Once released, pollutants are free to wander 1

Module 3.

Meteorology and Transport of Air Pollution in the Mid-Atlantic United States

by K.G. Paterson, Ph.D., P.E. ©2007 www.mtu.edu

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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. The other half is transported from more distant sources.

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Adapted from: http://www.deq.state.va.us/air/pdf/air/nitrogen.pdf

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 low altitudes (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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convection

Theory: Sea/Land Breezes

 Coastal locations are prone to additional transport influences from the land/sea interface, driven by temperature differences

Morning

Land heats more quickly than sea and creates circulation pattern with a sea breeze Sun Sun

Evening

Land cools more quickly and creates circulation pattern with a land breeze radiative cooling 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 NO 2 and other pollutants makes an excellent marker for inversion identification

Elevated inversion 16 Surface inversion

Theory: Inversions

 Topographical Influences  Valleys, mountains, hills can limit dispersion and allow inversions to persist

U U z

G

a

G

a U city T ocean 17

  

Application: Stability

Stability is a measure of the tendency for air to move vertically.

Emission plumes can be an estimator of the stability Fanning stable Looping unstable Coning neutral Fumigation elevated inversion Lofting ground inversion 18

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 NO x , 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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