Air Pollution

1
Air Pollution

• Lecture 2

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Key Concepts

• Source
• Place where pollutants emanate
• Natural and anthropogenic
• Plant and animal decay, volcanoes, forest fires
• Sinks
• Place where pollutants disappear from the air
• Soil, vegetation, structures, water bodies,
• Scavenging Mechanisms
• Mechanisms by which pollution is removed from the
  atmosphere (e.g. rain)
• Oxidationturns pollutants (NO, NO2, SO2) etc
  into acids, which then react with particulate
  matter to form salts

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Key Concepts

• Half-life
• Measure used for aging a pollutant
• Time it takes for ½ of a pollutant emanating from
  a source to disappear into one of its sinks
• Most pollutants have a short half-life (days
  rather than decades)
• Prevents accumulation
• Not all CO2
• Has been accumulating in the ATM
• Also Nitrous Oxide (NO2), Methane, CFCs

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CO2 Concentrations
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Key Concepts

• Receptor
• Something adversely affected by polluted air
• Person or animal
• Tree or plant
• Material Paper, leather, cloth
• Aquatic life
• Some soils

6
Key Concepts

• Transport
• The mechanism that moves the pollution from the
  source to the receptor
• Smoke stack and a person downstream
• The wind is the mechanism that moves the
  pollution
• Some pollutants can get above the lower
  atmospheric turbulence and travel hundreds or
  thousands of miles
• California Fires

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Diffusion

• What happens to the smoke from the stack?
• The plume changes shape
• Turbulent eddies move some of the plume into the
  surrounding air and vice versa
• If the wind speed ejection speed, the plume
  will get stretched
• The plume will meander as the wind direction
  fluctuates

Mixing, stretching, and meandering act to weaken
the concentration of the pollutant--Diffusion
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Averaging Time

• Variability of concentration at a receptor
• Inherent variability of diffusion and transport
• Time variability of source strengths
• Scavenging and conversion mechanisms in the ATM
• All result in an effective half life of a
  contaminant
• Not all measurements are created equal

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Measurements

• The averaging time is extremely important
• Only works one wayFrom A B, C, and D can be
  reconstructed

CNT
15m
1hr
6hr
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Why not only use Continuous Measurements?

• Too much information
• Samples turbulent nature of the atmosphere
• Must be filtered to extract out the useful
  information about the signal
• Time lags are built into the sampling, analysis,
  and/or recording of the data
• Result is data averaged over 1min, 3min, 5min,
  60min, etc

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Arrowhead Charts

• Abscissa (x)Averaging time in 2 different units
• Ordinate (y)Concentration of the pollutant at
  the receptor

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Example-1h averaging time for 1 yr

• 8760 data points
• Array in decreasing value (1 max, 1 min)
• The value 2628 from the max will be the value for
  which 30 are above and 70 are lower
• The value 876 from the max will be the value for
  which 10 are above and 90 are lower
• The 1 value is between the 87 and 88th values
  from the maximum
• The .1 value is between the 8 and 9th values
  from the maximum

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Example-1h averaging time for 1 yr

• The 50 valuethe median value
• Not necessarily the same as average

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Arrowhead Chart Example
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Composition of Clean, Dry Air at Sea Level
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Sources of Air Pollution

• Natural vs Anthropogenic Sources
• Volcanic ash
• Car Exhaust
• What about sand?
• What about sand under a layer of removed ground
  cover?

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Natural Sources

• Volcanic eruptions
• Particulate matter, SO2, H2S
• Harmful for great distances from the source
• Mt St. Helens
• (May 18, 1980)

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Natural Sources

• Forest and Brush Fires (Even if started by
  accident)
• Smoke, unburned hydrocarbons, CO, CO2, oxides of
  nitrogen, and ash
• Cause reduction in visibility and solar radiation
  350 km from fire

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Source Unknown
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Natural Sources

• Dust Storms
• Entrain large amounts of particulate matter
• Particulate concentrations 1 to 2 orders of
  magnitude greater than ambient quantities
• Cause severe highway accidents and disrupt air
  travel

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Dust Storms
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Natural Sources

• The Ocean
• AerosolsSalt particles
• Sand and shell particles may become airborne
• Plants and trees
• Major source of HC on Earth
• Reactions with volatile organic matter causes the
  Blue haze seen over forested regions
• Salt water lakes, hot sulfur springs
• Local effect

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Blue Haze
Les Vosges in France
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Anthropogenic SourcesIndustrial

• Manufacturing products of raw materials
• Iron from Ore
• Lumber from trees
• Gasoline from Crude oil
• Stone from quarries
• Industries that convert materials
• Automobile bodies from steel
• Furniture from lumber
• Paint from solids and solvents
• Asphalt paving from rock and oil

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Industrial Sources

• Stationary
• Each emits stable quality and quantity pollutants
• Generally controlled by applying technology

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Anthropogenic SourcesUtilities

• Utilitiesconvert energy from one form of the
  other
• If a large steam generating plant produces 2000MW
  of power, burns a million kg/hr of 4 ash coal,
  it must somehow dispose of 40,000 kg of ash per
  hour
• If 50 is removed in the furnace, and 50 goes up
  the stack in which there is a filtering system
  in place that is 99 effective, that still leaves
  200 kg of ash per hour emitted to the atmosphere

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Typical Utility Plant

• Gaseous emissions
• 341,000 kg of oxides of sulfur PER DAY
• 185,000 kg of oxides of nitrogen PER DAY
• What if this is too much?
• Purchase cleaner coal
• Change the furnace so less ash makes it to the
  stack
• Install more efficient post processing pollution
  control
• This all costs moneyso energy costs go up!

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Typical Power Plant
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Utilities

• Waste management
• Poorly managed sewage treatment plant
• Burning landfills (used to be commonplace)
• Cheapest method of waste reduction

Burn at low temperatures Release large amounts of
Toxins Increase numbers of rats
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Personal Sources

• Automobiles (largest contributors)
• Home Furnaces
• Home Fireplaces and Stoves
• Backyard barbeques
• Open burning of refuse and leaves
• Typical emission of pollutants from personal
  sources exceeds those from industrial sources and
  utilities combined!
• 72 kg particulates, 1840 kg gases per year per US
  family of 4

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Control of Personal Sources

• Regulation
• You may only BBQ when the atmosphere is mixing
  well
• Change of lifestyle
• How many people would trade in that car for the
  bus?
• Change to a less polluting source
• Coal? Natural gas
• Change the type of pollution
• Instead of burning leaves, take them to a
  landfill
• Whatever the choice, some people are unhappy

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Primary Pollutants

• Directly emitted from sources
• Carbon monoxide (CO)
• odorless, colorless, poisonous gas
• created by incomplete combustion (especially bad
  with older cars)
• generates headaches, drowsiness, fatigue, can
  result in death
• Oxides of nitrogen (NOx, NO)
• NO - nitric oxide
• emitted directly by autos, industry
• Sulfur oxides (SOx)
• SO2 - sulfur dioxide
• produced largely through coal burning
• responsible for acid rain problem
• Volatile organic compounds (VOCs)
• highly reactive organic compounds
• release through incomplete combustion and
  industrial sources
• Particulate matter (dust, ash, salt particles)
• bad for your lungs

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Primary Pollutants and their Sources
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Secondary Pollutants

• Form in the atmosphere through chemical and
  photochemical reactions from the primary
  pollutants
• Sulfuric acid H2SO4
• Can cause respiratory problems
• nitrogen dioxide NO2
• Gives air a brownish coloration
• Ozone O3
• Colorless gas
• Has a sweet smell
• Is an oxidizing agent - lung tissue to rubber
  products
• Irritates the eyes

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Pollutants

• Precursors
• Primary pollutants that react to form secondary
  pollutants
• Most primary pollutants are precursors

Many pollutants exist in both forms
simultaneously
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Types of PollutantsBased on Chemical Properties

• Sulfur compounds
• Major sources
• Combustion of sulfur containing fossil fuels and
  organic matter (A)
• Waste disposal (A)
• Pulp and paper manufacturing (A)
• Sea spray and Evaporation from oceans (N)
• Biological decay (N)
• Major ProblemSO2
• Colorless corrosive gas with a pungent odor
• Results in Sulfuric Acid (PP) and Sulfates (SP)
• Acid rain

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Ambient SO2 Concentrations
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Nitrogen Compounds

• Form oxides
• N2ONitrous Oxide
• Not considered a pollutant of significant concern
• Almost no anthropogenic sources (Fertilized
  soils)
• NO (Nitric Oxide) and NO2 (Nitrogen Dioxide)
  (NOx)
• Take part in the photochemical reactions that
  produce O3
• NO2 is a pungent, reddish brown irritating gas
• Sources
• High temperature combustion (A)
• Biological growth and decay (N)
• Lightning (N)
• Volcanoes (N)

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Nitrogen Oxides
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Inorganic Carbon Compounds

• Sources of CO and CO2
• Incomplete and complete combustion of carbon
  containing fossil fuels (A) Incineration of
  biomass of solid waste (A) Decomposition of
  organic material (N) Respiratory processes of
  animals (N)
• CO
• Colorless, odorless, non-irritating highly toxic
  gas (Dangerous asphyxiant)
• Motor vehicle emissions and fossil fuel burning
  (A)
• DecreasingCatalytic converters and cleaner
  burning
• Volcanoes, forest fires etc (N)
• Most of the increasing atmospheric concentration
  of CO and CO2 increase in is attributed to
  anthropogenic sources
• CO2 increasing at .5 per year

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Carbon Dioxide
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Organic Carbon Compounds(Hydrocarbons)

• Sources
• Volcanoes, fires, natural gas seepage, and
  biological processes (N)
• Transportation, fossil fuel burning, chemical
  plants, petroleum refining, solid waste disposal
  (A)
• Produce Volatile Organic Compounds (VOC)
• Organic compounds that evaporate at room
  temperature
• Methane (CH4)
• Sources include Natural wetlands and rice
  paddies rotting of dead plants in swamps
  bacteria in the guts of termites and ruminant
  animals
• Generally non-reactive poses threat as green
  house gas

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Organic Carbon Compounds

• Non methane hydrocarbons (NMHC)
• Anthropogenic VOCs
• Benzene, toluene, formaldehyde, vinyl chloride,
  phenols, chloroform
• Naturally occurring VOCs
• Released by trees
• Isoprenereleased by deciduous trees (Oak, aspen)
• Pinene and limonenereleased by coniferous trees
• Play an important role in the photochemical
  reactions that produce smog and ozone
• Tropospheric lifetimes of several months to hours

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Ozone

• Good Ozone
• Highly reactive bluish gas naturally formed at
  high altitudes in the stratosphere
• Absorbs UV radiation
• Bad Ozone
• Formed in the troposphere
• Complex chemical reactions between nitrogen
  oxides and VOCs in the presence of sunlight
• Acrid odor
• Causes eye irritation, respiratory difficulties
• One of the main ingredients of smog

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Halogen Compounds

• Biggest concerns are CFC and HCL
• Ozone depletion and acid rain

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Worldwide Annual Natural and Anthropogenic
Emission (106 tons)