Lec. 29: Human Effects: Air Pollution

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Lec. 29 Human Effects Air Pollution Heat
Islands (Ch 14)

• Atmospheric pollutants
• Atmospheric controls on air pollution
• Urban heat islands

http//www3.gov.ab.ca/env/air/index.html
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Science air pollution
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Science air pollution
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Science air pollution
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In air by resolved wind
Turbulent diffusion (same as turbulent
dispersion) is name given to mixing due to the
unresolved scales of motion, ie. the turbulent
component of the wind
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• 3. Responses/consequences
• deposition to soil, plant, ocean, animal

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• Particulates soot, pollen, etc. and (eg.)
  asbestos... strongly affect visibility, so most
  noticeable. Classified by size eg. PM10
  (diameter lt 10 ?m) remains suspended and can
  enter lungs PM2.5 (fine particles)
• Sources natural fires, eruptions, breaking ocean
  waves, wind-entrained dust and pollen.
  Secondary particulates formed by coagulation of
  gases.
• Small terminal velocities (slow gravitational
  settling) imply long residence time
  precipitation the most effective removal process
  (aerosols are the CCN at heart of precipitates
  and scavenging by falling droplets removes
  other particulates

• soil erosion dust dislodged by wind stress on
  surface in combination with bombardment by
  saltating particles in the saltation layer
  above which is the suspension layer
• soil condition (moisture, friability) plays a
  role
• leaving stubble strips to shelter the soil
  means to reduce wind stress on the soil (wind
  pulls on the straws instead)

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Human effects shelter controlling the
environment to mitigate soil erosion
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Human effects shelter research
observations
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Human effects shelter research
Lines - computations
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(This is just to give you a glimpse of what the
govering equations look like)

• Influence of windbreak is felt as a mean
  momentum sink...

U-mtm
horiz.U-mtm.flux
vert.U-mtm.flux
Windbreak sink ? kr U2 localised by
delta-function at x0, step function at zH

• and as a turbulent kinetic energy sink eg. in a
  2nd-order closure

?u2
horiz.flux
shear pro.
redistr.
heuristic
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iron
Zurich 700 trains/day on line studied
emissions of the railway lines are dominated by
iron particles, which contribute 67 to the
railway related PM10. The iron class particles
were appointed to the wear of tracks, as well as
wheels and breaks of the trains. In addition,
aluminium and calcium particles assigned to
abrasion of the gravel bed and re-suspension of
mineral dust contribute to the PM10 load 23 for
the aluminium and 10 for the calcium
particles. (Lorenzo et al., Atmospheric
Environment Vol. 40, 2006)
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• Carbon Monoxide (CO) from incomplete combustion
  of carbon fuels colourless, odourless, poisonous
• Sources fires, eruptions but taken up by soil
  micro-organisms so background levels low. Key
  anthopogenetic source vehicles

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• Sulphur oxide (SOx ) gases many natural sources
  but background levels low. SO2 the key primary
  sulphur gas, from burning sulphur-bearing fossil
  fuels. Colourless but smells, can cause
  respiratory problems. SO3 typically a secondary
  gas in moist air forms sulfuric acid ? acid rain

Fig. 14-3
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• Volatile Organic Compounds (VOCs or VOx)
  hydrocarbons, eg. methane (natural). Some
  carcinogenic. Involved in photo-chemistry of smog
• Nitrogen Oxides (NOx) Nitric oxide (NO)
  non-toxic, colourless, odourless formed
  naturally in soil, and this is balanced by
  natural sinks. Anthropogenic NO associated with
  combustion, produces secondary NO2 (nitrogen
  dioxide)
• NO2 toxic corrosive gives polluted air its
  yellow/red/brown colour. In moist air reacts to
  form nitric acid ? acid rain
• Ozone (O3) secondary pollutant formed when
  sunlight acts on other pollutants. Smells,
  irritates. Main ingredient of photochemical smog.

Fig. 14-5
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Anthropogenic pollutant sources in the U.S.
(other than vehicles eg. energy generation from
coal, oil, gas)
Fig. 14-1
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Anthropogenic pollutant sources in the U.S.
Fig. 14-1
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Atmospheric controls on air pollution

• wind can control or modulate source strength
  (eg. dust surface flux of methane off swine
  lagoons
• wind is the transport and mixing agent
• temperature affects reaction rates
  stratification influences the vertical wind, ie.
  mixing
• mixed layer is the short-term sink for
  pollutants

Fig. 14-6
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• elevation of plume means locally no pollution
• potential for severe local pollution
• high levels intermittently

From Meteorology Atomic Energy
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Box model of urban air pollution
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• Contours of mean summer maximum (afternoon)
  mixing depths h (unit 100 m)
• from Portelli, 1977
• Edmonton, winter, lt 300 m

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Urban heat island
9 pm LST July 4, 1972 (temperature near ground)
Fig. 14-9a
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• Maximal late evening and night, and during
  winter. Causes
• reduced albedo (multiple reflections)
• high heat capacity of ashphalt, concrete implies
  downwelling longwave
• precip rapidly drained, dry surfaces low QE
  results in high QH
• anthropogenic heat

Fig. 14-9a