3 RAQ Train the TrainerFebruary 26-28, 2007Did 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 RAQ Train the TrainerFebruary 26-28, 2007Course GoalsBy the end of this session, you will be able toExplain the role that atmospheric transport processes have on the movement of pollutants in the Mid-AtlanticIdentify atmospheric conditions that can elevate or reduce levels of air pollution
5 RAQ Train the TrainerFebruary 26-28, 2007How does this happen?Nitrogen in the waters of Chesapeake Bay can come from a mix of sources, some local, some notAbout 1/3 of the Nis 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 heatingStrong 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 movementClockwiseDownwardOutwardHigh pressure systems often createClear skies (Canadian high)Hazy skies (Continental high)Limited vertical mixingStagnationin northern hemisphere
8 Theory: Pressure Systems RAQ Train the TrainerFebruary 26-28, 2007Theory: Pressure SystemsLow pressure systemsCounter clockwiseUpwardInwardLow pressure systems often createRain/stormsStrong mixingDispersionImproved air qualityin northern hemisphere
9 Application: Pressure Systems RAQ Train the TrainerFebruary 26-28, 2007Application: Pressure SystemsA common problem in the summer for the Mid-Atlantic U.S. is the formation of the Bermuda HighPersistent high pressureWeeks of hot, humid weatherElevates air pollution levels, particularly haze and PMBrings upwind emissions to Mid-Atlantic statesOften combines with continental high that builds up pollutant levels through stagnationDecreases 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) airForces warm air upward, causing storms, cleaning airCold air is typically quite clean, thus ending air pollution episodesWarm front: warm (moist) air moving into area of colder (drier) airMore gradual transition, causing less intense rain, frontal zone is general cleaned of pollutants
11 Theory: Winds AloftLow 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 featuresForm in absence of of fronts and stormsFlows 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 RAQ Train the TrainerFebruary 26-28, 2007Application: Appalachian TroughThe 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 RAQ Train the TrainerFebruary 26-28, 2007Theory: Sea/Land BreezesCoastal locations are prone to additional transport influences from the land/sea interface, driven by temperature differencesMorning Land heats more quickly than sea and creates circulation pattern with a sea breezeEvening Land cools more quickly and creates circulation pattern with a land breezeSunSunradiativecoolingconvectionLandSeaLandSea
15 Theory: InversionsInversion: when a layer of the atmosphere has an inverted temperature profile; temperature increases with altitudeHighly stable layer of airSuppresses vertical movement of airPollution accumulates within or below inversion
16 Application: Inversions The brown haze from NO2 and other pollutants makes an excellent marker for inversion identificationElevated inversionSurface inversion
17 Theory: Inversions Topographical Influences Valleys, mountains, hills can limit dispersion and allow inversions to persistUUzTGaGaUcityocean
18 Application: Stability RAQ Train the TrainerFebruary 26-28, 2007Application: StabilityStability is a measure of the tendency for air to move vertically.Emission plumes can be an estimator of the stabilityVertical mixing influences ground level concentrations.FanningstableLoopingunstableConingneutralFumigationelevated inversionLoftingground inversion
19 RAQ Train the TrainerFebruary 26-28, 2007Theory: TransportTransport connects air pollutant point of release to point of impactSource = Point of releaseReceptor = Point of impactAirshed: The physical extent of all sources which can affect a receptor of interest
20 Theory: Transport Processes RAQ Train the TrainerFebruary 26-28, 2007Theory: Transport ProcessesAny given pollutant can be transported by one or more of the following processes in the Mid-AtlanticLarge-scale transportGlobal circulationHigh/low pressureFrontsSmaller-scale transportWinds aloftAppalachian troughSea/land breezesVertical 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 LearningPollutant 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, ppUCAR 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
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