73 A STUDY OF TURBULENT FLUX OF AIRBORNE PARTICULATE

O C E A N O L O G Y N o . 1 (1977)
73
CZESŁAW GARBALEWSKI
HENRYKA BEREK
AN NA BRZEZIŃSKA
A NNA TRZOSIŃSKA
DANUTA W IELBIŃSKA
Institute of M eteorology and W ater Economy
M aritime Branch — Gdynia
A STUDY OF TURBULENT FLUX OF AIRBORNE PARTICULATE
MERCURY PASSING FROM THE ATMOSPHERE INTO THE SEA*
C o n t e n t s : 1. Introduction 73, 2. Theory of turbulent flu x of adm ixtures 74,
3. The m ixing height 75, 4. Measuring techniques 77, 5. D iscussion of results 80;
Streszczenie 86; R eferences 86.
1. INTRO D U CTIO N
O nly sparse m a te ria l is to b e found in lite ra tu re so f a r on th e
occurrence m e rc u ry in th e sea a n d th e atm osphere. In p a rtic u la r, th e re
is v e ry little on th e q u estio n of m e rc u ry p re se n t in th e a ir above sea
w a te r areas. This is one of th e aspects concerning th e g en eral b u d g et of
m erc u ry circu latio n b e tw e en th e atm osphere and th e sea. In th is bugdet,
a p a rt fro m th e m e rc u ry in flu x in to this en v iro n m en t b y n a tu ra l geochem ­
ical processes, th e re is a rising sh are of pollution com ponents [10] due to
th e activ ities of M an.
O ne can assum e th a t th e n a tu ra l b ack g ro u n d fo r th e presence of
m e rc u ry in sea w aters, caused by th e rock w e a th erin g processes, is eq u al
to th e m ean Hg con cen tratio n in th e w orld ocean w hich is a t p re se n t
about 0.03 n-g/1 [10], T he data th a t are of p a rtic u la r in te re st to us are
those on th e m e rc u ry c o n cen tratio n s o b tain ed b y F itz g e rald and H u n t
[4] fo r th e n o rth -w e ste rn A tlantic. These concentrations in th e su rface
la y e r of th e ocean in th e Long Islan d nearsh o re zone are 0.032 txg/1 for
•the organic a n d 0.026 n-g/l fo r th e inorganic Hg com pounds. On a n a v e r­
age, m e rc u ry co n cen tratio n s in th e atm ospheric a ir above th e large
in d u stria l centres, such as O saka and Chicago are 2.2 and 4.8 n g /m 3
resp ectiv ely [2, 11], F o r th e a g ric u ltu ra l a re a s th e con cen tratio n s of
m erc u ry in th e air, reco rd ed in th e U SA so fa r a re from 1.4 n g /m 3 in
W illam ette [14] to 1.9 n g /m 3 in th e Chicago a re a [2],
* Prelim inary results of this study w ere presented at the X Scientific Session
of Physical Oceanography of the Polish National SCOR and published in ’’Studia
i M ateriały O ceanologiczne”, No. 14, 1976.
W e did not succeed in finding a n y ex act fig u res on th e d ry fallout
of m e rc u ry passing into th e sea, in lite ra tu re . T he p re se n t s tu d y aim s
at obtaining such d a ta for th e G ulf of G dańsk region, w hich — sim ilar
to th e w hole o f th e B altic — is alm ost u n ex p lo red as y e t in th is respect.
O u r know ledge does not go fa r beyond th e s ta te m e n t th a t th e sh are of
aerosol com ponent in th e process of exchange of m a tte r b e tw e en th e
a tm osphere a n d th e sea is q u ite essential. Its m ag n itu d e is confirm ed,
fo r instance, by th e fact, w e ll know n from lite ra tu re [9], th a t th e am ount
of stro n tiu m 90 passing from th e atm o sp h ere d ire c tly into th e B altic
d u rin g th e p ast fifte e n y ears w as fo und to be fo u r tim e h ig h er th a n th e
sh are of th is radioactive elem en t e n te rin g th e m arin e e n v iro n m en t w ith
th e riv e r discharges. In th e case of m erc u ry of course, th e data can be
expected to be d ifferen t. T h erefo re th e p roblem req u ires special studies.
2. TH EO R Y O F TU RBU LEN T FL U X O F A D M IX TU RES
If we assum e th a t aerosols are sp ra y e d in th e atm o sp h ere u p to height
H and th e self-cleaning process occurs by d ry sed im en tatio n only, th e n
assum ing th e ir hom ogeneous co ncentration, th e fallo u t velocity of p a r ­
ticles can be d eterm in ed from th e expression
v
=
- |-
(l)
w h ere t — is th e p a rticle resid en ce tim e in air. I t is th e eddy diffusion
th a t decides on th e effective fallo u t velocity of th e a irb o rn e p a rtic u la te
m atte r. T he in te n sity of diffusive spreading of th e aerosol p a rticles a n d
of th e a ir self-cleaning process due to th e tra n s fe r of th e atm ospheric
a d m ix tu re s in to th e sea can be in v estig ated th ro u g h th e sem i-em pirical
eq u atio n of eddy diffusion. U pon th is assum ption, th e fo rm u la fo r th e
spreading of passive aerosol p articles in a ir u n d e r n o n -sta tio n a ry condi­
tions, a n d w ith th e ho rizo n tal diffusion com ponent neglected in o u r
considerations, w ill rea d
„
<?qa
dt
_
¿ 2qa
z
~
.
O z2 — A q a
(2)
w here: qa — p a rtic le c o n cen tratio n in th e n e a r-w a te r atm ospheric layer,
K z — v e rtic a l eddy diffusivity, A — self-cleaning co n stan t, z — v e rtica l
distance in th e atm osphere. D ealing w ith th e process in th e n e a r-w a te r
atm ospheric la y e r w e m u ltip ly eq u ation (2) by H, w hich is th e h eig h t of
th e tu rb u le n t m ixing o v er th e sea su rfa c e a n d h a s been defined by D.L.
L aich tm an [12] as
H =
-------/ - ............Cl* G
2 coz V C i ( q / T 0) ( a T / ® z ) (Y a — Y) +
-........
m /4 cl
(3)
w here: ci — dim ensionless coefficient, eq u al to 2.3, x — th e K a rm a n
co n stan t, G — geostrophic w in d velocity, coz — v e rtic a l com ponent of the
E a rth ’s a n g u la r velocity T 0 1— te m p e ra tu re , a T — th e P ra n d tl n u m b er,
Ya an d y — th e d ry ad iabatic a n d m ean a c tu a l v e rtica l te m p e ra tu re
g rad ien t, m — constant defined by th e en erg y dissipation ra te . The
expression th u s o b tained w ill describe th e v e rtic a l flu x of airb o rn e p a rti­
c u late m a tte r, in w hich th e m ixing heig h t is th e p a ra m e te r d efin in g th e
d evelopm ent scale of th e tu rb u le n t exchange process. H ence, th e ra te
of tra n s fe r of p a rtic u la te m a tte r tow ard s th e sea surface a t th e height
a t w hich m easu rem en ts w ere tak e n , equal to about 10 m a.s.l., can be
given by
F 10 = H ( A q a _ K z
(4)
In o rd er to c a rry out these calculations we had to assum e th a t th e
aerosol co n cen tratio n s w ere hom ogeneous in th e h orizontal p lan e a n d
th a t th e v e rtica l d istrib u tio n of qa w as linear. T he m ag n itu d e of th e
self-cleaning constant, A = — , w as obtainable fro m the investigations
on th e a irb o rn e sa lt nuclei in th e n e a r-w a te r atm ospheric la y e r over th e
Baltic. Such investigations w ere carrie d o u t by one of th e a u th o rs [5]
of th e p rese n t rep o rt. T he self-cleaning constant obtained th e re fro m for
th e B altic a re a is A = 1. 12 X 10-5s_1. T his v alu e w as d e te rm in e d b y tw o
d iffe re n t m ethods, 1. an an aly sis of th e tra n sisto ry flu ctu atio n s of
— tim e dep en d en t changes in salt nuclei concentrations in th e n e a r­
w a te r atm osphere, a n d 2. b y exam ining th e p article size d istrib u tio n of
th e a irb o rn e p a rtic u la te m a tte r The above value fo r A w as o b tain ed
for th e w e stern a ir circu latio n conditions o v er th e B altic. I t is som ew hat
less u n d e r th e local circu latio n in th e in v estig ated w a te r area (A =
— 0.91 X 10—5s—1). Since in th e a re a of m easu rem en ts the w e stern circu la­
tion dom inates, it ap p ears reasonable to use th e fo rm er value, A =
= 1.12 X 10_5s—1 instead.
3. TH E M IX IN G H EIG H T
It is only in ra re cases th a t direct m ea su rem e n t resu lts of m ixing
h eight in th e a tm o sp h ere a re obtainable. S till, th e re is a n u m b er of
m ethods to d eterm in e th e m ixing heig h t in d irectly , e ith e r by th e o ry
[13] o r basing on th e p ractice used in ap p lied m eteorology including
synoptic p ractice [7]. T he ran g e of ap p licab ility for each of th e in d irect
m ethods w ill d epend on a larg e e x te n t on th e atm ospheric a n d m o rpho­
logical conditions fo r w hich th is heig h t is determ ined.
In o rd e r to assess th e v alu e of m ixing h e ig h t H in th e p re se n t study,
tw o m ethods w ere p rim a rily used. W henever Yiooo — th e m ean v e rtica l
te m p e ra tu re g rad ie n t up to 100 m above th e g round d id n o t exceed Ywa —
th e w e t-ad iab atic g rad ie n t v alu e — or did so to an insignificant e x te n t
only, w ith high w ind velocities occurring a t th e sam e tim e, we g en erally
used th e m ethods basing on form u lae of g en eral a p p licab ility in dynam ic
m eteorology [6, 12].
In th e cases of h ig h er g rad ien ts, ap p ro x im atin g th e d ry ad iabatic or
su p er — ad iabatic ones, th e m ix in g h e ig h t w as d e te rm in e d fro m aerological
diagram s [7]. C ertain m odifications w ere also in tro d u ced for th e condi­
tions not covered b y th e m ethods th a t w ere used b y various a u th o rs
[7, 12]. This refers, in p a rtic u la r, to th e cases w hen th e re w as a fro n t
w ith a low cloud la y e r or a continuous p rec ip ita tio n zone in th e sam pling
area. T he c h a ra c te r of th e sam pling area w as also considered being ge­
n e ra lly a coastal lan d or sea region, i.e. v e ry m uch d istu rb ed w ith resp ect
to th e unhom ogeneity of th e ir surface conditions.
T he follow ing m eteorological d a ta w e re d e te rm in e d an d used as
p a ra m ete rs fo r assessm ent of H in ty p ical cases:
— v e rtic a l sta b ility of a ir m ass, d e te rm in e d from th e aerological dia­
g ram s of the radio-sounding coastal sta tio n in Ł eba (taken a t 00.00
a n d 12.00 h o u rs GMT),
— th e d irection of a ir m ass advection, fro m th e synoptic charts,
— w a te r te m p e ra tu re a t sea surface, from shipborne m ea su rem e n ts or
m easured a t th e W ładysław ow o coastal station,
— m axim al a ir te m p e ra tu re o v er land,
— m inim al a ir te m p e ra tu re over land,
— th e geostrophic w ind velocity, G, according to th e synoptic charts,
av erag ed from th re e h o u rs of observation fo r th e ’’cool” p a rt of th e d ay
(00.00, 03.00 and 06.00 h o u rs GMT) a n d fro m fo u r h o u rs of o b servation
fo r th e ’’w a rm ” one (09.00, 12.00, 15.00 and 18.00 h o u rs GMT),
— v alu e of u — w in d v elo city ta k e n fro m th e radio-sounding data, from
Łeba, averaged fo r 0, 100, 300, 500 an d 1000 m above th e ground,
— h e ig h t of th e cloud la y e r an d th e c h a ra c te r of p rec ip ita tio n , if any,
— inversion h e ig h t w in d speed and direction.
It was c o m p arativ ely cool a n d w indy a t th e tim e th e investigations
w ere c a rrie d out. T he th erm o d y n am ic eq u ilib riu m w as fa irly h ig h ly
d iffe re n tia te d , a n d th e m ixing h e ig h t w as v e ry unstable. T he values
o b tain ed for H reach fro m a few m etres in th e cases of negative v e rtic a l
te m p e ra tu re g rad ie n ts in th e low est a ir lay ers a t low w ind velocities,
u p to a b o u t 2000 m, in cases of u n stab le conditions. F o r c e rta in sum m er
seasons hav ing a d istin ct d iu rn a l te m p e ra tu re course, th e d iu rn a l course
of H h ad inversion of e x tre m e H values above th e sea regions as com pared
w ith th e lan d areas. T he re su lts of th e analysis as ap p lied to H a n d Fio
calculations a re listed in T able 1.
4. M EASURIN G TEC H N IQ U ES
M arine aerosol and surface w a te r sam ples w e re ta k e n in th e G ulf of
G dańsk (Fig. 1) d u rin g th e e x p lo ra to ry cruises of th e research vessel
’’H y d ro m et”. A ir w as filte re d b y m eans of a w a te r filte r (air w asher).
E q uipm ent of th a t ty p e w as exposed in conjunction w ith a one-stage
Fig. 1. Hg m easurem ent stations in the G ulf of Gdańsk area
Rye. 1. Rozm ieszczenie stacji pomiarów rtęci na Zatoce Gdańskiej
cascade im p acto r to check th e effectiveness of c a p tu rin g th e a irb o rn e
p a rtic u la te m a tte r b y th e a ir w asher. A schem e of th e eq u ip m en t is
found in Fig. 2. A ir d ra w n b y a pum p e n te re d th e w a sh e r th ro u g h a glass
pipe placed 1— 2 cm above th e w a te r surface. Im m ersion of th e pipe end
in w a te r w as avoided to p re v e n t th e blow out effect of collected su b sta n ­
ces th a t m ight be passing fro m th e w a te r d u rin g th e b u rstin g of a ir b u b ­
bles a t th e w a te r surface.
T he p o rtio n of th e p a rtic u la te m a tte r th a t w as not c a p tu re d by w a te r
was collected on th e su rface of a glass p late in th e im pactor. To achieve
this, th e glass p la te w as tre a te d w ith a vaseline in p e tro leu m solution.
A fte r exposure of th e p la te a P u lfric h p h o to m e te r w as used a n d th e
unst.
h altitude of cloud
445
515
482
m
Hsea,
570
402
697
m
W
W,N,SE
unst.
10.5
H [and,
flow
H — adopted for the sam pling
area, m
direction
of air
300—800
14.1
G, m/s
base, m
10.9
12.9
245
282
227
SW—SE
9.4
0.27 to 0.85
u , m/s
0.40 to 0.85
0.44 to 0.95
0.27 to 0.78
rsea, c®/100 m
''land,
0.50 to 0.94
October
0.04 to 1.05
August
C°/100 rn
May
("klif of Gdańsk
392
393
351
NE
100—500
17.7
13.0
0.15 to 0.85
326
447
278
SW
300—700
11.5
10.8
0.68 to 0.90
0.40 to 0.63
October
Coastal Station
— 0.17 to 0.80
May
Gdynia
warstwy mieszania i wykorzystane do jej oszacowania
charakterystyki m eteorologiczne
dla rejonu Zatoki Gdańskiej w okresie przeprowadzonych badań w 1974 r.
Meteorological
Characteristics
Wysokość
Height of particle exchange layer and meteorological characteristics used for its assessm ent
in the Gulf of Gdańsk area, during the explorations carried out in 1974
Table
Tabela
1
1
fra c tio n collected on th e glass p late w as m easu red
by em ploying th e lig h t dispersion principle. To check
th e p a rticle c a p tu re effectiveness of th e a ir w asher,
glass p late s w e re exposed a fte rw a rd s w ith o u t th e use
of a n y w a te r filte r. T he effectiveness of c a p tu rin g
aerosol p article s in th e filte r w as slig h tly above 90
p e r cen t on th e average. The eq u ip m en t w as d e­
signed to sam ple a irb o rn p a rtic u la te m a tte r fro m
p ra c tic a lly u n lim ite d a ir volum es p e r sam ple. A n a ir
w a sh e r w as fille d w ith u p to 20 m l b id istilled w a te r
an d sam pling w as conducted u n d e r s tric t control of
th e w a te r level d u rin g th e exposition. T he a ir w asher
w as m ade of glass. E ven so, th e intense w a te r m ove­
m en t d u rin g exposure of th e equipm ent, th e sm all
surface of th e vessel an d th e re la tiv e ly sh o rt sam p­
ling tim e resu lte d in Hg losses, due to th e ab so rp tio n
Fig. 2. Schem e of
p o ssibility of th is elem en t on th e w ash er w alls, if
aerosol sam pling
any, being p rac tic a lly im perceptible. Im m ed iately af­
equipm ent
te r exposure w a te r ta k e n w ith th e sam ple w as
Rye. 2. Schem at
p o u red in to a p o ly eth y len e can w ith c o n c en tra te d
urządzenia zastoso­
n itric acid an d stored deep frozen in a re frig e ra to r.
wanego do pobiera­
T he sam ple w as th u s secu red against H g losses d u ­
nia próbek aerozolu
z powietrza atmo»
rin g storage.
sferycznego
A ir filte rin g took place on th e h ighest deck of
th e vessel, 6 m h ig h a.s.l. C are w as tak e n th a t th e
filtra tio n took place fa r fro m th e e x h a u st pipes on th e ship, w ith fre sh
a ir passing from th e outside. T he effect of th e vessel on th e p o llution
level of a ir a t th e filtra tio n site w as a c tu a lly negligible, as can be in fe rre d
from th e open sea m easu rem en ts. In th e open B altic th e m e rc u ry con­
c en tratio n s in a ir w ere fre q u e n tly fo u n d to equal o r a p p ro x im ate zero.
P a ra lle l w ith th e m ea su rem e n ts in th e open G ulf area, analogical filtra tio n
w as c a rrie d o u t in G dynia, a t th e p o in t on th e G ulf coast, w h e re the
described equ ip m en t w as exposed 12 m above sea level. T he sam pling,
storage procedure, a n d th e c a p tu re co n tro l weref th e sam e as a t sea.
W a te r sam ples fro m th e sea su rfa c e w a te r la y e r w e re collected by
m eans of p lastic b ottles. I t w as possible to sam ple w a te r fro m a la y e r
p rac tic a lly 0.5 m b e n e a th th e sea surface. F ro m th e v e ry m om ent of
sam pling, w a te r sam ples in poly eth y len e cans w e re sto re d in a re frig e r­
ato r dow n to — 20°C. M oreover, to avoid losses d u rin g storage sam ples
w ere tre a te d w ith a co n c en tra te d n itric acid, 10 m l p e r litre of sam pled
w ater.
M ercu ry co ncentrations in th e sam ples collected fro m th e atm osphere
and th e sea w a te r w ere m ea su red by m eans of th e B eckm an (m odel 448)
atom ic ab so rp tio n sp ectro p h o to m eter. Sam ples w ere cold-m ineralized w ith
p otassium p e rm a n g an a te a n d potassium p e rsu lp h a te . A flam eless tec h ­
niq u e w as used in th e m ea su rem e n ts a n d reco rd s w e re m ade a t th e 253.4
nm w avelength. T he d etectio n lim it of about 4 n g w as ad eq u ate to m ea­
su re Hg c o n cen tratio n s h ig h er th a n 0.1 n-g/l w ith a precision of 5 p e r cent.
The coefficient of v a ria tio n s in creased up to 50 p er cen t a t low concen­
tra tio n s a p p ro x im atin g th e detection lim it.
5. D ISC U SSIO N OF RESU LTS
T he applied m ethod enabled us to exam ine th e flu x of airb o rn e m e r­
c u ry passing into th e sea w ith o th er p a rtic u la te m a tte r suspended in air.
The m e rc u ry fra c tio n p re se n t in th e atm osphere (p re d o m in a n tly th e ga­
seous fo rm in m eth y l or d im e th y l m ercury), th eo re tic ally w ould dissolve
in w a te r u n til th e dinam ic e q u ilib riu m w as achieved. O u r m ea su rem e n ts
have proved th a t, on th e average, the am o u n t of organic m e rc u ry com ­
pounds p re se n t in aerosols an d atm ospheric precip itatio n s reaches 45 to
95 p e r c e n t of th e ir to ta l m e rc u ry content, pro b ab ly depending on th e
degree of in d u stria l pollution of th e atm osphere. I t is th u s concluded th a t
some organic m e rc u ry com pounds are n o t gaseous. P a r t of th em a re ap p a ­
r e n tly lin k ed w ith th e aerosols. I t m u st not be ex cluded th a t th e aerosol
p articles can a c t as effective H g sorbents, am ong these p a rtic u la rly the
carbon p articles.
T he to ta l m e rc u ry con cen tratio n s p er u n it volum e m easured in the
n e a r-w a te r atm ospheric la y e r in th e G ulf of G dańsk a re listed in T able
2. These values a re com pared against th e m ag n itu d e of Hg flu x directed
fro m th e a ir tow ard s th e G ulf surface, as calcu lated on th e ir basis. The
values of Fio and qa v a rie d d u ring th e m ea su rem e n t p eriod w ith in one
o rd er of m agnitude, a n d so did qw — th e m e rc u ry co n c en tra tio n in th e
G ulf of G dańsk surface w a te r la y e r (Table 2). T he m e rc u ry co ncentra­
tio n in sea w a te r is a p p ro x im ate ly one m illion tim es h ig h er th a n in th e
atm osphere.
T able 3 lists se p ara te ly th e m ean qw v alues fo r th e G ulf of G dańsk
coastal zone in th e T hree Tow ns C om plex (G dańsk— Sopot— G dynia)
(Fig. 1, S ta tio n s Nos. 1. ZN2, ZN3, N P , GD). T he average m erc u ry
concentrations a t these statio n s d u rin g th e m easu rem en t p eriod w ere
one an d a h a lf tim es h ig h er th a n those rec o rd e d fo r th e rem ote statio n s
in th e G ulf area. Such a d ifference in m e rc u ry concentrations is even
Table 2
Tabela 2
Total m ercury concentration and vertical flu x of m ercury over the G ulf of Gdańsk
C ałkowite stężenie i pionow y strum ień rtęci nad Zatoką Gdańską
Sam pling tim e
1974
A ir volum e
m*
Gulf
Gdynia
of
Gdańsk
318.7
68.0
6.4
August
38.7
2.9
October
6.1
59.7
8.0
May
Measured Hg
Concentration
in air, ng/m 3
Wind velocity,
m/s
D ata on aerosol sam pling
(water filter)
Open
G ulf
7.5
4.8
C alculated
F lu x F 10
ng/m 2 hour
Open
Gdynia
nearshore Gulf
area
0.25 ± 0.02
2.13 ± 0.18
<5.4
1.03 ± 0.09
18.5
1.09 ± 0.29
2.21 ± 0.18
10.8
Gdynia
nearshore
area
31.9
29.0
Table 3
Tabela 3
Total m ercury concentration in the surface w ater layer of the G ulf of Gdańsk and
the sedim entation of particulate m atter in air and the sea w ater
C ałkowite stężenie rtęci w powierzchniowej w arstw ie Zatoki Gdańskiej
i prędkość sedym entacji cząstek w powietrzu i w odzie
Hg Concentrations,
£«g/l
Data on Sea
W ater sam pling
Open
Sam pling tim e No. of
G ulf
1974
sam ples
May
A ugust
October
3
2
3
4
4
4
N earshore
(Three Towns
Complex) area
1.37 ± 0.04
1.01 ± 0.04
0.67 ± 0.04
Calculated Hg
sedim entation velocity, cm/s
In air
In w ater
0.65
0.42
0.50
0.01.10-5
0.09.10-5
0.08.10-5
0.27
0.37
0.06.10-5
0.68.10-5
1.81 ± 0.05
0.05 ± 0.04
0.12 ± 0.04
m ore clear fro m T able 2 fo r th e airb o rn e m erc u ry com pounds. The v a ­
lues fo r G dynia in th is respect are th re e tim es h ig h er th a n th e respective
d a ta obtained fo r th e open G ulf area. These d a ta m ig h t also be
indicative of th e source of p o llution and of th e d irectio n in w hich it is
sp reading fro m lan d to w a rd s th e sea. N othing defin ite how ever, can be
asse rte d on th e sh are of airb o rn e m erc u ry in its circu latio n b u d g e t in
6 — O c e a n o lo g ia n r 7
th e w a te r area itself. O ne w o u ld have to com pare these d a ta w ith the
ra te of th e m e rc u ry passing w ith riv e r inflow in to th e G ulf w a te rs
w hile th is am o u n t still rem ain s unknow n.
T he m e rc u ry flu x into th e G ulf of G dańsk w aters w ith th e airb o rn e
p a rtic u la te m a tte r d u rin g th e m ea su rem e n t period w as w ith in 5.4— 31.9
n g /m 2 p e r hour. A ll th e sam e, even w hen assessing m u ch h ig h er m e r­
c u ry concentrations in th e n e a rsh o re atm osphere, one should n o t ru sh
to th e conclusion th a t a ir is th e m ain source of w a te r pollu tio n in the
G ulf of G dańsk. As m ay be in fe rre d fro m previous investigations
[1], th e em ission of w a te r d ro p lets in to th e a ir fro m th e ocean surface
is of th e o rd e r of 100 d ro p lets/cm 2, s. H ence, th e m erc u ry em ission from
w a te r into th e atm o sp h ere w ith th e m arin e aerosols can be quite su b ­
sta n tia l. On th e o th e r hand, th e m e rc u ry m eth y l (or d im ethyl) vo lati­
lization can have q u ite a d iffe re n t m echanism . T he process of p article
em ission into th e atm o sp h ere in g en eral is p a rtic u la rly intense in th e
su rf zone, as explained, fo r instance, on th e exam ple of DDT spreading
in th e B altic [13]. This fact is due to th e p ecu liar dynam ics of th e sea
in its nearsh o re zone, adding to th e em ission of droplets passing into th e
air. The m echanism of th is em ission should be effective, above all, for
th e com ponents collecting in th e surface film of sea w ater. T he concen­
tra tio n d istrib u tio n of m icroelem ents in th e sea surface lay er, and
especially in its film , has not y e t been su fficien tly explored; one m ight
expect th a t h ig h er con cen tratio n s w ill be found in th a t v e ry film .
I t w ill be seen fro m th e d a ta listed in T able 3 th a t Va — tra n s fe r
velocity of airb o rn e p a rtic u la te m a tte r to w ard s th e G ulf w a te rs — r a n ­
ged d u rin g th e m ea su rem e n t p eriod b e tw e en 0.3 an d 0.7 cm /s on a v e r­
age. This is a velocity com parable w ith th e sed im en tan tio n velocity of,
say, sm oke p a rticle s in w indless air, w ith in th e rad iu s of th e o rd e r of
10-4 cm [3], i.e. fo r th e g ian t p a rtic le sizes, to w hich th e airb o rn e sea
sa lt nuclei fractions, ex am ined in th e stu d y [5], also belong. S till, in o u r
case th e velocities o b tain ed do not re fe r to th e sed im en tatio n in calm
w e a th er, b u t ra th e r to th e p a rticle tra n s fe r u n d e r th e eddy diffusion
conditions. T herefore its m ag n itu d e depends on th e m ixing h e ig h t and
on th e self-cleaning co n stan t A, d e te rm in e d p rev io u sly [5] fo r th e
tu rb u le n t conditions over th e B altic sea. H ence, th e v alues obtained m ay
not be re fe rre d to th e g ian t p articles only. T he a ir-to -w a te r tra n s fe r
velocities obtained, fo r instance, fo r C 0 2 a t th e average w ind speeds of
ab o u t 5— 7 m /s w ere of th e o rd er of (0.1-^0.3) • 10-2 cm /s [8] and w ith
th e w ind velocity increase th e v alu e fo r th e C 0 2 exchange qu ick ly rose
These are values b y a p p ro x im ate ly tw o o rd ers of m ag n itu d e low er th a n
th e ones obtained by us - being w h a t could be expected. A ll th e sam e, if
we consider th e tu rb u le n c e conditions d u rin g th e m ea su rem e n t period,
by com paring th e above v alues we can also su b sta n tia te our conclusions
as to th e sh a re of subm icron p articles in th e aerosol sam ples tested.
T he e x tre m e Fio values for a irb o rn e m e rc u ry w ere obtained b y open
a ir exposure of po ly v in y l tra y s of 800 cm 2 collection area, filled w ith
b id istilled w a te r. T he exposure w as accom plished d u rin g th e rese a rc h
vessel cruises in th e G ulf of G dańsk and also a t th e coastal sta tio n in
G dynia. To assess th e possible losses of H g due to th e ad so rp tio n on th e
tra y w alls p a ra lle l ex posure of p olyvinyl tra y s and p o ly th y len e cans
w as effectu ated .
D ifferences in th e losses how ever, escaped any evaluation. A n a n a ­
lysis of d ry sedim ent has p roved th a t Fio m ay v a ry w ith in a w ide ran g e
of m agnitudes (Fig. 3) also covering th e scope of calculated values. The
considerable deviations of m ea su red values, fo u n d to be in excess of th e
m ean ones, can u n d o u b ted ly be a ttrib u te d to th e m axim um of to ta l
m e rc u ry co n cen tratio n s in a ir in F e b ru a ry , coinciding w ith th e m eas­
u re m e n t period. A p a rt fro m these, i t should be stre sse d th a t e x p e r­
im e n ta l m ethods of d ry sed im en t testin g a re n o t devoid of difficulties,
and u n d e r such circu m stan ces e rro rs occur.
G enerally, an eq u ilib riu m b etw een th e diffusive Hg tra n s fe r fro m th e
atm o sp h ere into sea a n d th e diffusive H g sed im en tatio n should ex ist
in w a te r. O therw ise, w e could only speak of th e ten d en cy of continuous
rise or drop in th e m e rc u ry con cen tratio n s in th e sea surface lay er, as
caused b y d iffe re n t velocities of m ere v ertica l tra n sfe r. If w e th ere fo re
assum e th a t such an e q u ilib riu m does exist, w e conclude th a t
Fio — F w
i.e. th a t th e v e rtic a l tu rb u le n t flu x of m e rc u ry tra n s fe rre d into w a te r
fro m th e atm o sp h ere is eq u al in its m ag n itu d e to th e Hg flu x d ire c te d
tow ard s th e b ottom of th e sea. H ence on th e basis of th e values obtained
fo r q a, qw an d V a, w e can also calculate Vw, b ein g th e diffusive se d im e n ­
ta tio n velocity of p a rticles in th e sea w a te r surface lay er. T his v a lu e as
show n in T able 3 is on av erag e fiv e to six o rd ers of m ag n itu d e low er
th a n V a, i.e. too low in d eed to correspond to th e velocities of Hg sp re a d ­
ing in th e sea, as m ig h t be ex p ected upon consideration of th e in ten se
tu rb u le n t diffusion tak in g place in th e n e a r-su rfa ce w a te r lay er. T his
conclusion coincides r a th e r w ell w ith th e fa c t th a t th e a tm o sp h ere can­
not be th e only source of m e rc u ry p o llution in th e G ulf of G dańsk basin.
A t any ra te , th e re is no doubt about th e actu al occurrence of sudden
change in th e v e rtica l tra n s fe r velocity a t th e a ir-sea in terface. If th is is
so, we a rriv e a t th e effect of in e rtia in th e process of H g tra n s fe r th ro u g h
th e a ir-se a in terface, and th is in tu rn should considerably obscure
th e d ifference b etw een th e H g c o n ten t flu c tu atio n s in th e a ir and
Fig. 3. V ariations in total m ercury cencentration in air, from the m easurem ents
in Gdynia (solid line, dashed during the period of longer breaks in m easure­
m ents) and above the G ulf of Gdańsk (points w ith a dash, its length corresponding
to the num ber of observation days) and F10 valu es (dashes for Gdynia dotted lines
for the Gulf of Gdańsk area; their length corresponding to the number of obser­
vation days; dashes w ith zeros at their ends refer to the calculated F 10 values)
Rye. 3. Przebieg czasow y w ahań qa — stężenia całkow itej rtęci w powietrzu
w edług pom iarów w Gdyni (linia ciągła, w okresie z dłuższą przerwą w pomia­
rach — przerywana) oraz na Zatoce Gdańskiej (punkty z poziomą kreską o długości
odpowiadającej liczbie dni obserwacji) a także w ielkość F 10 (kreski ciągłe dla
Gdyni, kropkowane — dla Zatoki Gdańskiej; długość kresek odpowiada liczbie dni
obserwacji, zera na końcach odnoszą się do obliczonych w artości F10)
w a te r respectively. T he question of th is rela tio n sh ip is com plicated and
w ill need fu rth e r clarification. W hen in v estig atin g th e problem , one
should re ly on th e m ea su rem e n ts to be ta k e n in th e surface film of th e
sea. S u c h m easu rem en ts a c tu a lly w ere carrie d out.
F ilm w a te r sam ples w ere tak e n to check w h e th e r th e surface film
favours Hg accum ulation. The m ethod consisted in v e rtic a lly im m ersing
a glass p la te in to th e w a te r su rface layer; th e te st p la te w as 30 b y 40 cm,
4 m m thick. W hen ta k e n out of w a te r, th e film sam ple p re se n t on th e
glass w as scrap ed off w ith a p o ly eth y len e knife. Sam ples w ere collected
in to a p o ly eth y len e storage can, and th e m ethod to p re v e n t H g losses
w as in g en eral as described above. T he surface film sam ples th u s col­
lected d u rin g th e e x p lo ra tio n cruises in F e b ru a ry 1975 enabled us to
d eterm in e th e to ta l m e rc u ry c o n ten t p re se n t th ere; th is w as 258 n-g/1 in
th e G ulf of G dańsk. T he analysis show ed th a t th e re w ere one h u n d re d
p e r cen t in organic m e rc u ry com pounds. By c o n tra stin g th is value against
th e d a ta in T able 3 w e conclude th a t th e Hg c o n cen tratio n in th e surface
film is m uch h ig h er — b y tw o or th re e o rd ers of m ag nitude on average
— th a n in th e su rfa c e w a te r lay er. S till, th e c o n trib u tio n of th e tu rb u le n t
flu x of airb o rn e p a rtic u la te m a tte r to th e m echanism of m erc u ry accu m u ­
latio n in th e sea su rface film is f a r fro m being elu cid ated and f u rth e r
in v estig atio n s are necessary to ex p lain its significance.
ACKNOWLEDGEMENT
T his rese a rc h w as su p p o rte d b y th e U.S. E n v iro n m en tal P ro tectio n
A gency, p ro je c t No. P R 05.532-13.
86
O C E A N O L O G IA N r 7 (1977)
CZESŁAW GARBALEWSKI
HENRYKA BEREK
A N NA BRZEZIŃSKA
ANNA TRZOSIŃSKA
DANUTA W IELBIŃSKA
Instytut M eteorologii i Gospodarki Wodnej
Oddział Morski — Gdynia
BA D A NIA WIELKOŚCI TURBULENCYJNEGO STRUM IENIA RTĘCI
AEROZOLOWEJ PRZENOSZONEJ Z ATMOSFERY DO MORZA
Streszczenie
Turbulencyjny strum ień rtęci przenoszonej z cząstkam i aerozolu do morza ba­
dano na przykładzie Zatoki Gdańskiej. W tym celu zorganizowano pomiary stęże­
nia rtęci w powietrzu przywodnym , na zatoce i na stacjach brzegowych. K orzy­
stając z m ateriałów aerologicznych i synoptycznych, jednocześnie badano w arun­
ki m ieszania turbulencyjnego w rejonie pomiarów. W ielkość strum ienia obliczano
na podstaw ie oszacowanej w ysokości w arstw y m ieszania i w artości stałej sam o­
oczyszczania, określonej z badań nad jądram i kondensacji na Bałtyku. Obliczone
w artości porównuje się ze zm ierzonym i stężeniam i rtęci w powietrzu i pow ierzch­
niow ej w arstw ie morza oraz z eksperym entalnym i danym i sedym entacji rtęci aero­
zolowej w badanym rejonie. Pom iarów dokonano m etodą bezpłom ieniowej absorpcji
atom owej, techniką zim nych par.
W pracy stw ierdza się, że w ielkość turbulencyjnego przenoszenia rtęci z atm o­
sfery do morza w ahała się w okresie m aj—październik 1974 roku w granicach
jednego rzędu w ielkości. Podobnej w ielkości fluktuacje obserwow ano rów nież w
zakresie stężeń rtęci w powietrzu i w powierzchniowej w arstw ie morza.
Dochodzi się do w niosku, że już tylko w ystępujący na powierzchni rozdziału
atm osfery i morza duży skok efektyw nej prędkości dyfuzyjnego w ypadania rtęci
w w odzie i powietrzu w znacznej m ierze pow inien powodować w ystępow anie m ak­
sym alnych stężeń rtęci w błonie powierzchniowej morza. M aksym alne stężenia zo­
stały potw ierdzone drogą specjalnych pomiarów.
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