METEOHOLOGICAL J\Dl'ECTS OF AlH CLEANING

·Althou:::;h there are many topics which ahould be mentioned while

considering meteorological aspects of air cleanine, this opportunity is

is boing used to review the effects of vertical temperature gradient on

stack eas behavior and to show s~r.ie photographs from the National Reactor

Testine Station illustrating typical conditions.

The appearance of stack effluent plumes is regulated largely by the

conficuration of the vertical gradient of air density, or temperature • .

With respect to a high stack on nearby level terrain there are five

diff crent con.figurations of the vertical temperature gradient that occur,

and these usually have a diurnal cycle.

These configurations, along with the expected behavior of an effluent

plu.'11e, is sho\m schematically in Figure 1.

Looping - occurs with a superadiabatic (very unstable) temperature lapse

rate. The stack effluent, if visible, appears to loop because .

of relatively large thermal eddies in the w-.lnd flow. Diffusion

is rapid, but sporadic puffs having strong concentrations are

occasionally brought to the ground near the base of the stack.

Loopine is favored by fair weather with r.elatively light w.inds.

- occurs with a grad:i.ent lyine between dry adiabatic and

isotherp.:i.l. The effluent stream is shaped like a cone with

axis horizontal.. Thti distance from the stack that effluent first

coraes to the ground is greater thnn with looping. Mechanical

mixiti0 predo;ninc.tes. · Al th ouch this condition is ideal for

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calculatinc grotmd concentrations by means of diffusion

equ.:i.tions, it docs not often persist except durinc cloudy,

windy \·reather. Durine fair weather, it is transitional and is

most likely to occur only for a brief interval about sunset as

the strong daytime lapse condition is converted to an inversion.

Fanning - occurs with temperature inversion conditions. Such laminar flow

may also occur in n·layer of air that is isothermal, depending

on wind speed and roughness of terrain. The stack effluent

diffuses practically not at all' in the vertical, and the effluent

trail may resemble a meandering river, widening very gradunlly ;

with distance from the stack. Depending on the duration of the

stable period and the wind speed at stack level, the effluent

may travel for many railes with little dilution. With level

terrain ground concentrations of effluent ·ao not occur;. however,

isolated objects which 'extend up into the pl1Ji11e, or hillsides

.which are encountered, can receive large concentrations even

though miles away from the stack.

Lofting - is usually associated with the transition from lapse to jnvcrsion,

but may persist at times for one to several hours. Occasio:ially

the inversion does not build up to stack level durine an entire

night due to interference of winds and/or cloudiness. The zone ,·

uf stronger effluent concentration, as shovm by shadin0, will

depend on the heip,ht of the inversion. It is caused by trapping

by the inversion of effluent carried into the stable layer by

turbulcr.t eddies that penetrate the layer for a short distnnce.

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Except \";hen the top pf tho inver:;ion is very near t.he ground,

this t;ype muy be corwidcr.:?d as the most favorable diffusion

situJ.tion to l:c cncountcn:d. IJ.'hc invl!r.:;ion prevents effluent

from re;i.chin& the nround; and at the same tiMe the cf fluent may

be rapicily dilutccl in the lapse leyer above the inversion.

Fumigating - occurs at the ti;:ie that the nocturnal inversion is being

dissipated py he at from the morning sun. The lapse layer begins

at the ground and works its 1-1<1.y upHard, rapidly· in sUJ-:L11er, but ·

slowly in winter. At some time the inversion is just above the

t~p of the stack, and actj_ng :is a lid, forces the effluent strew'l

to dilute within the shallo'.r lapse layer near.the ground. Laree

concentrations are hrougj'lt to the grotmd ai·ong the entire effluent

strea.:'Il by thermc.:.1 eddies in ~he lapse layer. Sustained conccntra-

tions near the ground will be higher with this situ~tion than

with ~r other.

Smoke experiments were pe~fon:ied by the Weather L>ureal.J. using the

' · 250-foot Chemical Plarit st::i.cl< to detcrntine the validity of the associat:i,ons

of plume behavior with the temperature gradient configurations ju$t shmm.

Pictures of smo1<e behavior during so1r.e of these experiments are shown on

the slides to follow.

Figure 2 - Looping condition. 0945 ll..ST, April 9, 1952.

Tom1~rnturo 10.poe rato was moro than throo ti.moo the dry

adiabatic ruto (which is o.r;;4°F./100 ft.) in tho lowor

250 :foot.

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Figuro 3 - Coning condi tiono. 1910 MST, l.,,Pril 16, 1952.

Lnpoo rnto in loW'.cr 250 foot wo.s slightly leoo than tho I

dry ndinbutic ro.te.

Figuro 4 - Funning condition. 0722 MST, April 111 1952.

Pronounced tompornturo i~voroion from tho surface to

eomewhero above 500 feet.

Figure 5 - Lofting condition. 1945 MST, April 16, 1952.

Inversion, surface to 200 foot, with lapse nbovo 200 feet.

Figure 6A - Fumigating condition. 0746 MST, April 11, 1952·

Lapse lnyer has worked up just to the 250-;f'oot level. Note

that eddie'.3 in the lnpse layer have begim to penetrnto the

smoke-bearing ~er, as evidenced by streamers extending

downward from the concentrated plume.

Figure 6B - Fur:ligution {continued). 0748 MST. The first

·stream.er reached tho ground about 10 stack lengths from

the stack about two m:tnutes after streamers begnn to decend.

Inversion based about 300 feot.

Figuro 6c - Fumigntion {continued). 0802 Vi.ST. By this

time otrong omoke concentrations appeared on the ground

along almost tho entire visib1e length of the plurr.e. Note

that the concontrutod arn.oke .layer aloft that wo.s vioible

in Figu1·00 l~, 6A t:md. 6B is no longor vioiblo. The entire

plurr.c n;ppeo.ro to have been mixod downward. Inversion

baaod n1Jo'..lt 380 f'oot.

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It Yns mentioned cnr~ior thnt tho typoo of tomporatu1~ gro.diont uounlly

hnvo a diurno.l cyclo. Thia io illuotro.tod by fiE:,'1.U'O 7 which givoa :plota of

tomporo.turo soundingo on o. clonr dn.y. Noto tbnt tho ~igo.ting condition

(for o. 250-:foot stuck) wno prosont nt 0900 MST. By llOO MST the inveroion

hnd disoi:patod, and looping conditions provo.iled until tho inversion begun

to form in tho evening. Lofting conditions wore present at 1830 and 2000

11..ST, and fo..nning conditions, at 0200 through 0700 MST the following morning.

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