SCH4C

The Earth’s Atmosphere

UNIT 4: Chemistry in the Environment

Without the atmosphere, life on Earth would not be possible. Not only does it contain the oxygen required for living organisms, it also regulates the Earth’s temperatures through the greenhouse effect.

Structure of the Earth’s Atmosphere

The atmosphere is classified into 5 layers, each varying in composition and temperature.

Troposphere (0-15km)

· Weather occurs in this layer

· As altitude increases, air temperature decreases

Stratosphere (15-50km)

· Contains the ozone layer

· Heat is produced when ozone forms

· As altitude increases, air temperature increases

Mesosphere (50-85km)

· As altitude increases, air temperature decreases

· Air is much more dense, slowing and burning up meteors that enter the atmosphere from space

Thermosphere (85-600km)

· Auroras and satellites occur in this layer

· Radiation from the sun is absorbed in the thermosphere

· As altitude increases, air temperature increases

Exosphere (600km-10000km)

· Air is not dense at all in this layer

· Outer limit of atmosphere, beyond this is space

Composition of the Earth’s Atmosphere

The Earth’s atmosphere is composed of:

· nitrogen gas, N2(g)

· oxygen gas, O2(g)

· trace gases

Nitrogen, N2(g): 78%

· Nitrogen is removed from the atmosphere and deposited at the Earth's surface by specialized nitrogen-fixing bacteria, and also by lightning.

· This supplies nutrition for plant growth

· Nitrogen returns to the atmosphere primarily through biomass combustion and denitrification.

Oxygen, O2(g): 21%

· Oxygen is exchanged between the atmosphere and life through photosynthesis and respiration.

· Cellular Respiration: C6H12O6 + 6O2 6CO2 + 6H2O + energy

· Photosynthesis: 6CO2 + 6H2O + sunlight C6H12O6 + 6O2

Water vapour, H2O(g): 0-4%

· Water vapour varies in concentration, making up 0-4% of the atmosphere.

· Highest concentrations are near the equator over the oceans and rainforests.

· Water vapour is important for several reasons:

· Redistributes heat energy through latent heat energy exchange

· Condensation of water creates precipitation needed for plants and animals

· It warms the Earth’s atmosphere through the greenhouse effect

Carbon Dioxide, CO x(g): 0.036%

· Carbon dioxide is an important greenhouse gas.

· CO2 concentration has increased 35% in the last 300 years, mainly due to burning fossil fuels and deforestation.

· Naturally exchanged through photosynthesis and cellular respiration.

Methane, CH4(g): 0.00017%

· Methane is a very strong greenhouse gas, absorbing heat 200 times more than CO2.

· Methane concentrations have increased 150% since 1750, mainly through rice farming, livestock, land fills and coal mines

Nitrous Oxide, N2O(g): 0.00003%

· Concentrations of NO are starting to increase at about 0.2-0.3% per year, which can cause over-fertilization of ecosystems.

· Major sources of nitrous oxide are fossil fuel combustion, biomass burning and agriculture

·

Ozone, Ox(g): 0.000004%

Stratospheric Ozone (“Good Ozone”):

· 97% of the ozone in the atmosphere is found in the stratosphere as the ozone layer, where it is formed with the help of UV radiation.

· The ozone layer protects us from harmful UV radiation.

· Concentrations of ozone vary with season and location, the lowest concentrations are over Antarctica in the Spring.

· Low levels of stratospheric ozone occur because of the release of chlorofluorocarbons (CFCs and other ozone-depleting chemicals in air conditioners and aerosol spray cans.

Tropospheric Ozone (“Bad Ozone”):

· Near the Earth’s surface, ozone forms by reacting with primary pollutants (hydrocarbons and nitrogen oxides) in the presence of sunlight.

· Ozone triggers a variety of health problems even at very low levels and may cause permanent lung damage after long-term exposure.

· Ozone also leads to the formation of photochemical smog, causing additional problems such as a decrease in visibility as well as damage to plants and ecosystems.

What is Air Pollution?

Air pollution is a problem that affects life all over the world. There are many kinds of air pollutants. The Ministry of Environment and Climate Change calculates the Air Quality Health Index (AQHI) for three major air pollutants: ground-level ozone, fine particulate matter and nitrogen dioxide. Ozone and fine particulate matter are two common pollutants found in many parts of the country. Carbon monoxide, reduced sulfur compounds and sulfur dioxide are other pollutants monitored by the Clean Air Acts.

Many human activities create air pollution. In turn, the pollution causes problems for the health of humans and other life on our planet. To slow down that process, we can learn about what causes poor air quality and how to protect our life on Earth.

You will use the Air Quality Ontario website (http://airqualityontario.com/ ) to investigate air quality and complete the table on the back of this page.

What’s in My Air?

Pollutant

How can I be exposed?

Impact on my Health?

Ozone, O3

Fine Particulate Matter

Sulfur Dioxide

Carbon Monoxide

Total Reduced Sulfur Compounds