Organosulfur Aerosols Likely Carried Sulfur MIF Signatures in the Early Earth’s Atmosphere

Signatures of mass‐independent fractionation (MIF) of sulfur in Archean sulfide and sulfate minerals are widely thought to record an anoxic early Earth’s atmosphere. While experiments of ultraviolet irradiation of SO2 produce significant sulfur mass‐independent fractionation (S‐MIF) in reaction products (elemental sulfur and residual sulfur dioxide), they have not been able to reproduce the isotope patterns, in particular Δ36S/Δ33S ratios, observed in the geologic rock record. Studies that focused on organic sulfur gases and hazes in Archean did not report organosulfur aerosol photoproducts as major contributors to Archean S‐MIF chemistry. Here we show, for the first time, that photochemical reactions of SO2 in the presence of gaseous hydrocarbons (CH4, C2H2, and C2H4) produce haze‐like organosulfur aerosols bearing S‐MIF with variable Δ36S/Δ33S ratios. The isotope trends for the organosulfur photoproducts produced in our experiments suggest that in addition to elemental sulfur, organosulfur compounds—in particular methanesulfonic acid—are a key component of S‐MIF signals from the atmosphere to the ocean and sediments with possible links to Archean atmosphere warmed by a methane greenhouse.


Introduction
Geochemical evidence suggests that the chemistry of the atmosphere during the first 2 billion years of Earth history was fundamentally different from that seen today (Farquhar et al., 2000;Lyons et al., 2014).Although it is thought that microbes capable of oxygenic photosynthesis evolved before 2.5 Ga (Giga annum before present), biological oxygen production was not sufficient to overcome Earth's early reducing capacity (Farquhar et al., 2011;Izon et al., 2017;Kurzweil et al., 2013;Ostrander et al., 2021).This history of early Earth atmospheric oxygenation is constrained by the preservation of sulfur mass-independent fractionation (S-MIF) signatures (Halevy, 2013;Zerkle et al., 2012).Growing knowledge of the potential isotopic variability for S-MIF caused by Earth's atmospheric chemistry has prompted scientists to investigate the different relationships that exist for all four stable sulfur isotopes (Izon et al., 2015).Of particular interest is the disappearance of S-MIF as evidence of an irreversible rise in atmospheric oxygen at ca. 2.4 Ga (Claire et al., 2014;Zerkle et al., 2012).
Variations in S-MIF (recorded as non-zero Δ 33 S and Δ 36 S values that vary in both magnitude and direction) are apparent in the Archean rock record and have been recognized to potentially reveal the source mechanisms and pathways of anoxic Earth atmospheric sulfur chemistry (Halevy et al., 2010;Liu et al., 2019).In addition to geologic evidence, various experimental studies have led to the hypothesis that variations in S-MIF are potentially linked to atmospheric SO 2 photolysis reactions and the oxygenation of the Archean Earth's atmosphere (Endo et al., 2019;Ono, 2017).Under low oxygen (O 2 ) conditions in the Neoarchean eon, it is likely that hydrogen (H 2 ) and methane (CH 4 ) were important electron donors that reacted with sulfur dioxide (SO 2 ) and Abstract Signatures of mass-independent fractionation (MIF) of sulfur in Archean sulfide and sulfate minerals are widely thought to record an anoxic early Earth's atmosphere.While experiments of ultraviolet irradiation of SO 2 produce significant sulfur mass-independent fractionation (S-MIF) in reaction products (elemental sulfur and residual sulfur dioxide), they have not been able to reproduce the isotope patterns, in particular Δ 36 S/Δ 33 S ratios, observed in the geologic rock record.Studies that focused on organic sulfur gases and hazes in Archean did not report organosulfur aerosol photoproducts as major contributors to Archean S-MIF chemistry.Here we show, for the first time, that photochemical reactions of SO 2 in the presence of gaseous hydrocarbons (CH 4 , C 2 H 2, and C 2 H 4 ) produce haze-like organosulfur aerosols bearing S-MIF with variable Δ 36 S/Δ 33 S ratios.The isotope trends for the organosulfur photoproducts produced in our experiments suggest that in addition to elemental sulfur, organosulfur compounds-in particular methanesulfonic acid-are a key component of S-MIF signals from the atmosphere to the ocean and sediments with possible links to Archean atmosphere warmed by a methane greenhouse.
Plain Language Summary Experimental ultraviolet irradiation of SO 2 demonstrably induces an anomalous or mass-independent fractionation of sulfur (S-MIF) as evidence of an irreversible rise in atmospheric oxygen at ca. 2.4 Ga.Hitherto, such in vitro approaches did not completely confirm the variation in the S-MIF archived in early Earth's rock record.Here, we show that the photolysis of SO 2 in the presence of reduced hydrocarbon gases produced haze-like organosulfur aerosol photoproducts that are thought to be strongly modulated by early Earth's atmospheric sulfur cycling and its role in S-MIF transfer and preservation in Archean sedimentary rock record.
Earlier modeling efforts suggested that a combination of high pCO 2 and supplemental CH 4 fluxes contributed to the greenhouse warming of the Earth's early atmosphere (Pavlov et al., 2000;Trainer et al., 2006).More recently, it was hypothesized that the early Earth atmosphere oscillated between CO 2 -rich and CO 2 -CH 4 hazy conditions (Izon et al., 2015;Reed et al., 2022).These observations may have contributed to the formation of organic aerosols (organic haze) similar to that found in Titan's atmosphere (Arney et al., 2016;Trainer, 2013).Although the formation of organic haze has been previously recognized to depend on the changes in atmospheric CH 4 /CO 2 ratios, the photochemistry, formation mechanisms, and their connections to early Earth's atmospheric history have not been well-studied.
Here, we show that the photochemistry of SO 2 in the presence of reduced hydrocarbon gases (such as methane (CH 4 ), acetylene (C 2 H 2 ), and ethylene (C 2 H 4 )) produced haze-like organosulfur aerosol photoproducts.The isotopic measurements yielded S-MIF signatures with variable Δ 36 S/Δ 33 S ratios that depend upon the wavelength of radiation and the hydrocarbon species.The measured sulfur isotope compositions of these organosulfur haze photoproducts and the intermediate adducts provide a new cogent picture about the variability on the preservation patterns of S-MIF formation pathways that are likely to be produced in the early Earth's atmospheres and other Archean-like exoplanets.

UV Photolysis Experiments
Aliquots of SO 2 (∼13 mbar) and hydrocarbons (∼67 mbar) were mixed in a glass cylindrical photochemical reaction cell (25.5 cm length, 4.0 cm inner diameter-shown) equipped with UV-grade quartz windows and irradiated for 2 hr under a high powered 150 W, UV-enhanced Xenon-Arc lamp detailed in Whitehill and Ono (2012) and Guo et al., 2010 (also shown in Figures S1a and S1b in Supporting Information S1).A UV-radiation of the gas mixtures (SO 2 -CH 4 , SO 2 -C 2 H 2, and SO 2 -C 2 H 4 ) under full spectrum produced aerosol particles within 15 min.After 2 hr of irradiation, UV-radiation was stopped and the photoproducts were allowed to stand for 10-20 min until the hazy-like, cloudy aerosol products condensed and later deposited on the walls of the photocell and the quartz cell windows (Figures S1b and S1c in Supporting Information S1).The aerosol products present on the walls of the photocell and the quartz cell windows (Figures S1d and S1e in Supporting Information S1) were immediately rinsed from the photocell with a few milliliters of methanol-water (7:3) mixture.Residual sulfur gases (i.e., SO 2 ) from photoproducts were captured cryogenically (using liquid nitrogen), and converted into barium sulfate (BaSO 4 ) using 2-3 mL of concentrated H 2 O 2 and 1.0 M BaCl 2 solution.Details of all experimental parameters including gas-mixing ratios, UV-irradiation under full spectrum, and photolysis time are presented Table S1 in Supporting Information S1.Portions of the solvent extracts were treated with chloroform to remove negligible elemental sulfur residues (if any) before hydro-desulfurization with Raney Nickel and in excess bayerite to quantitatively convert organic-bound sulfonic and ester sulfonates into Ag 2 S for fluorination to SF 6 for sulfur isotope measurement (Oduro, 2022;Oduro et al., 2011).Precipitated BaSO 4 was then reduced with Thode reducing solution (consisting of a mixture of 320 mL HI, 180 mL HCl, and 156 mL of H 2 PO 3 ) to H 2 S (Forrest & Newman, 1977).It should be pointed out that limiting the amount of water in the Thode reducing solution (by increasing the concentration of HI-67% w/v and decreasing the concentration of HCl-36% w/v) promotes a complete barite reduction and afford a quantitative yield of H 2 S according to the net reaction: BaSO 4 (aq) + 2NaH 2 PO 2 (aq) + 10HI (aq) → Ba(H 2 PO 2 ) 2 (aq) + 2NaI (aq) + 4I 2 (aq) + H 2 S (aq) + 4H 2 O.In all distillation-reduction reactions, evolved H 2 S was captured by AgNO 3 /HNO 3 buffer solution to convert it into Ag 2 S for S-isotope analyses using SF 6 gas.A subset of aqueous aerosol extracts (rinsed from the cell and dissolved in 7:3 methanol-water mixture above) were injected into electrospray ionization mass spectrometry (ESI-MS) in negative ionization mode with a spectral scan over the range m/z 50-250.

Characterization of Organosulfur Photoproducts
Organic aerosol products from UV-photolysis were analyzed directly by ESI-MS according to the methods described by Oduro et al., 2012.The ESI employed a negative ionization mode of an Accu-TOF (JEOL USA, Inc., Peabody, MA) time-of-flight mass spectrometer (TOF-MS).The mass spectrometer used an electrospray Writing -review & editing: Harry Oduro, Shuhei Ono, Daniel L. Eldridge ionization source (ESI) and had a mass resolving power (m/Δm) of 6000 full width at half maximum (fwhm).The spray voltage was set to 2.3 kV, and the capillary and orifice temperatures were maintained at 250°C and 80°C, respectively.The instrument was typically operated at the following potentials: orifice 1 = 30 V, orifice 2 = 5 V, and ring lens = 10 V.The RF ion guide voltage was generally set to 1000 V to allow detection of ions greater than m/z = 50.

Quadruple Sulfur Isotope Ratio Measurements
Stable sulfur isotope ratio measurement (δ 34 S, Δ 33 S, and Δ 36 S) was conducted using a Thermo Finnigan MAT 253 isotope ratio mass spectrometer with fully automated fluorination lines.Approximately 1 mg samples of Ag 2 S were allowed to react in Ni vessels with ten-fold excesses of fluorine gas (F 2 ) at 320 o C for 8-12 hr for quantitative conversion of Ag 2 S to SF 6 .The SF 6 product was cryogenically separated from F 2 at −196°C and then distilled from HF and other trace contaminants.Final purification of SF 6 by gas chromatography was performed on a composite column comprised a 1/8 inch diameter, 1.8 m packed column containing a type 5A molecular sieve, followed by a 1/8 inch diameter, 3.7 m Hayesep-QTM column.The sulfur isotope composition of purified SF 6 was determined using four collectors arranged to measure the intensity of ).Results for the various sulfur fractions and standard reference materials are normalized to the Vienna-Canyon Diablo Troilite (V-CDT) scale.Uncertainties in S-isotope measurements and chemical extractions (which are not expected to be significant) are derived from repeated analysis, and are consistent with the long-term reproducibility of 0.016, 0.008, and 0.100 ‰ (1σ) for δ 34 S, Δ 33 S, and Δ 36 S, respectively.The four sulfur isotope compositions for the organosulfur photoproducts that are expressed by the conventional δ-notation: δ x S = [( x S/ 32 S) sample /( x S/ 32 S) standard −1], where x = 33, 34, or 36 and the standard is V-CDT.The magnitudes of mass-independent fractionation are reported using the capital-delta notation: Δ 33 S = δ 33 S − 1,000 × [(1 + δ 34 S/1,000) 0.515 − 1]; and Δ 36 S = δ 36 S − 1,000 × [(1 + δ 34 S/1,000) 1.90 − 1].All the sulfur isotope measurements for aerosols and residual gases are summarized in Tables S2 and S3 in Supporting Information S1, respectively.

Results and Discussion
Photolysis of SO 2 -CH 4 , SO 2 -C 2 H 2 , and SO 2 -C 2 H 4 gas mixtures were accompanied by the appearance of white haze-like deposit materials, which adhered to the internal walls of the photolysis cell and the entrance of the windows.Figure S1 in Supporting Information S1, shows the deposition of aerosol photoproducts, which were found to grow in particle sizes throughout the experimental runs.The aerosol formation times were comparable with the observed aerosol particle formation growth of SO 2 -allene mixture photolysis (Luria et al., 1974).Electrospray ionization mass spectrometry (ESI-MS) results in negative ionization mode for the polar extracts revealed the composition of organosulfur aerosol photoproducts of methylsulfone (CH 3  SO3− , m/z = 79), methanesulfonic acid (subsequently MSA) (CH 3  SO3− , m/z = 95), methylene sulfate (CH 2 -O-SO 3, m/z = 108) and alkoxysulfonate products ranging from polymeric methyl sulfonate 1).The major sulfur-containing photoproducts formed in all three SO 2 -C x H y gas mixtures were MSA, with yields ranging from 20% to 50% (Figures 1a-1c) and minor components of volatile organic sulfur compounds, which escaped from the SO 2 trapping solution.The overall spectrum gaps appear to be dependent on the intermediate adducts and reduced hydrocarbon molecules.The characteristic nature of these haze-like organosulfur photoproducts produced in our experiments has also been recognized in previous laboratory simulation experiments and has been linked to either Titan-like haze atmospheres (Dewitt et al., 2009;Trainer et al., 2006) or early Earth's reduced hydrocarbon-rich atmosphere (Arney et al., 2018;Domagal-Goldman et al., 2008).Evidence of these attributes can be addressed and connected to anoxic atmospheric sulfur cycling by investigating the four sulfur isotope signatures for the haze-like organosulfur photoproducts which were not analyzed experimentally in previous studies.
Sulfur isotope analyses for the haze-like organosulfur photoproducts revealed positive non-zero Δ 33 S (as shown in Figure 2) with isotopic fractionation of δ 34 S varying from +7.4 ‰ to maximum enrichment of 60.8 ‰ relative to the starting SO 2 composition (Figure 2; Table S2 in Supporting Information S1).The slopes of minor isotope compositions (Δ 36 S/Δ 33 S) derived from the photoproducts ranged from −2.79 to +1.28 with a very distinctive S-MIF vector of −1.9 observed for SO 2 -CH 4 gas mixtures, and appear to be closer to the Archean reference fractionation line (RFL = −1.5 shown in Figure 2) (Izon et al., 2015;Zerkle et al., 2012).The large sulfur isotope variability and trends of Δ 36 S/Δ 33 S and Δ 33 S/δ 34 S signify that the organosulfur aerosol-preserved S-MIF anomalies that are exclusively dependent on the photochemical excitation of the reduced hydrocarbon and SO 2 gases.Sulfur isotopic mass balance between the initial SO 2 , residual SO 2 , and aerosol photoproducts were also investigated for their S-MIF enrichment (Figure 2; Table S3 in Supporting Information S1).The comparison of Δ 36 S-Δ 33 S trends including the aerosol photoproducts, residual SO 2 gases, and organosulfur products yield distinct S-MIF trends that all passes directly through the origin with different intercepts for the residual gases (Figure 2).This observation demonstrates that isotope mass balance is preserved within ±0.10 ‰.Small variations in Δ 36 S/Δ 33 S intercepts and amplitudes for the three experiments are interpreted to result from differences in the concentrations of SO 2 -C x H y flow rates, wavelength-sensitive reactions of SO 2 -C x H y species, variation in yields of photoproducts, and loss of fractionated volatile organic sulfur that was not trapped by the trapping solutions due to the experimental designed.We infer that these observations indicate the principal differences in amplitude and loss pathway yielding significant Δ 33 S, variability in Δ 36 S that is associated with significant δ 34 S fractionations (in Figure 3) interpreted to reflect mass conservation isotope effects related to mixing of fractionated S-pools in the reaction network operating during the photolysis reactions.Overall, the following trends arise from the experimental data: (a) negative Δ 36 S/Δ 33 S slopes were observed for both SO 2 -CH 4 and SO 2 -C 2 H 2 photoproducts whereas positive Δ 36 S/Δ 33 S slopes were observed for SO 2 -C 2 H 4 aerosol photoproducts; (b) Δ 33 S/δ 34 S ratios are linearly correlated among experimental products and reactants (Figure 3); and (c) the SO 2 -CH 4 photoproducts exhibit negative Δ 36 S/Δ 33 S slopes of −1.90 that are almost similar to observed Archean Δ 36 S/Δ 33 S arrays (Farquhar et al., 2011;Zerkle et al., 2012).
The experimental results add to the growing body of evidence for the connection between reduced hydrocarbonsparticularly methane-and S-MIF production and preservation that may have played an important role during the first half of the Earth's history (Izon et al., 2017;Liu et al., 2019;Reed et al., 2022).The correlative Δ 36 S/Δ 33 S ratio of −1.9 for SO 2 -CH 4 photolysis experiments from typical Archean arrays of −0.90 and −1.5 also points to a contemporaneous organosulfur aerosol contribution as evidence of changing S-MIF chemistry in the Archean Earth's atmosphere with organosulfur haze as a possible exit channel (Arney et al., 2016;Farquhar et al., 2007;Domagal-Goldman., 2008).In such photochemically-active environments, it is expected that atmospheric mixing of other gases could potentially alter the chemical complexity of the aerosols that will possibly fluctuate the magnitudes and ratios of Δ 33 S/δ 34 S and Δ 36 S/Δ 33 S, and its haze nucleation-forming propensity in early Earth atmospheres.It is noteworthy that a range of Δ 36 S/Δ 33 S ratios (−2.3 to −12.4; −3.3 to −5.9) has also been observed in previous pure SO 2 photolysis experiments with no added reduced hydrocarbons (Masterson et al., 2011;Ono, 2017;Ono et al., 2013).The Δ 36 S/Δ 33 S trends in SO 2 photolysis experiments are more negative than the observed −1.9, and do not replicate the −0.90 and −1.5 trends recorded in early Earth's sedimentary rocks.
A further comparison of the distribution of organosulfur photoproducts indicates that methanesulfonic acid (MSA) is among the major organic aerosol products (Figure 1).Variations in compositions of photoproducts produced from gas-to-aerosol particle conversion point to a dominant S-MIF mechanism that influences the experimental results, suggesting that organic sulfur serve as an important sulfur reservoir for preserving S-MIF, as shown in Figure 3.This observation is very critical in our experiments and may perhaps shed light on the S-MIF pathways that are distinct from pure-SO 2 photochemical investigations (Ono, 2017).The yields of photoproducts can also be linked to the differences in reactants (and associated reaction pathways), and or optically thick aerosol product condensation on the cell windows affecting the available UV-radiation.These effects can influence the radiative scattering and the absorption cross-sections of SO 2 as well as the condensed-phase aerosol photoproducts, which may impact the Δ 33 S/δ 34 S and Δ 36 S/δ 33 S ratios in Figure 2   Quadruple S-isotope data from organosulfur photoproducts and residual SO 2 gas collected after 2 hr of UV-irradiation.Showing a cross plot of sulfur mass-independent fractionation (S-MIF) trends of organosulfur photoproducts (on the right side) compared to the corresponding residual SO 2 (on the left side) including interpretations of Neoarchean S-MIF arrays that is based conventional view expected for early Earth's sedimentary sulfur exit channels with Archean reference fractionation line (RFL = − 0.9 and −1.5; Zerkle et al., 2012;Kurzweil et al., 2013, Farquhar et al., 2013;Izon et al., 2015).The Δ 36 S/δ 33 S slope for CH 4 -SO 2 photoproduct (Slope = −1.9)nearly consistent with the Archean reference fractionation window).The analytical uncertainty on the plotted slopes (not shown) is estimated (to be ±0.1)from least squares linear regression as ±1 s.e (standard error).et al., 2019).An attempt to characterize the variations in absorption cross-sections for the various gas mixtures (SO 2 -CH 4 , SO 2 -C 2 H 2, and SO 2 -C 2 H 4 )-which is beyond the scope of this study-was hampered by the appearance of white hazy deposit materials, which grew after 10 min of irradiation and adhered to the entrance of the photocell windows (Figures S1d and S1e in Supporting Information S1).
A combination of radiative scattering of optically thick aerosol products and the absorption cross-sections of condensed-phase aerosol photoproducts can produce wavelength-sensitive reactions that can cause one or more exit channels to produce S-MIF signatures that are different from those observed exclusively in SO 2 photolysis in broadband and unstructured light sources (Farquhar et al., 2001;Whitehill & Ono, 2012).In such conditions, we suspect that the S-isotopic fractionations of organosulfur photoproducts could have been continuously trapped in organic forming haze enriched in S-MIF.While another isotopic fraction associated primarily with residual SO 2 gas photo-oxidation would have escaped from the atmosphere to space or other planets, with, or without isotope selection of the lightest isotopes.The combination of these two processes over long periods of time provides a key process for explaining the evolution of S-MIF effects of haze-like organosulfur aerosols in the atmosphere over time during the Archean era.Our experimental results suggest that the organosulfur photoproducts from SO 2 -CxHy in an anoxic atmosphere were the primary origin of these signals that could undergo diagenetic overprints of primary signatures by another single sulfur source (such as the mantle derived sulfur origin: e.g., Farquhar & Wing, 2003) that has been observed in Archean archives (Figure 3).The conditions in our experiments also account for organosulfur photoproducts and the intermediate adducts, in particular MSA, as the major exit channels and rule out the possibility of forming elemental sulfur analogs as part of the major photoproducts usually observed in most SO 2 experiments (Farquhar et al., 2001;Masterson et al., 2011).
From the aerosol photoproduct spectra (Figure 1), it is clear that a substantial amount of S-O bond cleavage occurs during the course of the photolysis that corresponds mainly due to the absorption SO 2 (ã 3 B 1 ) → SO 2 (X 1 A 1 ) in  , 2022;Farquhar et al., 2010, Selvaraja et al., 2019).
10.1029/2022GC010777 7 of 9 the photocell.We infer that the organosulfur aerosol products appear to have been formed by at least two major pathways.The first of these corresponds to the direct photo-dissociation of SO 2 (SO 2 + hν → SO + O) in the 190-220 nm region.Whereas the second seems likely to have arisen from photo-excitation (SO 2 + hν → SO 2 , where (*) represents excited states of SO 2 ) in the 260-340 nm region.Other molecular fragments and intermediate adducts produced in the above photolysis reactions may initiate secondary reactions with reduced hydrocarbon species.This will in turn contribute to different reaction channels and networks proposed in the reaction scheme in Figure 4 via (a) hot H-atom abstraction by O( 3 P) and (b) direct photo-oxidation of excited state *SO 2 (singlet 1 A 2 -1 B 1 states as well as triplet 3 B 1 ) (Danielache et al., 2012;Ono, 2017).From the proposed reaction networks, it is evident that the photo-dissociation of the S-O bonds produces excited state radical species, which retain some of the excess electronic energy to initiate reactions (e.g.,CH 4 + O( 3 P) → *CH 3 + OH) through molecular hydrogen abstraction from reduced hydrocarbons (C x H y ) to form the corresponding alkylated radicals (Luria et al., 1974;Sutherland et al., 1986).Further pathways for both saturated (CH 4 ) and unsaturated (C 2 H 2 and C 2 H 4 ) hydrocarbons are crucial parameters governing the gas-to-aerosol particle interaction rates yielding different organosulfur aerosol photoproducts under photo-oxidation (using O( 3 P) and *OH) or photo-excitation conditions (Figure 4).Despite the large difference in spectral photon distributions for CH 4 -SO 2 , SO 2 -C 2 H 2 , and SO 2 -C 2 H 4 gas mixtures, our data demonstrate that organosulfur aerosols, particularly MSA, may potentially be a key "exit channel" in our experiments and may perhaps play a significant role in reduced Archean atmosphere.The possibility of other inorganic photoproducts (i.e., SO 2 + OH → HSO 3 ) depicted in Figure 1a mass spectra acting as intermediates Archean S-MIF aerosol achieved in early Earth's rock cannot be completely excluded.

Conclusion
Our experimental results suggest that organosulfur aerosol and organic haze-like features could have undergone a complete overprint of primary signatures that are likely to be observed in the Archean Earth's sulfur isotope records or Archean-like exoplanets (e.g., Antonelli et al., 2014;Fakhraee & Katsev, 2019;Reed et al., 2022).From the collection of sulfur isotope data from Archean rocks (also shown in Figure 3), it has been recognized that there is a general coherence for Δ 33 S versus δ 34 S and Δ 36 S versus Δ 33 S but variability exists that is not straightforward to explain without invoking a change in the atmospheric S-isotope signatures.One suggestion has been that these variations reflect wholesale changes in the atmospheric chemistry of aerosols typically caused by the high altitude shielding effects of organic haze plumes.It is also possible that a change in atmospheric gaseous composition through time could generate multiple chemical reaction channels and pathways that could compete with each other to produce S-MIF variations achieved in haze-like organosulfur aerosol photoproducts.Our results are relevant to this issue in that they suggest a role for haze-like organosulfur aerosols that could respond to changing UV by high altitude shielding while also reflecting different reaction pathways and raising the possibility of deposition from S-MIF via different atmospheric exit channels.This work also raises an important question regarding the ultimate fate of MSA aerosols in early Earth's atmospheric history.It is possible that these fractionated organosulfur aerosol pools could have been more susceptible to further photo-oxidation or wet deposition.In such a dynamic atmosphere, stable acidic sulfate and sulfonate products with S-MIF signals can be formed that will be achieved in Archean ocean and sediments that can undergo a complete overprint of another sulfur source to attenuate or preserve S-MIF signatures observed in the Archean era.Further work is still in progress to extend this isotopic approach to better constrain the magnitudes and trends of δ 34 S/Δ 33 S and Δ 36 S/Δ 33 S signatures for sulfur-bound organic sulfonates, sulfides, thiophenes, and sulfo-lipids observed in early Earth sedimentary rock records.This work was supported by Agouron Geobiology Fellowships (AI-GB27.13.2MIT) to HO and NASA Exobiology (Grant NNX10AR85G) to SO.The authors would like to thank Drs. Yue Li and Charles West for analytical and technical assistance.Thoughtful comments, discussions and insights from Prof. James Farquhar and Dr. Mark Claire, who helped to improve an earlier version of the manuscript.

Figure 1 .
Figure 1.Photoproduct ESI mass spectrum for organosulfur aerosols.Photolysis of (a) SO 2 -CH 4 , (b) SO 2 -C 2 H 4 , and (c) SO 2 -C 2 H 2 gas mixtures after irradiated for 2 hr under a 150 W, UV-enhanced Xenon-Arc lamp.The spectrum recorded shows accurate mass intensities of methanesulfonic acid (MSA) and other organic alkyloxysulfonate adducts as the major haze photoproducts in all the three gas mixture experiments.

Figure 2 .
Figure2.Quadruple S-isotope data from organosulfur photoproducts and residual SO 2 gas collected after 2 hr of UV-irradiation.Showing a cross plot of sulfur mass-independent fractionation (S-MIF) trends of organosulfur photoproducts (on the right side) compared to the corresponding residual SO 2 (on the left side) including interpretations of Neoarchean S-MIF arrays that is based conventional view expected for early Earth's sedimentary sulfur exit channels with Archean reference fractionation line (RFL = − 0.9 and −1.5;Zerkle et al., 2012;Kurzweil et al., 2013, Farquhar et al., 2013;Izon et al., 2015).The Δ 36 S/δ 33 S slope for CH 4 -SO 2 photoproduct (Slope = −1.9)nearly consistent with the Archean reference fractionation window).The analytical uncertainty on the plotted slopes (not shown) is estimated (to be ±0.1)from least squares linear regression as ±1 s.e (standard error).

Figure 3 .
Figure 3. Quadruple S-isotope data from derivatives of organosulfur aerosol photoproducts and complementary residual SO 2 showing variability and mixing scenario in Δ 33 S versus δ 34 S cross-plots that is superimposed on the previously published data set from global Archean compilation data set depicting possible overprinting sulfur mass-independent fractionation signatures (Source: Bosco-Santos et al., 2022;Farquhar et al., 2010, Selvaraja et al., 2019).

Figure 4 .
Figure 4. Proposed reaction schemes showing the various exit channels and networks for the formation of haze-like organosulfur photoproducts.The reaction scheme commences with UV-photo-dissociation and photoexcitation of atmospheric SO 2 , followed by subsequent H-abstraction, radical condensation, and subsequent incorporation of excited sulfoxy and C x H y species to produce organosulfur photoproducts.The solid lines and dashed lines have been color-coded to differentiate the dominant reaction channels via MSA formation consistent with Dewitt et al., 2009.