JOURNAL OF GEOPHYSICAL
RESEARCH,
VOL. 101, NO. D3, PAGES 6883-6897, MARCH 20, 1996
Processescontrolling the compositionof precipitation at a
remote southern hemispheric location: Torres del Paine
National Park, Chile
JamesN. Galloway and William C. Keene
Departmentof EnvironmentalSciences,Universityof Virginia
Charlottesville
Gene E. Likens
Instituteof EcosystemStudies,Millbrook, New York
Abstract. Precipitationcompositionmeasuredat Torres del Paine National Park, Chile
(TdP) (51ø10'S, 71ø58'W), between1984 and 1993 was acidic (volume-weighted-
average
pH of 4.96) witha diluteseawater
component.
H + wasthedominant
non-seasalt(nss)cation;in decreasing
orderof abundance,
nssanionswereHCOO-, CI-, SO4=,
CH3COO-,andNO3-. Relativeto lowerlatitude,remotelocations,concentrations
and
per-eventdepositions
of nssSO4=, NO3-,andNH4+ at TdPwerelower;thoseof
HCOOt (HCOO- + HCOOH)andCH3COOH
t (CH3COO-andCH3COOH
) were
similar;andthoseof CH3SO3- werehigher. Concentrations
anddeposition
fluxesof
HCOOt,CH3COOt,nssSO4=, CH3SO3-,
andNH4+ variedseasonally
withsummer
maximaand winter minima. Carboxylicacidsprobablyoriginatedfrom both direct
terrestrialemissionsand oxidationof hydrocarbons
emittedby marine and terrestrial
biota. NssSO4= andCH3SO3- originated
primarilyfromoxidationof biogenic(CH3)2S
emittedfromthe southern
PacificOcean. Directemissions
of NH3 fromupwind
terrestrial
andmarineecosystems
probably
accounted
for mostobserved
NH4+. NO3concentrations
and depositionswere highestduringthe latter part of australwinter and
springsuggesting
abioticcontrols. Transportof precursorsfrom lightning,biomass
burning,and fossil-fuelcombustionat lower latitudesandpossiblytransportof reactive
N from the stratosphere
apparentlycontributedoxidizedN to the southernPatagonian
troposphere.Althoughthe ionic strengthof precipitationat TdP is currentlyamongthe
world's lowest, future changesare likely becauseof increasesin local and regional
populationand energyand food production.
This paper reports the annual and monthly volumeweighted-average
(VWA) concentrations and associated
Many importanttroposphericcompoundsare producedby
terrestrialand marine organisms. Several of thesechemical wet-depositionfluxes of major chemical constituentsin
species(or their reactionproducts)(e.g., SO4=, CH3SO3-, precipitationat TdP. On the basisof thesedata and related
NO3-, NH4+, HCOOH, CH3COOH
) haverathershort information,we investigatedthe major processescontrolling
atmosphericlifetimes (e.g., less than 1 week) and are lost tropospheric chemistry in the region with a focus on
interactions. We also assessedthe
from the atmospherevia deposition. For such species, biosphere-atmosphere
measured concentrationsand deposition rates provide potentialimpactsthatmay resultfrom projectedincreasesin
importantconstraintson sourcestrengthsassociatedwith the anthropogenicemissionsover the next few decades.
These data were generatedunder the auspicesof the
corresponding
biologicalprocesses. However, the pervasivenessof humaninfluencesover mostof the globecompli- GlobalPrecipitationChemistryProject (GPCP). From 1979
catesthe assessmentof natural linkages between the atmo- to 1994 the GPCP operateda network of stationsto detersphereand the biosphere. In extremely remote locations, mine the processescontrollingprecipitationcompositionin
such as Torres del Paine National Park (TdP) in southern regions of the world remote from the influencesof human
Introduction
a baselinefor comparisonwith
Chile (51ø10'S, 71ø58'W) (Figure 1), these relationships activitytherebyestablishing
can be investigatedwith reasonableconfidence. TdP is more populatedregions.
downwind
of the
southern
Pacific
Ocean
human-population
and industrialinfluences.
and
far
from
Methods
Copyright
1996by theAmerican
Geophysical
Union.
Site Description
Papernumber95JD03229.
TdP is 400 km north of PuntaArenas (Figure 1). The
park covers approximately240,000 ha and, in 1978, was
0148-0227/96/95JD-03229505.00
6883
6884
GALLOWAY
ET AL.:
PRECIPITATION
80 ø
70 ø
AT A REMOTE
60 ø
SITE IN CHILE
50øW
30 ø
30 ø
40 ø
40 ø
Atlantic
Ocean
50øS
50øS
Pun
Tierr del Fueg,
90 ø
80 ø
70 ø
60 ø
50øW
Figure1. Torres
delPaineNational
Park,Chile,andsurrounding
areas.
declared a member
of the International
Network
of Bio-
sphere Reserves by the United Nations' Man and the
Biosphereprogram. TdP and its surroundingsare formed
by a great diversity of landforms, glaciers, snowfields,
valleys,lakes,rivers, moraines,plains,andmountains.The
water bodies are of glacial origin and some lakes are still
connectedto glaciers. Mountainswith elevationsof 3,050
m dominatethe landscape. The impactof the Pacific Ocean
on precipitationin TdP is diminishedby the AndesMountains, which are between the Pacific Ocean and TdP,
creatinga continentalmicroclimate[Santanaet al., 1992].
Solarradiationvariesseasonallydrivingstrongvariabilityin
associatedmeteorological conditions. Average monthly
temperaturesbetween 1979 and 1984 rangedfrom a minimum of 1.9 Cø in July to a maximumof 12.1 Cø in
February (Meteorological Data Report, Torres del Paine
NationalPark). Precipitationis fairly uniformlydistributed
thenanalyzed
forpH, SO4= , CI-, NO3-,HCOOt (HCOO-+
HCOOH),CH3COO
t (CH3COO-4- CH3COOH
), NH4+,
Na+, Mg++, Ca++, andK+. CH3SO
3-wasmeasured
in
all samplescollectedafter December 15, 1989. Details of
the analyticaland quality-assurance
proceduresare reported
by Likenset al. [1987], exceptfor CH3SO3- whichwas
measuredusing proceduressimilar to thoseof Bardwell et
al. [1990]. Concentrations
of non-sea-salt
(nss)SO4=, CI-,
Mg++, Ca++, andK+ werecalculated
as described
by
Keeneet al. [1986]usingNa+ asthereference
species
and
Wilson's [1975] compositionof surface seawater. Nine
sampleswere analyzedat the Institutefor EcosystemStudies
for orthophosphateusing the phosphomolybdenum
blue
methodon an Auto Analyzer II [Murphy and Riley, 1962].
Thesesampleswere collectedin August, 1990 (1); October,
1990 (1); November, 1990 (2); January, 1991 (1); March,
1991 (2); and April, 1991 (2).
over the year.
Representativeness
of Database
Precipitation Collection and Analysis
Precipitationwas sampledby storm event with an Aerochem Metrics collector at two sites in the park between
During the study period, 52% of all precipitationwas
sampledfor chemical analysis(Figure 2). The collection
efficienciesfor individualyears typicallyvaried from about
March 23, 1984, and December 19, 1993. From March 23,
35% to 70%.
1984, to January30, 1985, precipitationwas sampled2 km
north of the Administration Building. After a nearby
wildfire, precipitationwas sampledat a similar elevation
approximately2 km away where it remainedfrom February
1, 1985, to July 19, 1987. On July 20, 1987, the collection
stationwas movedback to the original site.
greatly over the year and, in some years, seasonalsubsampling was not representative,it was impossibleto
Becauseprecipitationcompositionvaried
reliablyanalyzeinterannualvariability. We interpretedonly
the average compositionsand depositionsfor the entire
samplingperiodand for eachmonth(i.e., compositing
data
for all Januarys,etc.) assumingthat precipitationsampled
After collection,0.5 mL CHC13was addedto 250-mL during each period was a representativesubset of all
aliquots(or lessfor smallvolumeevents)to preventbiologi- precipitationthat fell during that period. During January,
cal activity[Keeneet al., 1983;Keeneand Galloway,1984]; February, and Octoberthe efficiencieswere 27 %, 27 %, and
becauseof problemswith siteoperations
sampleswere subsequentlystored on site in a cool, dark 35%, respectively,
location and periodically (within one month of collection) usuallyin the earlier yearsof the record. Samplingefficienshippedby air to the Universityof Virginia. Sampleswere cies in the other monthsrangedfrom 42 % to 68%.
GALLOWAY
ET AL.'
PRECIPITATION
AT A REMOTE
SITE IN CHILE
6885
9O
120
8O
100
70
=
60
80 •
4o
60•
-g
40
a• 20
20
10
19•
1985
19•
1987
1988
1989
1990
1991
1992
1993
Figure2. Annualprecipitation
amountsat Torresdel PainefromMarch23, 1984,to December31, 1993,
(left axis) for total amountsrecorded(grey columns),amountssampled(opencolumns),and collectionefficiencypercentage(solid line, right axis).
(e.g., HCOO- and SO4=)' unmeasured
speciescan cause
Quality Assurance
Of the 234 precipitation samples collected, 198 met
quality-assurance
criteria. We excludeddatafor 36 samples
from the analyses:Precipitationgaugedatawere missingfor
4 samples;supportingdescriptivedata (e.g., date collector
installed) were missing for 9; insufficient volume was
sampledto allow completechemicalanalysesof 7; gross
contaminants(e.g., by bird feces) were presentin 10; the
collector malfunctioned for 3; and 3 were apparently
significantionic imbalances.Thereforewe did not useionic
balances to assessthe data quality, only to investigate
patternsin unmeasuredions. Specifically,a plot of the two
functions, Eanion-Ecation and Eanion/Ecation, showed that
most samplescontainunmeasuredanions(Figure 3). The
median value of Eanion/Ecation
was 0.80
and the median
valueof Eanion-Ecation
was-3.8 •eq L-1. Thusthemedian
concentration
of unmeasured
anionswas 3.8 t•eq L-1,
corresponding
to 20% of total anions. Low concentrations
of
several
species
intermittentlypresentprobablycontributed
In pastanalysesof GPCP data,we excludedsamplesthat
to
this
pool
of
unmeasured
anions. Likely candidates
failed to meet criteria involvingionic balances(e.g., samples
includedcarboxylicanions,suchaspropionate,oxalate,and
with ratios of the sum of anions to sum of cations outside a
definedlimit were excluded). This procedurewas appropri- pyruvate,andinorganicanions,suchas nitrite,bicarbonate,
ate for samplesfrom remote marine regions becausethe and bisulfite among others.
ionic strengthof precipitationis dominatedby seasalt; thus
an ionic imbalanceprovidesinsightsinto the quality of the
Results and Discussion
analysis of sea-salt constituents. However, in remote
regionsnotimmediatelyadjacentto oceans,suchasTdP, the
In the following sectionswe report variability in concenoverall ionic compositionof precipitationis significantly trationsandper-eventdepositions
of major chemicalconstitlower and controlled to a greater degree by nss species uents in precipitationat TdP and assessthe controlling
biogeochemical
processes. We also comparethe TdP data
contaminated
by Na+ or Mg+ +.
with measured
1.2
ß
= 1.0
•-
0.8
•
0.6
..• 0.4
ß
!
•4 0.2
0
-30
I
I
I
I
-20
-10
0
10
Y•anion-Ecation,[xeqL' 1
Figure 3. Pattern of 22anion/Ecation
versusEanion-Ecation
in precipitationsampledat Torres del Paine.
and modeled
conditions
at other locations
within the region and around the globe. Caution is warrantedin suchcomparisons
due to regionaldifferencesin the
frequency,size, and natureof precipitationevents;associatedwater-accumulationrates (i.e., dilutioneffects);and, for
data from snow and ice samples,post-depositional
changes
in composition.Despitethesepotentialcomplications,these
comparisonsdo provide useful diagnostic information
concerningmajor biogeochemicalinteractionsin the remote
troposphere.
a+
Precipitationat TdP was slightly acidic and contained
both sea-salt (ss) and non-sea-salt components, which
averaged
34.0/•eqL-1and22.4/•eqL-1,respectively.
The
6886
GALLOWAY
ET AL.'
PRECIPITATION
Table 1. The Volume-Weighted-Average
Concentrations
of ChemicalSpeciesin Precipitationand Corresponding
Annual Ratesof Wet Deposition(Basedon Annual
Precipitation
of 0.75m yr-1)atTorresdelPaine
Concentration,
Deposition,
/•eqL-1
Total
H+
Na +
K+
Mg++
Ca ++
NH4+
NO3C1-
eqha-1yr-1
nss
Total
10.9
13.2
0.4
10.9
--0.2
81.8
99.0
3.0
3.2
0.2
24.0
1.1
0.5
0.6
0.5
0.6
0.5
17.0
1.6
nss
81.8
--1.4
1.5
8.3
3.8
4.5
3.6
4.5
3.6
128
12.0
21.3
1.5
SITE IN CHILE
Na +
TheVWA concentration
of Na+ was13.2/xeqL-1,the
annual
deposition
was99.0 eqha-1 yr-1 (Table1). Na+
concentrations
and per-eventdepositionexhibiteda modest
seasonalpattern(Figure 5a); concentrations
were somewhat
lower duringaustralsummerand occasionalhigh concentrations and depositionswere measuredduring australspring
whenwind speedsare highest[Santanaet al., 1992].
Sea salt was relatively lessimportantat TdP than at sites
closerto the oceanbut still more significantthan in regions
fartherinland.Forexample,
theannualVWA Na+ concen-
trationat Amsterdam
Island,IndianOcean,is 269/xeqL-1
andannual
deposition
is 3000eqha-1yr-1(based
onannual
VWA concentrations[Moody et al., 1991] and annual
precipitationamount[Miller et al., 1993]), aboutan orderof
magnitudegreater than at TdP (Table 1). In contrast,at
SOn=
CH3SO3-
2.8
0.19
1.2
0.19
HCOO-
4.9
4.9
......
Katherine, Australia, a continental GPCP site about 200 km
CH3COO-
0.5
0.5
......
fromtheocean,
theVWA Na+ concentration
is 3.3/xeqL-1
Concentration,
Deposition,
t•molL-1
HCOO.
9.0
1.5
AT A REMOTE
molha-1yr-1
Total
nss
Total
5.5
5.5
41.3
nss
41.3
CH3
C(50
t
1.0
1.0
7.3
7.3
PO4
0.06
0.06
0.5
0.5
In table nss is non-sea-salt concentration.
nsscomponent
was dominated
by H + andHCOO, with
smaller
contributions
byCI-,SO4
=, CH3COO
t,NH44, and
[Likens et al., 1987], a factor of 4 less than at TdP.
Cl'
AnnualandmonthlyVWA concentrations
anddepositions
for C1- exceededthe contributionsexpectedfrom seawater
by 1.6/xeqL-1 and12.0eqha-1 yr-1 (Table1 andFigure
5b),assuming
thatNa+ wasanunbiased
reference
species
for sea salt [Keene et al., 1986]. Although typically
referred to as nssCI-, seawaterwas probablythe sourceof
most excessC1-. Poorly understoodchemicalprocesses
involving sea-salt aerosol in the marine boundarylayer
(MBL) convertparticulateC1-to one or more inorganicC1
NO3-. Theannual
VWA H+ expressed
aspH was4.96
(H•: = 10.9/•eqL-1,Table1),whichwaswithintherange gasesincludingHC1,C12,HOC1,andC1NO2 [e.g., Graedel
of valuesreportedfor precipitationin other remotemarine
(e.g., Amsterdam Island, 5.1; Moody et al. [1991]) and
continentalregions(e.g., Katherine, Australia, 4.7; Likens
et al. [1987]). On the basis of ionic ratios, the maximum
contributions
of HCOOH, HC1, H2SO4, CH3COOH,and
HNO3 to precipitation
aciditywere45, 15, 11, 5, and5 %,
and Keene, 1995]. The latter three gases are rapidly
convertedto HC1 following photolysisand H-abstraction
reactionswith hydrocarbons. Assuming that the reacted
aerosoland HC1 were efficientlyscavenged
by atmospheric
droplets,a shorteratmosphericlifetime againstdry deposition for the aerosolrelative to HC1 would lead to an appar-
in total (ss q- nss)C1-relativeto ss-Na+ in
respectively. When we excludedan early period of record ent enrichment
precipitation[e.g., Moody et al., 1991].
(March 23, 1984, to July 19, 1987) during which HCOOH
The nss C1- concentrations
and depositionswere someconcentrations
were significantlylower (seecarboxylicacids
sectionbelow), the maximumcontributionschangedslightly what more variable from month to month than were other
species(Figures 5 and 6). This resultedin part from the
(51, 12, 8, 4, and 4%, respectively).
MonthlyVWA H + concentrations
rangedfrom6.7/•eq relatively greater uncertaintiesin calculatednss C1- [e.g.,
L-1 in Juneto 19.7/•eqL-1 in December
(Figure4). By Keene et al., 1986]. A generalpattern was evident, howsubtracting
the concentrations
of HCOO- and CH3COO- ever, with higher concentrationsand depositionstypical
from the concentrationsof measured H + we estimatethat
during the warmer months and lower values during the
ona monthly
basis,
H+ contributed
primarily
bystron•
mineralacidsrangedfrom4.2 /•eq L-1 to 8.2/•eq L-I
(Figure 4). By comparison,the acidity from carbonicacid
in equilibrium
withatmospheric
CO2 is2.5/•eqL-1. The
•'
20
16
strongseasonalityof both organicand mineral acidsat TdP
* 12
suggeststhat seasonalvariability in ecosystemmetabolism
and productivityled to distincttemporalpatternsin emissionsof precursorcompounds
controllingacidityin precipitation. Seasonalvariability in oxidative capacityand in
other physical processes,such as wind velocity which
J
F M A M J J A S O N D
partially controlssea-air exchange,may also have contributed to the observedpatterns. During the australwinter, Figure4. Monthlyvolume-weighted-average
(VWA) H +
concentrations of most anions from acids were lower but still
concentrations
for all acids(top line, opensquares)andonly
measurablesuggestingnonbiogenicsources(local or re- strongacids(middleline, closedsquares)relativeto the pH
mote), residual local biogenic emissions,or long-distance of purewaterin equilibriumwith atmospheric
CO2 (bottom
transportofbiogenicmaterialfrom lower (warmer)latitudes. line, no squares).
• 8
I
i
t
I
t
I
I
I
I
I
I
GALLOWAY
ET AL.'
PRECIPITATION
AT A REMOTE
1200
20
800
m.
lO
[••
0 ['•-]
...........
ß
6887
0.4
16
0.3
12 l:l
• _•0.2
8•
400
0
_
b
0.1
•Z
o.o. : ß ß ß .•.•.
BB
, ,
4'
.o •
160
• •, 3
120•
••2
0
,
:
ß
:.
:
ß
ß
I 80
'
:-'.
:
.0
d
•
IN CHILE
a
a
30
4
SITE
2
80
•,
60
•
4o '•
o
20
....
J
Figure 5.
:
F
M
A
.
M
:
J
,
J
,
A
:
S
:
O
:
N
.
I•
o
D
Monthly volume-weighted-average(VWA)
0.8
d
35
3o
0.6
25
0.4
20
0.2
10
s
O.
'
J
Figure 6.
......
F
M
:
A
M
J
J
A
:
S
:
O
:
N
.0
D
Monthly volume-weighted-average(VWA)
concentrations
(columnsleftaxes)andper-event
deposition concentrations(columns,left axes) and per-eventdeposition
(vertical
lines,righta•es)of (a)Na•-, (b)nssCI-,(c) (verticallines,rightaxes)of (a) CH3SO3-,(b) nssSO4= , (c)
HCOOt,and(d)CH3COO
t atTorresdelPaine.Thevertical NH4+ , and(d) NO3-at TorresdelPaine.Theverticallines
linesindicatepercentiles(10th at top, 50th at crossbar, 90th
at bottom)of per-eventdeposition.Nine sampleswere taken
in January,16 in February, 15 in March, 23 in April, 21 in
May, 22 in June, 14 in July, 26 in August, 15 in September,
12 in October, 12 in November, and 13 in December.
indicatepercentiles(10th at top, 50th at crossbar, 90th at
bottom) of per-event deposition. For all speciesexcept
CH3SO3-,thenumbers
of samples
arethesameasin Figure
5:9 in January, 16 in February, 15 in March, 23 in April,
21 in May, 22 in June, 14 in July, 26 in August, 15 in
September, 12 in October, 12 in November, and 13 in
December.For CH3SO3-,6 samples
weretakenin January,
winter. The seasonalpatternin nss-C1-was the oppositeof
15 in February, 12 in March, 16 in April, 9 in May, 7 in
July, 19 in August, 7 in September,8 in October, 5 in
thatof Na+ (Figures5a and5b) buttheinverserelationship November, and 10 in December.
may havebeenlargelyfortuitous.The VWA concentrations
for Na+ suggested
thatseasaltwastransported
to thesite
more efficiently during the colder months (May through
October) than during the summer. In contrast, we expect
processesthat dechlorinatesea-salt aerosol to be more
important during the summer when concentrationsof
Like the situation on Amsterdam Island [Moody et al.,
1991] and at other marine locations [e.g., Graedel and
Keene, 1995], substantialconcentrationsof nss C1- suggest
thatHC1 may have significantlycontributedto the acidityof
precipitationat the site (Table 1). The ultimatesourceof
OH, peroxy radicals, etc.), were presumably higher. this acidity remainsan open question. Acid-displacement
Compared
to themoreremoteMBL, elevatedconcentrations reactions
involvingH2SO4 andHNO3 [e.g., Brimblecombe
of such speciesin pollutedregionsare associatedwith and Clegg, 1988] do not generateatmosphericacidity.
Protonsare simply transferredfrom one classof mineral
greaterC1-deficitsrelativeto seasalt [e.g., Martenset al.,
1973; Keene et al., 1990]. Assumingthat dechlorination acids(H2SO4 and HNO3) to another(HC1). If, however,
wasmoresignificantduringwarmermonths,higherconcen- photochemicallyactive C1 gases volatilize from sea-salt
trationsof volatile C1 and differentialatmosphericlifetimes aerosolandproduceatomicchlorinein significantconcentraagainstdepositionmay have contributedto the observed tions [e.g., Keene et al., 1990; Finlayson-Pitts,1993],
subsequent
hydrogenabstraction
reactionswill generateHC1.
seasonalpattern in riss C1-.
reactantspecies,suchas SO2, N gases,andoxidants(e.g.,
6888
GALLOWAY ET AL.'
PRECIPITATION AT A REMOTE SITE IN CHILE
compositionof incident precipitationduring the period of
operation.
Alternatively, changesin environmentalconditionsmay
have contributed to long-term temporal variability in
50
•
40
ß
ß
ß
ß
E
30
ß
HCOOt. As mentioned
above,the precipitation
collector
ß
was reinstailed at the original sampling site during July,
1987, after regrowthof nearbyvegetationthathad burnedin
a wildfire two years earlier. This move coincidedwith the
ß
•
20
L•
10
ß
ß ß ß ß ß ß
ß
mm
mm ß•
e• mm
increased
HCOOt. The fire mayhaveled to increases
in
.•. •.4:!. ;...! .
•'__•_
: ._
•'•.•' ß '• • • ' • • •', •
local emissions of HCOOH or precursor hydrocarbons
throughchangesin flora (e.g., isoprene-emitting
vegetation),
fauna (e.g., formicine ants; although according to TdP
CumulativeJulian Day
personnel, there were no large ant populations),or soil
Figure7. HCOOt concentrations
in individual
precipitationmicrobes. As discussedbelow, however, it is likely, given
0
1•
2•0
3•0
40•
eventsat Torres del Paine for cumulativeJuliandaysfrom
January 1, 1984, to December 19, 1993.
Chemicalprocessesinvolving sea-saltaerosolcouldthen be
an important source for atmosphericacidity in marine
regions.
Carboxylic Acids
its closeproximityto the ocean,thata portionof HCOOt
deposited at the site originated from marine sources.
Therefore local influences such as fires probably did not
completelyaccountfor the observedtemporalpattern. We
also used standardlinear regressionanalysisto assessthe
relationship
between
variabilityin HCOOt andtheintensity
of E1 Nifio periods(G. Bell, personalcommunication,1994)
but found no significantrelationship. On the basis of the
above analysis,we were not able to ascertainthe causeof
temporally
variabilityin HCOOt.
HCOOt exhibitedan unusualtemporalpatternoverthe thelong-term,
VWA concentrations
andannualdepositions
of HCOOt
t were5.5 •molL-1 and1.0•molL-1 and
per-event
depositions
of HCOOt weremeasured
in samples andCH3COO
courseof the study: Significantlylower concentrations
and
collected before July, 1987, relative to those collected
thereafter(Figure 7).
41.3molha-• yr-• and7.3molha-• yr-•, respectively
(Table
and per-eventdepositionsof
This abrupt and puzzling change 1). The VWA concentrations
suggestedone of two possibilities: Either (1) the chemical
HCOOt and CH3COO
t variedseasonally;
highestvalues
were duringspring, summer,and autumnwhen temperature
and solar insolationwere higher (Figures5c and 5d). This
strongseasonalcycle is typical of carboxylicacidsat many
data. We examined the available information for evidence
remote locations [e.g., Keene and Galloway, 1988] and
of artifacts. All plasticware (sample bucketsand bottles) suggeststhat biogenic emissions, including both direct
used in the GPCP were purchasedfrom the samevendors emissions[e.g., Graedel and Eisner, 1988; Talbot et al.,
and washed,qualityassured,packaged,and shippedat the 1990; Sanhueza and Andreae, 1991] and emissionsof
University of Virginia using standard,testedprocedures precursor hydrocarbonsfrom both marine and terrestrial
[Galloway et al., 1982, 1993]. After receipt, all GPCP sources[e.g., Jacob and Wofsy, 1988; Gallowayet al.,
sampleswere analyzed in the central laboratoryduring 1989; Madronichand Calvert, 1990] may control atmomixed analyticalruns (i.e., samplesfrom numerousGPCP sphericconcentrations.
Seasonal
variabilityin the producsites were included) incorporatinginternal and external tion of photochemicaloxidantsmay also contributeto the
composition
of precipitationchangedsignificantlyduringthe
studyperiod or (2) systematicnegative(beforeJuly, 1987)
or positive(afterJuly, 1987) artifactssignificantly
biasedthe
quality-assurance
procedures.Despiteoverlapping
rangesin
concentrations, data for other GPCP sites did not exhibit
similartemporal
variabilities
in HCOOt overtheperiodin
question. This suggeststhat, if artifactsdid occur, they
were uniqueto the Chilean site and musthave resultedfrom
some on-site influence. However, available evidencebased
on bothdetailedqueriesof siteoperators
andthe operators'
notes on forms returned with the samplesindicatedthat
standardprotocols were followed throughoutthe entire
periodof operation.Althoughcleanplasticware
andsamples
were storedat differentlocationsin TdP duringthe period,
the changesin locationdid not correlatewith the variability
in the data. In addition,visitingscientists
exposeddeionized
water blanksat storageand samplinglocationsand subse-
seasonality
in concentrations.Althoughthe aqueous-phase
oxidationof HCHO in cloudshad been thoughtto be a
potentiallyimportantsourceof tropospheric
HCOOH [e.g.,
Chameidesand Davis, 1983; Jacob, 1986], recentmeasurementssuggestthat this mechanismmay be relativelyunimportant [e.g., Facchini et al., 1992; Sanhuezaet al., 1992;
Keene et al., 1995a].
VWA concentrations
andmedianwet depositions
at TdP
duringthe warm monthswere abouta factorof 2 greater
than those observed at Amsterdam Island in the southern
Indian Ocean [Moody et al., 1991] althoughwintertime
valuesweresimilar. Thusseasonal
excursions
in carboxylic
speciesat TdP were relativelymorepronounced.Terrestrial
regionstypicallyexhibit substantially
higher concentrations
quentanalyses
revealedno significant
HCOOt contamina-of tropospheric
HCOOHandCH3COOHrelativeto marine
tion. Finally,otherbiologically
activespecies
(NH4+ and regionssuggesting
greatersourcestrengths
overcontinents
CH3COOt)didnotvarysignificantly
between
theearlyand [Keeneand Galloway, 1988]. DifferencesbetweenAmsterlaterperiodssuggesting
that the samples
were adequately dam Islandand TdP may, therefore,indicatesignificant
preservedagainst microbial degradation. Therefore we
contributions from terrestrial sources in southern Chile.
concludethat no obvioushandlingor analyticalartifacts Alternatively,
strongermarinesources
for carboxylic
acids
caused
theabruptchange
in HCOOt;themeasured
temporal upwind of TdP relative to thoseat AmsterdamIsland or less
variabilityappeared
to reflectactualchanges
in thechemical efficientremovalof marine-derived
carboxylics
during
GALLOWAY
ET AL.'
PRECIPITATION
6889
factorsleadingto the high correlationsbetweenHCOOH and
5O
CH3COOHin aqueousandvaporphases[e.g., Keeneand
•] 40
Galloway, 1988]. Since both acids appearto be controlled
by similarprocesses(biogenicemissionsandphotochemical
oxidationof precursors,direct biogenicemission,and short
lifetimesagainstdeposition),it is not surprisingthat they are
highly correlated. All these processesare driven to greater
or lesser extent by seasonal variability in atmospheric
physics (radiation, temperature, wind velocity, and
precipitation).
ß
I• 30
•
AT A REMOTE SITE IN CHILE
2o
• lO
!
0
1
2
3
I
4
CH3COOt,gmolL'•
Sulfur
Figure8. Concentrations
of HCOOt versusCH3COOt in
individual precipitationevents at Torres del Paine from
March 23, 1984, to December 19, 1993, showing the
reducedmajor axis regression(solid line).
$04 = and CH3SO3- were the two major S species
measuredin TdP precipitation. VWA concentrationswere
2.8 /•eqL-1 and0.19 /•eqL-1, respectively,
andannual
deposition
rateswere21.3eqha-1and1.5eqha-1 respectively. VWA concentrations
of ss and nss SO4= were
transportover landmay alsohavecontributed
to the differences between sites.
1.6/•eqL-1 and1.2 /•eqL-1, respectively'
corresponding
deposition
rateswere12.3eqha-1and9.0 eqha-1,respec-
Concentrationsof carboxylic acids in ice from coastal tively (Table 1).
Concentrations
of nssSO4= in TdP precipitation
(Figure
Antarctica[Legrandand Saigne, 1988] are 2 to 3 ordersof
magnitudelower than those at TdP. These results are 6b) were within the range of those at other high-latitude
consistentwith the lack of significantbiogenic sourceson areas in the southern hemisphere(Table 2, Figure 9).
the Antarctic continentand suggestthat marine sourcesof However,nss SO4= concentrations
in six snowsamples
precursorsupwindof easternAntarcticaare relativelylow from southPatagonia(60 km north) (Table 2) are a factorof
2 lower than at TdP. These differences are probably
comparedto other regions.
Aqueous-andvapor-phase
concentrations
of HCOOH and associatedwith the closer proximity of TdP to marine
of (CH3)2S(seebelow). In addition,thePatagonian
CH3COOHareusually
highlycorrelated
suggesting
thatboth sources
compounds
are controlledby similarprocesses[e.g., Keene
et al. , 1986; Keene and Galloway, 1988' Talbot et al. ,
samplescorrespondto winter snowfallduring periodsof
minimum(CH3)2Semissions
[Bateset al., 1992]. Other
1988, 1995]. A reduced major axis (RMA) regression
[Hirsch and Gilroy, 1984] for the TdP data yielded a slope
of 7.52 +_ 0.24, an intercept of-2.27 _+ 0.34, and a
correlation coefficient of 0.89 (Figure 8). A previously
reportedslopeof 1.01 + 0.20 for the regressionof carboxylic speciesat TdP [Keeneand Galloway, 1986] corresponds
factorspossiblycontributingto these regional differences
include orographic influences on precipitation amount,
variability in rain- versussnow-scavenging
processes,and
elevational gradients in precursor gas and aerosol
concentrations.
CH3SO3-in precipitation
hasbeenmeasured
at onlya few
to the early record when HCOOHt concentrations
were high-latitudesitesin the southernhemisphere. Concentrasignificantlylower (see above). Althoughabsoluteconcen- tions at TdP (Figure 6a; Table 1) were within the range of
trationsof HCOOt and CH3COO
t in precipitation
in TdP measurementsfrom coastal Antarctica. Maupetit and
were within the range of values at other remote and im- Delmas[1992] reportthat CH3SO3- concentrations
in 13
pacted sites, the slope for the TdP data was higher by snowsamplescollectedin 1984 at the coastalsiteof Dumont
factorsof 2 to 5 [e.g., Keene and Galloway, 1986]. Since d'Urville range from below detectionto 44 ppb (0.46 /•eq
meanof 6.5 ppb(0.068/•eqL-l).
there would probablyhave been little spatialvariability in L-1)withan arithmetic
the relative losses of the two acids through deposition, CH3SO
3- in snowdeposited
duringJune-December,
1984,
sourcestrengthsof HCOOH upwindof TdP may have been on the coastat Mirny-Vostok ranged from about 3 ppb to
considerably
higherthanthosefor CH3COOHrelativeto
23ppb(0.03/•eqL-1 to 0.24 /•eqL-1) [Legrand
et al.,
3- concentrations
in an ice core
many otherregionsof the Earth. There has beenrecurring 1992, Figure4]. CH3SO
Islandare1 to2/•eqL-1 [Mulvaney
etal.,
speculationover the years concerningthe biogeochemical fromDollerman
Table 2. PrecipitationComposition
at Torresdel PaineComparedto OtherHigh-LatitudeSitesin the
SouthernHemisphere
nssSO4=
NO3-
NH4+
Median
1.06
Range
0.39-3.94
N
34
0.66
0.17-3.33
35
0.06
0.04-0.17
4
Drake Passage
1.1
0.6
2.6
Amsterdam Island
3.4
1.3
1.8
Patagoniaice cap
0.6
0.3
0.8
Torres del Paine
1.2
0.5
0.6
Unitsare/•eqL-1.
Reference
Delmas [1996]
Antarctica
Pszennyet al. [1989]
Moody et al. [ 1991]
Aristarain and Delmas [1993]
this paper
6890
GALLOWAY
ET AL.'
PRECIPITATION
2.4
lO
2.0
1.6
1.2
0.8
I
I
I
I
i
I
I
i
i
i
I
2.0
8
1.2
0.8
2 •
0.4
0.0
I
I
I
i
I
I
I
I
I
I
I
c
4
0.6
J
_ •
:
:
=
F
A
M
J
M
typically covary over marked seasonal cycles at
high-latitude, marine-influenced sites in the southern
hemisphereincluding TdP (Figure 10a), Amsterdam Island
(Figure 10b) [Nguyenet al., 1992], Cape Grim, Tasmania
[Ayerset al., 1991], and Antarctica [Legrand et al., 1992;
Savoieet al., 1993]. Such relationshipssupportthe hypo-
the period when both specieswere measured was 0.17
(Figure 10c), within the range of 0.05-0.4 reported for
coastalAntarctica [Berresheim,1987; Pszennyet al., 1989;
Legrandet al., 1992; Delmas, 1996] but substantially
higher
than that for Amsterdam Island (0.04, calculatedfrom Table
3). Monthly equivalentratios (based on VWA concentrations) at TdP were lower during the austral summer and
higher during the winter (Figure 10c); that is, relative
seasonal
variabilityin CH3SO3- wasgreaterthanthatof nss
SO4= . Ratiosat Amsterdam
Islandexhibitedsomewhat
less
seasonal
variability(Figure10c). SinceCH3SO3
H appears
to be moreefficientlyproduced
from(CH3)2Soxidation
by
OH at colder temperatures[e.g., Hynes et al., 1986], we
expecteda relatively more pronouncedseasonalexcursionin
nssSO4= at TdP assumingboth speciesoriginatedexclusivelyfrom (CH3)2Sandhadsimilaratmospheric
lifetimes.
The greaterseasonalvariabilityin CH3SO3- suggests
the
possibilityof a significantanthropogenic
contributionto nss
0.4
0.2
SITE IN CHILE
thesisthatseasonally
varyingemissions
of biogenic(CH3)2S
fromthe southern
oceansaremajorsources
for CH3SO3H
andH2SO4 in the overlyingMBL. The equivalent
ratiofor
VWA concentrations
of CH3SO
3-tonssSO4= atTdPduring
0.4
0.0
AT A REMOTE
J
A
S
O
N
D
a
Figure 9.
Monthly volume-weighted-average
(VWA)
concentrations
of (a)nssSOn
= , (b)NH4+, and(c)NO3-at
Torres del Paine (open squares;left axes) and Amsterdam
Island (solidsquares;right axes).
0.4
0.3
;,0.2
•o.1
0.0
1992] (as reviewed by Delmas [1996]). For the Drake
Passage, Pszenny et al. [1989] report a range from 8
precipitation
samples
of 0.02to 0.12txeqL-1.
Possiblesourcesof precursors
for nssSO4= in precipita-
'
•0.2
•0.0
major volcanicactivity upwind of the site duringthe study
period, volcanic emissionswere probably an insignificant
regional source of S (although we cannot discount the
possibilityof nonexplosiveventingof S). Thus the following analysis will focus on assessingthe biogenic-versusanthropogenicsourcesof nss S in precipitationat TdP. At
•
'
'
'
'
'
'
'
•.•0.3
0.4
gases(primarily(CH3)2Sfromtheupwindocean);thelongdistance
transportof combustion-derived
SO2 fromremote,
SO2. CH3SO3- is thoughtto originatealmostexclusively
fromtheoxidation
of biogenic(CH3)2S.Sincetherewasno
'
b
tion at TdP include biogenic emissionsof reduced sulfur
primarily anthropogenicsources'and volcanic emissionsof
•
8•
6 •
4,,=•
,
,
,
,
,
,
,
,
,
,
,
O•
'•"0.4c
0.3
0.0
,
J
F
M A
M
J
J
A
S
O
N
D
the latitudeof TdP, (CH3)2Sis the mostimportant
reduced
(VWA)
S gas emittedto the atmosphereand marine ecosystems
are Figure 10. Monthly volume-weighted-average
substantiallystronger sourcesthan terrestrial ecosystems concentrationsat (a) Torres del Paine and (b) Amsterdam
[Bateset al., 1992]. The oxidationof (CH3)2Sby OH
producesboth H2SO4 and CH3SO3H[Yin et al., 1990].
Islandof CH3SO3- (opensquares,
left axes)andnssSO4=
(solidsquares,
rightaxes);(c) the CH3SO3-/nss
SO4= ratios
at Torres del Paine (open squares)and Amsterdamisland
Relative production appears to be strongly temperature (closedsquares). The AmsterdamIslanddataare for paired
dependent;
CH3SO3His produced
in greaterabundance
at measurements(n= 198) from July 31, 1989, to March 28,
lower temperatures[Hyneset al., 1986].
1994 (J. N. Galloway and W. C. Keene, University of
CH3SO3' and nssSO4= relationships.Aqueousand Virginia, GlobalPrecipitationChemistryProjectunpublished
particulate-phase
concentrations
of CH3SO3- andnssSO4=
data, 1995).
GALLOWAY
ET AL.'
PRECIPITATION
SO4= in precipitation
at thesite. A complicating
factormay
involve differential seasonalvariabilities in atmospheric
lifetimesfor CH3SO3- andrissSO4= . Relativeto rissSO4= ,
CH3SO
3- is associated
with coarseraerosol(e.g., Pszenny
AT A REMOTE
SITE IN CHILE
6891
.,5ø
I
!• •o
[1992] amongothers). Thus seasonalvariabilityin physical
processes,such as sea-salt aerosol production, associated
scavenging,and subsequentdry deposition,could lead to
relative differencesin the seasonalityof removal rates for
the two species.
C1 chemistry may also complicate interpretation of
sourcesfor riss S in the MBL basedon presumedratios of
ß
•
.
• 10 ., :l
' ... •.
..
0 '•[l•---II
Ill ß:: :l I I
0.0
sulfonated
products
fromtheoxidation
of biogenic(CH3)2S.
0.2
•
ß
:
'
0.4
0.6
CH3SO3', p•eqL'1
In contrastto OH, there is no evidencethat oxidationby
of HCOOt versus
CH3SO
3- in
atomicC1leadsto the production
of CH3SO3H[Keeneet Figure12. Concentrations
al., 1996]. Thus latitudinalor seasonalvariability in the
individual precipitationevents at Torres del Paine from
relativeimportance
of C1versusOH oxidationof (CH3)2S December16, 1989, to December19, 1993, showingthe
maycontribute
to observed
patterns
in tropospheric
CH3SO3- reducedmajor axis regression(solid line).
andrissSO4=. Sincethe spatialandtemporaldistributions
of Cl-atom concentrationsin the MBL are very poorly
constrained[e.g., Graedel and Keene, 1995], it is impossi- at TdP using standardlinear regressionof measuredconcenble, at present,to critically assessthe potentialimportance trations versus an index of E1 Nifio intensity (G. Bell,
Climate Analysis Center, National Weather Service, NOAA,
of this chemicalprocessin the troposphericS cycle.
unpublisheddata, 1994). Although concentrations
of both
CH3SO3- is enrichedrelative to nss SO4= in coastal
to be greaterduringE1
Antarctic ice during strong E1 Nifio Southern Oscillation nssSO4= and CH3SO3- appeared
eventssuggesting
thatincreased
(CH3)2Semissions
during Nifio periods(Figures11a and l lb), only nssSO4= was
statisticallysignificant. In addition, the ratios of the two
E1 Nifio periodsmay contributeto interannualvariability in
absoluteand relative concentrationsof sulfonatedproducts speciesshowedno apparenttrend (Figure 1l c). A similar
analysisof precipitationamountat TdP versusthe index of
[Legrand and Feniet-Saigne, 1991]. We investigatedthe
relationshipbetweenE1 Nifio and S speciesin precipitation E1 Nifio intensity revealed no significant relationship.
Although our results are not completelyconsistentwith
variabilityin CH3SO3- andnssSO4= measured
in Antarctic
ice [Legrandand Feniet-Saigne,1991], they do supportthe
hypothesis
that fluxesof (CH3)2Sfrom the southernocean
8
to the atmosphereincreaseduring strongE1 Nifio periods.
Such variability may have important implications for the
direct
and
indirect
effects
of
S aerosol
on the
Earth's
radiative balance and climate [e.g., Charlsonet al., 1992].
Spatial heterogeneityin ecosystems,their responsesto E1
Nifio, atmospheric oxidation processes, or atmospheric
lifetimes may contribute to regional variability in tropo.,
sphericCH3SO3- andnssSO4= relativeto E1Nifio events.
0.5
ß
• 0.4
ß
ß
_-L 0.3
Apossibleexplanationfor the lack of consistencybetween
our data and those of Legrand and Feniet-Saigne[1991] is
that our data spannedonly 10 years whereastheir analysis
correspondsto a longer period (1922 to 1984).
ß
ß
ß
ß
ß
ß
ß
ii
ß
i II
•
L)
0ol
0
ß
ß
ß
ß
Ii
ß
i
ß
II
ß
i
ß
ß
ß
ß
Ii
I
ß
I
HCOOt and CH3SO3' relationships. HCOOt and
CH3SO3- in precipitationat TDP were also significantly
1.0
correlated(Figure 12). A RMA regressionyielded a slope
of 53.1 _+ 3.4, an interceptof-2.35 _+0.79, and a correlation coefficientof 0.70 suggestinga possibledirect chemical
link betweenthe cycling of S and HCOOH. The oxidation
0.8
of (CH3)2Sproduces
bothHCHO andCH3SO3- [Yinet al.,
0.4
1990]' the subsequentvapor- or aqueous-phase
oxidationof
HCHO generatesHCOOH [e.g., Jacob, 1986]. However,
much of the HCHO in the rural and remote troposphereis
1.2
ß
o
I
-4
ß
.:•.:..:.
0.2
I ß
-3
-2
' lal
-1
ß
ß
I
0
thoughtto originatefromthe oxidationof CH4 [e.g., Logan
'
I
1
EI Nino (increasingstrengthto left)
et al., 1981' Duce et al., 1983] and isoprene[e.g., Shepson
et al., 1991; Munger et al., 1995]; thus, the relatively minor
contribution
from (CH3)2Soxidationwouldnotbe expected
Figure 11. The relationshipbetweenthe E1 Nifio indexand to result in strong correlationsbetweenCH3SO3- and
themonthlyvolume-weighted-average
(VWA) concentrations HCOOH via this pathwayalone. The major precursorsfor
of (a) rissSOn=, (b) CH3SO3-,and(c) CH3SO3-/nss
SOn= HCOOH in marine air are probably other hydrocarbons
ratio.
emittedfrom the oceansurface. It is likely that the observed
6892
GALLOWAY
ET AL.'
PRECIPITATION
AT A REMOTE SITE IN CHILE
correlationbetweenCH3SO3- and HCOOt reflectsthe Nitrogen
common influence of physical processes on essentially
independentbiogenicsources,the subsequent
photochemical
oxidation of precursor compounds,and deposition. Like
NH4+ . TheVWA concentration
of NH4+ in TdPwas
0.6 tteqL-1(Table1). Thisvalueisgreater
thantherange
in Antarctica
(0.04to0.17tteqL-1)butlessthan
HCOOH, CH3SO3- is produced
fromthephoto-oxidation
of observed
a biogenic precursor and is lost from the atmospherevia that for other high-latitude,non-Antarcticsites(Table 2).
A pronounced
seasonal
cycleof NH4+ concentrations
and
depositionto the surface.
had maximaduringspringand fall and
Sulfur budget. Estimating the annual budget for nss per-eventdepositions
sulfurrequiresinformationon emissions
of (CH3)2S,wet- a minimumduringwinter (Figure 6c). The seasonalpattern
depositionrates of CH3SO3- and nss SO4=, and dry- at AmsterdamIsland [Moody et al., 1991] also peaksduring
deposition
ratesof CH3SO3-,SO2, and nss SO4=. The springbut absolutevalues are substantiallyhigher, suggestannualwet-deposition
ratesof CH•SO¾ and nss SO4= at ing greater sources in that region (Figure 9b). Strong
seasonal
patterns
in NH4+ wetdeposition
areconsistent
with
TdPwere
1.5
ec[
ha-1yr-1and9.0
e•ha
TM
yr-1,respectively
1
-•
1
1
(1.5 mol ha- yr- and 4.5 mol ha- yr- , respectively)(Table
1).
Estimates of wet-depositionrates for nss sulfur in polar
biologicalsources. Both terrestrialand marine ecosystems
emitNH3 [Denlener
and Crulzen,1994]. Giventhesimilarity of natural emissionsfrom the marine and terrestrial
(15molha-1yr-1and36molha-1yr-1,respectively)
andmarineregions
rangefromabout1 molha-1 yr-1 to systems
30molha-1 yr-1 [Galloway,
1985];wet-deposition
ratesat [after Dentener and Crutzen, 1994], we expect that both
TdP fell within this range. On the basisof eight precipita- contributed
to NH4+ in TdP precipitation.Agricultural
tion samplescollectedin the austral fall on a cruise in the materials (fertilizer, animal waste) can also be important
Drake Passage, Pszenny el al. [1989] estimate a wet- sources
of NH3 [Gallowayel al., 1995]. Theprimaryterrestrial ecosystemat TdP is grassland,some of which is
deposition
rate
for
CH3SO
3and
nss
SO4
=
of
0.26
ttmol
rn
-2
•
2
1
d- and 1.7 ttmol m- d- , respectively. These scaleup to usedto raisesheepwhosewasteemitsNH3 [Schlesinger
and
0.9 molha-1yr-1and6.3molha-1yr-1,respectively,
which Hartley, 1992].
are similar to the TdP data. Pszenny el al. [1989] and
Thewet-deposition
rateofNH4+atTdPwas4.5eqha-1
Galloway [1985] estimatethat dry depositionof nss sulfur yr-1(Table1). Dentener
andCrutzen
[1994]usea three(SO2 +nss SO4=) is aboutone quarterand lessthanone dimensional, chemical-transportmodel to calculate global
half of the wet-deposition
flux of nss SO4=, respectively. distributions
of NHx emissions
and depositions.For the
Assumingthatdry-deposition
ratesfor SO2 andnssSO4= at southwestcoast of Chile, they estimate emissionsto be
TdP were onethird of the nssSO4= wet-deposition
rate, we approximately
20 to 50 mgN m-2 yr-1 (14to 36 eqha-1
wet-deposition
ratesareof thesame
calculate
a fluxof 1.5molha-1 yr-1. Total(wetplusdry) yr-1). Theirestimated
deposition
of nssSO4= was thusestimated
to be 6.0 mol magnitude,or about 3 to 8 times higher than our measure-
ha-1 yr-1. Pszenny
el al. [1989]estimate
thatthe dry- ments. There are several possibleexplanationsfor these
deposition
rateof CH3SO3- is aboutonethirdof wetdepo- differences' Dentenet and Crutzen's model may overestisition, which, at TdP, would have yieldeda dry deposition mateNH3 emissions'
NHx mighthavebeenscavenged
and
of 0.5 molha-1yr-1. Therefore
thetotaldeposition
of nss
depositedupwind of TdP' or there might have been substan-
sulfurto TdPwasabout
8 molha-1 yr-1, withCH3SO
3- tial dry deposition
of NH3. Langfordel al. [1992]notea
providingabout25% of the total with SO2 and nssSO4=
providingthe balance.
rapiduptakeof emittedNH3 within the grasslandcanopy
andthuslittlenetNH3 emission
to theatmosphere
abovethe
Berresheim
[1987]estimates
that(CH3)9S
emissions
from canopy. Such rapid recycling could possiblyaccountfor
2
1
the SouthernOcean average 4.9 ttmol m- d- over a year.
some apparent differences between the measured and
Balesel al. [1992]estimate
(CH3)2Semissions
frommarine modeled fluxes. In another study, Quinn el al. [1988]
ecosystemsin the same latitude range as Torres del Paine estimatean NH 3 flux from the northeastern
PacificOcean
areabout2.21 ttmolS m-2 d-1 in winterand4.96ttmol during
spring
of 7/•molm-2d-1 or about
25molha-1yr-1.
S m-2 d-1 in summer. The annualmarine fluxesof Berre- This flux is also substantiallyhigherthan our measurements.
sheim
andBates
etal. areabout18molha-1yr-1and13mol However, spatialand temporalvariabilitiesin emissionsand
ha-1 yr-i, respectively,
or abouta factorof 2 greaterthan associateduncertaintiesin extrapolationscompromisethe
ourestimated
deposition
fluxof 8 molha-1yr-1. However, reliability of direct comparisonsbetween Quinn's estimates
TdP is not surroundedby ocean; it is 50 km inland and and our measurements.
separatedfrom the oceanby a significantmountainchain.
NO3- The VWA concentration
of NO3- at TdP was
Thus we expectS depositionat TdP was influencedby both 0.5/mq
'L-1(Table
1),slightly
higher
than
atthePatagonian
marine and terrestrial emissionsand by S depositionin the ice cap(0.3 tmqL-1, Table2) [Aristarain
andDelmas,
overland fetch. Bales el al. [1992] estimate S emissions 1993]. NO3- concentrations
at othersouthern
high-latitude
from terrestrial ecosystemsin the same latitudeas TdP are sites fall within the range of Delmas' [1996] estimatesof
•eqL-1,witha median
of0.66•eqL-1similar
to
0.02ttmolS rn-2d-1and0.19ttmolS rn-2d-1in winterand 0.17-3.33
summer, respectively. The annual rates would be about
1
1
0.4 mol ha- yr-, significantlyless than our estimatedS
depositionrates at TdP. Our estimatedtotal depositionof
nss S at TdP falls between the estimatedbiogenic S emissions in upwind marine and terrestrial ecosystems;the
consistencyof theseestimatesprovidesindependentcorrobo-
thatat TdP (Table2). NO3- in precipitation
at TdP (Figure
ration of their reliability.
1984; Moody et al., 1991].
9c) and at AmsterdamIsland [Moody el al., 1991] exhibit
similarseasonalpatterns. However, long-distance
transport
of pollutantNO3- fromsouthern
Africa to Amsterdam
Island
contributesto the springtimepeak and larger annualVWA
NO3-concentration
of 1.3/•eqL-1[Galloway
andGaudry,
GALLOWAY ET AL.' PRECIPITATION AT A REMOTE SITE IN CHILE
The seasonalityin VWA concentrationand per-event
deposition
of NO3- at TdP are differentfrom thoseof
6893
equal. Becauseof the diverseand poorly quantifiedsources
of oxidizedN species,it was difficult to compareour results
emissions
aswe didfor nssSO4=, andNH4+ .
NH4+, HCOOt, CH3COO
t, msSO4= andCH3SO3-.NO3- to estimated
peaks during australwinter throughlate spring, the others
peak during the austral summer (Figures 5 and 6). The
However, theseestimatesprovideda usefulconstraintfor the
combinedsourcesof oxidized N upwind of TdP.
differentpatternof NO3- suggests
abioticcontrols.Several
processes
(fossil-fuelcombustion,
biomassburning,tramport
from the stratosphere,
or lightning)couldhavebeenresponsible. Given the long fetch over the Pacific and modest
upwindemissionsfrom fossil-fuelcombustion,it is unlikely
Phosphorus
thatthelong-distance
transport
ofanthropogenic
NOywasa
for other regionsare limited. At Lago Yelcho near Puerto
Monte, Chile, the concentrations
of orthophosphate
andtotal
phosphorus
in six precipitationsamplesrangedfrom below
majorcontributorto NO3- measuredin precipitation
at TdP.
However, under conditionsof cold temperaturesand low
The VWA concentrationof the nine samplesanalyzedfor
orthophosphate
(PO4)was0.06/•mol
L-1(Table1),witha
rangeof 0.02/•molL-1to0.10/•molL-1. Phosphorus
data
[NO]/[NO2] ratios typical of the high-latitude,southern detection
limitsto0.08/•molL-1andfrom0.1 to0.2/•mol
Pacific during the austral winter and spring, peroxyacetyl L-1, respectively
(D. Soto,unpublished
data,Universidad
nitrate(PAN' a reservoirspeciesfor NOx producedin more Austral de Chile, 1994). At Katherine, Australia, the VWA
pollutedregions)is sufficientlystableto be transportedlong
concentration
forL-,
P?4in
ten
during
1990
distances[e.g., Crutzen, 1979; Singh and Hanst, 1981' was
0.10 /•mol
with
asamples
rangecollected
of 0.08/•mol
L-1
to
Singhet al., 1985]. PollutantN oxidestransportedas PAN
0.14/•molL-1 (K. Weathers,
unpublished
data,Institute
of
may,therefore,havecontributed
to thehigherNO3- concen-
EcosystemStudies, 1994).
trationsin precipitationand associated
wet-depositionfluxes
at TdP during this period. NO producedby regional
biomassburning was a possiblesource [Fishmanet al.,
Atmosphere-BiosphereInteractions
1991] (H. Levy II, personalcommunication,1995). In the
winter when wind speedsdecrease,burning is prevalent
The atmosphereand biosphere are integrally linked.
acrosssouthernChile (D. Soto, personalcommunication, Ecological processesin terrestrial and aquatic systems
1994)although
the concentrations
of nssK+ (a tracerof control,to varyingdegrees,emissionsof nitrogenandsulfur
biomassburning;Andreae[1983]) at TdP were low (annual compoundsto the atmosphere. For instance,seasonal
VWA nssK+ was0.2 /•eqL-1, Table1) andshowed
no relationships
in our datasuggestthat the biosphereexerted
considerablecontrol over atmosphericconcentrationsof
seasonal
signal.Transport
of NOyfromthestratosphere
may have been important. Mayewskiand Legrand [1990]
NH4+, nssSO4=, CH3SO3-,HCOOt, and CH3COO
t at
TdP. In addition,atmosphericdepositionis a major source
Antarctica during the austral spring possibly becauseof of water, nutrients, and toxic substancesfor aquatic and
transportfrom the lower stratosphereassociatedwith terrestrialecosystems[e.g., Gorham, 1961' Likens et al.,
formation of polar stratosphericclouds and, therefore, 1977]. Atmosphericdepositionmay be an important N
connected with the Antarctic ozone hole. Long-range sourcefor freshwaterecosystems
in the TdP region. Prelitransportof NOx (and its reactionproducts)producedby minaryinformationsuggeststhat freshwatersystemsin TdP
lightningin the low-latitudetroposphereand lower strato- are oligotrophicand perhapsN limited [Sotoet al., 1994].
sphereand NOx producedby N20 oxidationwithin the For example, Lago Toro, the largest lake in TdP, has a
lowerstratosphere
mayalsobe importantsources
for NO3- water volumeof 30.2 km3 with a theoreticalturnovertime
13years.Thedominant
cations
areCa+ +
in precipitationin high-latituderegions of the southern ofapproximately
hemisphere [Legrand and Kirchner, 1990]. However, and Na+' the dominant
anionsare HCO3- and SO4=
Likens et al. [1987] report no correlation between the [Camposet al., 1994a, b]. BetweenSeptember1988 and
of NO3- range
frequency
of locallightningandNO3- in rainfallat Kather- January1991, the nutrientconcentrations
reporthigherNO3-concentrations
at DomeC andVostokin
0.36tzmol
L-• and2.0tzmol
L-• andthose
ofPO4
ine, Australia. Seasonal
variabilityin NO3- overthe high- between
latitude southernoceans is caused by multiple factors of
unknown magnitude (see also, Savoie et al. [1993]).
Relative to other species(e.g., nss SO4=, CH3SO3-,
HCOOt,CH3COOt),biological
processes
appeared
tobeless
important
sources
for NO3- in TdP precipitation.
Theannualwet-deposition
rateof NO3-at TdPwas3.6 eq
ha-1 yr-1 (3.6 molha-1 yr-1) (Table1). Thisflux was
somewhatlower thanLevy et al.'s recentmodelestimate(H.
Levy II et al., NOAA's GeophysicalFluid Dynamics
Laboratory, Princeton University, Global depositionand
distributionof reactive nitrogen in the troposphere,manu-
between
0.06tzmolL-1 and0.66tzmolL-1. TheN:Pratio
by weight for thesedissolvedinorganicnutrientsis usually
below 5, as are the TN:TP molar ratios. In contrast, the
N:P ratiosin precipitationfor thosesamplesin which both
elementsare measuredis 12, with a range of 3-37. These
ratiosindicatea potentialnitrogenlimitationfor phytoplankton growth in Lago Toro [Sotoet al., 1994].
Like many high-latitudeterrestrial ecosystemsin the
southernhemisphere[McGuire et al., 1992], terrestrial
ecosystems
in TdP are nutrientpoor and someare N limited
[Soto et al., 1994]. These systemsreceive nitrogen from
scriptin preparation)
of 6 molha-1 yr-1. However,
when severalsources,includingatmosphericdeposition,nitrogen
we accountedfor the differencesin precipitationamounts fixation, mineralization, and migrating animals. Net
(Levyetal.use100cmyr-1;weused75cmyr-1),theLevy primary production(NPP) by terrestrialecosystemsat the
ofTdPrequires
360-2,600
molha-1yr-1ofnitrogen
et al. estimate
dropped
to 4.5 molha-1yr-1,similar
to our latitude
2
1
measuredvalue. Levy et al. estimatea total NO,• deposition (0.5-3.7 g N m- yr- [Melillo et al., 1993]). Since the last
of 14.5 mol ha-1 yr-;1 wet and dry fluxesare approximately
•
glaciationabout 10,000 years ago, these ecosystemshave
6894
GALLOWAY ET AL.'
PRECIPITATION AT A REMOTE SITE IN CHILE
Table 3. ChemicalSpeciesin Precipitation
at RemoteMarineandContinental
Sites
Torres del
Paine, Chile
AmsterdamIsland,
IndianOcean
Katherine,
Australia
Barbados,
WestIndies
Lijiang,
China
Volume-weighted
average
(VWA)
concentration,
I•eqL-1
H + , total
H+, mineral
pH, mineral
K+
10.9
5.5
5.26
0.2a
8.0
4.5
5.35
0.4a
17.1
5.4
5.27
0.8b
Mg++
0.2a
1.9a
NH4+
NO3-
0.6
0.5
1.3a
2.4
1.0
1.0b
1.5b
2.8
3.6
SO
4-
1.2a
3.2a
3.0b
CH3SO
3-
0.19
0.13
3.0
9.6
CH3COO-
0.5
0.5
2.1
HCOO.
5.5
3.2
CH3C(50
t
1.0
0.8
Ca++
C1-
HCOO-
0.5a
1.6a
7.3a
4.9
6.1b
---
62
23
5 64
9.6
5.9
5.23
0 3a
23 a
4 5a
0.3b
0.4 b
2.0b
28
29
5.4 a
4.0
1.5
4.0 a
1.9b
5.7b
0.06
2.7
1.2
2.9
0.8
___
Volume-weighted-average
(VWA)
concentration,
i•mol
L4
10.5
4.2
2.8
3.1
1.8
1.4
Concentrations
of K+, Mg++, $O4=, CI-,andCa++ forTorres
delPainearefromthisstudy;
forAmsterdam
Island,IndianOcean,from GPCP unpublished
data(J. N. GallowayandW. C. Keene,Universityof Virginia, 1995);
for Katherine,Australia, from Likenset al. [1987]; for Barbados,from J. N. Gallowayand W. C. Keene (University
of Virginia,unpublished
data, 1995);andfor Lijiang,ChinafromKeeneet al. [1995b].
aNon-sea-salt concentrations.
bTotal concentrations.
beginto increasebecause
of enhanced
nitrateformationand
fixationof N2, (2) atmospheric
deposition
of nitrogenfixed discharge[Hedin et al., 1995]. Hence, as the terrestrial
at TdP receiveadditionalN, mobilization
of N
by lightningor by other ecosystems(terrestrialand marine) ecosystems
may increase.
and then transportedto TdP via the atmosphere,or (3) to the downstreamaquaticecosystems
migratingorganisms. Over the centuriesso much external
receivedmost nitrogen from external sourceseither by (1)
N has accumulatedin the TdP ecosystemsthat internal
cycling (N mineralization)has becomethe primary source.
For exampleN mineralizationin high-latitudeboreal forests
PrecipitationCompositionat TdP VersusOther
same range as required for NPP. Current rates of N
deposition(Table 1) are relativelyminor nutrientsourcesfor
biota when comparedto the N suppliedby mineralization.
Galloway et al [1994] estimatethat in 2020 NO depoß will increaseto about40 mol hay lyr-1
sition in this region
informationaboutthe likely compositionof precipitationin
the northern hemispherebefore the industrial revolution.
Consequently,
it can be used as a baselineagainstwhich
precipitationcompositionin more populatedareas can be
assessed[Galloway et al., 1982; 1984; 1987]. The concen-
andgrasslands
supplies
from640to 1900molha-1yr-1 (9- Regions
Precipitationcompositionin remote regions provides
27 kg N ha-1yr-1 [McGuire
et al., 1992]),whichis in the
compared
to the ---15 molha-•yr-1thatcurrently
exists. trations
of nssSO4= , NO3-,andNH4+ in precipitation
at
TdP were within the rangesof those at other high-latitude
sitesin the southernhemisphere(Table 2) but were substantially lower thanthoseat marine(Barbados,AtlanticOcean,
beontheorderof 100Tg N yr-•. GiventheirN-limited and Amsterdam Island, Indian Ocean) and continental
status,future increasesin N depositionwill probably first (Lijiang, China, andKatherine,Australia)locationsat lower
result in additionalproductivity of freshwater ecosystems. latitudes(Table 3). Galloway et al. [1984, 1987] compare
For terrestrialecosystems,our projectionof 2020 N deposi- precipitationcompositionin remote regions to that in
tion is well below the estimatedmineralizationsupply rate populatedregions of the developedand developingworld.
Assumingfertilizer use and other agriculturalactivitiesin
upwind regionsresultsin an equivalentincreasein NH x
deposition,total N depositionin the next few decadeswill
anddepositions
of nssSO4= and
of 640-1900
molha-1yr-•. However,
increased
ratesof N In all cases,concentrations
depositionmay indirectly enhanceprojectedincreasesin NO3-aresignificantly
greaterin thepopulated
regions.The
NPP from risingCO2 andperhapstemperature.Melillo et TdP data are consistentwith theserelationships.
In contrast to the situation for strong mineral acids,
al. [1993] suggestthat the responseof NPP in high-latitude
and per-eventdepositionsof carboxylicacids
ecosystems
to suchincreaseswill be dampenedbecauseof concentrations
N limitation. If this limitation is modified by increased fell within the rangesof valuesat otherremoteand impacted
atmospheric
deposition,then NPP may increase,which, in locations[e.g., Keeneand Galloway, 1988]. Suchrelationshipssupportthehypothesis
thatcarboxylicspeciesprimarily
turn, could affect earth's albedo, water balance, etc. In
addition, as N depositionto old-growthforestsincreases originatefrom biogenicprocessesthat involve either direct
fromlessthan70 molha-1 yr-• to levelsgreaterthan emissionsor emissionsof precursorhydrocarbons.Anthro300molha-• yr-1, nitrogen
losses
fromwatersheds
may pogenic processesappear to be relatively unimportant
GALLOWAY
ET AL.:
PRECIPITATION
sourcesfor HCOOH and CH3COOH in the global
troposphere.
Any comparison of precipitation acidity in different
regions is complicatedbecause pH is not conservative;
carboxylic acids and, to a minor extent, the bicarbonate
systemprovide finite buffering capacity. Thus the addition
of pollutantmineral acids to precipitationdoes not corre-
AT A REMOTE
SITE IN CHILE
6895
aerosolandotheratmospheric
constituents.Nss SO4= and
CH3SO
3-primarilyoriginated
fromtheoxidation
of (CH3)2S
from marinebiogenicsources.NO3- probablycamefrom
several sources,includinglocal biogenic emissions,lightning, transport of emissions from biomass or fossil-fuel
combustion in lower latitudes, and transport from the
stratosphere.
The concentrations
of nssSO4=, NO3-, and
spondto a proportionate
changein H + concentrationsNH4+ in precipitation
atTdPwerewithintherangeof those
[Keene et al., 1983]. In addition, many programsdo not
adequatelypreserveprecipitationsamplesagainstmicrobial
degradationafter collection. Thus biologically important
at other high-latitudesites in the southernhemispherebut
were substantiallylower than those at marine (Barbados,
Atlantic Ocean, and Amsterdam Island, Indian Ocean) and
constituents
(e.g., carboxylic
acidsand NH4+) are often continental (Lijiang, China, and Katherine, Australia)
metabolizedandlost from untreatedsamplesbeforeanalysis,
which causessystematicchanges(typically increases)in the
original pH [e.g., Keene and Galloway, 1984]. Becauseof
thesecomplications,caremustbe exercisedwhencomparing
pH measuredin differentregionsby differentprograms.
Likenset al. [1987] infer a backgroundpH from mineral
locations at lower latitudes.
In the next few decades,precipitationcompositionat TdP
will most likely change becauseof internal and external
factors, includingpopulationgrowth, and energy and food
production. IncreasedN depositionhas the potentialto
increasethe productivityof N-limited aquaticecosystems.
acids of approximately5.08 based on the analysisof
unpreservedaliquots of precipitationfrom Katherine,
Australia. This approachmay slightly overestimatethe
actual contributionof mineral acids to free acidity for two
reasons:(1) residualconcentrations
of carboxylicacidsare
occasionally
presentin suchsamples[e.g., Gallowayet al.,
Acknowledgments. Researchperformedin remote regions
requiresthecooperation
of manypeopleandinstitutions.In Chile,
we appreciate
the supportof CarlosWeber, CorporacionNacional
Forestal(CONAF), Santiago,and of the staff of CONAF in Punta
1982],and(2) NH4+ is consumed
[e.g.,Keeneet al., 1983]
Arena. We thank Guillermo Santana, Director of TdP National
Park, and Jovito Gonzales and Cristina Yanez who collected the
possiblycontributing
to free acidity. Becauseuntreated samples
andmaintained
theequipment.A specialnoteof appreciaaliquotsof samplefrom TdP were not routinelyanalyzed tion to Doris Soto B. who providesa bridgebetweenscientists
and to eliminatethe potentialfor the above problems,we
speaking
two differentlanguages
and who participated
in helpful
on the influenceof atmospheric
deposition
on aquatic
adopteda differentapproachfor estimatingthe background discussions
ecosystems.In the UnitedStates,we gratefullyacknowledge
Tom
pH corresponding
to mineralacids.
TheVWA concentration
of H + contributed
by carboxylic Butler, Alex Pszenny,KathleenWeathers,andBruceWiersmawho
andmineral
acidsin precipitation
atTdPwas10.9/xeq
L-1
(pH = 4.96). To comparethiswithunpreserved
samplesof
precipitationfrom pollutedregions(and ignoring minor
influences of the carbonate system), we subtracted the
contributions
of dissociated
HCOOH andCH3COOHto free
acidity;
theresidual
fraction
of H+ contributed
by mineral
acids
was5.5/xeqL-1(pH= 5.26).Similar
calculations
for
data from other remote sites in both marine and continental
assisted
in establishing
andmaintaining
thesite. ConnieKnighting,
John Maben, Judy Montag, and Cheryl Reinhartanalyzedthe
samples;Ishi Buffamaidedin datareduction. Financialsupport
was providedby the U.S. National Oceanicand Atmospheric
Administrationand the U.S. Departmentof State. We also
appreciate
theassistance
of GerryBell andBobWoodin obtaining
the SouthernOscillationIndex data; the helpful discussions
with
Rick Artz, Lars Hedin, Hiram Levy II, JohnMiller, Bill Schlesinger, and Kathleen Weathers; and the constructivecommentsof two
anonymousreviewers.
regionsyielded a tight pH range of 5.23 to 5.64 for the
VWA contributionsof mineral acids to free acidity (Table
3). This estimated range reflects upper limits for the
influence
of
mineral
acids
from
natural
sources
since
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