Transcript Module # and Title

Once released, pollutants are free to wander
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Module 3. Meteorology and Transport
of Air Pollution in the Mid-Atlantic
United States
by K.G. Paterson, Ph.D., P.E. ©2007
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www.mtu.edu
www.marama.org
Did You Know?
~30% of the nitrogen deposited in
Chesapeake Bay is from air pollution
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Course Goals
By the end of this session, you will be able to
 Explain the role that atmospheric transport processes have
on the movement of pollutants in the Mid-Atlantic
 Identify atmospheric conditions that can elevate or reduce
levels of air pollution
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How does this happen?
Nitrogen in the waters of Chesapeake Bay can
come from a mix of sources, some local, some not
About 1/3 of the N
is deposited from the air
(rivers and runoff are
other major sources)
Emissions from basin states (PA, MD, VA, DE, NY, WV)
account for about 1/2 of the atmospheric deposition.
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The other half is transported from more distant
Adapted from: http://www.deq.state.va.us/air/pdf/air/nitrogen.pdf
sources.
Theory: Global Circulation
Driven by tropical
heating
Strong convection in
tropics (aids rainfall)
Strong downward air near
sub-tropics (dries air)
Influences general
placement of certain
ecosystems (deserts and
rain forests, for example)
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Theory: Pressure Systems
 High pressure system air movement
 Clockwise
 Downward
 Outward
in northern hemisphere
 High pressure systems
often create
 Clear skies (Canadian high)
 Hazy skies (Continental high)
 Limited vertical mixing
 Stagnation
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Theory: Pressure Systems
Low pressure systems
 Counter clockwise in northern hemisphere
 Upward
 Inward
Low pressure systems
often create
 Rain/storms
 Strong mixing
 Dispersion
 Improved air quality
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Application: Pressure Systems
 A common problem in the summer for the Mid-Atlantic
U.S. is the formation of the Bermuda High
 Persistent high pressure
 Weeks of hot, humid weather
 Elevates air pollution levels,
particularly haze and PM
• Brings upwind emissions to
Mid-Atlantic states
• Often combines with continental
high that builds up pollutant
levels through stagnation
• Decreases natural cleansing
(e.g. rainout, dispersion) of
atmosphere from storms
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Theory: Fronts
Fronts are the boundaries between air masses
Cold front: colder (drier) air moving into area of
warmer (moist) air
Forces warm air upward, causing storms, cleaning air
Cold air is typically quite clean, thus ending air
pollution episodes
Warm front: warm (moist) air moving into area
of colder (drier) air
More gradual transition, causing less intense rain,
frontal zone is general cleaned of pollutants
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Theory: Winds Aloft
Low level jet: rapid winds that form at lowaltitudes (above surface inversions) during
the night.
More common where plains meet mountains
due to temperature differences at same altitude
above these land features
Form in absence of of fronts and storms
Flows from the SW to NE in the Mid-Atlantic,
along the contours of the Appalachians
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Application: Winds Aloft
This diagram depicts where and when the low
level jet forms. Note the dependence on a
nighttime surface inversion.
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Application: Appalachian Trough
The Appalachian Lee
Side Trough diverts
the regional transport
to the northeast,
thereby connecting
emissions in the
Midwest and Southeast
to receptors in the
Mid-Atlantic
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Theory: Sea/Land Breezes
Coastal locations are prone to additional
transport influences from the land/sea
interface, driven by temperature differences
Morning
Evening
Land heats more quickly than sea and
creates circulation pattern with a sea breeze
Land cools more quickly and creates
circulation pattern with a land breeze
Sun
Sun
radiative
cooling
convection
Land
Sea
Land
Sea
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Theory: Inversions
Inversion: when a layer of the atmosphere
has an inverted temperature profile;
temperature increases with altitude
Highly stable layer of air
Suppresses vertical movement of air
Pollution accumulates within or below
inversion
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Application: Inversions
The brown haze from NO2
and other pollutants makes
an excellent marker for
inversion identification
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Surface inversion
Elevated inversion
Theory: Inversions
Topographical Influences
Valleys, mountains, hills can limit dispersion
and allow inversions to persist
U
U
Ga
z
Ga
U
T
ocean
city
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Application: Stability
 Stability is a measure of the tendency for air to move vertically.
 Emission plumes can be an estimator of the stability
 Vertical mixing influences ground level concentrations.
Fanning
stable
Looping
unstable
Coning
neutral
Fumigation
elevated inversion
Lofting
ground inversion
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Theory: Transport
Transport connects air pollutant point of
release to point of impact
Source = Point of release
Receptor = Point of impact
Airshed: The physical extent of all sources
which can affect a receptor of interest
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Theory: Transport Processes
 Any given pollutant can be transported by one or more
of the following processes in the Mid-Atlantic
 Large-scale transport
Global circulation
High/low pressure
Fronts
 Smaller-scale transport
Winds aloft
Appalachian trough
Sea/land breezes
Vertical mixing inhibition
(inversions)
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Application: Long Range Transport
For some air quality
issues, the Mid-Atlantic
U.S. receives
considerable upwind
contributions from far
away, like NOx, as
shown here.
©2002 Connecticut Department of Environmental Protection
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Application: Long Range Transport
 Long-range transport can
influence local air quality.
Example: Canadian forest
fires (red dots) affected
the Mid-Atlantic U.S. with
particulate pollution
during this July 7, 2002
event. A high pressure to
the southwest of the fires
created the southerly flow
and a smoke plume
several hundred miles in
length.
Source: NASA GSFC,
http://veimages.gsfc.nasa.gov/3339/Canada.A2002188.1635.2km.jpg
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Further Learning
 Pollutant Transport Analyses, one of the PAMS workshops on ozone transport,
http://epa.gov/oar/oaqps/pams/analysis/transport/txpsac.html
 Unisys Weather, online meteorological observations and forecasting,
http://www.wxp.unisys.com
 A Guide to Mid-Atlantic Regional Air Quality, Part III: Meteorology and
Transport in Air Pollution Episodes, pp. 31-46.
http://www.marama.org/reports/Guide-MidAtlantic_RegAQ_Final.pdf
 UCAR Supporting Military Emergency Response During Hazardous Releases.
http://www.meted.ucar.edu/dispersion/afwa
http://www.meted.ucar.edu/dispersion/basics
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Reflection: Transport
Question: Can we do anything about air
pollution transported to our city?
Action: As a class, discuss the ramifications
of “living downwind”
Time: 5 minutes
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Thanks for making
this a great class!
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