the atmosphere, air pollution and ozone...
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The Atmosphere,Air Pollution and Ozone Depletion
The Atmosphere
‣ The mixture of gases known as air, protects life on Earth by absorbing ultraviolet radiation and reducing temperature extremes between day and night.
‣ The atmosphere is not static. Interactions involving the amount of sunlight, the spin of the planet and tilt of the Earth’s axis cause ever changing atmospheric conditions.
The auroras occur in the thermosphere and are caused by
interactions between the Earth’s atmosphere and charged
particles streaming from the Sun.
Weather occurs in the troposphere. Gaseous water
molecules held together by intermolecular forces cause the
formation of clouds.
The Atmosphere
‣ Earth's atmosphere contains roughly:
The Earth’s atmosphere (where pressure becomes
negligible) is over 140 km thick. Compared to the bulk of
the planet, this is an extremely thin barrier between the
hospitable and the inhospitable.
78% nitrogen
20.95% oxygen
0.93% argon
0.038% carbon
dioxide
Trace gases
1% water vapour
All images: NASA
Atmospheric
Layers
‣ The atmosphere consists of
layers around the Earth,
each one defined by the way
temperature changes within
its limits.
‣ The layer boundaries are:
Tropopause
Stratopause
Mesopause
‣ The outermost, the
thermosphere, thins slowly,
fading into space with no
boundary.
Troposphere
Air mixes vertically and
horizontally. All weather
including global warming
occurs here and this layer
contains 75% of the mass
of the atmosphere.
Stratosphere
Temperature is stable to
20 km, then increases due
to absorption of UV by the
thin layer of beneficial
ozone.
Mesosphere
Temperature is constant in
the lower mesosphere, but
decreases steadily with
height above 56 km.
Thermosphere
This layer extends as high
as 1000 km. Temperature
increases rapidly after
about 88 km.
Aurora, caused by collisions
between protons and
electrons from the Sun and
oxygen and nitrogen atoms in
the atmosphere.
Meteor burning up
‣ The activities of humans make a make a major contribution to global air pollution, but natural processes can also be responsible.
Lightning causes forest fires,
oxidizes nitrogen, and creates ozone.
‣ Volcanic activity releases toxic and corrosive gases. Volcanic particulates can also block out sunlight and contribute to global cooling.
Natural
Processes
‣ Air pollution comprises gases, liquids, or solids present in the atmosphere at concentrations high enough to harm living things or cause damage to materials.
It does not only exist outdoors; the air enclosed in spaces such as cars and buildings may have higher levels of air pollutants than the outside air.
Sick Building Syndrome occurs when air pollution inside a building causes a range of health ailments to the building’s inhabitants. Sick buildings are
determined by 20% of the people reporting adverse health effects, relief outside
the building, or chronic respiratory / nerve / allergic / muscle symptoms.
Air Pollutants
Pollution over Mexico City Smoke from chimney stacks
Causes of Air Pollution
Motor vehiclesHydrocarbons HC
Nitric oxide NO
Carbon monoxide CO
Smoke and lead
IndustrySulfur doxide SO2
Nitrogen dioxide NO2
Carbon monoxide CO
Hydrogen sulfide H2S
Dust, smoke
Volcanoes
Sulfur oxides
Carbon dioxide
Volcanic dust
Photochemical smogIn the presence of direct sunlight, the
mixture of pollutants from primary
sources reacts to form ozone, nitric
acid, PANs (peroxyacyl nitrates), and
organic compounds such as
formaldehyde.
Petrol and diesel
combustion engines
Emissions from power
plants and industry,
as well as burning
fossil fuels
Volcanoes and forest
fires are a natural source
of air pollutants
Methane from the belching
and flatus of ruminants
‣ Major primary pollutants produced by human activity
(anthropogenic):
Sulfur oxides (especially SO2)is produced from industrial processes
that burn fossil fuels like coal and is implicated as a precursor to acid
rain. Volcanoes are a non-anthropogenic source of SO2.
Nitrogen oxides (especially NO2) are emitted form high temperature
combustion like power plants for energy production and automobile
engines NO2 can also lead to acid deposition.
Carbon oxides: carbon monoxide is odorless and colorless
poisonous gas emitted form the incomplete combustion of fossil fuels
especially for transportation and has a stronger affinity for
hemoglobin than oxygen in the blood. Carbon dioxide is also emitted
from combustion and volcanoes and is a primary cause of climate
change.
Volatile organic compounds (VOCs) like methane (CH4) are
emitted from rice production, landfills, cow, sheep or human
flatulence by anaerobic respiration and motor vehicles.
Particulate matter (PM) are tiny particles of solid or liquid
suspended in a gas and are derived from volcanoes, dust storms,
and fires.
Outdoor Air Pollution
‣ Secondary pollutants result from reactions
with light and primary pollutants:
Photochemical smog is a mixture of
sunlight, NOx, VOCs, particulates and ozone.
Smog occurs in places like Mexico City or
Los Angeles because of ample sunshine
thermal inversions and lots of cars.
Ground level ozone (O3) forms from NOx,
VOCs and light and results from motor-
vehicle exhaust. For humans this is a
respiratory irritant and can cause stress on
plants from leaf damage.
Peroxyacetyl nitrate (PAN) is also formed
from NOx, VOCs and light causes respiratory
problems and can also damage plant tissues.
Sulfuric Acid forms form SO2, O, and water
vapor and can irritate the eyes, nose or
throat or loss of soil fertility because of
decreased pH.
Outdoor Air Pollution
Johanth
eg
host C
C 3
.0
Temperature Inversion
‣ Temperature inversion occurs when a layer of warm air sits on
top of a layer of cold air.
The cool dense air remains close to the ground and disrupts normal
convection currents and diffusion, preventing pollutants such as smoke
rising to higher altitudes.
When this happens in a city, pollutants from cars and factories can be
concentrated near the surface, creating serious health issues.
Altitude
Temperature
Inversion layer
‣ Major indoor air pollutants:
Radon is a radioactive gas that results from the decay of radium and uranium found in the bedrock under buildings. Responsible for tens of thousands of lung cancer deaths each year. Prevention: Remove radon by sealing or ventilating where radon enters the home.
Molds and allergens are caused by moisture induced growth of mold and mildew and the release of animal dander and plant pollen. Prevention: filtration, humidity and dust control methods
Carbon monoxide can be released from tobacco smoke, space heaters that use fossil fuel and wood burning stoves. Causes headaches and dizziness. Prevention: Proper ventilation
Indoor Air Pollution
Radon
Molds &
Allergens
Carbon Monoxide
FormaldehydeAsbestos
Lead
‣ Major indoor air pollutants:
VOCs like formaldehyde that can be associated with new building material like furniture and carpeting. Causes irritation of eyes, nose, throat and lungs Prevention: Ventilation or alternative materials
Asbestos fibers are present in floor or ceiling tiles and insulation materials of older buildings. Long term inhalation can lead to lung disease or cancer. Prevention: Removal or sealing
Lead can be found in old plumbing pipes and fixtures, older paints, and some ceramic glazes. Causes impaired mental and physical development. Prevention: alternative paints or plumbing
Indoor Air Pollution
Radon
Molds &
Allergens
Carbon Monoxide
FormaldehydeAsbestos
Lead
‣ A thin veil of renewable ozone exists in a band of the upper stratosphere,17-26 km above the Earth’s surface and is formed by UV rays reacting with oxygen.
‣ Stratospheric ozone absorbs about 99% of the harmful incoming ultra violet (UV) radiation (A, B and C) from the sun and prevents it from reaching the Earth’s surface.
Stratospheric Ozone
Ozone (O3)
Effects of UV Radiation‣ As well as all the well known health problems associated with
ultraviolet radiation, e.g. sunburn, cancers and cataracts, UV-B radiation is likely to cause:
decrease in the productivity of forests and surface dwelling plankton because of the disruption of photosynthesis
disruption of food chains
immune system suppression in animals
lower crop yields
increase in smog
change in the global climate
Photo
: N
CI
Melanoma skin cancer
‣ The ozone depleting chemicals (below) drift into the stratosphere, where UV causes the release of highly reactive free chlorine.
Chlorofluorocarbons (CFCs) are used in:
coolants in fridges and air-conditioners
propellants for aerosol cans
styrofoam insulation and packaging
medical sterilizers
Halons are used in many fire extinguishers
Methyl chloroform is used to degrease metals
Methyl bromide is used as a fumigant
Carbon tetrachloride is used in many
industrial processes.
Ozone Depleting
Chemicals
Discarded refrigerators leak coolant
Many aerosols use CFC propellants
Ozone
Depletion
Ozone
Oxygen
molecule
Chlorine oxide
molecule
Ozone2 oxygen molecules
Cholofluorocarbon
(CFC)
Free
chlorine
Chlorine reacts
with ozone
Chlorine oxide
reacts with ozone
Uv light hits a CFC molecule
and releases a chlorine atom
The following mechanism for
ozone depletion is shown in
detail on the following slides
Free
chlorine
Ozone
Depletion
Ozone
Ozone
Cholofluorocarbon
(CFC)
O3
O3
CCl3F
Oxygen
molecule
O2
Chlorine reacts
with ozone
Uv light hits a CFC molecule
and releases a chlorine atom
Cl
Free
chlorine
Chlorine oxide
molecule
ClO
2 oxygen molecules
2O2
Chlorine oxide reacts
with ozone
Ozone Depletion
CFCl3 + uv CFCl2. + Cl.
Cl. + O3 OCl + O2
OCl + O3 Cl. + 2O2
‣ 2 ozone molecules react to form 3 oxygen molecules
‣ Reactive chlorine (Cl.)is freed to continue the process.
+ uv + 2O3 CFCl2. + 3O2 + Cl.
2+ + + +3
‣ CFCl3
‣ The Dobson Unit (DU) is a measurement of column ozone levels (the ozone between the Earth’s surface and outer space).
‣ The size and intensity of the ozone hole is growing each year, as can be seen in the satellite photos below. In recent years, a similar hole has developed over the Arctic.
In the tropics, ozone levels are typically between
250-300 DU year-round.
In temperate regions,
seasonal variations can
produce large swings in the ozone levels and they
can occur even in the
absence of ozone depletion.
Dobson Units (DU)
Monthly mean ozone, from the Southern Hemisphere
‣ In 2000, the extent of the ozone hole over Antarctica was the largest ever.
The ozone ‘hole’ is defined as a region
with lower than 220 Dobson units. Its not really a “hole”, but more of a substantial
thinning of the ozone layer over Antarctica
The readings were taken between
the South Pole (90 degrees south)
and 40 degrees latitude.
Data were collected in the
Southern Hemisphere springeach year (between 7 September
and 13 October.
The Ozone “Hole”
Antarctic Ozone Hole,
Minimum Values
The dark blue area
indicates <200DU
‣ The problem of ozone depletion was first detected in 1984 when researchers discovered the region of thinner ozone over Antarctica.
Since 1987, nations have cut their
consumption of ozone-depleting substances by 70%.
‣ Free chlorine in the stratosphere peaked around 1999 and is projected to decline for more than a century.
‣ Ozone loss is projected to diminish gradually until around 2050 whenthe polar ozone levels will return to1975 levels.
‣ It will take another 100-200 yearsfor full recovery (to pre-1950 levels).
Ozone Recovery
Air Pollution Prevention
‣ Pollution prevention is the management and control of emissions into the air. The changes in air quality often requires adaptation.
‣ Many laws and protocols have been enacted to help with the prevention of air pollution.
Clean Air Act and National Ambient Air Quality Standards
Kyoto (1997) and Montreal (1987) protocol
Cap-and-trade policy, carbon taxes and other
mitigation practices
‣ Aiding in pollution prevention requires practice but pollution can also be managed using pollution control devices like:
Electrostatic precipitators, wet scrubbers, and catalytic converters
Wet scrubbers remove pollutants by passing
gases through liquids, reduces gases like SO2
Electrostatic precipitators remove dust and
other particulate matters with an electric charge
Air Pollution Legislation
‣ The US Clean Air Act (1963) is federal law that authorized the EPA to establish the
National Ambient Air Quality Standards (NAAQS) and the Air Quality Index. The
Clean Air Act has been amended several times, and now:
Monitors six “criteria” air pollutants but does NOT monitor carbon dioxide.
The six criteria pollutants are
Particulate matter
Photochemical oxidants and tropospheric ozone
Carbon monoxide
Sulfur oxides
Nitrogen oxides
Lead
The 1990 amendment provided “carbon credits” and set up cap-and-trade policies
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