Large sulfur-isotope anomaly in nonvolcanicsulfate aerosol and its implications for theArchean atmosphereRobina Shaheena, Mariana M. Abaunzaa, Teresa L. Jacksona, Justin McCabea,b, Joël Savarinoc,d, and Mark H. Thiemensa,1

aDepartment of Chemistry and Biochemistry, University of California, San Diego, La Jolla, CA 92093; bPacific Ridge School, Carlsbad, CA 92009; cLaboratoirede Glaciologie et de Géophysique de l’Environnement, Centre National de la Recherche Scientifique, Unité Mixte de Recherche 5183, F-38041 Grenoble, France;and dLaboratoire de Glaciologie et de Géophysique de l’Environnement, Université Grenoble Alpes, Unité Mixte de Recherche 5183, F-38041 Grenoble, France

Edited† by Barbara J. Finlayson-Pitts, University of California, Irvine, CA, and approved July 18, 2014 (received for review April 8, 2014)

Sulfur-isotopic anomalies have been used to trace the evolution ofoxygen in the Precambrian atmosphere and to document pastvolcanic eruptions. High-precision sulfur quadruple isotopemeasurements of sulfate aerosols extracted from a snow pit atthe South Pole (1984–2001) showed the highest S-isotopic anoma-lies (Δ33S = +1.66‰ and Δ36S = +2‰) in a nonvolcanic (1998–1999)period, similar in magnitude to Pinatubo and Agung, the largestvolcanic eruptions of the 20th century. The highest isotopic anom-aly may be produced from a combination of different stratosphericsources (sulfur dioxide and carbonyl sulfide) via SOx photochemis-try, including photoexcitation and photodissociation. The source ofanomaly is linked to super El Niño Southern Oscillation (ENSO) (1997–1998)-induced changes in troposphere–stratosphere chemistry anddynamics. The data possess recurring negative S-isotope anoma-lies (Δ36S = −0.6 ± 0.2‰) in nonvolcanic and non-ENSO years, thusrequiring a second source that may be tropospheric. The genera-tion of nonvolcanic S-isotopic anomalies in an oxidizing atmo-sphere has implications for interpreting Archean sulfur depositsused to determine the redox state of the paleoatmosphere.

UV photolysis | sulfur isotopes

Sulfur is a ubiquitous element on Earth. Its multiple valencestates (S−2 to S+6) permit it to participate in a range of

photochemical, geochemical, and biochemical processes, and itsfour stable isotope (32S, 33S, 34S, and 36S) allow tracing of chemicalreactions at a molecular level. Multiple sulfur isotopes (δ33S, δ34S,and δ36S) and concomitant anomalies (Δ33S and Δ36S)‡ in paleo-sediments [>2.5 giga-annum (Ga)] have been used to trace theorigin and evolution of life and rise of oxygen in the Earth’spaleoclimatic history (1–3). In the present atmosphere, theconcentration of sulfate in ice cores and associated S-isotopeanomalies has served as a forensic tool to help understand thedynamics of volcanic emissions, such as transport and trans-formation of sulfur to the stratosphere and its impact on ozonechemistry (4–7). The low concentration of sulfate (SO4

2-) in icecores during volcanically quiescent periods and associated ana-lytical challenges to analyze all four S-stable isotopes at highprecision have restricted studies of the temporal distribution ofsulfur mass-independent signatures. Here, we present a high-resolution seasonal record (1984–2001) of quadruple S-stableisotopes and concomitant isotope anomalies of sulfate aerosolsextracted from a snow pit (1 × 1 m) at the South Pole (89.5° S,17.3° W; 2,850 m) (8) to gain further insight into sources, pho-tochemistry, and associated sulfur transformations of strato-spheric sulfate aerosols (SSAs). The time period encompassestwo major volcanic eruptions and three large El Niño SouthernOscillation (ENSO) events. A recent study has attributed a globalwarming hiatus (9) to a super ENSO event (1997–1998); therefore,data from this period are timely for understanding changes instratospheric sulfate aerosol chemistry that play an important role inmitigating global warming trends via scattering of incoming solarradiation. Oxygen triple isotope measurements of sulfate aerosols

(1980–2002) have recently revealed how ENSO-driven changesaffect the global transport and transformation of sulfate aero-sols from the troposphere to the stratosphere and across hemi-spheres (10).

Results and DiscussionThe highest SO4

2- concentration in snow [154 parts per billion(ppb)] is observed after volcanic activity (Pinatubo, June 1991;Cerro Hudson, August 1991). The addition of volcanic sulfate to thestratospheric baseline sulfate aerosol (or background sulfate aerosolas defined in SI Appendix, Section 2) produced a significant de-crease in heavy sulfur isotopes. The baseline sulfate aerosol value ofδ34SBG= 12‰ dropped to ∼3‰ (Fig. 1A) following the Pinatuboeruption, and δ33S, δ36S tracked this isotopic trend. The contribu-tion of sea salt sulfate at the South Pole is <9%, indicating long-range transported aerosol to be the main sulfate component (10). Abroad range in δ33S (1.61–11.32‰), δ34S (2–20‰), and δ36S (2.8–37‰) values for the sampling time period indicates the originof sulfate aerosols from various sulfur sources and chemical anddynamical processes. A significant positive correlation of δ34S

Significance

The highest S-isotope anomaly is observed in a nonvolcanicperiod, and the magnitude of anomaly is similar to the largestvolcanic eruptions of the 20th century. S-quadruple isotopedata provided the first evidence of how super El Niño SouthernOscillation (ENSO) events (1997–1998) have affected the trans-port and transformation of aerosols to the stratosphere; thus,record of paleo-ENSO events of this magnitude can be tracedwith the S-isotopic anomaly. High-resolution and high-precisionS-isotopic fingerprinting also revealed that the troposphericsulfate produced during fossil-fuel and biomass burning con-tributes to the stratospheric sulfate aerosol layer, a contributionpreviously unrecognized. The distribution of sulfur anomaliesmimics the Archean isotope record, which is used to track theorigin and evolution of oxygen on earth.

Author contributions: R.S., J.M., J.S., and M.H.T. designed research; R.S., M.M.A., and T.L.J.performed research; R.S., J.M., and M.H.T. contributed new reagents/analytic tools; R.S.,J.S., and M.H.T. analyzed data; and R.S. wrote the paper.

The authors declare no conflict of interest.†This Direct Submission article had a prearranged editor.1To whom correspondence should be addressed. Email: mthiemens@ucsd.edu.

This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1406315111/-/DCSupplemental.

‡MIF. Here, delta denotes the ratio of the least abundant to the most abundant isotope{e.g., δ33S = [(33S)/(32S)sample/(33S)/(32S)std − 1) × 1,000]} relative to the same ratio instandard, which is Canyon Diablo Troilite (CDT) and expressed in parts per thousand (‰).Most natural processes fractionate S isotopes in proportion to mass differences and aredescribed by δ33S ≈ 0.515*δ34S, and δ36S ≈ 1.91*δ34S, except UV photolysis of SO2. Thedeviation from mass-dependent fractionation (MDF) is called anomalous or mass-inde-pendent fractionation (MIF) and quantified by Δ33S and Δ36S.

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with δ33S and δ36S (δ33S = 0.508*δ34S + 0.2, r = 0.97; δ36S =1.94*δ34S – 0.876, r = 0.99) is observed (SI Appendix, Fig. S2).The maximum S-isotopic anomalies of Δ33S = +1.6‰ and

Δ36S = +2.0‰ observed in 1998–1999 (Fig. 1B) occurs after thestrongest El Niño event (1997–1998) of the decade. The peak isassociated with a sharp increase in potassium (K) concentration(up to 42 ppb). This anomaly (Δ33S) is ∼2 times higher than thePinatubo signal (Δ33S = +0.9‰) whereas the Δ36S is similar inmagnitude to the Agung eruption (Δ36S = +2.5‰) (5), thelargest volcanic eruption of the 20th century.These S-isotopic anomalies are within the reported volcanic

sulfate isotopic ranges between Δ33S = −1‰ to +0.9‰ andΔ36S= −5‰ to +3‰ (5, 11), suggesting similar photochemicalprocesses (Fig. 2A). Laboratory experiments have demonstratedthat the S-MIF originates during SO2 photolysis at short wave-lengths (λ < 300 nm), producing sulfate with positive Δ33S andnegative Δ36S values, and a wide array of slopes (Δ36S/Δ33S),ranging from −1.1 to − 4.3 depending on wavelength (12),pressure, and composition of the gaseous mixture (13) . Theobservations suggest that the S-isotope anomaly in sulfateaerosol in 1998–1999 is a consequence of SOx (SO2, SO3)photochemistry (5, 6, 12, 14) in the short UV (<200 nm) regionof the solar spectrum above the ozone layer (>25 km) where this

wavelength is available in the present-day atmosphere, as will bediscussed. The S-isotopic anomalies observed in volcanic sulfateaerosols are accompanied by a significant increase in sulfateconcentration (4, 5, 11). The Pinatubo and Cerro Hudsoneruptions in 1991 produced a factor of 3.7 sulfate concentrationincrease in the snow record. The observed unprecedentedS-isotope anomaly is not accompanied by a massive Pinatubo-sizeincrease in sulfate concentration, thus requiring new, or highlyperturbed, chemical, photochemical, and dynamical processes.Our high-resolution, seasonally resolved sulfate aerosol data reveal

the presence of a negative S-isotope anomaly (Δ36S(avg) ∼ −0.6‰)during nonvolcanic and non-ENSO baseline periods (SI Appendix),suggesting the presence of a second isotopically anomaloussulfate source. The S-isotopic anomaly during these time periodsis within the range reported for tropospheric sulfate aerosols(15) of Δ36S= −0.3‰ to −2‰ (Fig. 2B). In the present atmo-sphere, short UV is blocked by the O3 layer; thus, the negativeanomaly in tropospheric sulfate aerosol cannot be attributed toshort-wavelength SOx photolysis. Romero and Thiemens (15)suggested possible transport of stratospheric S-isotope anomalyto the troposphere at low and mid latitudes. Considering thetropospheric S burden (16) (SO2 from fossil-fuel combustion ∼78 Tg S·yr−1, biomass burning ∼ 2 Tg S·yr−1, and natural sources∼ 25 Tg S·yr−1), it is unlikely that even a 10% transport of SSA(0.01 Tg S·yr−1) can produce such a significant isotopic change intropospheric sulfate aerosols. Alternatively, a 0.01% transport ofanomalous sulfate from the troposphere to stratosphere cancause a significant change (Δ36S = −0.9‰) in the isotopic com-position of SSA (SI Appendix), provided tropospheric sulfur isanomalous. Laboratory studies demonstrate that a negative S-iso-tope anomaly can be produced by nonphotochemical processes,such as primary sulfate produced during fossil-fuel combustion(Δ36S = −0.8‰ to −1.7‰) and biomass burning (Δ36S = −0.1‰to −2‰) (SI Appendix, Table S3) (17). The mechanism that gen-erates the negative anomaly in such processes is unknown (radicaldriven or recombination reactions may be operative, for example),but, clearly, high-temperature sulfur oxidation processes are a via-ble source for the tropospheric negative anomaly. The S-isotopiccomposition (δ34S, Δ33S, and Δ36S) of baseline sulfate suggeststransport of SO2 and SO4 to the stratosphere despite its normalshort tropospheric life time (∼2–5 d).The observed positive sulfur anomaly during 1998–1999

requires a stratospheric photochemical process involving SO2. Itis generally accepted that only explosive volcanic eruptions[volcanic explosivity index (VEI) > 4] have sufficient energy totransfer tropospheric boundary material into the stratospherethat attain altitudes where short UV region at λ < 300 nm isavailable. The Smithsonian database of global volcanic eruptions(www.volcano.si.edu) and Stratospheric Aerosol and Gas Experi-ment II (SAGE II) archives (18), however, do not list any significantplinian volcanic activity in 1998–1999, ruling out volcanic SO2 inputto the stratosphere as a source for the observed positive S-isotopicanomaly. Increased SO4 concentrations from local (Antarctic)sources is ruled out because sea salt sulfate and sulfate producedfrom DMS oxidation is isotopically normal (5, 6). A potential newsource of the increase in sulfate concentration and S-isotopicanomaly could be the higher altitude transport of SO2 and po-tentially from carbonyl sulfide (COS) by deep convection to thetropical tropopause layer, followed by SO2 photochemistry uponstratospheric COS oxidation (19). COS, the most abundanttropospheric S compound [∼500 parts per trillion (ppt)], istransported to the stratosphere (19) and removed by photolysis(∼70%) to SO2 above 25 km. Increased COS (20–50%) in thetropical tropopause layer (the main entry region to the strato-sphere), along with a substantial increase in other tracers ofbiomass burning (BB), including CO, HCN, CH3Cl, NOx, NOy in1996 and 1999–2000, has been observed (20). Potassium (K),a tracer of BB, can serve in certain circumstances as a tracer of

Fig. 1. (A) The concentration profile (1983–2000) of SO4 and δ33S, δ34S, δ36Ssulfate aerosol extracted from snow-pit samples at the South Pole. Noteanticorrelation between SO4 concentration and S-stable isotopes of SO4 aerosolafter Pinatubo and Cerro Hudson eruptions. (B) Sulfur-isotope anomaly (Δ33Sand Δ36S) of sulfate aerosols extracted from the snow-pit samples at the SouthPole (1983–2000). For comparison, the ENSO-O3 Index is also shown. Notethat 1997–1998 biomass burning increased the O3 concentration in the uppertroposphere/lower stratosphere (42) followed by a sharp decline in O3 andconcomitant increase in S-MIF. Purple bars indicate strong El Niño SouthernOscillation events, and M stands for moderate ENSO.

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forest fires (21, 22), and ice-core data have revealed increased Kconcentration after intensive biomass burning events from 1750to 1980 (23). There are no global measurements of trace gases

available from 1998 to 1999 BB events. Andreae and Merlet (24)estimated ∼1.8 Tg of S (∼15% contribution from COS), K (1.9Tg), NOx (20.7 Tg), and CH3Cl (∼0.65 Tg) emissions from globalBB events. El Niño Southern Oscillations are known to signifi-cantly affect chemistry, temperature, and dynamics of the tro-posphere and stratosphere (25) (SI Appendix). ENSO-inducedvariations in the upper troposphere/lower stratosphere (UT/LS)ozone levels (26) have been captured in the oxygen triple isotopedata of sulfate aerosols (1981–2004) retrieved from the SouthPole through its effect on the SO2 oxidation pathways (10). The1998–1999 and 1984 peaks are the only deviants from the bulkS-isotope anomalies (Fig. 1B), and special processes are requiredfor these two time periods. Assuming COS and SO2 from wildfiresas the source of sulfur in this period with higher altitude trans-port to the stratosphere (18, 19) via pyrocumulus nimbus clouds(27), subsequent photochemistry of COS produced SO2 above25 km could provide an extra S-isotope anomaly source. Thealtitude for both SO2 photo excitation and photolysis in this caselikely differs from volcanic SO2 due to its production above theozone layer. Additionally, S-MIF signatures recorded in ice coresafter major volcanic eruptions are actually a mixture of anoma-lously produced sulfate via SOx photolysis and mass-dependentlyproduced sulfate via SO2 + OH reaction (∼90% for Pinatubosulfate), thus diluting the actual S-MIF signal (6, 7).The origin of the S-MIF is a function of the actinic light

spectrum for both photoexcitation and photodissociationprocesses of SO2 (12, 28). Laboratory experiments have shownthat COS photolysis at λ < 220 nm produces elemental sulfurS0 with no S-isotope anomaly (29). In an oxidizing environ-ment, however, COS photolysis produces SO2 (19), and sub-sequent photochemical transformations at short wavelengths(<280 nm) can produce S-MIF in sulfate (12, 14). A recentmodel that considers SO2 photoexcitation rather than pho-tolysis and volcanic plume chemistry (including heteroge-neous stratospheric chemistry) suggests that UV photoexcitation of SO2 is another route to the observed S-MIF involcanic sulfate. This new mechanism may also provide in-formation about the ozone-depletion chemistry in the plume(30) and is relevant for the present data. Laboratory experimentsindicate that SO2 photodissociation is wavelength-dependent(Δ36S/Δ33S slopes vary from −1 at λ = 193 nm to −4 at λ = 248 nmas shown in Fig. 2), and the deviant sulfate circled points (1998–1999) may result from photochemistry at shorter wavelength, likelyin the bands below 220 nm. There are no numeric simulations(including stratospheric heterogeneous chemistry and photo-chemical transformations) that are directly applicable to thepresent case where the dynamics and chemistry are perturbed asa result of changes in stratosphere–troposphere dynamics and in-tensive global BB following the super ENSO event (1997–1998),and it is difficult to quantify the excess sulfur reaching an altitudefor the required wavelength (<220 nm). Based on the SO2 pho-tolysis experiments at short wavelength (193 nm) by Farquharet al. (12), if Δ36S(SO4)= 20‰ is assumed as an upper limit{isotopic mass balance; Im [(Δ36S(SO4) = 20‰) = (2‰_ENSO +2.6‰_BG + ENSO)*40 ppb_background sulfate/excess SOxfrom biomass burning]}, isotope mass balance suggests that theincremental SOx required above background level in the strato-sphere (>25 km where λ < 200 nm light is available) to produceΔ36S = 2‰ is 5 ppb.The potential importance of different sulfur sources (e.g.,

COS and differing SO2 photochemistry) and the second tropo-spheric source may have further consequences in the Earth’searly atmosphere (31). Mass-independent isotopic compositionsin S-bearing molecules have been observed in the Earth’s oldestrocks, which are interpreted as reflecting lowered oxygen andozone concentrations in the atmosphere allowing troposphericSO2 photochemistry at short wavelengths (1). There is debate asto the oxidation state of Earth’s atmosphere–hydrosphere before

Fig. 2. (A) Comparison of the sulfur-isotopic anomaly in aerosols (1983–2001) extracted from the snow pit (1 × 1 m) at the South Pole station (greensquares) with the volcanic sulfate aerosol retrieved from ice cores (4–6, 11). (B)Comparison with tropospheric aerosol collected at various sites in the UnitedStates (15) [La Jolla, CA (blue circles); Shenandoah National Park, VA (redcircles); and Bakersfield, CA (yellow circles] (SI Appendix, Table S4) and fossil-fuel and biomass burning signatures (magenta triangles) (SI Appendix, TableS3). Δ36S/Δ33S slope of SO2 photolysis experiments using ArF excimer (193 nm)and KrF (284 nm) Xe-lamp (continuum from 220 nm to longer wavelength)are also shown for comparison(12). (C) S-isotope anomalies in sulfate andsulfide deposits from Precambrian rocks record (32) to the present-day sedi-ments and comparison with aerosols in the present-day atmosphere.

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∼2.4 Ga. Large mass-independent fractionation of S isotopes inpre-2.4 Ga sedimentary rocks and their absence in post-2.4 Gacounterparts support the hypothesis for a reducing Archeanatmosphere–hydrosphere (32, 33). Models assume that UV pho-tolysis of volcanic gaseous SO2 in a low pO2 atmosphere (3, 14,34) is the source of S-isotope anomaly. The rate of volcanicsupply of SO2, COS, H2S, photochemical transformation, andfurther reactions to form sulfates (S+6), sulfite (S+4), elemental S(S0), and sulfide (S−2) determines the overall signature preservedin the rock (35, 36). Processes that can remove SO2 from theatmosphere, such as homogeneous oxidation with OH radicaland heterogeneous chemistry with O3 and H2O2 in the cloud, canreduce the S-MIF in the atmospheric S pools (35). However, thepresence of large S-MIF in the Archean rock record (Δ33S = −2‰to +12‰ and Δ36S= −10‰ to +2 ‰) (36) is used to constrainthe upper limit of 10−5 present atmospheric level (PAL) of at-mospheric oxygen levels in the Archean atmosphere (34). Themixing of atmospherically derived S-MIF pool with the micro-bially derived S-MDF pools in the marine sediment lowers theoverall magnitude of atmospherically derived S-MIF signal.Comparison of the S-isotope anomaly of marine paleo-sediments(sulfates and sulfide) with present-day sulfate aerosol, includingtropospheric aerosols (Fig. 2C), reveals that the S-isotopeanomaly resides in a similar S-quadruple isotope space althoughthe magnitude of S-isotope anomaly in ice-core data is smallerthan the Precambrian record. The result suggests that both maybe produced by the same SOx photochemical processes and thatfactors such as photolysis wavelength and pressure may be impor-tant in accounting for some of the differences (12, 13). The pres-ence of S-MIF in the present-day atmosphere in nonvolcanicaerosols (encircled points) after the super ENSO 1997–1998 sug-gests that these two sources (SO2 and COS) could contribute tosulfur-isotopic anomalies in the Archean. Thermodynamic gasphase equilibrium shows COS to be a stable product of reactionssuch as CO2 +H2S → COS +H2O and CO +H2S → COS+H2 inreducing and oxidizing environments and has been detected interrestrial geothermal fluids and present-day volcanoes (37), theatmosphere of Venus (38), and dense molecular clouds and comets(39, 40). Consequently, COS is another plausible S species in a re-ducing early earth environment. Numeric simulations of the CO2-rich (1%) early Archean atmosphere suggest that COS (5 ppm) mayhave provided a greenhouse effect (41). If COS undergoes hydro-lysis reactions, it could lead to SO2 in both oxidizing and reducing

environments, and the anomaly observed may be a consequence ofboth SO2 and COS photochemical transformations in early Earth.This observation suggests that it is imperative to consider suchreactions in the early Earth models to facilitate the optimal un-derstanding of the Earth’s early atmosphere and its oxygen record.The present work suggests that modeling efforts on the con-

sequences of COS emissions from past sources should be explored,especially isotopically, and should include aerial and subaerialvolcanoes, fumaroles, and oceans. It is apparent from the S-isotopeanomaly plots (Fig. 2) that short UV-processed aerosols producedby potentially amplified COS/SOx sources lie within the rangereported for the early Archean sediments (sulfide and sulfates) andfor the two largest volcanic eruptions of the century, Pinatuboand Agung; therefore, new models of the Archean folding inCOS and additional sulfur isotopic chemistry are needed to fur-ther resolve the early Earth environment. A long-term record ofS-quadruple isotopes along with other tracers of biomass burning,such as soot and other tracers, is needed to quantify past ENSOand BB events and to assess future impact on stratospheric O3chemistry during time periods of increased biomass burning in thepresent-day atmosphere and stratospheric inputs.

Materials and MethodsSulfate aerosol were extracted from a 1 × 1 m snow pit at the South Pole(2,850 m high; snow accumulation rate 84 kg·m−2·a−1; mean annual tem-perature −49.5 °C), Antarctica (8). The sample preparation for O-isotopeanalysis and SO2 collection for sulfur isotope analysis were described earlier(10). SO2 gas was converted to SF6 for S-quartet isotope analysis followingthe method developed earlier in our laboratory (3, 12, 43). The δ33S, δ34S,δ36S, Δ33S, and Δ36S showed standard deviations of 0.06‰, 0.1‰, 0.4‰,0.05‰, and 0.2‰, respectively, over the course of one year (sample size = 1–2 μmole; SI Appendix, Table S2).

The mass independent signatures of S are measured as (3):

Δ33S = δ33S − 1,000*[(1 + δ34S/1,000)0.515 − 1]Δ36S = δ36S − 1,000*[(1 + δ36S/1,000)1.91 − 1].

ACKNOWLEDGMENTS. We thank anonymous reviewers for critical evalua-tion that greatly improved our manuscript. The National Science FoundationAtmospheric Chemistry Division and polar program are recognized for theirsupport through Awards ATM0960594 and OPP0125761. J.S. thanks theAgence Nationale de la Recherche [ANR-NT09-431976-volcanic and solarradiative forcing (VOLSOL)] and the Centre National de la RechercheScientifique/Projet International de Coopération Scientifique exchange pro-gram for their financial support for maintaining the collaboration with theUniversity of California, San Diego.

1. Thiemens MH, Shaheen R (2014) 5.6-Mass-independent isotopic composition of ter-restrial and extraterrestrial materials. Treatise on Geochemistry, eds Holland HD,Turekian KK (Elsevier, Oxford), 2nd Ed, pp 151–177.

2. Thiemens MH (2006) History and applications of mass-independent isotope effects.Annu Rev Earth Planet Sci 34:217–262.

3. Farquhar J, Bao H, Thiemens M (2000) Atmospheric influence of Earth’s earliest sulfurcycle. Science 289(5480):756–759.

4. Baroni M, Savarino J, Cole-Dai J, Rai VK, Thiemens MH (2008) Anomalous sulfur iso-tope compositions of volcanic sulfate over the last millennium in Antarctic ice cores. JGeophys Res 113(D20):D20112.

5. Baroni M, Thiemens MH, Delmas RJ, Savarino J (2007) Mass-independent sulfur iso-topic compositions in stratospheric volcanic eruptions. Science 315(5808):84–87.

6. Savarino J, Romero A, Cole-Dai J, Bekki S, Thiemens MH (2003) UV induced mass-independent sulfur isotope fractionation in stratospheric volcanic sulfate. GeophysRes Lett 30(21):2131.

7. Savarino J, Slimane B, Cole-Dai J, Thiemens MH (2003) Evidence from sulfate massindependent oxygen isotopic compositions of dramatic changes in atmospheric oxi-dation following massive volcanic eruptions. J Geophys Res 108(D21):ACH7-1-6.

8. McCabe JR, Thiemens MH, Savarino J (2007) A record of ozone variability in SouthPole Antarctic snow: Role of nitrate oxygen isotopes. J Geophys Res 112(D12):D12303.

9. Tollefson J (2014) Climate change: The case of the missing heat. Nature 505:276–278.10. Shaheen R, et al. (2013) Tales of volcanoes and El-Niño southern oscillations with

the oxygen isotope anomaly of sulfate aerosol. Proc Natl Acad Sci USA 110(44):17662–17667.

11. Lanciki A, Cole-Dai J, Thiemens MH, Savarino J (2012) Sulfur isotope evidence of littleor no stratospheric impact by the 1783 Laki volcanic eruption. Geophys Res Lett 39(1).

12. Farquhar J, Savarino J, Airieau S, Thiemens MH (2001) Observation of wavelength-sensitive mass-independent sulfur isotope effects during SO2 photolysis: Implicationsfor the early atmosphere. J Geophys Res Planets 106(E12):32829–32839.

13. Masterson AL, Farquhar J, Wing BA (2011) Sulfur mass-independent fractionationpatterns in the broadband UV photolysis of sulfur dioxide: Pressure and third bodyeffects. Earth Planet Sci Lett 306(3-4):253–260.

14. Pavlov AA, Kasting JF (2002) Mass-independent fractionation of sulfur isotopes inArchean sediments: Strong evidence for an anoxic Archean atmosphere. Astrobiology2(1):27–41.

15. Romero AB, Thiemens MH (2003) Mass-independent sulfur isotopic compositions inpresent-day sulfate aerosols. J Geophys Res 108(D16):4524.

16. Myhre G, Berglen TF, Myhre CEL, Isaksen ISA (2004) The radiative effect of the an-thropogenic influence on the stratospheric sulfate aerosol layer. Tellus B Chem PhysMeterol 56(3):294–299.

17. Lee CCW, Savarino J, Cachier H, Thiemens MH (2002) Sulfur (S-32, S-33, S-34, S-36) andoxygen (O-16, O-17, O-18) isotopic ratios of primary sulfate produced from combus-tion processes. Tellus B Chem Phys Meterol 54(3):193–200.

18. Bauman JJ, Russell PB, Geller MA, Hamill P (2003) A stratospheric aerosol climatologyfrom SAGE II and CLAES measurements. 2. Results and comparisons, 1984-1999.J Geophys Res 108(D13):16.

19. Bruehl C, Lelieveld J, Crutzen PJ, Tost H (2012) The role of carbonyl sulphide asa source of stratospheric sulphate aerosol and its impact on climate. Atmos Chem Phys12(3):1239–1253.

20. Notholt J, et al. (2003) Enhanced upper tropical tropospheric COS: Impact on thestratospheric aerosol layer. Science 300(5617):307–310.

21. Pratt KA, et al. (2011) Flight-based chemical characterization of biomass burning aerosolswithin two prescribed burn smoke plumes. Atmos Chem Phys 11(24):12549–12565.

22. Vodacek A, et al. (2002) Remote optical detection of biomass burning using a potas-sium emission signature. Int J Remote Sens 23(13):2721–2726.

23. Whitlow S, Mayewski P, Dibb J, Holdsworth G, Twickler M (1994) An ice-core-basedrecord of biomass burning in the arctic and sub-arctic, 1750-1980. Tellus B Chem PhysMeterol 46(3):234–242.

4 of 5 | www.pnas.org/cgi/doi/10.1073/pnas.1406315111 Shaheen et al.

24. Andreae MO, Merlet P (2001) Emission of trace gases and aerosols from biomassburning. Global Biogeochem Cycles 15(4):955–966.

25. Rieder HE, et al. (2013) On the relationship between total ozone and atmosphericdynamics and chemistry at mid-latitudes. Part 2. The effects of the El Niño/SouthernOscillation, volcanic eruptions and contributions of atmospheric dynamics andchemistry to long-term total ozone changes. Atmos Chem Phys 13(1):165–179.

26. Ziemke JR, Chandra S (2003) La Nina and El Nino-induced variabilities of ozone in thetropical lower atmosphere during 1970-2001. Geophys Res Lett 30(3):1142.

27. Fromm M, et al. (2005) Pyro-cumulonimbus injection of smoke to the stratosphere:Observations and impact of a super blowup in northwestern Canada on 3–4 August1998. J Geophys Res 110(D8):D08205.

28. Danielache SO, et al. (2012) Photoabsorption cross-section measurements of S-32,S-33, S-34, and S-36 sulfur dioxide for the (BB1)-B-1-X(1)A(1) absorption band.J Geophys Res 117(D24301).

29. Lin Y, Sim MS, Ono S (2011) Multiple-sulfur isotope effects during photolysis of car-bonyl sulfide. Atmos Chem Phys 11(19):10283–10292.

30. Hattori S, et al. (2013) SO2 photoexcitation mechanism links mass-independent sulfurisotopic fractionation in cryospheric sulfate to climate impacting volcanism. Proc NatlAcad Sci USA 110(44):17656–17661.

31. Hattori S, et al. (2012) Isotope effect in the carbonyl sulfide reaction with O(3P). J PhysChem A 116(14):3521–3526.

32. Farquhar J, Johnston DT (2008) The oxygen cycle of the terrestrial planets: Insightsinto the processing and history of oxygen in surface environments. Oxygen in theSolar System, Reviews in Mineralogy & Geochemistry, eds MacPherson GJ, MittlefehldtDW, Jones JH, Simon SB (Mineralogical Society of America, Chantilly, VA), Vol 68, pp463–492.

33. Domagal-Goldman SD, Kasting JF, Johnston DT, Farquhar J (2008) Organic haze,glaciations and multiple sulfur isotopes in the Mid-Archean Era. Earth Planet Sci Lett269(1-2):29–40.

34. Kasting JF, Pavlov AA (2001) Photochemical modeling of mass-independent sulfurisotope fractionation in low-O2 atmospheres. Astrobiology 1(3):399–400.

35. Halevy I, Johnston DT, Schrag DP (2010) Explaining the structure of the Archean mass-independent sulfur isotope record. Science 329(5988):204–207.

36. Farquhar J, Wu NP, Canfield DE, Oduro H (2010) Connections between sulfur cycleevolution, sulfur isotopes, sediments, and base metal sulfide deposits. Econ Geol105(3):509–533.

37. Chiodini G, Cioni R, Raco B, Scandiffio G (1991) Carbonyl sulphide (COS) in geothermalfluids: An example from the Larderello field (Italy). Geothermics 20(5):319–328.

38. Krasnopolsky VA (2010) Spatially-resolved high-resolution spectroscopy of Venus 2.Variations of HDO, OCS, and SO2 at the cloud tops. Icarus 209(2):314–322.

39. Palumbo ME, Geballe TR, Tielens A (1997) Solid carbonyl sulfide (OCS) in dense mo-lecular clouds. Astrophys J 479(2):839–844.

40. Mumma MJ, et al. (2003) Remote infrared observations of parent volatiles in comets:A window on the early solar system. Interpretation of the Remote and In-Situ Ob-servations of Small Bodies, Advances in Space Research, eds Worms JC, Klinger J(Pergamon, Kidlington, UK), Vol 31, pp 2563–2575.

41. Ueno Y, Danielache SO, Johnson MS, Yoshida N (2009) Carbonyl sulfide (OCS) in theArchean atmosphere. Geochim Cosmochim Acta 73(13):A1358.

42. Ziemke JR, Chandra S, Oman LD, Bhartia PK (2010) A new ENSO index derived fromsatellite measurements of column ozone. Atmos Chem Phys 10(8):3711–3721.

43. Savarino J, Alexander B, Darmohusodo V, Thiemens MH (2001) Sulfur and oxygenisotope analysis of sulfate at micromole levels using a pyrolysis technique in a con-tinuous flow system. Analytical Chemistry 73(18):4457–4462.

Shaheen et al. PNAS Early Edition | 5 of 5

EART

H,A

TMOSP

HER

IC,

ANDPL

ANET

ARY

SCIENCE

S

Supplement: Large Sulfur Isotope Anomaly in Non Volcanic Sulfate and its 1

Implications for the Archean Atmosphere 2

R. Shaheen1, M. Abaunza

1, T. Jackson

1, J. McCabe

1,2, J. Savarino

3,4, M. H. Thiemens

1* 3

1University of California San Diego, Dept. of Chemistry and Biochemistry, La Jolla, CA-92093, 4

USA. 5 2Pacific Ridge School, 6269 El-Fuerte Dr. Carlsbad, CA-92009, USA. 6

3CNRS, LGGE (UMR5183), F-38041 Grenoble, France 7

4Univ. Grenoble Alpes, LGGE (UMR5183), F-38041 Grenoble, France. 8

*Corresponding author: mthiemens@ucsd.edu 9

10

Supplement Section S1: 11

Materials and Methods: 12

Sulfate aerosol were extracted from a 1x1 m snow pit at the South Pole (2850 m high, snow 13

accumulation rate 84 kg.m-2

.a-1

, mean annual temperature -49.5oC), Antractica (1). The sample 14

preparation for O-isotope analysis and SO2 collection for sulfur isotope analysis is described 15

earlier (2). SO2 gas was converted to SF6 for S-quartet isotope analysis following method 16

developed earlier in our laboratory (3-5). The 33

S, 34

S, 36

S, 33

S, and 36

S showed standard 17

deviations of 0.06‰, 0.1‰, 0.4‰, 0.05‰, and 0.2‰ respectively over a course of one year 18

(sample size =1-2 mole Table SII). 19

The mass independent signatures of S are measured as (4): 20

33

S = 33

S -1000*[(1 + 34

S/1000)0.515 -1] (1) 21

36

S = 36

S - 1000*[(1 + 36

S /1000)1.91

- 1] (2) 22

23

Supplement Section2: 24

2

Regular variation in sodium concentration with depth was used for annual layer counting from 25

1984-2001. Spikes in nss-SO4 (156ppb) concentration and low S- isotopic values (34

S= 1.4-2.6) 26

served as independent corroborator of age estimates as explosive volcanic activity of Pinatubo 27

(15.13 oN, 120.35

oE, 1,745m, June 1991); and Cerro Hudson (45.90

oS, 72.97

oW, 1,905m; Aug 28

1991) led to excess deposition of aerosol sulfates (1991-1993) at the South Pole. Higher 29

concentrations of nss-sulfate in the ice cores from Antarctica (Dome C and South Pole) and 30

Greenland has been used to spot paleo volcanic activities (6-8). The reported sample dates for 31

are calculated from a high resolution (~1cm) cations (Na, K, Mg) and anions (Cl, SO4, NO3, 32

MSA) concentration profiles (1). The actual date of the composite samples used for both S and O 33

isotopes may be shifted by + 4 months. 34

The background S- isotope signal (33, 34, 36

S = 6.5 + 0.7, 12 + 1.4 and 21 + 2.7‰ respectively) 35

was estimated from samples with sulfate concentrations ~ 40ppb 2ppb using volcanic quiescent 36

period from 1985 to 1988. This period reflects photochemically produced sulfate aerosols in 37

steady state conditions and is considered to arise from all other contributors to nss-SO4 except 38

volcanoes. The estimated 34

S for the background is close to the non sea salt S-isotope signal 39

34

S =11 + 0.3 ‰ observed in aerosols collected directly on filter papers at the South Pole for the 40

entire year in 1999 (9). The isotopic signature (34

S) of SO4 from marine biogenic sources and 41

sea salt are well constrained at ~18 and 21‰ (10-12) (13). The isotopic signature of volcanic 42

sulfate can be estimated as: 43

34

Svolcanic = (34

Snss – (1-fbg) x 34

Sbg )/fbg (1) 44

Here 1-fbg denotes fraction of sulfate from the volcanic activities. Substituting 34

Sbg =12‰ with 45

constant background input (fbg =40 ppb) in eq. 1, the volcanic signal showed highest depletion in 46

3

S-stable isotopes 33

S,34

36SstageI(1991.6 -1992.1) =-4.4‰,-13‰, -30‰;

33S,

34

36SstageII (1992.8) 47

= -12.6‰ -23‰,-45‰. 48

In a steady state, background stratospheric sulfate aerosols (SSA) is produced by the photo 49

oxidation of S species (COS photolysis ~43%, convective uplift of SO2 containing polluted air 50

masses into the stratosphere ~26%, SO2 from aviation ~1% and remaining 30% is direct SO4 51

transport to the stratosphere from the tropical tropopause) to H2SO4, followed by 52

nucleation/condensation, downward and polewards transport under the influence of global 53

planetary waves and has a residence time ~ 3-4 yr(14, 15). There is an ongoing debate on the 54

relative contribution of S from various sources (anthropogenic and natural) towards persistence 55

increase in SSA (16-19) over the last two decades. Current understanding of the contribution of 56

different sources to the SSA layer is restricted by the lack of quantitative distinction between 57

different sources of SO4 aerosols to the stratosphere and details of in-situ chemical reaction 58

mechanisms of S- species. 59

The isotopic signature (33

S,34

36S) of various sources are well constrained, therefore a high 60

resolution record of sulfate aerosol retrieved from the South Pole snow pit can help to understand 61

the sources and photochemical transformations. A week correlation of 33

S and 36

S with 34

S is 62

observed (Fig. S3) which is interpreted to reflect change in the sources of S over time (1983-63

2001) and it may reflect shift in wavelength of the light available for photochemical processing 64

of S-carrying species in the stratosphere (SO2, OCS, H2SO4). Laboratory data have shown that 65

photochemically produced sulfate and elemental sulfur (So) leads to positive or negative 66

correlation depending on the wavelength used for photolysis of SO2. 34and

36S of SSA falls 67

in the range noted for biomass burning and fossil fuel combustion suggesting transport of 68

anomalous sulfate to the stratosphere. Considering S-load in the atmosphere, tropospheric 69

4

sulfate = 105 Tg, stratospheric sulfate aerosol = 0.013Tg (20). Ratio of troposphere/stratospheric 70

sulfate =1.24 x10-4

g. Assuming initial SSA with

36S=0 and tropospheric aerosol with

36Savg = 71

−1.2‰ (21). A simple mass balance suggests 0.01% transport of tropospheric sulfate can change 72

36

S of SSA by −0.9‰. 73

74

Supplement Section3: 75

K, a classic tracer of biomass burning(22) is released as KCl and K2SO4 from plant tissues at 76

higher temperatures (800 oC -2000

oC) and its emission spectra has been documented during wild 77

fire season of 1998-99 (23, 24). ENSO driven meteorological conditions such has high 78

temperatures, severe droughts and low precipitation might have triggered extensive wild fire and 79

biomass burning from 1998-99 (25-28). Satellite based estimates of the fire activities and 80

biochemical modeling (29) indicated excessive carbon emission to the atmosphere (2.1 0.8 81

petagram) due to the release of CH4, CO2 and CO from wild fires in Southeast Asia (60%), 82

Central and South America (30%) and boreal regions of Eurasia and North America (10%) (28, 83

30, 31). A significant correlation between CO mixing ratio in southern hemisphere (10-30oS) 84

and southern oscillation index was observed with highest concentration of CO (almost double ~ 85

200ppb) at 250 hPa due to severe fires in both hemispheres after strongest ENSO event of the 86

decade in 1997-1998 (25, 30). Long term record (1940 to1998) of North American fires also 87

revealed fire-ENSO teleconnections (correlation between time series of atmospheric pressure, 88

temperature and rainfall) with 15 out of 17 biggest fires were reported after moderate to strong 89

ENSO events (32-34). 90

The increase in K, NO3, Cl and SO4 concentrations in the snow samples deposited after the 91

biomass burning events in 1998-99 and 1984-85 (Fig. 1a, and S1) lend some additional support 92

5

to the transport of BB signal to the South Pole, however, NO3 and Cl concentration may also 93

increase due to photochemical transformation of other anthropogenic compounds in the 94

stratosphere (e.g. CFC and NOx), we consider K as a more reliable tracer of BB. 95

96

Fig. S1. Higher resolution concentration profile of Na+, K

+, NO3

-, Cl

- from 1982-2001 of snow samples extracted 97

from the 1x1 m snow pit at the South Pole. 98

99

100

101

6

102 Fig. S2. Sulfur four isotope plot of the sulfate aerosols (1983-2001) extracted from the 1x1 m snow pit at the South 103

Pole and comparison with the previous volcanic sulfate aerosol acquired from the Dome C and the South Pole ice 104

cores (7) and tropospheric aerosol collected at La Jolla CA, USA(21). 105

7

106 Fig. S3. Sulfur four isotope plot of the sulfate aerosols (1983-2001) extracted from the 1x1 m snow pit at the South 107

Pole and comparison with the previous tropospheric sulfate aerosol. Open symbol = 33

S, closed symbol =36

S. La 108

Jolla, CA (blue circles) Shenandoah National Park, VA (red circles), Bakersfield, CA (blue triangles), fossil fuel and 109

biomass burning signatures (magenta triangles). 110

111

112

113

114

115

116

117

118

119

120

121

122

123

124

125

126

127

128

129

130

131

132

8

Table.S1. S-isotope composition and concomitant S-isotope anomalies of sulfate aerosol retrieved from a 1x1 m 133

snow pit at the South Pole. Depth profile indicate initial and final ice layer of the composite samples used. 134

Sample Depth

(cm)

Year 33

S (‰

34

S (‰

36

S (‰

33

S (‰

36

S (‰

70-86 2000.6 -2000.3 6.74 13.31 25.24 -0.084 -0.334

87-94 2000.2 -1999.9 7.42 14.51 27.51 -0.024 -0.338

103-108 1999.6-1999.3 8.41 13.67 25.95 1.397 -0.324

108-113 1999.3-1999.0 8.92 14.29 26.70 1.582 -0.784

113-117 1998.3-1998.9 6.99 13.39 27.79 0.118 2.056

122-133 1998.6-1998.4 6.47 12.78 24.08 -0.086 -0.479

140-148 1997.5-1997.6 7.99 15.86 30.43 -0.147 -0.093

154-162 1997.2-1996.9 8.23 16.51 30.70 -0.239 -1.073

168-176 1996.4-1996.2 6.32 12.57 23.13 -0.129 -1.027

177-188 1995.9-1995.7 6.10 12.0 22.72 -0.059 -0.322

194-200 1995.6-1995.0 6.03 12.57 22.34 -0.429 -1.822

250-256 1993.5-1992.9 3.47 7.01 13.34 -0.129 -0.093

268-274 1992.8-1992.6 1.61 3.55 6.60 -0.212 -0.183

274-279 1992.5-1992.3 3.97 7.71 14.25 0.005 -0.536

279-284 1992.2 -1991.9 2.08 2.23 2.82 0.929 -1.451

289-295 1991.6-1991.3 2.38 2.86 3.65 0.905 -1.826

295-305 1991.2-1990.9 11.32 20.01 36.76 1.069 -1.781

305-316 1990.8-1990.4 8.06 14.77 27.55 0.477 -0.862

316-320 1990.3-1990.1 7.63 14.75 28.15 0.067 -0.215

320-328 1990.1-1989.9 6.44 12.61 23.90 -0.034 -0.332

328-338 1989.8-1990.6 7.09 13.68 25.32 0.067 -0.973

338-347 1989.5-1989.2 7.05 13.89 26.25 -0.073 -0.448

347-356 1989.1-1988.6 5.99 11.83 21.87 -0.081 -0.844

356-365 1988.6-1988.4 6.36 12.83 22.76 -0.227 -1.902

365-378 1988.3-1988.0 6.58 12.97 23.81 -0.078 -1.120

386-397 1987.7-1987.3 5.36 10.50 19.34 -0.028 -0.813

402-412 1987.0-1986.4 6.57 12.96 24.63 -0.088 -0.285

420-428 1985.9-1985.3 7.58 14.82 28.04 -0.026 -0.472

428-441 1985.3-1984.9 6.85 13.28 25.90 0.037 0.379

441-445 1984.8-1984.2 5.68 11.09 21.59 -0.021 0.286

456-465 1984.2-1983 5.42 10.90 20.28 -0.171 -0.640 Sea salt contribution is ~ 7-9% and no correction is applied to S-isotope values. 135

136

137

138

139

140

141

142

143

144

145

146

147

9

Table.S2. S-isotope composition and concomitant S-isotope anomalies of SF6 and Ag2S converted to SF6 148

using method described earlier (4). 149

Date of Analysis

SF6

(µmole)

33S

(‰

34

S (‰

36

S (‰

33

S (‰

36

S (‰

09/19/2011 1 -2.01 -3.89 -7.42 0.002 -0.038

10/12/2011 1 -2.01 -3.92 -7.39 0.008 0.082

10/18/2011 1 -1.97 -3.809 -7.40 -0.01 -0.14

01/05/2012 1 -2.06 -3.79 -7.35 -0.11 -0.17

06/11/2012 1 -1.99 -3.95 -7.43 0.03 0.10

07/16/2012 1 -1.86 -3.66 -6.59 0.02 0.39

Avg 1.98 -3.83 -7.26 -0.01 0.03

SD 0.06 0.106 0.33 0.05 0.20

04/22/2011 0.26 -2.14 -3.86 -6.74 -0.14 0.62

04/22/2011 0.50 -2.37 -3.24 -7.69 -0.08 0.79

04/22/2011 0.31 -1.93 -3.74 -6.55 -0.01 0.59

Avg -2.14 -3.61 -6.99 -0.07 0.66

SD 0.22 0.32 0.61 0.06 0.10

*T3z-Z758 2.85 2.63 5.13 9.54 -0.003 -0.28

*T3z-Z763 2.49 2.67 4.97 9.04 0.11 -0.48

*T4z-Z779 3.63 2.52 4.94 8.90 -0.018 -0.56

*T4z-Z793 1.04 2.27 4.44 8.30 -0.008 -0.200

*T4z-Z974 1.32 2.39 4.65 9.18 0.001 0.268

*T4z-Z749 2.18 2.10 4.14 7.60 -0.02 -0.321

Avg 2.43 4.71 8.76 0.01 -0.26

SD 0.21 0.37 0.69 0.04 0.29 Here * represent Ag2S converted to SF6 and analyzed for S- quadruple isotopes on Mat 252 isotope ratio mass 150

spectrometer. 151

152

153

Table.S3. S-isotope composition and concomitant S-isotope anomalies of primary sulfate produced during burning 154

process (35). 155

Materials Sulfate

(µmole)

33S

(‰

34

S (‰

36

S (‰

33

S (‰

36

S (‰

Mix savanna grass flaming 4.9 5.9 11.84 22.2 -0.18 -0.536 savanna grass-flaming 6.3 7.6 14.75 27.6 0.031 -0.761 savanna grass-smoldering 12.5 8.07 15.99 28.7 -0.133 -2.063 Lamto grass flaming 6.5 7.99 15.70 30.1 -0.065 -0.101 Rice straw flaming 10.7 4.68 9.55 17.0 -0.227 -1.32 Hay france flaming 23.1 7.86 15.48 28.5 -0.083 -1.275 Diesel fuel-Idle 4.6 6.83 13.28 24.7 -0.013 -0.818 Diesel fuel-accelaration 16.5 8.42 16.42 29.9 -0.003 -1.696 156

157

158

159

10

Table.S4. S-isotope composition and concomitant S-isotope anomalies of aerosol sulfate collected at Bakersfield and 160

Shenondoah National Park, VA. 161

162

Sample ID Sampling date 33

S (‰

34

S (‰

36

S (‰

33

S (‰

36

S (‰

SS-1 2nd 30 Dec 1998-4Jan 1999 4.15 7.94 14.9 0.07 -0.3

SS-1 3rd 30 Dec 1998-4Jan 1999 3.89 7.35 13.8 0.11 -0.3

SS-1 4th 30 Dec 1998-4Jan 1999 2.32 4.14 7.7 0.19 -0.3

SS-1 BU 30 Dec 1998-4Jan 1999 2.68 4.63 8.6 0.3 -0.3

SS-3 1st 9-12Jan 1999 5.04 9.76 18.5 0.02 -0.2

SS-3 2nd 9-12Jan 1999 3.23 6.16 11.6 0.06 -0.2

SS-3 3rd 9-12Jan 1999 1.71 3.21 6 0.06 -0.1

SS-3 4th 9-12Jan 1999 1.65 3.05 5.6 0.08 -0.2

SS-3 BU 9-12Jan 1999 2.26 4.17 7.5 0.11 -0.4

SS-5 2nd 13-16Jan 1999 2.18 3.95 7.3 0.14 -0.3

SS-5 3rd 13-16Jan 1999 2.05 3.42 6.1 0.29 -0.5

SS-5 4th 13-16Jan 1999 2.25 3.57 6.2 0.41 -0.6

SS-5 BU 13-16Jan 1999 2.57 4.09 7.2 0.46 -0.6

SS-7 2nd 16-20 Jan 1999 2.84 5.22 9.9 0.15 -0.1

SS-7 3rd 16-20 Jan 1999 2.91 4.88 8.9 0.4 -0.4

SS-7 4th 16-20 Jan 1999 3.48 6.33 11.4 0.23 -0.7

SS-7 BU 16-20 Jan 1999 5.67 10.79 20.1 0.12 -0.6

SS-9-BU 21-27Jan 1999 2.4 3.75 6.6 0.47 -0.5

SS-9 2nd-4th 21-27Jan 1999 2.96 4.98 8.7 0.39 -0.8

Shenandoah National Park, VA, USA

SNP01-BU 13-20Aug2001 2.85 4.68 7.4 0.44 -1.5

SNP01-6th 13-20Aug2001 2.73 4.57 7.6 0.38 -1.2

SNP01-5th 13-20Aug2001 2.53 4.2 7.1 0.36 -0.9

SNP01-4th 13-20Aug2001 2.87 4.91 8.5 0.34 -0.9

SNP01-3rd 13-20Aug2001 3.54 6.37 11.3 0.26 -0.9

SNP01-1st 13-20Aug2001 4.32 8.11 14.5 0.15 -1

SNP01-2nd 13-20Aug2001 4.28 8.11 14.9 0.11 -0.7

SNP02-BU 20-27 Aug2001 2.6 4.22 7.9 0.43 -0.1

SNP02-6th 20-27 Aug2001 2.34 3.8 6.2 0.38 -1.1

SNP02-5th 20-27 Aug2001 2.55 4.27 7.4 0.35 -0.8

SNP02-4th 20-27 Aug2001 2.62 4.48 7.6 0.31 -1

SNP02-3rd 20-27 Aug2001 3.44 6.24 10.9 0.23 -1

SNP02-2nd 20-27 Aug2001 3.8 7.03 12.3 0.18 -1.2

SNP03-BU 27Aug-03 sep 2001 2.6 4.12 6 0.48 -1.9

SNP03-6th 27Aug-03 sep 2001 2.34 3.74 5.4 0.42 -1.7

SNP04-BU 03-10 sep 2001 2.75 4.31 6.8 0.53 -1.5

SNP04-6th 03-10 sep 2001 2.75 4.45 7.4 0.45 -1.1

163

164

1. McCabe JR, Thiemens MH, & Savarino J (2007) A record of ozone variability in South Pole Antarctic 165

snow: Role of nitrate oxygen isotopes. Journal of Geophysical Research-Atmospheres 112(D12). 166

2. Shaheen R, et al. (2013) Tales of volcanoes and El-Niño southern oscillations with the oxygen isotope 167

anomaly of sulfate aerosol. Proceedings of the National Academy of Sciences. 168

11

3. Savarino J, Alexander B, Darmohusodo V, & Thiemens MH (2001) Sulfur and oxygen isotope analysis of 169

sulfate at micromole levels using a pyrolysis technique in a continuous flow system. Analytical Chemistry 170

73(18):4457-4462. 171

4. Farquhar J, Bao HM, & Thiemens M (2000) Atmospheric influence of Earth's earliest sulfur cycle. Science 172

289(5480):756-758. 173

5. Farquhar J, Savarino J, Airieau S, & Thiemens MH (2001) Observation of wavelength-sensitive mass-174

independent sulfur isotope effects during SO2 photolysis: Implications for the early atmosphere. Journal of 175

Geophysical Research-Planets 106(E12):32829-32839. 176

6. Savarino J, Bekki S, Cole-Dai JH, & Thiemens MH (2003) Evidence from sulfate mass independent 177

oxygen isotopic compositions of dramatic changes in atmospheric oxidation following massive volcanic 178

eruptions. Journal of Geophysical Research-Atmospheres 108(D21). 179

7. Baroni M, Savarino J, Cole-Dai J, Rai VK, & Thiemens MH (2008) Anomalous sulfur isotope 180

compositions of volcanic sulfate over the last millennium in Antarctic ice cores. Journal of Geophysical 181

Research-Atmospheres 113(D20). 182

8. Lanciki A, Cole-Dai J, Thiemens MH, & Savarino J (2012) Sulfur isotope evidence of little or no 183

stratospheric impact by the 1783 Laki volcanic eruption. Geophysical Research Letters 39. 184

9. Savarino J, Romero A, Cole-Dai J, Bekki S, & Thiemens MH (2003) UV induced mass-independent sulfur 185

isotope fractionation in stratospheric volcanic sulfate. Geophysical Research Letters 30(21). 186

10. Patris N, Delmas RJ, & Jouzel J (2000) Isotopic signatures of sulfur in shallow Antarctic ice cores. Journal 187

of Geophysical Research-Atmospheres 105(D6):7071-7078. 188

11. Patris N, et al. (2002) First sulfur isotope measurements in central Greenland ice cores along the 189

preindustrial and industrial periods. Journal of Geophysical Research-Atmospheres 107(D11). 190

12. Patris N, Mihalopoulos N, Baboukas ED, & Jouzel J (2000) Isotopic composition of sulfur in size-resolved 191

marine aerosols above the Atlantic Ocean. Journal of Geophysical Research-Atmospheres 192

105(D11):14449-14457. 193

13. Pruett LE, Kreutz KJ, Wadleigh M, Mayewski PA, & Kurbatov A (2004) Sulfur isotopic measurements 194

from a West Antarctic ice core: implications for sulfate source and transport. Annals of Glaciology, Vol 39, 195

2005, Annals of Glaciology, ed Jacka J), Vol 39, pp 161-168. 196

14. Pitari G, Mancini E, & Grewe V (2002) Deep convective transport in a two-dimensional model: Effects on 197

lower stratospheric aerosols and ozone. Meteorologische Zeitschrift 11(3):187-196. 198

15. Deshler T (2008) A review of global stratospheric aerosol: Measurements, importance, life cycle, and local 199

stratospheric aerosol. Atmospheric Research 90(2-4):223-232. 200

16. Chin M & Davis DD (1995) A REANALYSIS OF CARBONYL SULFIDE AS A SOURCE OF 201

STRATOSPHERIC BACKGROUND SULFUR AEROSOL. Journal of Geophysical Research-202

Atmospheres 100(D5):8993-9005. 203

17. Pitari G & Mancini E (2002) Impact of future supersonic aircraft on the distribution of stratospheric tracers: 204

Chemical and dynamical perturbations. Meteorologische Zeitschrift 11(3):215-223. 205

18. Crutzen PJ (1976) POSSIBLE IMPORTANCE OF CSO FOR SULFATE LAYER OF STRATOSPHERE. 206

Geophysical Research Letters 3(2):73-76. 207

19. Bruehl C, Lelieveld J, Crutzen PJ, & Tost H (2012) The role of carbonyl sulphide as a source of 208

stratospheric sulphate aerosol and its impact on climate. Atmospheric Chemistry and Physics 12(3):1239-209

1253. 210

20. Myhre G, Berglen TF, Myhre CEL, & Isaksen ISA (2004) The radiative effect of the anthropogenic 211

influence on the stratospheric sulfate aerosol layer. Tellus Series B-Chemical and Physical Meteorology 212

56(3):294-299. 213

21. Romero AB & Thiemens MH (2003) Mass-independent sulfur isotopic compositions in present-day sulfate 214

aerosols. Journal of Geophysical Research: Atmospheres 108(D16):4524. 215

22. Rudolph J, Khedim A, Koppmann R, & Bonsang B (1995) FIELD-STUDY OF THE EMISSIONS OF 216

METHYL-CHLORIDE AND OTHER HALOCARBONS FROM BIOMASS BURNING IN WESTERN 217

AFRICA. Journal of Atmospheric Chemistry 22(1-2):67-80. 218

23. Vodacek A, et al. (2002) Remote optical detection of biomass burning using a potassium emission 219

signature. International Journal of Remote Sensing 23(13):2721-2726. 220

24. Pratt KA, et al. (2011) Flight-based chemical characterization of biomass burning aerosols within two 221

prescribed burn smoke plumes. Atmospheric Chemistry and Physics 11(24):12549-12565. 222

25. Matsueda H, Taguchi S, Inoue HY, & Ishii M (2002) A large impact of tropical biomass burning on CO 223

and CO2 in the upper troposphere. Science in China Series C-Life Sciences 45:116-125. 224

12

26. Novelli PC, et al. (2003) Reanalysis of tropospheric CO trends: Effects of the 1997-1998 wildfires. Journal 225

of Geophysical Research-Atmospheres 108(D15). 226

27. Spichtinger N, et al. (2004) Boreal forest fires in 1997 and 1998: a seasonal comparison using transport 227

model simulations and measurement data. Atmospheric Chemistry and Physics 4:1857-1868. 228

28. Duncan BN, Martin RV, Staudt AC, Yevich R, & Logan JA (2003) Interannual and seasonal variability of 229

biomass burning emissions constrained by satellite observations. Journal of Geophysical Research: 230

Atmospheres 108(D2):4100. 231

29. van der Werf GR, et al. (2006) Interannual variability in global biomass burning emissions from 1997 to 232

2004. Atmos. Chem. Phys. 6(11):3423-3441. 233

30. Kondo Y, et al. (2004) Impacts of biomass burning in Southeast Asia on ozone and reactive nitrogen over 234

the western Pacific in spring. Journal of Geophysical Research-Atmospheres 109(D15). 235

31. Wooster MJ, Perry GLW, & Zoumas A (2012) Fire, drought and El Nino relationships on Borneo 236

(Southeast Asia) in the pre-MODIS era (1980-2000). Biogeosciences 9(1):317-340. 237

32. Le Page Y, et al. (2008) Global fire activity patterns (1996&ndash;2006) and climatic influence: an 238

analysis using the World Fire Atlas. Atmos. Chem. Phys. 8(7):1911-1924. 239

33. Hess JC, Scott CA, Hufford GL, & Fleming MD (2001) El Nino and its impact on fire weather conditions 240

in Alaska. International Journal of Wildland Fire 10(1):1-13. 241

34. Schoennagel T, Veblen TT, Romme WH, Sibold JS, & Cook ER (2005) Enso and pdo variability affect 242

drought-induced fire occurrence in Rocky Mountain subalpine forests. Ecological Applications 15(6):2000-243

2014. 244

35. Lee CCW, Savarino J, Cachier H, & Thiemens MH (2002) Sulfur (S-32, S-33, S-34, S-36) and oxygen (O-245

16, O-17, O-18) isotopic ratios of primary sulfate produced from combustion processes. Tellus Series B-246

Chemical and Physical Meteorology 54(3):193-200. 247

248

249