Air Pollution
Structure of the Atmosphere
Basics
• Atmosphere behaves like a fluid
• It is also the fastest flowing fluid in the environment
o Therefore it’s a convenient way to dispose of unwanted materials
• Air pollution not modern
o Acid rain first described in 17th Century
o Acid rain known to have negative effects on plants in 19th Century
o The word smog (a combination of smoke and fog) introduced in 1905
• Source classification
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Point sources
Area sources
Fugitive sources
Mobile sources
General Effects
• Air pollution affects:
o Visual qualities
• Discolouration of atmosphere
• Reduction in visibility
o Vegetation
• Physical damage to leaves and fruit
• Reduced/supressed growth
• Increased susceptibility to diseases, pests and adverse weather
• Disruption of reproductive processes
o Animals
• Impairment of respiratory system
• Damage to eyes, teeth and bones
• Increased susceptibility to disease, parasites and other stress-related
environmental hazards
• Reduced ability for successful reproduction
• Loss of food source (e.g. vegetation)
General Effects
• Air pollution affects:
o Soils
• Precipitation of pollutants can be toxic
• Leaching of minerals due to pollutants forming acids
o Water quality
• Precipitation of pollutants can be toxic
o Natural and artificial structures
• Discoloration
• Increased weathering (e.g. marble)
o Human health
• Significant factor in death rates
• Primary effects are cancer, birth defects, eye and respiratory system
irritation, greater susceptibility to heart disease, aggravation of
chronic conditions such as asthma and emphysema
Types of Air Pollutants
• Primary Pollutants: Air pollutants emitted directly into
the atmosphere.
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Particulates (small particles of solid or liquid substances)
Sulphur dioxide
Carbon monoxide
Nitrogen oxides
Hydrocarbons
• Secondary Pollutants: Air pollutants produced
through reactions between primary pollutants and
normal atmospheric compounds
o Ozone
• Pollutants not distributed uniformly across earth but
tend to be produced, released and concentrated
either locally or regionally
Types of Air Pollutants
• Pollutants can be of natural origin
o Sulphur dioxide from volcanic eruptions
o Hydrogen sulphide from geysers and hot water springs and anaerobic
decay in bogs and marshes
o Ozone in troposphere due to unstable meteorological conditions
o Particulates due to veldfires
o Hydrocarbons from natural hydrocarbon seeps
Common Pollutants
• Sulphur Dioxide (SO2)
o General:
• Colourless and odourless gas present at Earth’s surface in low
concentrations
• Once emitted can be converted to particulate sulphate (SO4-2)
o Removed from atmosphere by wet/dry deposition
o Anthropogenic sources:
• Burring of fossil fuels (mostly coal)
• Variety of industrial processes ranging from petroleum refining to the
production of paper, cement and aluminium
o Effects:
• Adverse effects depends on concentration and dose
• Injury or death to animals/plants
• Severely damages lungs of people and other animals especially in
sulphate form
• Important precursor to acid rain
Common Pollutants
• Nitrogen oxides (NOx)
o General:
• Emitted largely as nitric oxide (NO) and nitrogen dioxide (NO2)
• NO2 is a reddish-brown to yellow-brown gas
o Major anthropogenic source:
• Automobiles and power plants burning fossil fuels
o Effects:
• NO2 can be converted to NO3-2 within small water particulates
leading to a reduction of visibility
• Both NO and NO2 are major contributors to smog
• NO2 contributor to acid rain
• NOx contributes to nutrient enrichment of surface water sources
(eutrophication)
• NOx causes irritation of eyes, nose, throat and lungs and increases
susceptibility to diseases such as influenza
• Dissolved in water NOx forms acids that can harm vegetation BUT
when converted to nitrates they can promote plant growth
Common Pollutants
• Carbon monoxide (CO)
o General:
• Colourless, odourless gas
o Major anthropogenic source:
• 90% of CO emitted naturally
• 10% emitted from anthropogenic sources
o Fires, cars
o Sources of incomplete burning of organic compounds
o Effects:
• CO toxic to animals and people in even very small concentrations
o CO has a strong affinity for haemoglobin
o Haemoglobin bonds with CO 250X faster than with oxygen.
Preferential transport of CO to internal organs
o Effects range from dizziness to death
• Can cause birth defects, including mental retardation and impaired foetal
growth
• Effects worse at high altitudes where oxygen concentrations are lower
Air Toxics
• Toxic air pollutants
• Those pollutants who are known to cause cancer or
other serious health problems after either short term
or long term exposure
• Include gases, metals and organic chemicals that
are emitted in relatively small volumes
• Health effects
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Respiratory diseases
Neurological diseases
Reproductive diseases
Immune diseases
Some can be carcinogenic
Air Toxics
• Hydrogen sulphide (H2S)
o General:
• Highly toxic corrosive gas
• Easily identified by its rotten egg odour
o Sources:
• Produced from natural sources such as swamps, bogs and geysers
• Human sources are metal refineries
o Effects:
• Functional damage to plants
• Health problems ranging from toxicity to death in humans and
animals
Air Toxics
• Methyl Isocyanate (C2H3NO)
o General:
• Highly toxic chemical and extreme care needs to be taken to prevent
introduction to environment
• Colourless gas
• Case study:
o Dec3, 1984 the chemical leaked from a pesticide plant in Bhopal,
India
o Leak vaporized and formed a deadly cloud that settled over 64km2
causing 2000 deaths and more than 15 000 injuries
o Sources:
• Ingredient in some pesticides and insecticides
o Effects:
• Severe irritation (burns on contact) to eyes, nose, throat and lungs
• Breathing gas at a few ppm causes violent coughing, swelling of the lungs,
bleeding and death
• Less exposure cause a variety of problems including blindness
Smog
• A mixture of smoke and fog that produces
unhealthy air
• Two types:
o Sulphurous smog
• Aka London-type smog
• Produced primarily by burning coal or oil at large power plants.
Sulphur oxides and particulates combine under certain
meteorological conditions to produce a concentrated form of this
fog.
o Photochemical smog
• Aka LA-type smog
• Directly related to automobile use and solar radiation. Reactions that
occur in the development of smog are complex and involve both
nitrogen oxides and hydrocarbons in the presence of sunlight
Smog Over Los Angeles
Controlling Pollutants
• Most reasonable ways to control emissions:
o Reducing emissions (environmental preference)
o Capturing emissions before they reach the atmosphere
o Removing them from the atmosphere
• Sulphur Dioxide
o Reduction measures before, during or after combustion
o Technology exists to clean up coal so it will burn more cleanly (makes fuel
more expensive)
o Switching from high-sulphur coal to low-sulphur coal (only applicable in
certain regions)
o Washing coal
• Finely ground coal is washed with water allowing pyrite to settle out
• Ineffective for removing organic sulphur bound up with
carbonaceous material
• Method is expensive
Controlling Pollutants
• Sulphur Dioxide (cont.)
o Scrubbing removes sulphur from
stationary sources such as power
stations
o Wet scrubbing
• Uses a lot of water and
produces a wet end product
• Done after the coal is
burned
• The SO2 rich gasses are
treated with a slurry of lime
(CaO) or limestone (CaCO3)
• Sulphur oxides react with Ca
to produce calcium sulphite
which is collected and
disposed of
• Sulphite can be used to
produce gypsum
Stratospheric Ozone Depletion
• Ozone (O3)
o Degradation of the ozone starts in the troposphere
o O2 = diatomic oxygen; O3 = triatomic oxygen
o In the troposphere O3 is a pollutant, in the stratosphere it serves to protect us
from UV radiation
• Ultraviolet Radiation
o UVA
• Longest wavelength and least energy
• Can cause some damage to living cells
• Not affected by stratospheric ozone and is transmitted to surface
o UVB
• Energetic and strongly absorbed by stratospheric ozone
• Ozone only known gas known to absorb UVB
• Known to be hazardous to living things
o UVC
• Shortest wavelength and the most energy
• Possesses enough energy to break diatomic oxygen
• Strongly absorbed in the stratosphere with negligible amounts reaching
the surface
Stratospheric Ozone Depletion
• Creation of Ozone
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Photodissociation whereby O2 is broken into two O atoms by UVC
These O atoms react with another O2 molecule to form O3
O3 broken into O and O2 by UVC
O recombines with another O2 to produce O3
As part of this process UVC radiation is converted to heat
Dynamic balance between ozone destruction and creation
• Destruction of Ozone by CFC’s
1. There are no tropospheric sinks for CFC’s (destruction by sunlight, rain-out and
oxidation do not break down CFCs)
2. When CFCs travel to the upper part of the stratosphere reactions occur
3. UVC splits CFCs releasing Cl
4. Cl reacts with O3 producing chlorine monoxide (ClO) and O
5. ClO reacts with O to produce Cl and O2
6. Cl can is the free to react with O3
7. Termed a catalytic chain reaction
8. Each molecule of CFCs can destroy 100 000 molecules of O3
Indoor Air Pollution
• Today people spend 70% to 90% of their time in
enclosed spaces
o Homes
o Workplaces
o Automobiles etc
• Pathways and processes
o Both natural and human processes create differential pressure that move
air and contaminants from one area of a building to another
• Pressure differences between windward and leeward side of a
building
• Open and closing of doors cause pressure differentials
• Chimney effect
o Relies on the movement of air based on temperature
Indoor Air Pollution
• Sick buildings
o An entire building can be considered sick due to environmental problems
o Two types of sick buildings:
• Buildings with identifiable problems such as toxic moulds or bacteria
known to cause disease. These diseases are known as building-related
illnesses (BRI)
• Buildings with sick-building syndrome (SBS) where the symptoms
people report cannot be traced to a known cause
o A number of people report adverse health effects they believe are
related to the amount of time they spend in the building
o Complaints range from funny odours to more serious symptoms
(headaches, dizziness, nausea)
o In many cases it may be difficult to establish what may be causing the
sick building syndrome
o It has sometimes been found to be related to poor management and low
worker morale rather than toxins