Transcript Module # and Title
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
QuickTime™ and a TIFF (LZW) decompressor are needed to see this picture.
www.marama.org
Did You Know?
~30% of the nitrogen deposited in Chesapeake Bay is from air pollution
3
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
4
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.
5
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)
6
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
7
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
8
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
9
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
10
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
11
Application: Winds Aloft
This diagram depicts where and when the
low level jet
forms. Note the dependence on a nighttime surface inversion.
12
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
13
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
14
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
15
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
19
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)
20
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
21
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
22
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
23
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
24
Thanks for making this a great class!
25