atmospheric dispersion transport l.
Download
Skip this Video
Loading SlideShow in 5 Seconds..
Atmospheric Dispersion & Transport PowerPoint Presentation
Download Presentation
Atmospheric Dispersion & Transport

Loading in 2 Seconds...

play fullscreen
1 / 41

Atmospheric Dispersion & Transport - PowerPoint PPT Presentation


  • 227 Views
  • Uploaded on

Reading: Chap 3.1. Atmospheric Dispersion & Transport. Overview Wind Turbulence Ambient Stability & Inversion Plume Rise and Transport Plume Characteristics Long Range Transport Planetary Transport. Example?. The Atmosphere as a Sink .

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'Atmospheric Dispersion & Transport' - Gabriel


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
atmospheric dispersion transport

Reading: Chap 3.1

Atmospheric Dispersion & Transport
  • Overview
  • Wind
  • Turbulence
  • Ambient Stability & Inversion
  • Plume Rise and Transport
  • Plume Characteristics
  • Long Range Transport
  • Planetary Transport
the atmosphere as a sink

Example?

The Atmosphere as a Sink
  • Volcanoes and pollutants from other natural sources
  • Pollutants from human activities
    • From the discovery of the utility of fire to the present
  • Imperfect sink: limited ability to carry away (transport), dilute (dispersion) and remove (deposition) pollutants
    • Local or regional overloading
    • Topographical barriers
    • Scale of air motion
    • Atmospheric stability and inversion
    • Atmospheric chemical reactions
dispersion and transport

What’s the depth of PBL?

Dispersion and Transport
  • Transport - air motions carry pollutants from one region of the atmosphere to another
  • Dispersion - mixing of pollutants with air
  • Planetary Boundary Layer (PBL): Pollutants are initially released into PBL
    • PBL well mixed in the context of a few months
    • In shorter time scales pollutant mixing limited by atmospheric conditions
  • Air in Free Troposphere above the PBL is relative stable
slide5

Maximum height of wind profiles indicate where effects of surface roughness end and where gradient wind begins

Fig 3.1

Wind

What are the two components in describing wind?

  • Affected by:
    • Horizontal pressure gradients
    • Horizontal temperature gradients
    • Friction related to surface roughness
slide6

Meteorological Station

Is wind dilution mor effective in urban area or countryside?

www.infomonitors.com/weather_station.htp

Wind

Is wind speed measured at the ground level?

  • Effect of wind on emission: dilution of plume
    • Doubling of the wind speed decreases pollutant levels by 50 %
  • Wind Direction
    • Prevailing flows
    • (Anti-)Cyclonic flows
    • Effects of topography
      • In a valley
      • Along sea and lake coasts
wind in a valley
Wind in a Valley

What is the wind direction at night? During the day?

sea land breeze and circulation
Sea/Land Breeze and Circulation

What is the wind direction at night? During the day?

Will sea breeze continue inland for a long distance?

http://ess.geology.ufl.edu/ess/Notes/AtmosphericCirculation/daynight_lg.jpeg

wind rose
Wind Rose

Wind speed and direction are typically quite variable

164/720 = 23%

16/720 = 2.2%, 24/720 = 3.3%, 70/720 = 9.7%

slide10

Land-Sea

Valley

monthly wind rose of gainesville

What is the major wind direction in Gainesville?

What is the impact on local air quality if the wind is variable? What if it’s persistent?

Monthly Wind Rose of Gainesville
turbulence

What is the effect of turbulence on pollution?

Is turbulence desired?

Turbulence
  • Circular eddies of air movements over short timescales than those that determine wind speed (unstable)
  • Mechanical Turbulence:
    • Caused by air moving over and around structures/vegetation
    • Increases with wind speed
    • Affected by surface roughness
  • Thermal Turbulence:
    • Caused by heating/cooling of the earth’s surface
    • Flows are typically vertical
    • Convection cells of upwards of 1000 - 1500 meters
atmospheric stability

Does dry or moist air have a larger temperature change for the same change in elevation? Why?

Does lapse rate have anything to do with air quality?

Atmospheric Stability
  • Concept that describes (non-)movement of air near the surface
  • Characterized by vertical temperature gradients (Lapse Rates)
    • Dry adiabatic lapse rate () = 0.976 oC/100 m ~ 1 oC/100 m
    • International standard lapse rate = 0.0066 oC/m
slide14

= 0 for adiabatic expansion

Lapse Rate

How much is dT/dZ if Cp = 1.0034103 m2/s2-K? What if Cp = 1.856103 m2/s2-K? (for dry air and moist air)

  • First Law of Thermodynamics
  • Barometric Equation
superadiabatic lapse rates unstable
Superadiabatic Lapse Rates (Unstable)
  • Temperature decreases are greater than -10o C/km
  • Occur on sunny days
  • Characterized by intense vertical mixing
  • Excellent dispersion conditions
neutral lapse rates
Neutral Lapse Rates
  • Temperature decreases are similar to the adiabatic lapse rate
  • Results from:
    • Cloudy conditions
    • Elevated wind speeds
    • Day/night transitions
  • Describes good dispersion conditions

Isothermal Lapse Rates (Weakly Stable)

  • Characterized by no temperature change with height
  • Atmosphere is somewhat stable
  • Dispersion conditions are moderate
inverted lapse rates strongly stable

Inversion

www.co.mendocino.ca.us/aqmd/Inversions.htm

www.ew.govt.nz/enviroinfo/air/weather.htm

Inverted Lapse Rates (Strongly Stable)
  • Characterized by increasing temperature with height

Does it occur during the day or at night?

Is it associated with high or low pressure systems?

Does it improve or deteriorate air quality?

inversion
Inversion
  • Definition: temperature increases with altitude
inversion20
Inversion

http://www.co.mendocino.ca.us/aqmd/pages/Inversion-Art-(web).jpg

inversion21
Inversion
  • Two major types of inversion:
    • Subsidence Inversion: descent of a layer of air within a high pressure air mass
    • Radiational Inversion: radiation at night from the earth’s surface into the local atmosphere
radiational inversions

Fig 3.3

www.co.mendocino.ca.us/aqmd/Inversions.htm

What happens to inversion when sun rises?

Radiational Inversions
  • Result from radiational cooling of the ground
  • Occur on cloudless nights – nocturnal
  • Typically surface based
  • Are intensified in river valleys
  • Cause pollutants to be “trapped”
radiational inversions23
Radiational Inversions
  • Breakup after sunrise
  • Breakup results in elevated ground level concentrations
  • Breakup described as a fumigation

de.wikipedia.org/wiki/Smog

radiational inversions24
Radiational Inversions
  • Elevated inversions are formed over urban areas
    • Due to heat island effect
    • Due to dust dome

Fig 3.4

subsidence inversion
Subsidence Inversion
  • Associated with high-pressure systems
  • Inversion layer is formed aloft
  • Covers hundreds of thousands of square kms
  • Persists for days

Fig 3.5

apollo.lsc.vsc.edu/.../smog_var_geo.html

subsidence inversion26

Where else on earth would have similar phenomenon?

Subsidence Inversion
  • Migrating high-pressure systems: contribute to the hazy summer conditions in Midwest, SE and NE
  • Semi-permanent marine high-pressure systems
  • Results in a large number of sunny calm days
  • Inversion layer closest to the ground on continental side
  • Responsible for air stagnation over Southern California

www.oceansatlas.org/.../datard.htm

inversions
Inversions
  • Frontal - warm air overrides cooler air
  • Advective - warm air flows over a cold surface or cold air

www.atmos.ucla.edu/.../inversions/Note03.html

mixing height mh

Why is agricultural burning allowed only during the daytime?

Mixing Height (MH)
  • Height of air that is relatively vigorously mixed and where dispersion occurs

What is the MH in a radiational inversion?

When does the max MH occur during a day? Min MH?

Which season has the max MH? Min MH?

Why does Phoenix have a larger MH than New Orleans?

dispersion from point sources

Why does plume expand downwind?

What are the factors that influence the history of plume?

Impact on air quality depends on dispersion, which depends on the height of plume

Dispersion from Point Sources
  • Pollutants emitted in plume form

www.epa.gov/.../muncpl/landfill/sw_combst.htm

dispersion from point sources30

Under what conditions can we have a higher Effective Stack Height?

Dispersion from Point Sources
  • Plume rise affects transport
    • Effects maximum ground level concentrations (MGLCs)
    • Effects distance of MGLCs

www.atmos.ucla.edu/.../chimneyplumes/Note03.html

stack plume looping
Stack Plume: Looping

Strong turbulence

http://www.med.usf.edu/~npoor/3

Is it at stable or unstable condition? High or low wind speed?

Does it happen during the day or night?

Is it good for dispersing pollutants?

slide32

Stack Plume: Coning

Strong wind, no turbulence

What is the stability class? Good vertical mixing?

On sunny or cloudy days?

Good for dispersing pollutants?

What is the ground level concentration as a function of distance from the stack?

slide33

Stack Plume: Fanning

http://www.med.usf.edu/~npoor/4

What is the stability class?

What is the top view of the plume?

What is the ground level concentration as a function of distance from the stack?

slide34

Stack Plume: Fumigation

Why can’t the pollutants be dispersed upward?

Does it happen during the day or night?

What is the ground level concentration as a function of distance from the stack?

What’s your opinion about requiring power plants to reduce their power output from 3 am to 3 hours after sunrise?

slide35

Stack Plume: Lofting

Why can’t the pollutants be dispersed downward?

When does it happen?

What is the ground level concentration as a function of distance from the stack?

slide36

Stack Plume: Trapping

What is the stability class?

What is the ground level concentration as a function of distance from the stack?

long range transport

Examples?

Why only long-lived?

Long-Range Transport
  • Transport of pollutants hundreds/thousands of miles; resulting in air quality problems far away from the source

Planetary Transport

  • Stable air above PBL retards vertical mixing
  • Transport out of PBL to free troposphere takes few hours to few days
  • Transport to top of troposphere with uniform mixing takes about a week (for long-lived pollutants, e.g. CO2, CH4, CFC)
planetary transport

Why?

Planetary Transport
  • Significant concentration differences between two hemispheres; cross equatorial mixing takes approximately one year

Stratosphere -Troposphere Exchange

Is the exchange fast or slow? Why?

www.newmediastudio.org/.../Trade_Winds.html

stratosphere troposphere exchange
Stratosphere - Troposphere Exchange
  • Mass exchange of troposphere with stratosphere takes 18 years
  • Mass exchange of stratosphere with troposphere takes 2 years

Fig 3.9

stratospheric circulation
Stratospheric Circulation
  • Characterized by horizontal airflows (due to thermal gradients between the equator and poles, and diabatic heating associated with O3 absorption of UV light)
    • North-South (meridianal)
    • East- West (zonal)
  • Driven by atmospheric pressure waves
    • Poleward in the winter Hemisphere
    • Significantly affects transport of O3
    • Affects the movement of CFCs

www.newmediastudio.org/.../Easterly_Waves.html