Presentation on theme: "1 Once released, pollutants are free to wander. Module 3. Meteorology and Transport of Air Pollution in the Mid-Atlantic United States by K.G. Paterson,"— Presentation transcript:
3 Did You Know? ~30% of the nitrogen deposited in Chesapeake Bay is from air pollution
4 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
5 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. Adapted from:
6 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)
7 Theory: Pressure Systems High pressure system air movement Clockwise Downward Outward High pressure systems often create Clear skies (Canadian high) Hazy skies (Continental high) Limited vertical mixing Stagnation in northern hemisphere
8 Theory: Pressure Systems Low pressure systems Counter clockwise Upward Inward Low pressure systems often create Rain/storms Strong mixing Dispersion Improved air quality in northern hemisphere
9 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
10 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
11 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
12 Application: Winds Aloft This diagram depicts where and when the low level jet forms. Note the dependence on a nighttime surface inversion.
13 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
14 Theory: Sea/Land Breezes Coastal locations are prone to additional transport influences from the land/sea interface, driven by temperature differences Land Sea Sun Morning Land heats more quickly than sea and creates circulation pattern with a sea breeze Land Sea Sun Evening Land cools more quickly and creates circulation pattern with a land breeze convection radiative cooling
15 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
16 Application: Inversions The brown haze from NO 2 and other pollutants makes an excellent marker for inversion identification Elevated inversion Surface inversion
17 city Theory: Inversions Topographical Influences Valleys, mountains, hills can limit dispersion and allow inversions to persist z T aaaa U aaaa ocean U U
18 Application: Stability Looping Fanning Coning Fumigation Lofting stable unstable neutral elevated inversion ground inversion 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.
19 Receptor = Point of impact Theory: Transport Transport connects air pollutant point of release to point of impact Source = Point of release Airshed: The physical extent of all sources which can affect a receptor of interest
20 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)
22 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,
23 Further Learning Pollutant Transport Analyses, one of the PAMS workshops on ozone transport, Unisys Weather, online meteorological observations and forecasting, A Guide to Mid-Atlantic Regional Air Quality, Part III: Meteorology and Transport in Air Pollution Episodes, pp UCAR Supporting Military Emergency Response During Hazardous Releases.
24 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