Transcript Transp&Depos_DGay

Transport &
Deposition
of Air Pollutants
David Gay
Coordinator
National Atmospheric Deposition Program
University of Illinois, Champaign, IL
217.244.0462, [email protected]
The Basics
1. The Atmosphere has no boundaries
2. What goes into the Atmosphere, must come out.
emissions & deposition
3. It just doesn’t come out in the same place
transport
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If…
1. If you know when, where and how much of a pollutant is emitted
2. If you know where it will move to…
3. If you know how it will change while moving…
4. And if you know how, where, and when it will deposit…
Then you have the answer….
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The Cycle we will discuss
Transport
• where
• How fast
• Will it react chemically on the way?
(atmospheric chemistry)
Emissions
• When
• Where
• How much &
• What compounds
Removal
• How, where & when
• By what mechanism
(deposition,
rain, impaction)
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The driver of transport and removal is
physics & chemistry of the atmosphere
We are generally only interested in troposphere
◦ First 10 kilometers of the atmosphere
◦ Where the weather occurs
In the vertical direction
◦ Temperature varies with altitude
◦ Typically warm at the surface, cold aloft,
which makes the atmosphere buoyant
◦ Density decreases as we move up
◦ Windspeeds typically increase
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Emissions
Pollutant Emissions…..
Emissions are made up of a variety of
◦ Solids (particles and aerosols)
◦ Gases
◦ Conversion between gases & solids
(and back again)
And a variety of emission sources:
◦ Natural
◦ Anthropogenic
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Transport & Chemical Changes
Transport & Chemical Change
1.
Transport is the collection of mechanisms that
moves pollution
2.
Chemical changes occur during the movement
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Transport of Pollutant has 4 Keys
1. Diffusion
◦ Random motion of the molecules
2. Advection
◦ movement due to movement of the atmosphere
3. Lifting & Buoyancy & Stability
◦ Turning over of the atmosphere
4. Transformation (chemistry)
◦ Reaction to form different compounds
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Diffusion
an intermingling of molecules, ions, etc., resulting from
random thermal agitation, as in the dispersion of a vapor in
air.
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Advection
the transfer of heat or matter by the flow of
a fluid, especially horizontally in the
atmosphere or the sea.
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Lifting & Buoyancy & Stability
buoyancy is an upward force exerted
by a fluid that opposes the weight of an
immersed object.
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Chemical Reactions During Transport
A chemical reaction is a process that
leads to the transformation of one set of
chemical substances to another.
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It can be very difficult to track movement
◦ Number of sources of same
pollutant
◦ Several large sources
◦ Multiple small sources
◦ Diurnal patterns
◦ Day to Night
◦ Heating cooling, changes in wind,
solar radiation
◦ Different number of Pollutants ◦ Height of release
◦ In valley
◦ Sources that move, such as
◦ From stacks
Vehicles
◦ Meteorological Effects
◦ Wind speeds different at different
heights
◦ Updrafts and downdrafts
◦ Topography
◦ Mountains and valleys
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Different Scales of Transport
◦Local
◦Urban
◦Regional
◦Continental
◦Global
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Some Basics of Transport
Stable atmospheric conditions mean less atmospheric mixing,
therefore higher pollutant concentrations at ground-level
◦
◦
◦
◦
No air movement
Trapping of air
Emissions build
e.g., lack of wind; hot, dry days
Unstable atmospheric conditions allow ground-level pollution
to readily disperse
◦ Ground-level concentrations reduced
◦ Recharging occurs more frequently
◦ Example: cold fronts & thunderstorms
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Some Basics of Transport
Key weather parameters
◦ Sunlight
◦ Temperature
◦ Vertical temperature structure
◦ Surface winds
◦ Aloft winds
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Some Basics of Transport (cont.)
Synoptic-Scale Flow
(weather systems)
◦ Ridge – high pressure
◦ Trough – lower pressure
◦ Frontal Boundaries
Black lines are isobars=
contoured areas of same
atmospheric pressure
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Chemical Reactions: oxidation
• The atmosphere is dominated
by oxygen
Most primary pollutants
become oxidized
–Sulfur
–Nitrogen
–Ammonia
–Carbon compounds
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Chemical Reactions: Photochemistry
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Removal
Deposition
airborne pollutants deposited back on land
and water, either
◦ Wet Deposition
◦ i.e., in precipitation
◦ Washout
◦ Rainout
◦ Dry Deposition
◦ Deposit due to gravity
◦ Both particles and gases
Often have undergone chemical transformation
Often transported great distances in atmosphere
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Wet Deposition: Rainout & Washout
Removal Processes for Particles:
Deposition
When particles collide
◦ Get larger through agglomeration (stickiness)
Gravity pulls them down
◦ Settling out, or sedimentation to the surface
◦ “dry deposition”
Washed out of the atmosphere
◦ “wet deposition”
◦ Snowflakes
◦ Rain
◦ Hail
◦ Mist
◦ Fog
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Removal Processes (cont.)
◦Others leave by impaction and adherence
◦ Vegetation
◦ Soil
◦ Buildings
◦ Metals
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Removal Processes (cont.)
◦Sinks: places where pollutants are deposited
◦ Water bodies (ocean!)
◦ Soil
◦ Buildings
◦ Retention properties
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Modeling
Atmospheric Model:
An atmospheric model is a mathematical model constructed around
the full set of primitive dynamical equations which govern
atmospheric motions. It can supplement these equations
with parameterizations for turbulent diffusion, radiation, moist
processes (clouds and precipitation), heat exchange, soil,
vegetation, surface water, the kinematic effects of terrain, and
convection.
Several types of models, but the
basic idea is:
• To calculate the 3-dimensional
flow (advection)
• the energy flow (sunlight,
temperature, etc.), and
• the chemical changes (chemical
reactions)
• Tend to focus on one particular scale
• global, local, urban, etc.
• Many that we would be interested in, and attempt
to calculate the chemical reactions
• Typically trying to estimate location and ultimate
disposition (wet deposition, etc. of the pollutant)
• When
• Where
• How
Intercontinental Transport of Pollutants
Short Video
Intercontinental flow
Movie 1 & 2
Thank You
Questions?
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