AIR POLLUTION

4/24/12

What is Atmospheric Density?

• Density is the ppm measure the concentration of gases.

• Density = Mass/Volume (units of kg/m3)– At surface, 1.2 kg of air per cubic metre.

• Concentration = parts per million (ppm)

• Air is compressible.– Gas molecules are not attached to each other, and resist

being squeezed closer together.

– Because of compression from the weight of overlying air, the atmosphere is denser near the surface than above.

What is atmospheric pressure?

• The force or mass per unit area of a column of air.

How does pressure affect density?

Due to compressibility,atmospheric massgradually “thins out”/becomes less densewith height.

less overlying weight

more overlying weight

What is a Vertical Pressure Profile?

Pressure always decreases with height.

Pressure at surface = 1000 mbPressure at 5.5 km = 500 mb

500 mb / 1000 mb = 50% above 5.5 km

Pressure at surface = 1000 mbPressure at 18 km = 100 mb

100 mb / 1000 mb = 10% above 18 km or 90 % below 18km

What is the Vertical Structure of the Atmosphere?

Thermal Layers of the Atmosphere

Four distinct layers of the atmosphere emerge from identifiable temperature characteristics with height

Troposphere

Stratosphere

Mesosphere

Thermosphere

What is the troposphere?

The lowest layer, named as this region promotes atmospheric overturning

Layer of virtually all weather processes

Warmed at the surface by solar radiation

Identified by a steady temperature decrease with height

Thinnest layer, but contains 80% of the mass

Due to thermal expansion, the tropopause is roughly 16 km over the tropics, but only 8 km at poles

An excess of ozone is “Bad” here.

Vertical Structure of the Atmosphere

Flattened Anvil cloud top reveals the top of troposphere

Updraft has “overshot” the tropopause and entered the lower stratosphere

What gases compose the atmosphere?

• Nitrogen - 78.084%Oxygen - 20.95%Argon - 0.934%Carbon Dioxide - 0.036%Neon - 0.0018%Helium - 0.0005%Methane - 0.00017%Hydrogen - 0.00005%Nitrous Oxide - 0.00003%Ozone - 0.000004%

• Water = 1-4% usually when air is wet

What is the stratosphere?

Area of little weather (“stratified”)

A layer where temperature increases with height

Inversion caused by the absorption of ultraviolet radiation by ozone

Although the ozone layer exists through an altitude between 20-30 km (12-18 mi), actual concentration of ozone can be as low as 10 ppm

The ozone layer is “good” here

How does burning fossil fuels affect the atmosphere?

• Releases Sox, Nox, CO2 , CO, particulate matter and hydrocarbons into the atmosphere.

• Increases • likelihood of • acid rain/Increases acid

deposition• Air Quality Index (AQI) =

measures emissions from fossil fuels

What is an electrostatic precipitator?

• Can be used to reduce particulate matter.

What is Global Warming? • An increase in the earth's average atmo

spheric temperature.– Mean temperature globally has increased

0.5ºC in the past 100 years– Absorption of infrared radiation by

atmospheric greenhouse gases, increases the avg. temp of the atmosphere.

– Irreversible tipping point of global warming is 450 ppm. (recall from “an inconvenient truth” that it had never gone above 300ppm)

What could result from global warming?

• 1) coastal flooding and submerged low lying areas

• 2) Thermal Expansion of oceans, which result in an increase in sea level.

• 3) Expanding range of tropical diseases• 4) More intense hurricanes and typhoons• 5) Increase in crop damage from pests and

diseases. • 6) Loss of carbon sinks such as coral reefs, which

are composed of CaCO3

How is the artic especially affected by global warming?

• Positive feedback loop- increase in global warming results in a decrease in ice (which reflects much of the sun’s rays), increasing surface area of water, which absorbs most of the sun’s rays, heating the water and perpetuating the cycle.

What are energy waves?

1)UV rays2)Light

rays3)Infrared

rays

What are greenhouse gases?• Any atmospheric gas that effects

the atmosphere by absorbing the infra-red radiation that is reflected off the surface of the earth. – Carbon dioxide (CO2)

– Nitrous oxides (N2O)

– Methane (CH4)– CFC’s (chlorinated

flourohydrocarbons)

What are nitrous oxides?• Nitrogen and oxygen compounds (Nox)

that can be oxidized by oxygen gas or ozone in the troposphere to create Acid Rain/Acid deposition (HNO3).

• Green house gases produced by burning fossil fuels.

• Formed in a process of nitrification.

Where does methane come from?

• Methane (CH4) is frequently produced from decomposing organic matter, such as fecal matter from domestic livestock.

Where does carbon dioxide (CO2) come from?

• The primary concentration of carbon dioxide (CO2) in the atmosphere is due to burning fossil fuels.

• It is also released when organic matter becomes due to respiration of decomposing bacteria.

• It is released through respiration. • Concentrations of CO2 are decreased by light

reactions of during photosynthesis.

What does sulfur dioxide? • Mostly

produced by burning fossil fuels and volcanoes, coal mines (acid mine drainage).

• Causes acid deposition in the form of H2SO4 (sulfuric acid)

What is Acid deposition? • commonly known as acid rain• occurs when emissions from

burning fossil fuels and other industrial processes undergo chem. reactions in the atmosphere and fall to the earth as wet deposition (rain, snow, cloud, fog) or dry deposition (dry particles, gas)

• An increase in concentration of heavy soluble metals in a local pond = acid deposition

What is particulate matter?• Small particles, which liquids stick

to. • Particle pollution is made up of a

number of components, including acids (such as nitrates and sulfates), organic chemicals, metals, and soil or dust particles.

What is Ozone?

• Ozone is a molecule formed by 3 atoms of oxygen bonded together.

What is ozone?

• Ozone in the troposphere (ground level)= bad– Due mostly to motor vehicles– Strong oxidant– Respiratory irritant

What is Ozone?

• Ozone in the stratosphere = good– Absorbs harmful Ultraviolet radiation (UV-C and

UV-B) that cause Basal cell carcinoma (most common) and melanoma (deadliest).

UV radiation= light with wavelengths less than 320 nm

– We are “burning a hole” in the ozone layer in the stratosphere with CFC’s (reduced by Montreal Protocol)

Where is zone located?

• Ozone particles are diffused throughout the atmosphere, but concentrated at specific altitudes.

What are CFC’s?

• Human Made Chemicals called CFC s:• CFCs are chlorofluorocarbons; they are

small molecules that contain chlorine, fluorine and carbon atoms. Usually there are only 1-2 carbon atoms.

• CFCs are referred to by a number. The most common CFCs are: CFC-11 (CFCl3), CFC-12 (CF2Cl2), CFC-113 (CF3CCl3).

What do CFC’s do?

• Deplete the ozone layer in the stratosphere, which typically helps to keep out unwanted UV-C and UV-B rays.

Why do Human Beings use CFCs?

• These chemicals were used as refrigerants in air conditioners and refrigerators / freezers.

• They were used as propellants in cleaners, room deodorizers, furniture polishes, hair spray, perfumes and more.

• They were used as blowing agents in the production of styrofoam, foam rubber, and more.

How do humans pollute the air?

• 1) Industry• 2) Transportation • 3) Energy production

What? A hole in the ozone?!

• In 1985, a Russian team of scientists discovered an area over Antarctica where the level of ozone was much lower than normal.

• This came to be called the Ozone hole. • It’s discovery shocked and scared the world…• And encouraged it into action!

The Montreal Protocol

• Two years later, the leaders of the world met in Montreal, Canada to take action against the problem.

• They created a document called The Montreal Protocol which gradually eliminated all CFC use.

• All countries who signed it had to switch to new chemicals.

The situation today

• In the "Scientific Assessment of Ozone Depletion 2010" report, UN scientists announced that the ozone layer in the upper atmosphere has ceased diminishing.

• The scientists say the area of the ozone that has thinned out should largely be restored by mid century,

What if we hadn’t acted?

What are potential solutions to other air pollutants?

• 1) Use renewable resources to replace fossil fuels. – i.e. replace coal burning electricity

with wind or solar farms. • 2) Increase policy incentives and

regulations to reduce fossil fuel emissions and push the economy toward more sustainable practices. – i.e. fund public transit options,

creation of bike lanes and green building practices.

Renewable Energy

• Geothermal Energy• Hydroelectric energy• Solar energy= perpetual energy source• Carbon sequestration• Biofuels• Wind