pollution dispersion presentation

7/21/2019 Pollution Dispersion Presentation

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Atmospheric dispersion

Once pollution is minimised where does it go, what are

the consequences?

David Hudson

Environment Manager (Midlands Central Area)



Pollution Dispersion

• Adapted from notes from Lyndon State

College course on atmosperic pollution

•ttp!""apollo#lsc#vsc#edu"classes"met$%&"

• 'irst of all understand te pysical

process

• Secondly develop a matematical modelto emulate it

• est it against real measurements

http://apollo.lsc.vsc.edu/classes/met130/

http://apollo.lsc.vsc.edu/classes/met130/



Cimney Plume Dispersionn te sta*le atmospere case (producing a

fanning plume)+ tere is ori,ontal dispersion ata rigt angle to te -ind due to tur*ulence anddiffusion# n te vertical+ dispersion issuppressed *y te sta*ility of te atmospere+so pollution does not spread to-ard te ground#is results in very lo- pollution concentrationsat te ground#n unsta*le air+ te plume -ill -ip up and do-n

as te atmospere mi.es around (-enever anair parcel goes up+ tere must *e air going do-nsomeplace else to maintain continuity+ and teplume follo-s tese air currents)# is gives teplume te appearance tat it is looping around# An inversion aloft -ill trap pollutants underneatit+ since te sta*le inversion prevents verticaldispersion# Pollution released underneat te

inversion layer -ill fumigate te mi.ed layer#/ote tat if te smo0estac0 -as ig enoug torelease te pollution -itin te inversion layer+te plume -ould fan *ecause te plume occurs-itin sta*le air#



More on Chimney Plume Dispersion

n te neutral atmospere case+ te ori,ontaldispersion at a rigt angle to te -ind is due totur*ulence and diffusion+ -ic occurs at tesame rate as te vertical dispersion+ -ic isnot *eing opposed nor encouraged *y testa*ility (or lac0 of it) in te atmospere# So+ teplume spreads e1ually in te vertical andori,ontal as it propagates do-nstream+ forming

a coning plume#n te lofting case+ pollution dilutes up-ard# isproduces muc lo-er pollution concentrations atte ground at a distance do-nstream tan testraigt sta*le case (fanning plume)+ *ecausemolecular diffusion and some tur*ulence allo-smo0e to reac te ground eventually+ and tefanning plume does not ave te up-ard

dispersion tat te lofting plume as#



Enhancing Dispersion: Flow Obstructions•e tur*ulent -a0e *eind a *uilding elpsmi. pollutants to te ground tat migt notave *een tere normally+ in a sta*leatmospere#•Do-n-as is especially *ad -en tere are

pollution sources on te top of te *uilding#•t is important to get te pollution emitted igenoug a*ove te *uilding so tat it does notget caugt in te do-n-as and get carrieddo-n to te ground



Enhancing Dispersion with ChimneysPollution emitted from a taller stac0 as to travel a

longer distance to get to te ground+ so it -ill*ecome more dilute# Also+ it may *e possi*le for taller stac0s to geta*ove lo-2level inversions####



Tall and Short Smoe Stacs

3it a tall enoug smo0estac0+ pollution is

emitted -itin te inversion aloft+ forming afanning plume tat does not pollute te areanear te smo0estac0# f it4s not tall enoug+ it-ill fumigate te countryside#S-itcing te layers so tat te inversion isat te ground+ -e need te stac0 tall enougto *e a*ove te ground inversion+ so tat a

lofting plume is formed# Arcitects -ill needto 0no- te average dept of te nocturnalradiation inversion in order to 0no- o- tallto *uild te stac0•



E!it "elocity

e faster te smo0e guses out+ te more

momentum it as+ and te iger it -ill fly

*efore it levels out and disperses to-ard te

ground#



Methods #or $ncreasing E!it

"elocity

/arro-ing te stac04s opening forces

te smo0e out as a faster streaming+

narro-er 5et#

6ac0pressure from te smalleropening may reduce te efficiency of

te flo- of smo0e out of te cimney+

o-ever+ partially offsetting te

increasing in plume momentum#



E.it emperature

e iger te temperature+ te greater

te positive *uoyancy in smo0e

streaming out of te stac0#

e smo0e as to rise iger *efore it

as adia*atically cooled to a neutral

*uoyancy temperature



3at is availa*le7

• 8S EPA 9AE:M;D<

= ---#epa#gov"scram&&$

•8> system 98>ADMS< = ---#cerc#co#u0"environmental2

soft-are"ADMS2model#tml

• Many more for specific purposes (long

range incidents+ road emissions etc#)



Map of ground level

concentrationsE!ample:

Predicted annual

mean PM$&

concentrations for

all Ceme. :ug*y

sources for ?&&?(@g"m%)

(from Ceme. yre rial

:eport ?&&)

pollution dispersion presentation

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