Air and Noise Pollution Studies

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Air and Noise Pollution Studies
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Atmospheric Dispersion and Transport

• Air pollutants are dispersed in the atmosphere in
  both horizontal and vertical directions.
• Winds and the atmospheric stability are important
  factors on the degree of dispersion.

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Atmospheric Dispersion and Transport

• If emission is constant from a source, the
  concentration is an inverse function of the wind
  speed. (Thus doubling wind speed will halve the
  pollutant concentration.)
• Wind direction is also important as it affects
  the concentration of pollutant at downwind
  location.

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Atmospheric Dispersion and Transport

• Horizontal wind speed is affected by friction
  which is proportional to surface roughness

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Wind rose
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Pollution rose
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Lapse rate and stability

• Dilution in the vertical direction depends
  strongly on the atmospheric stability.
• Adiabatic expansion if an air parcel is lifted,
  it would undergo adiabatic (no exchange of heat
  between the parcel and the surrounding
  environment) expansion and cool. This cooling
  rate is called adiabatic lapse rate. The dry
  adiabatic lapse rate is -1C/100 m.
• Environmental lapse rate is the rate of change of
  temperature with height in the actual atmosphere.
  This parameter characterizes the stability of the
  atmosphere and greatly affects the vertical
  movement of air and dispersion of pollutants.

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Lapse rate and stability
Adapted from The Atmosphere, Eighth edition, by
F. Lutgens and Tarbuck, Prentice Hall
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Warm air rise/ Cool air sink

• Unstable
• Neutral
• Moderately Stable
• Very Stable

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Unstable conditions often involve strong heating
of earth surface
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Topography related wind

• Land and Sea (Lake) breezes This mesoscale wind
  is caused by differential heating and cooling of
  land and water.

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Topography related wind
Adapted from The Atmosphere, Eighth edition, by
F. Lutgens and Tarbuck, Prentice Hall
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Land Sea breezes in HK airport
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Mountain-valley wind
Adapted from The Atmosphere, Eighth edition, by
F. Lutgens and Tarbuck, Prentice Hall
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Dispersion of a point source
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6 characteristic shapes under different stability

1. Looping (unstable, clear sunny day with light
   winds)
2. Coning (neutral to slightly unstable, cloudy or
   windy day or at night)
3. Fanning (inversion)
4. Lofting (superadiabatic lapse rate above a
   inversion, at sunset on a clear evening)
5. Fumigating
6. Trapping

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Long range transport

• Large-scale wind can transport pollution to a
  long distance.
• Transport of Asian dusts to the Pacific Ocean
• Westerly winds transport Asia pollution across
  the Pacific Ocean
• Transport of air pollution from the Pearl River
  Delta to Hong Kong

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Effects of air pollution on the atmosphere

• After air pollutants are emitted into the
  atmosphere. They cause significant changes of
  atmosphere on local, regional and global scales.
  The changes and impacts can be short- or
  long-term.
• Visibility
• Urban climate
• Rainfall
• Precipitation chemistry
• Stratosphere O3 depletion
• Global warming and cooling

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Visibility

• Visibility implies that an object can be seen in
  by an observer.
• A key element is the contrast between an object
  and the surroundings. Without contrast, an object
  can not be seen.

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Visibility reduction - natural

• Scattering of light by air molecules (Rayleigh
  scatter) responsible for the blue color of sky.
• Clouds, fogs, and aerosols produced from natural
  emissions of SO2, HCs ec.

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Visibility reduction - anthropogenic

• Primarily due to light scattering by particles
  and to a less extent by absorption of light by
  gases such as NO2.
• Light can also be absorbed by dark soot and large
  windblown dust.
• Particles with size 0.4-0.7 µm are most effective
  in scattering. Pollution-induced visibility
  reduction has received both scientific and
  regulatory attention. (urban photochemical
  smog and regional haze.)

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Visibility impairment trends
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Contributions to visibility in HKbackground (Hok
Tsui)
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Contributions to visibility in HKurban (Tsuen
Wan)
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Thermal air pollution

• Excess heat from urban area alter the atmospheric
  environment, thus can also be considered a form
  of air pollution.
• Urban heat island - urban area warmer than
  surrounding countryside caused by
• waste heat dumped into the environment from
  energy-utilizing processes,
• solar energy absorption and storage properties of
  urban surfaces,
• decreased urban ventilation due to increased
  surface roughness.

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Thermal air pollution

• Urban heat island effects on city climate
• longer frost free seasons,
• less frequent fog,
• decreased snow accumulation,
• low relative humidity,
• decreased likelihood of surface-based nocturnal
  inversion,
• increased rainfall downwind, and
• a distinctive circulation pattern.

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Air pollution effect on precipitation

• -Particles serve as sites for the condensation of
  water vapor.
• Acidic precipitation
• Increasing acidity (H) of precipitation via
  conversion of SO2 and NOx to sulphuric acid
  (H2SO4) and nitric acid (HNO3).
• Acid rain has adverse impact on fish in lakes,
  forest trees, and agricultural crops.
• In 1980s US carried out a national acid rain
  study program NAPAP, and started to control the
  SO2 and NOx emission from the electricity utility
  industry.
• Acid rain has also been a serious problem in
  China due to the use of large quantity of coal
  (some with high content of sulfur).

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Stratospheric Ozone Depletion

• O3 is produced naturally via photolysis of O2
  molecules by short-wave UV radiation (lt242 nm)
• O2 hv -gt O (1D) O (1D)
• O (1D) O2 M -gt O3 M
• O3 is destroyed via
• O3 hv -gt O2 O (1D)
• O3 O (1D) -gt 2O2
• The above processes convert solar energy to heat
  which causes rise in temperature with height in
  the stratosphere.

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Role of CFCs in Destroying Stratospheric O3

• CFCs can be photolysed by short wave UV at lt230
  nm and release free F and Cl atoms. Such
  wavelengths do not penetrate to the low
  atmosphere. Thus CFCs can be transported to
  stratosphere, where they are photolysed to
  produce Cl and F. They in turn destroy O3
• Cl O3 -gt ClO O2
• ClO O (1D) -gt Cl O2
• The sinks for Cl inlcude
• Cl CH4 -gt HCl CH3
• ClO NO2 M -gt ClONO2 M

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The Antarctic Ozone Hole

• Large scale of ozone depletion has been observed
  over the South Pole (the O3 Hole)
• It is caused by complex heterogeneous reactions
  in polar stratospheric clouds formed under the
  unique meteorological conditions.
• The reactions promote conversion of stable HCl
  and ClONO2 into photolycally active Cl2 . The
  latter can be photolyzed to form Cl which will
  destroy O3.
• The major concern is that the decreasing O3 would
  increase harmful UV-B at the Earths surface,
  which would increase the risk of skin cancer and
  harm life forms on earth.

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Global Climate

• The concern is that with the increasing
  concentrations of greenhouse gases in the
  atmosphere, temperature of the earth will
  increase, which could have significant impacts on
  agriculture, forests, land use, and biological
  systems, as well as human beings. (Sea level
  rise, change of rainfall, and increased
  desertification etc.)

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Greenhouse gases and their relationship with
global warming
CO2 CH4 CFC-11 CFC-12 N2O O3a
Concentration
Preindustrial 280 ppmv 0.8 ppmv 0 ppmv 0 ppmv 288 ppbv 11 ppbv
1990 353 ppmv 1.72 ppmv 280 pptv 489 pptv 310 ppbv 21 ppbv
Annual increase
1990 1.8 ppmv (0.5) 0.015 ppmv (0.9) 9.5 pptv (4) 17 pptv (4) 0.8 ppbv (0.25) 0.02 ppbv (1)
Radiative effectiveness (relative to CO2) 1 21 13,400 15,800 206 2000
Relative contribution to global warming (1990)b 55 11 (24) (24) 6
aTroposheric O3 aTroposheric O3 aTroposheric O3 aTroposheric O3 aTroposheric O3 aTroposheric O3 aTroposheric O3
bStaratospheric water vapor 4 bStaratospheric water vapor 4 bStaratospheric water vapor 4 bStaratospheric water vapor 4 bStaratospheric water vapor 4 bStaratospheric water vapor 4 bStaratospheric water vapor 4
From Elsom, D.M. 1992. Blackwell Publishers, Oxford, UK From Elsom, D.M. 1992. Blackwell Publishers, Oxford, UK From Elsom, D.M. 1992. Blackwell Publishers, Oxford, UK From Elsom, D.M. 1992. Blackwell Publishers, Oxford, UK From Elsom, D.M. 1992. Blackwell Publishers, Oxford, UK From Elsom, D.M. 1992. Blackwell Publishers, Oxford, UK From Elsom, D.M. 1992. Blackwell Publishers, Oxford, UK
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Greenhouse Effect

• The prediction of the climate warming by
  greenhouse is complicated by the fact that
  climate varies naturally and that anthropogenic
  aerosols (like sulfate) tend to cool the
  atmosphere by scattering solar radiation.

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Air Pollution Health Effects

• A strong relationship between a pollutant and
  its health effect is suggested when there is a
  convergence of evidence from epidemiological and
  toxicological studies, and studies of those who
  have been occupationally exposed.
• Epidemiological studies are conducted to
  determine potential relationships between a
  variety of environmental factors and human
  disease. (In general they become more important
  as the risk from atmospheric pollutants becomes
  smaller and the duration of exposure required to
  produce effects becomes longer.)

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Air Pollution Health Effects

• Toxicological studies (or controlled biological
  studies) are conducted on humans or animals to
  determine the functional, structural, and
  biochemical effects of toxic substances. One
  major advantage of this method is that the
  investigator can control many variables that
  often confound epidemiological studies.
• Occupational exposure studies look into the
  relationships between health of industrial works
  and exposures to work environment.

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Effects of the pollutants regulated by ambient
air standard
Pollutant Effects
CO Reduction in the ability off the circulatory system to transport O2Impairment of performance on tasks requiring vigilanceAggravation of cardiovaslur disease
NO2 Increased susceptibility to respiratory pathogens
O2 Decrement in pulmonary functionCoughing, chest discomfortIncreased asthma attacks
Lead Nerurocognitive and neuromotor impairmentHeme synethesis and hematologic alternations
SO2/PM Increased prevalence of chronic respiratory disease Increased risk of acute respiratory disease
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Welfare effects

• Air pollutants not only affect human health but
  also cause other non health-related effects
  (usually refereed to as welfare effects).
• These include damage to vegetation (forest and
  agricultural corps), damage to materials, injury
  to livestock, odor pollution, and reduced
  visibility.
• Many studied have shown that economic losses from
  these effects can be very significant.

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HKEPD O3 stations