GEOPHYSICAL
RESEARCH
LETTERS,
VOL.23,NO. 8, PAGES841-844,
APRIL15,1996
This file was created by scanning the printed publication.
Errors identified by the software have been corrected;
however, some errors may remain.
Measurementsof upward turbulent ozonefluxes
above a subalpinespruce-fir forest
Karl Z½ller and Ted Hchn
USDA/For½stService,Fort Collins, Colorado
Abstract. High ruralconcentrations
of ozone(03) arethoughtto
be eitherstratospheric
in origin, advectedfrom upwindurban
sources,or photochemicallygeneratedlocally as a result of
naturaltrace gas emissions.Ozone is known to be transpoaed
veaicallydownwardfrom the above-canopy
atmospheric
surface
layer and destroyedwithin stomataor on otherbiologicaland
mineral surfaces.However, here we repoa winter-time eddy
correlationmeasurements
of veaical 03 flux abovea subalpine
canopyof Picea engelmanniiandAbieslasiocarpain the Snowy
RangeMountainsof Wyomingthat indicateanomalousupward
height,400 m southwest
of ourBrooklynLaketowersiteduring
1993 were within 1 ppb [Wooldridgeet al., 1994].
Thesepositive03 flux measurements
are unusualand deserve
a critical examination.Here we describethe experimentand
presentthe resultsof measured03 fluxes, concentrations,
and
summarized
meteorological
datacollectedduringfive periodsin
1992. Theseperiodscontrastthe 03 flux differencebetween
winter (snowcover)and summer(no snowcover)and capture
the springandautumn03 flux directionaltransitions.
03fluxes.
Upward
fluxes
of 0.5•tgm'2s'l (11kgkrn
'2day
'l)
Methods
were routinely measuredduring the 1991-92 winter season.
Decreasing
03 concentration
from severalhoursto severaldays Site
that relateto increasingpositive03 flux magnitudesand visa
Data were collectedat the Brooklyn Lake tower site situated
versa,suggest
03 maybetemporarily
storedin thesnowbase.
in an EngelmannSpruce - SubalpineFir forest opening
approximately30 meters in diameter.The site is within the
U.S.D.A. ForestService'sGlacierLakesEcosystemExperiment
Introduction
Site (GLEES) area in the SnowyRange of the Medicine Bow
Forestecosystems
play a role in the uptakeanddestruction
of National Forest,Wy. The GLEES complexis describedby
tropospheric
03. This role and the tropospheric
03 budgetin Musselman [1994]. The 29 m Brooklyn Lake tower (base
remoteforestedecosystems
is unceaain[Chameid½s
and Lodge, elevation3,186 m, 41ø22'N, 106ø 14.5'W) is approximately
1992]. Ozone deposition,rapid duringthe growingseasonand 3 km southeastof the Snowy Rangeridge (3,460 m average
slowerduringwinter months[Wesely,1983], is retardedfurther elevation). The average forest stand height is 17 m with
by surfacesnowco•,er[Stockeret al., 1995]. Our datashowthe representative
displacementheight, d, 11.7 m and roughness
unexpected
effectof snowcoveron 03 fluxesabovea subalpine length,zo, 1.7 m. The terrainwithin I km of the tower slopes
spruce-firforest.In the presenceof below-canopy
surfacesnow +2.5% from west to east and -9.7% from noah to south. This site
they reversedirectionfrom negative(downward)to positive is relatively complex for eddy flux experiments,however
(upward)[Zeller and Hehn, 1994]. Positive03 fluxesattributed concurrent measurements of momentum and sensible heat fluxes
to veaical
entrainment
of
clean
air
from
aloft
have
provided
reasonable
values.
Fitzjarrald
andMoore[1992]found
been
measuredby aircraft[Lenschowet al., 1982] andmodeled[Gao
scalar flux measurements
in non-homogeneous
regionswere
and Wesly,1994]in the upperatmospheric
boundary
layer. robustandrepresentative
of theupwindfootprint.Upwindterrain
Measurementsof negativeveaical 03 profiles above forested in the predominantwind direction,west-noahwest,is forested
canopies
haveleadto 'counter-gradient'
03 flux claimsassuming with a flat +2.2% slopefor at leastI km.
03 only depositstowardsthe Eaah's surface[Fontanet al.,
1992; Enders, 1992; Denmeadand Bradley, 1985]. Galbally and
Allison [1972] repoaedwinteaimeupwardozonefluxes(1.6 gg
Flux Measurements
Ozoneconcentration
andflux datapresented
were collectedin
m'2 S'l) overfreshsnowbasedon gradient
measurements
at
1992 during five distinctperiods:April 16-26 with 1 m snow
1807m in SE Australia.
the subalpine
winterenvironment;
April 28 SnowyRangehourly03 concentrations
average
45 to 60 ppb coverrepresenting
year round [Wooldridgeet al., 1994], and are typical of clean May 4, beginningtransitionperiodwith rapid snowmelt; May
highaltituderuralsites[Wunderliand Gehrig,1990].The above-' 7-18, the transitionperiodduringthe final daysof springsnow
30 canopydiumal.O3 concentration
at thislocationdoesnot exhibit melt;July2-8, a subalpinesummerscenario;andSeptember
October
7,
during
the
autumn
to
winter
transition.
the largeday/nightmaximum/minimum
patterntypicalof urban,
The eddy correlationsystem[Zeller et al., 1989] used to
photochemically
dominated
air masses
at any time duringthe
year [Woo!dridgeet al., 1994]. However,below-canopy,
3 m, measure03, sensibleheat, and momentumfluxes, 03
temperature
and wind speedwas employedat
summertime03 concentrations
have a predominantday/night concentrations,
23 m (6 m above canopy) on the Brooklyn tower. Standard
pattern:minimum values can drop to 10 ppb at night. Ozone
sensorg
arepermanently
mountedat 10 and29 m
concentrations
appear to be horizontallyuniform in the meteorological
for
routine
GLEES
meagurements
[Musselman,
1994].The
surrounding
area:simultaneously
daytime03 concentrations
near
are the uvw Gill
Centennial,.WY, 8 km southeast,during 1990 were within essentialsensorsfor 03 flux measurements
1-2 ppbof thosewe measuredat 3 m heightandvaluesmeasured
at a U.S. EPA NationalDry Deposition
Site (NDDN) 10 m
Thispaperisnotsubject
to U.S.copyright.
Published
in1996bytheAmerican
Geophysical
Union.
anemometer and the chemiluminesence ambient air monitor
(CAAM1) [Ray et al., !986]. The CAAMI was continuously
calibrated using a TECO49 commercialUV adsorption
instrument.Ambientair was sampledfrom the 23 m height
througha 25 m length,1.6 cm diameterteflontube.The intake
systemlag time,h, wastypically2.4 s. A Gill uvw anemometer
wasusedin placeof a sonicanemometer
for itsgreaterdurability
in harsh alpine weather. The 13 Hz 03 eddy deviations,
Papernumber96GL00786
c' = c - •'
841
(•"
3 minute recursivefilter average
concentra•tion)
andturbulent
windcomponents
u', v' andw', are without those correctionsas they would typically increasethe
multipliedthen averaged
over half-hoursamplingperiods magnitudeof the upward03 fluxes slightlymore than the
Orderof magnitud
e and flux direction
are not
[McMillen,
1986]
to obtain
thevertical
flux,Fc (•tgm-2s-1, downward.
and makethe reported
equation 1) after a vector coordinaterotation tbr affectedby the lackof thesecorrections
upwardflux valuesconservative.
Neutral stability micrometeorological
statisticsfor wind,
Fc = w'(t- tl)C'(t)
(1) temperature
and 03 are fairly consistent
from periodto period
Here,negative
Fc indicates
downward
flux. Sensible
heatand andequivalent
to resultsfrom otherfield studies.For example
the •-
=
0 streamline:
momentumflux are obtainedlikewise. Coordinaterotationsdo
•Sw/U,
wasconsistently
1 _+0.2 compared
to 1.3 for flat terrain.
not effect scalarflux sign and have a very small effecton Dimensionless wind
shear, (•m---kz / u, (Ou/ Oz),was
measured
flux magnitudes.
Fluxeswith associated
streamlinesconsistently
1.1_+0.3 where u, = ¾-w'u' was calculatedfrom
within ñ5ø of horizontalaccountfor 98% of the datapresented the momentum flux. There are no aberrant values in Table 1 to
here. Gill uvw anemometerdata were correctedin real time for indicatea sampling
problemwitheitherthesensors,
thesampling
the inherentcosineresponse
problem[Massman
and Zeller, systemor thetowerconfiguration.
1988].ThePRTfastresponse
temperature
sensor
wasroutinely
damaged
by harshweather
hencesensible
heatflux wasalso Results
estimated(Table 1) usingmeasured
eddy diffusivities
for
The eddy correlationmeasurements
showconsistent
upward
momentum,assumingsimilaritywith heat diffusivityand
winterperiodsand
temperature
lapserate between10 and 29 m, to provide daytime03 fluxesduringtwo snow-covered
directionaland intensitycomparisons
with measured
sensible downwardfluxesduringthe growingseasonwith the absenceof
snow
cov2er.
• Half-hour
average
upward
03 fluxes
exceeded
heatand03 fluxes.
day
'l) during
April14-27,
1992.
These
Businger's[1986] list of eddy correlationmeasurement0.5•tgm' s' (11kgkm-:
asthedownwardfluxesmeasured
concerns
wereusedfor dataevaluationandediting.Ozoneflux valuesarethe samemagnitude
shiftsin
corrections
[equation12,LueningandMoncrieff,1990]for vapor duringJuly 1992 at the samelocation.Sign-change
ß ' '
-i-7 I.tg m-2 s-1¾
patternsoccurred
duringthe 13-day
effectswere]ns]gn]ficant
(_lx10
). Databelowthe daytime03 flux movement
and
scale
height,
ht <l w'c'/(0•/0t)I of 23 m wereculled.
A May 6-19, 1992samplingperiodsnow-meltwascompleted,
digitalbutterworth
filterwasappliedin realtimeto account
for againduringthe 8-dayperiodin autumnwhensnowreturned.
aliasing. Instrumentresponseand instrumentseparationThere are severalexampleswhen nighttime03 flux doesnot
lapserate and
corrections
wouldtypicallyincrease
flux magnitudes
by 20 to ceaseas mightbe expected.On theseoccasions,
80% [Zelleret al., 1989].Thelatterdonoteffectthemainresult wind data indicateneutralstabilitywhich allowsfor continued
03
(03 flux direction),hencethe flux data are presented
here turbulenttransport.Figs.I through3 show03 concentrations,
Table 1. Daily Ozone,OzoneFluxandMeteorological
Values
Julian 03 03Flux 03Flux T
RH Heat
FluxHeat
FluxRadiation
-
U'W' --
-
Precip.
Snow
(ppb)
(mgm'2)(•tgm'2s
4)Max/Min
(øC)Max/MinMax
(%)(Wattsm.2)(Wattsm.2)(Watts
.2.(ms'•)(m
(m
Day
Max/Min
Total
Max
1/2
hrEstimate
Max
U ••S-2)
lll)
**
**s-•)(Degree)
**
23 m
106 59/ 42
107
108
109
110
111
112
113
114
115
116
60 / 48
59 / 42
52 / 46
49 / 40
51/40
51 / 47
57 / 46
65 / 51
64 / 54
61/49
23 m
23 m
29 m
29 m
23 m
3
0.3
6/ -2
98/ 73
-
5
12
19
17
18
15
19
14
9
7
117 62/ 44 5
61 / 54
12
120 64/ 49 6
119
0.4
0.35
0.6
0.42
0.6
0.58
0.51
0.3
0.26
0.28
73 / 64
67 / 36
60/46
12
15
4
124
62 / 50
2
0.08
125
126
128
129
130
131
132
133
134
63 / 51
60 / 51
55 / 47
55/41
56 / 44
62 / 43
51 / 45
52 / 42
54 / 45
1
2
3
-1
5
10
5
4
17
0.07
0.08
0.2
0.08*
0.6*
0.23
0.8
0.5
0.9*
136
137
138
139
184
61 / 49
58 / 46
52 / 46
57 / 49
34 / -
-2
4
-5
-8
-0.2*
-0.1
-0.2
-0.27
-0.2
186
187
188
189
190
274
59 / 50
48 / 35
42 / 30
53 / 33
63 / 50
58 / 49
-18
-10
-8
-1
-23
-5
276
277
278
279
280
70 /
54 /
50 /
45 /
50 /
-3
-4
1
0
-3
185 54/ 37 -•2
275 55/ 47 -5
48
46
39
34
27
281 - / 25
2
97 / 90
95 / 79
96 / 93
95 / 92
95/75
87 / 45
94 / 65
93 / 43
55 / 26
32/20
-
0.21 10/-4 36/ 20 0.35
2 / 10 35 / 20
320
0.2! 4/ 12 25/ 20 310
121
122
123
135 54/ 46 -3
2 / -1
5 / -2
-4 / -9
-4 / -8
-1/-9
6 / -6
4 / -2
-2 / -7
3 / -9
8/-6
0.22
0.65
0.19
7 / 13
2/ 9
-1 / 7
23 m
50e
25e
25e
15e
10e
85e
50e
50e
110e
90e
29 in
830
23 m
23 m
23 m
23 m
1.8 -0.2 0.01 150
1.5 m
5
640
770
730
410
930
1050
930
810
980
960
3.1
9.2
7.0
7.4
10.0
4.9
5.2
8.9
6.8
3.0
-0.5
-2.1
-1.8
-1.5
-2.8
-1.0
- 1.1
-2.6
-1.8
-0.5
0.15
0.52
0.25
-1.50
-0.05
0.17
0.37
0.55
0.19
0.00
270
260
300
320
320
290
280
290
300
310
3
21
25
8
5
0
5
4
0
3
0
0
3
113
-
85e 970 4.3 -0.8 0.00 310 0 1•3
980
4.5
-1.4
0.18
280
0
350e 960 4.0 -0.8 0.36 250 0 1•0
380e
25 / 18
96 / 21
96 / 25
340
250
350
410e
450e
200e
1000
990
1090
7.5
7.1
1.3
-2.0
-1.9
-0.1
0.52
0.44
-0.06
240
260
v.
2/ 9
32 / 19
340
280e
1000
2.2
-0.4
0.00
300
1
-
1 / 10
3 / 10
13 / 1
11/2
1/ 9
4 / -5
9 / -1
10 / 2
7/ 0
43 / 21
60/29
69 / 33
92/45
95 / 57
95 / 50
85 / 35
90 / 30
99 / 70
340
340
400
90
280
-
290e
200e
300e
50e
200e
310e
350e
350e
25e
1020
1010
1050
660
810
1000
1000
990
770
1.9
2.3
3.7
1.2
5.0
5.5
8.4
5.3
5.0
-0.3
-0.3
-0.7
-0.1
-0.8
-1.8
-2.8
-1.2
-1.2
0.00
-0.16
-0.05
0.05
0.36
0.33
0.57
0.25
0.28
300
340
310
210
230
270
260
280
270
0
0
4
0
3
0
1
4
8
45
-
12 / 3
10 / 1
14 / 0
16 / 4
-/ 1
60 / 30
90 / 30
64 / 20
55 / 19
- / 90
12/ 2 95/ 39
120
320
290e
290e
250e
240e
-700e
950
980
1030
1060
800
5.0
6.8
3.0
3.5
4.7
-1.1
-1.7
-0.5
-0.6
-1.1
0.40
0.35
0.26
0.26
0.15
250
280
250
270
295
0
0
0
1
5
0
0
0
0
0
-0.6
-0.3
-0.28
0.51
-0.63
-0.2
19 / 2
19 / 9
19 / 9
12 / 4
13 / 6
16 / 4
55 / 22
42 / 20
48 / 28
94 / 42
70 / 42
33 / 18
300
290
300
200
140
-0.27 17/ 5 35/ 17
2•0
350e
300e
390e
100e
120e
150e
1040
995
990
760
660
770
5.7
6.3
7.4
7.1
3.9
1.8
-1.6
-1.8
-2.3
-1.7
-1.0
-0.1
0.42
0.43
0.50
0.35
0.25
0.03
245
255
270
265
255
160
0
0
0
8
0
0
0
0
0
0
0
0
-0.15
-0.21
+0.15'
+0.08*
+0.4*
16 / 3
16 / 6
9/ 1
7/-2
7 / -2
32 / 17
35 / 18
80 / 40
95 / 52
98 / 43
200
370
360
230
330
100e
310e
350e
90e
240e
750
740
735
750
730
3.9
3.9
5.3
3.0
4.5
-0.2
-0.6
-1.4
-0.4
-1.0
0.10
0.70
0.40
-0.08
0.30
150
220
270
140
270
0
0
0
0
5
-
-0.11 10/ 1 90/ 33
-0.6
+0.3* -7/-11 97/45
-
-
-
260e 1000 5.0 -1.1 0.20 280 0
•)
250e
0
180e
1000 5.0 -1.4 0.33 270
750 2.0 -0.2 0.07 260
0
0
100e 7-60 5.9 -1.3 0.02 320 2
- Missing
data
ornomeasurement
taken;* Positive
andnegative
ozone
fluxonthestone
day;
e Estimated; v Variable; ** Midday(10:00-15:00MST) average
0
•
fluxesandverticallyintegratedtime rate of Os changefor three
of the five multi-dayperiodsgivenin Table 1.
Table 1 summarizesthe meteorologicaland Os data.Midday
meteorological
valuesare representative
averagesbetween10:00
and 15:00 MST, the diurnalhoursof greatestOs flux activity.
Total Os flux was obtainedby integratinghalf-hour values
0.6
- 70
0.5
0.4
60
0.3
0.2
50
'rle 0.1
o.o
40
commencing
midni.gsht
each
day.
Themaximum
daily
deposition
value, -23 mg m',
on Julian day (JD) 190 comparesin
magnitude
tothemaximum
upward
flux,19mgm'2onJD113.
In additionto the presenceof snow,ambienttemperature
appears
to effectOsflux direction.
Between
5 to 10øC,03 fluxescanbe
eitherup or down,below5 øCtheyare mostlypositive,and
above10 øC theyaremostlynegative.Ozoneflux directionis
-0.3
30
-0.4
-0.5
-0.6
20
184
(dashed)in partsper
neither effected by vertical wind speed or direction nor Figure 2. Half-houraverage03 concentration
timerate
horizontal wind direction;both would indicate a terrain induced billion(ppb),03 flux (solidlines)andverticallyintegrated
of03change
(+)inpgm'2s'fortheperiod
July2 toJuly9, 1992.
bias.
Fig. 1, April 14 - 27, 1992 (JD 106-117),showsthe day-today consistency
of the upwardOs fluxes.Temperatures
ranged (•=F=0), assuming w'c'o= 0, and neglectingmolecular
from 10 øC to -9 øC duringthis period.Ozonefluxesreached diffusiongivesequation2.
0.6ggm'2s4. TheApril29- May4, 1992(JD119- 126)period
23m
(Table 1) showsa decreasein Os flux afterJD 123. This change
wasprecededby a sharpdropin Osconcentration
associated
with
a simultaneous
jump in Os flux followedby sustainedlower
wind speeds.Temperaturesranged from -1 (occurredbriefly
-
23m
I -•z+ I aw'c'•5
0
0
(2)
- 23m
• 23m
-I23m_
I Ox z- 2•m
Oz+
Oy
midnightJD 123) to 13 øC. May 6-19, 1992 (JD 127-140),
0
0
0
0
coversthe period snowmeltended and the daytime Os flux
As seen in Figs. 1 - 3 the ve•ical flux (secondte•,
directionswitchedfrom upward to downward.Ozone fluxes
rangedfrom positiveto negativeduringthis periodbut remain equation2) is at least• orderof magnitudegreaterth• the local
predominatelynegativeafter JD 138. Temperaturesrangedfrom time rate of ch•ge (first te•) hence the local time rate of
-5 to 16 øC(belowzerovalueswerebriefnighttimeexcursions changedoesnot signific•tly contributeto the ve•ical flux. If
on JD 131-2) Fig. 2, July 2-9, 1992 (JD 184-191),showsthe horizontal advection (third through fiRh terns) were
typicalnegativeO3 fluxesthat occurduringgrowingseasons. insignific•t, the positiveve•ical fluxes would be due to either
The downwarddiurnal flux patternwas briefly interruptedon locallygeneratedO3 (lastte•) or ve•ical advectionte• which
JD 189 when it rained 0.3 mm. This is the only incidentwhen was c•celed to obtainequation2. Given the presumedlack of
positiveOs flux was directlycorrelatedwith a precipitation O3 precursorsin this winte•ime scen•io it is unlikely O3 is
event. Similar brief summertimeeventshave been reportedby generatedlocally •d ve•ical advectiondoesnot seema likely
Enders [1992] and Kelly and McTaggart-Cowen[1968]. expiration given the lack of co,elation betweenflux direction
(Table 1). Horizontal advection is • unlikely
Temperatures
duringthisperiodrangedfrom 1 to 19 øCbut •d •.
contributor
based
on measurement
comprisonsbetweenour site,
remainedbelow 7 øC on JD 189. Fig. 3, September29 OctoberS, 1992 (JD 274-281), shows the transition from the NDDN site and the Centennial,WY site, suggestingthe
negativedaytimeOsfluxesto positivefluxes.Duringthisperiod, horizomal gradient te•s •e also veu small. This leaves R
temperatures
dropped
below0 øCandRH increased
from30 to indicatingeither w'c'_o is not zero as assumed•d/or the
80% as Osfluxesturnedpositive.Basedon meteorological
data existenceof a negativeve•ical O3 profileat me•urementheight.
it is likely snowflurriesstartedJD 278 with snowaccumulating Atmosphericboundau layer O3 usuallyrequiresnitric oxide
and ultravioletener• to drive
on the groundby JD 279. Priorto JD 278 daytimetemperatures •O), nonmeth•e hydrocarbons
its photochemicalproduction[Ols•na et al. 1994]. Forests•e
ranged
from3 to 17øC.
sourcesof naturalnonmeth•e hydrocarbons,
which •e known
precursors
for O3 productionand a possiblecauseof higherrural
Discussion
O3 concentrations.
Concentrations
of nitrousoxide•20) above
Upwardfluxessuggesteithersurfaceor canopyemissions
of •pical roblent levels have been menured under and abovethe
Os and/or in the case of complexterrain,horizontaland/or snow cover at GLEES [Sommerfeldet al., 1993]. Sincethe sine
verticaladvectionof Os. The potentialcontributions
of localOs microorganismswhich generate N20 also generate NO
production(or destruction),
R, andadvectionbelow23 m canbe [Hutchinsonand Davidson, 1993], the possibili• of • NO
roughly estimated from the measureddata by vertically source during winter months exists, however the likely
is veu low.
integratingthe equationfor O3 conservation
from the surfaceto concentration
measurementheight. Using the average wind streamline
- 70
0.7
- 70
0.8 --
0.7
4
0.6
.- 60
0.5
- 60
0.6
0.,4
- 5O
ß• 0.3
0.5
0.4
',.,•
50
•E 0.2
4O
•0.1
40
0.0
30
-0.1
0.1
- 30
-0.2
-0.3
0.0
t '"
.0.1
,- 20
.0.2
273
i
i
i
274
275
276
278
279
280
281
282
Julian
Day
105 106 107 108 109 110 111 112 113 114 115 116 117 118 119
JulianDay
- 20
277
Figure 3. Half-houraverageOs concentration
(dashed)in partsper
timerate
Figure1. Half-houraverage
03 concentration
(dashed)
in partsper billion(ppb),Osflux (solidlines)andverticallyintegrated
(+)inggm'2s4 fortheperiod
September
30,1992,
to
billion(ppb),03 flux (solidlines)andverticallyintegrated
timerate ofOschange
of03change
(+)inggm'2s4 fortheperiod
April14to27,1992.
October 7, 1992.
844
ZELLER AND HEHN: OZONE FLUXES ABOVE SUBALPINE SPRUCE-FIR FOREST
Fontan,J, A. Minga, A. Lopez and A. Druilhet,Vertical ozone
profilesin a pineforest.Atto.Env.26A, 863-869,1992.
adsorption
is morelikely. Laboratoryexperiments
indicate03 Galbally,I. and I. Allison, Ozone fluxes over snowsurfaces.or.
Geophys.Res.,77:21, 3946-3949, 1992.
adsorption
to ice reachessaturation
quickly(< I s) with no Gao,
W. andM.L. Wesely,Numericalmodelingof turbulentfluxes
furtheruptake[Dlugokencky
and Ravishankara,
1992]. Using
of chemicallyreactivetracegasesin the atmospheric
boundary
50ppb03 (9 x 10TMmolecules
cm-3),
an03 to icesticking layer,or.Appl.Met., 33, 835-847,1994.
coefficientof 0.001 (range0.01 - 0.0001).[Dlugokencky
and Hutchinson,G.L. andE.A. Davidson,Processes
for productionand
Ravishankara,
1992]and3 x 104cmS'1 for 03 molecular consumption
of gaseous
nitrogenoxidesin soil,in Agricultural
velocity,we estimatethe rate of 03 adsorption
to snowto be
ecosystem
effectson tracegasesandglobalclimatechange,pp.
2.7x 1016
molecules
cm'2s-1.Taking9 x 107cm2 m-3asthe
79-93, Spec.Pub.55. AmericanSocietyof Agronomy,1993.
Verticalgradientof net
specific•urfacefor freshsnow[Sommerfeld
andRocchio,1993] Kelly, J.J.,Jr. andJ.D. McTaggart-Cowen,
oxidantnearthe groundsurfaceat Barrow,Alaska,d. Geophys.
and aceelating
03 saturation
within I s, thereare potentially
Galballyand Allison [1972] speculated
03 mightabsorbon
fresh snow without total destruction, however we suggest
2.4x 102øO3
molecules
m-3ina I m snow
base.
It would
take
4.5days
(range
0.5-
Res., 73, 3328-3330, 1968.
Lenschow,D.H., R. Pearson,Jr. andB.B. Stankov,Measurements
of
452da•,s
) toexpel
this03assuming
a
ozoneverticalflux to oceanandforest,. d. Geophys.Res.,87:Cll,
constantflux of 0.5 !.tgm- s-. Largerdownward03 fluxesare
8833-8837, 1982
typicallyassociated
with higher03 concentrations
as seenin Leuning, R. and J. Moncrieff, Eddy-covariance
CO2 flux
Fig. 2. Fig 1. however,shows03 concentrations
decreasing
with
measurements
using open- and closed-pathCO2 analyzers:
increasing
positiveflux for severaldays,thendecreasing
with
corrections
for analyzerwatervapoursensitivity
anddampingof
fluctuationsin air samplingtubes.Bdy. Lyr. Met., 53, 63-76,
increasing
concentrations
for the next few days.On JD 122, a
1990.
suddendropin 03 is associated
with a sharpincrease
in upward
03 flux. Given an equilibrium between ambient 03 Massman,W.J. and K.F. Zeller, Rapid methodfor correctingthe
concentrationsand ice surface saturation,this inverse behavior
non-cosineresponseerrorsof the Gill propelleranemometer,
d.
affectstomatalfunction.The measuredfluxesare usuallydiurnal
Collins, Colo., 1994.
Atto. and Oc. Tech., 5:6, 862-869, 1988.
addscredenceto the possibility03 is temporarilystoredin the
McMillen, R.T., A BASIC program for eddy correlationin
snowfield andreleasedby turbulentair interactions
throughthe
non-simpleterrain, Tech.Rep. ERL ARL-147, 32 pp., NOAA
poroussnowinterface.
ATDD Lab., Oak Ridge,Tenn., 1986.
The delineating
factorfor upwardversusdownward
03 fluxes Musselman,R. C., (Ed.), The GlacierLakesecosystem
experiments
appearsto be snow cover and (to a lesserextent)ambient
site(GLEES):an alpineglobalchange
research
studyarea,Tech.
temperature.
Both are environmental
factorsthat potentially
Rep.RM-249, 94 pp., U.S.D.A. ForestServiceRMFRES, Ft.
K.J.,E.M. Bailey,R. Simonaitis
and[Others],
03 andNOy
in naturereflectingdaytimeturbulent03 masstransfer.Some Olszyna,
measurements
show continuedbut weaker upward 03 fluxes
relationships
at a rural site, d. Geophys.Res.,99:D7, 14557-
14563, 1994.
duringnightswith strongwinds.Treephysiology
alsoappears
to
Prentice,I.C., C. Wolfgang, S.P. Harrison, R. Leemans,R.A.
playa roleasthe springandautumntransition
between
positive
Monserudand A.M. Solomon,A globalbiomemodelbasedon
andnegative
03 fluxesoccurs
around
5øC,a minimum
ambient
temperature
for conifergrowth[Prenticeet al., 1992].
Conclusions
plantphysiologyanddominance,
soil properties
andclimate,d.
Biogeography,
19, 117-134,1992.
Ray, J.D.; D.H. Stedmanand G.J. Wendel,Fastchemiluminescent
method for measurementof ambient ozone, Anal. Chem., 58,
598-600, 1986.
D.; K. Zeller and D. Stedman,03 and NO2 fluxesover
The 03 flux datameasured
by eddycorrelation
at theGLEES Stocker,
snow measuredby eddy correlation,Atto. Env.,.29:11, 1299Brooklyntower, SnowyRange,Wy, showreasonable
summer
1305, 1995.
growing
season
deposition
(-0.5!.tgm-2s-l).During
winter
and
Sommerfeld,R.A., A.R. Mosier and R.C. Musselman,CO2, CI-h,
nongrowingseasons,
upward03 fluxesweremeasured.
The late
andN20 flux througha Wyomingsnowpack
andimplications
for
winter upwardfluxesare the samemagnitudeas the summer
globalbudgets,
Nature,361,140-142, 1993.
on
downwardfluxes.As 03 doesnot readilydepositon snow,the Sommerfeld,R.A. and J.E. Rocchio,Permeabilitymeasurements
new and equitemperature
snow, Water Res., 29:8, 2485-2490,
lneasured
rateof 03 deposition
is expected
to decrease
duringthe
winter but not reverse direction. The flux directional transition is
1993.
commonin
apparently
seasonal.
The explanation
for the upward03 fluxes Wesely,M. L., Turbulenttransportof ozoneto surfaces
the eastern half of the United States; in Advanced Science
remainsunknownbut suggesteither: (1) the possibilityof 03
Technology:
12, pp. 345-370,Wiley,N.Y., N.Y., 1983.
storedin the surfacesnowbase;or (2) negative03 profilesabove
Wooldridge,G.L., K.F. Zeller and R.C. Musselman,Ozone
the forestcanopy.
concentrationcharacteristics
in and over a high-altitudeforest,
23rd Int'l Conf. for Alpine Met., Lindau, Germany,Sept 5-9,
References
1994.
Wunderli,S. and R. Gehrig,R., Surfaceozonein rural, urbanand
regionsof Switzerland,Atto. Env., 24A:10, 2641-2646,
Businger,
J.A.Evaluation
of theaccuracy
withwhichdrydeposition alpine
1990.
canbe measuredwith currentmicrometeorological
techniques.
d.
Zeller, K.; W. Massman,D. Stocker,D. and [others],Initial results
Clim.& Appl.Meteor.25,1100-1124,1986.
from the Pawneeeddycorrelationsystemfor dry aciddeposition
Chameides,W.L. and J.P. Lodge,Tropospheric
ozone:formation
research,Gen. Res. Pap. RM-282, 44 pp., U.S.D.A. Forest
andfate,in SurfaceLevelOzoneExposures
andtheirEffectson
ServiceRMFRES, Ft. Collins, Colo., 1989.
Vegetation
editedbyA.S.Lefohn,.pp.
5-20,LewisPub.,Chelsea,
Zeller, K. and T. Hehn, Wintertimeanomaliesin ozonedeposition
MI. 5-30, 1992.
above a subalpinespruce-firforest,Proc. 4th U.S.D.AForest
Denmead,O.T. and E.F. Bradley,Flux-gradient
relationships
in a
Service S. Sta. Chem. Sc.: Research and Applications of
forestcanopy,in TheForest-Atmosphere
Interaction.
editedby
ChemicalSciencesin Forestry,131-138,Feb. 1-2, 1994.
Hutchison,B.A andB.B. Hicks,pp. 421-442,D. Reidel,Boston,
Mass.
K. Zeller andT. Helm, USDA/ForestService,240 WestProspect,
Enders,G. Depositionof ozone to a mature spruceforest:
measurements
andcomparison
to models,Env.Poll., 75, 61-67, Fort Collins, Colorado80526.
1992.
Fitzjarrald,
D.R. andK.E. Moore,Turbulent
transports
overtundra. (ReceivedDecember21, 1994;revisedJuly 13, 1995;accepted
J. Geophys.
Res.,97:D15,16717-16729,1992.
February6, 1996.)