

CFC-Chlorofluorocarbons

• Refrigerants• Solvents• Pesticides• Aerosols (Old)

Ozone (O3)

Stratospheric ozone is GOODIt shields us from the harmful UVB rays of the sun.

Ozone depletion is the thinning of the stratospheric ozone shield (mostly over the South Pole)

Analogy – Stratospheric O3 is like sunscreen for the earth.

Tropospheric ozone is BADIf we breath it, it causes lung damageIt is also a greenhouse gas

The Making of Ozone

• O2 + UVB (280 – 320 nm more energetic) O + O

• The free O bonds to existing O2 (O + O2)

• Ozone is made (O3)

• O2 + UVB O + O ; O + O2 O3

The Destruction of Ozone

• O3

• CFC – chlorofluorocarbons• Cl – FC (UV rays breaks bond)• The free Cl “attacks ozone”• O3 + Cl O2 + (Cl – O)

• Cl – O is unstable so the bond will break and the Cl will “attack” another ozone molecule

Greenhouse Effect

• Troposphere

• Traps heat near the Earth’s surface

• Water vapor, carbon dioxide, methane

• Globing warming

Ozone shield

• Stratosphere

• filters UV radiation

• Oxygen gas, Ozone gas

• Ozone depletion more UV cancer

Where?

What Happens?

Which gases?

Problem?

The End

http://www.eoearth.org/article/AP_Environmental_Science_Chapter_24-_Environmental_Laws_and_Regulations