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