{"id":"8e014832-444a-4178-b212-871a8684a256","arxiv_id":"1908.07781","paper_version":1,"verdict":"CONDITIONAL","confidence":"HIGH","novelty_score":6.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":1,"one_line_summary":"Molecular diffusion and phase separation cannot produce the proposed Venus nitrogen gradient; diffuse volcanic CO2 degassing is a plausible but unproven source.","lead":"The paper tests which physical processes could create a proposed nitrogen gradient in the deep atmosphere of Venus and finds that molecular diffusion and phase separation cannot do it. It suggests that carbon dioxide seeping up from the surface, at rates comparable to some volcanic systems on Earth, could explain the gradient.","discovery_kind":"new_application","skeptic_critique":{"model":"deepseek-v4-flash","headline":"Volcanic origin claim is undercut by the paper's own mass-budget admission: the required global CO2 flux doubles Venus's atmosphere in <10^4 yr with no known sink, so the terrestrial-flux analogy does not carry the conclusion.","rationale":"The paper's negative results—molecular diffusion is far too slow, phase separation is unsupported by both laboratory and simulation evidence—are convincingly argued and rest on independent molecular-dynamics calculations, an equation of state, and radial distribution functions. I do not object to those parts. The load-bearing weakness is in the positive volcanic suggestion. The required CO2 flux is computed as a planet-wide average, but the comparison is made to local terrestrial diffuse-degassing measurements. Moreover, the paper itself concedes that such a flux would double the mass of the Venus atmosphere in less than 10^4 years, with no known sink. That concession is not just a caveat; it means the proposed steady-state volcanic source cannot be maintained without a removal mechanism that has not been identified. The reader's weakest_assumption concerned the reality of the gradient; I regard that as a legitimate prior concern, but the paper explicitly conditions its analysis on the gradient being real. Even granting the gradient, the mass-budget inconsistency remains. This strengthens the case for a conditional verdict, but does not change the verdict: the negative conclusions stand, while the volcanic origin should not be accepted without resolving the sink problem or reframing the claim as a transient, localized possibility.","tokens_in":15659,"tokens_out":3591,"duration_ms":38748,"concrete_test":"Integrate F_CO2,min ≈ 8×10^-4 mol m^-2 s^-1 over the full Venus surface area (≈4.6×10^14 m^2) to obtain a planet-wide emission rate. Compare this to (i) the total present-day terrestrial volcanic CO2 emission and (ii) Venus's atmospheric CO2 inventory to compute the atmospheric doubling time. If the integrated flux exceeds terrestrial total volcanic output by orders of magnitude and the doubling time is <10^4 yr, the volcanic-degassing explanation as stated is unsustainable. A second check: repeat the flux calculation for a localized vent area consistent with VeGa-2's descent path; if the required local flux then exceeds any measured diffuse degassing, the local-source version also fails.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The positive conclusion—that the proposed N2 gradient may be sustained by diffuse CO2 degassing 'not so different' from terrestrial volcanic systems—rests on F_CO2,min ≈ 8×10^-4 mol m^-2 s^-1 computed in Section 3 from replacing 1.6×10^5 mol m^-2 of N2 over τdyn ≈ 2×10^8 s. This number is treated as a global average: multiplied by Venus's surface area it yields an emission rate that, as the paper itself states a few paragraphs later, 'would lead to the doubling of the mass of the Venus atmosphere in less than 10,000 Earth years' with neither atmospheric escape nor chemistry able to compensate. The terrestrial analogues cited (e.g., Roaring Mountain median ≈ 2.7×10^-4 mol m^-2 s^-1) are local hot-spot measurements, not planet-wide fluxes. Comparing a globally required flux to local measured fluxes is therefore not a valid basis for 'a similar effect at work on Venus.' The mass budget is not a peripheral caveat; it directly undermines the only extrinsic mechanism the paper offers. Without an identified sink or a transient-formation scenario, the volcanic suggestion is an order-of-magnitude inconsistency rather than a supported conclusion.","agreement_with_reader":"partial"},"referee_report":{"model":"deepseek-v4-flash","summary":"The paper addresses the proposed ~5 ppm m^-1 vertical gradient of molecular nitrogen in the deep atmosphere of Venus, inferred from VeGa-2 probe data, and asks which physical processes could produce it. It first tests intrinsic mechanisms: molecular diffusion under ideal and non-ideal equations of state, and phase separation or droplet formation. Using a CO2-N2 equation of state and molecular dynamics simulations, the authors find that diffusion yields a nitrogen gradient of ~0.6 ppm m^-1, an order of magnitude smaller than the proposed value, and that the diffusion timescale is ~10^13-10^14 s, far exceeding the ~2x10^8 s dynamical mixing time. The MD radial distribution functions show no clustering, and the authors argue that phase separation is unlikely for Venus's deep-atmosphere conditions. They then consider an extrinsic origin: a crustal release of CO2 that would dilute N2 near the surface, estimating a minimum flux F_CO2,min ~8x10^-4 mol m^-2 s^-1 over the dynamical timescale, and comparing it with terrestrial diffuse volcanic degassing (e.g., Roaring Mountain median ~2.7x10^-4 mol m^-2 s^-1), suggesting a volcanic source. The paper acknowledges, but does not resolve, that such an average flux would double the mass of the Venus atmosphere in less than 10,000 years with no known sink.","tokens_in":15953,"tokens_out":14810,"duration_ms":143640,"significance":"The intrinsic-mechanism analysis is a solid and valuable negative result: the ideal and non-ideal diffusion models are mutually consistent, the MD simulations give diffusion coefficients around 10^-6 m^2 s^-1 and gas-like g(r) with no cluster formation, and the derived timescales robustly rule out molecular diffusion and phase separation as origins of the proposed gradient. If the gradient is real, this is an important constraint. However, the positive claim of a volcanic origin is not established in the present form: the flux estimate is compared to local terrestrial hot-spot measurements, but the paper extends it to a global average, and its own mass-budget statement directly undermines the conclusion. The paper would be significant if it were revised to clearly separate the robust negative result from a carefully qualified extrinsic hypothesis, with a quantitative treatment of the CO2 budget and the local versus global nature of the observed gradient.","major_comments":[{"comment":"The positive conclusion for a volcanic origin is not supported by the mass budget: the paper's own statement that an average outgassing rate of ~10^-3 mol m^-2 s^-1 would double the mass of the Venus atmosphere in less than 10,000 years, with neither atmospheric escape nor chemistry able to compensate, applies directly to the estimated F_CO2,min ~8x10^-4 mol m^-2 s^-1 if that flux is treated as a global average; the doubling time for F_CO2,min is actually closer to 10^3 years. Because the terrestrial fluxes cited (e.g., the Roaring Mountain median, 2.7x10^-4 mol m^-2 s^-1) are local hot-spot measurements, they cannot justify a 'global diffuse release' hypothesis. The manuscript must either restrict the claim to a local source at the VeGa-2 landing site and then discuss source area and plume structure, or identify a viable CO2 sink or a transient-formation scenario; without this, the 'similar effect at work on Venus' conclusion is an order-of-magnitude inconsistency rather than a supported inference.","section":"Section 3"},{"comment":"The flux estimate F_CO2,min ~8x10^-4 mol m^-2 s^-1 is presented as a deterministic number with no uncertainty budget. It is the ratio of an assumed column density of N2 (1.6x10^5 mol m^-2, itself based on the assumed initial uniform profile) to an assumed dynamical timescale (tau_dyn ~2x10^8 s), and both inputs carry substantial systematic uncertainty that is not propagated. The subsequent comparison to terrestrial fluxes spans more than two orders of magnitude (Yellowstone average ~3x10^-6 mol m^-2 s^-1 versus the Roaring Mountain median 2.7x10^-4 mol m^-2 s^-1), so the statement that the needed flux is 'not so different' from terrestrial values requires a quantitative error analysis. In addition, the quoted Roaring Mountain flux '10^3 g m^-2 s^-1' is numerically inconsistent with the stated 2.7x10^-4 mol m^-2 s^-1 (by a factor of roughly 10^5), suggesting a typographical error that should be corrected.","section":"Section 3"},{"comment":"The turbulent-mixing scenario for a crustal CO2 source is asserted rather than demonstrated. The paper invokes the similarity of gaseous turbulent jets to argue that the CO2 abundance from a local injection would 'firmly decrease with altitude, possibly yielding to the proposed gradient,' but it does not compute the concentration profile in the Venus deep atmosphere or show that a surface source can sustain a nearly linear ~5 ppm m^-1 N2 gradient over 7 km. Given the short dynamical homogenization time (tau_dyn ~2x10^8 s), it is not obvious that a localized source would produce the observed vertical structure; a full boundary-layer or plume model is needed to make the extrinsic mechanism quantitative. This is a load-bearing gap in the only positive mechanism the paper offers.","section":"Section 3"},{"comment":"The entire explanatory problem and the derived flux estimate are conditional on the reality of the N2 gradient proposed by Lebonnois & Schubert (2017), but the paper does not independently verify the VeGa-2 data analysis that underlies that gradient; it only notes in the introduction that the gradient is 'if accepted as real.' The abstract and title, however, present the volcanic suggestion without this caveat. The authors should either provide an independent re-analysis of the probe data or explicitly and prominently state that all quantitative conclusions are conditional on an unconfirmed measurement, since the positive conclusion would collapse if the gradient is an artifact of the measurement.","section":"Section 1"}],"minor_comments":[{"comment":"The subject headings list 'Planets and satellites: individual: Titan' but the paper is about Venus; this should be corrected to 'Planets and satellites: individual: Venus'.","section":"Title page"},{"comment":"The reference for Werner & Brantley (2003) is given as 'Icarus, 4, 1061'; this paper appears in Geochemistry, Geophysics, Geosystems, 4(7), 1061, and the citation should be corrected so readers can locate it.","section":"References"},{"comment":"The molecular dynamics production run is described as spanning 1 ns, but the method of computing the mean-squared displacement and its statistical error (e.g., number of blocks, time origins, inclusion of the 100 ns equilibration phase) is not specified; please provide these details to justify the reported uncertainties and allow reproduction.","section":"Section 2.1"},{"comment":"The Stokes settling calculation uses a droplet diameter of D1 ~ 1 mm, but the paper does not discuss why this value is representative; since the detailed analysis later finds no droplet-formation mechanism, the settling timescale is a purely illustrative exercise and should be labeled as such in the text.","section":"Section 2.2"},{"comment":"The notation for the thermal diffusion ratio appears inconsistently as 'kT 1,2' in Eq. (1) and 'kT,12' in Eq. (4); please unify the notation.","section":"Section 2.1"}],"recommendation":"major_revision","confidential_remarks":"The negative result on intrinsic mechanisms (molecular diffusion and phase separation) is sound and likely publishable. The main problem is the overreach of the positive volcanic conclusion, which is contradicted by the paper's own mass-budget statement and by the invalid comparison of a global average flux to local terrestrial hot-spot measurements. These issues can be addressed within the manuscript's scope by reframing the volcanic hypothesis as a speculative, spatially localized scenario, providing an uncertainty budget for the flux, and clearly stating the conditional nature of the entire analysis on the unconfirmed VeGa-2 gradient. I would encourage the editor to seek a revision rather than reject, because the intrinsic-mechanism analysis is a useful contribution to the Venus atmospheric chemistry literature."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Colleague, here's my read.\n\nThe genuinely useful part of this paper is the negative result. The authors take the proposed 5 ppm/m N2 gradient in the lower 7 km of Venus's atmosphere and ask whether any intrinsic fluid property can make it. They check molecular diffusion using an ideal-gas model and a non-ideal EoS, find the equilibrium gradient is about an order of magnitude too small, and then run MD simulations of a 97/3 CO2/N2 supercritical mixture at two Venus state points. Their diffusion coefficients are around 10^-6 m^2/s, which makes the diffusion timescale millions of years—far longer than the ~2×10^8 s dynamical homogenization time from prior GCM work. They also compute radial distribution functions and see no CO2 clustering, so the phase-separation/droplet route is also ruled out. That part is careful and convincing. The MD work is new and reproducible in principle, with force-field parameters and simulation details given.\n\nThe soft spot is the positive claim. The paper suggests the gradient, if real, could be sustained by global diffuse CO2 degassing at a flux around 8×10^-4 mol/m^2/s, comparable to some terrestrial volcanic hot spots. But the comparison is apples-to-oranges: the terrestrial numbers are local vent or zone measurements (Roaring Mountain, Katla), while the Venus number is a planet-wide average needed to replace 1.6×10^5 mol/m^2 of N2 within the dynamical timescale. Multiplying that flux over Venus's surface gives an emission rate that, as the paper itself admits, would double the atmosphere's mass in under 10,000 years, with no known sink. That is not a peripheral caveat; it means the only extrinsic mechanism offered is not an order-of-magnitude fit. The authors are honest about the problem, but then still conclude \"a similar effect at work on Venus.\" I don't think the conclusion follows.\n\nThe underlying weakness is that the gradient itself is never independently verified. All the flux arithmetic presumes the Lebonnois & Schubert interpretation of VeGa-2 data is correct. The paper flags this conditionally, but the volcanic suggestion inherits the uncertainty.\n\nWho is this for? Anyone working on Venus's deep atmosphere or supercritical CO2-N2 mixtures. The negative results deserve a serious referee, and the volcanic suggestion is a useful cautionary example of why local terrestrial analogies do not scale to global budgets. I'd send it to review, but I'd expect the authors to either find a sink or reframe the volcanic idea as a transient/unknown process rather than a supported hypothesis.\n\nMy recommendation: engage with it, but treat the volcanic conclusion as speculative.","headline":"A solid negative result on molecular diffusion and phase separation in Venus's deep atmosphere, paired with a volcanic-flux suggestion that does not survive contact with the paper's own mass budget.","tokens_in":16436,"tokens_out":2252,"would_cite":true,"duration_ms":21412,"reading_group":"yes","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":[],"model":"deepseek-v4-flash","headline":"Neither molecular diffusion nor phase separation can build Venus's deep nitrogen gradient; the required CO2 flux instead matches diffuse volcanic degassing seen on Earth.","keywords":["Venus deep atmosphere","nitrogen gradient","supercritical CO2-N2 mixture","molecular diffusion","phase separation","volcanic degassing","molecular dynamics simulation","VeGa-2 probe data"],"falsifier":"Re-analyze the VeGa-2 descent measurements of atmospheric composition below 7 km with full instrumental calibration and independently reconstruct the nitrogen altitude profile; if the recovered gradient is much smaller than $\\sim 5\\,\\mathrm{ppm\\,m^{-1}}$, the volcanic-flux explanation is unnecessary. Alternatively, a lander measuring surface CO2 flux directly would test the required $8\\times 10^{-4}\\,\\mathrm{mol\\,m^{-2}\\,s^{-1}}$; finding a flux orders of magnitude lower would falsify the degassing scenario.","tokens_in":15467,"feed_emoji":"🌋","tokens_out":13887,"duration_ms":110879,"temperature":0.7,"pith_summary":"This paper asks what could create the sharp drop in nitrogen abundance reported in the lowest 7 km of Venus's atmosphere, a gradient of roughly $\\sim 5\\,\\mathrm{ppm\\,m^{-1}}$. It first tests the fluid's own ability to separate carbon dioxide and nitrogen: gravity-driven molecular diffusion, thermal diffusion, and possible phase separation in the supercritical CO2–N2 mixture. All intrinsic mechanisms fail, either because the equilibrium gradient is an order of magnitude too small or because the required diffusion time exceeds the atmospheric mixing time by a wide margin. The paper then computes what a surface source would need to supply and finds a CO2 flux near $8\\times 10^{-4}\\,\\mathrm{mol\\,m^{-2}\\,s^{-1}}$, the same order as diffuse volcanic degassing measured at some terrestrial volcanic systems. Its conclusion is that the gradient, if real, is most plausibly a crustal CO2 release rather than an atmospheric fluid effect.","feed_headline":"Venus nitrogen drop points to volcanic outgassing","feed_subtitle":"The CO2 flux needed to sustain the gradient matches diffuse volcanic degassing on Earth.","key_machinery":"The argument is carried by the steady-state diffusion equation for a binary supercritical mixture, written as a flux with three terms: Fickean concentration diffusion, pressure diffusion that can segregate species by gravity, and thermal diffusion (the Soret effect). The paper integrates this equation along the measured Venus pressure–temperature profile, using an equation of state for CO2–N2 to evaluate fugacity and partial molar volume, and supplements the result with molecular dynamics simulations that supply independent CO2 and N2 diffusion coefficients and the radial distribution function of the fluid. The load-bearing comparison is timescale: diffusion would need roughly $10^{13}$ to $10^{14}$ seconds to build a gradient, while the atmospheric circulation re-homogenizes the deep layers in about $2\\times 10^{8}$ seconds, so no diffusive mechanism can survive. This timescale argument, together with the absence of cluster formation in the simulated fluid, is what forces the paper toward an external source rather than an intrinsic one.","core_discovery":"On the paper's own terms, the central discovery is that the proposed nitrogen gradient cannot arise from any intrinsic property of the CO2–N2 supercritical fluid in Venus's deep atmosphere. Integrating the steady-state diffusion equation along the VeGa-2 pressure–temperature profile gives a nitrogen gradient near $0.6\\,\\mathrm{ppm\\,m^{-1}}$, about an order of magnitude below the proposed $\\sim 5\\,\\mathrm{ppm\\,m^{-1}}$, and even the non-ideal equation of state does not change this because the Venusian atmosphere lies far from the binary critical point where the relevant derivative vanishes. Molecular dynamics gives diffusion coefficients around $10^{-6}\\,\\mathrm{m^{2}\\,s^{-1}}$, making the diffusion timescale roughly $1.6$ to $16$ Myr, while the deep atmosphere is homogenized by circulation in about $2\\times 10^{8}$ seconds. Phase separation is dismissed on both theoretical and experimental grounds: the fluid's radial distribution function shows gas-like behavior with no CO2 clustering, and the laboratory reports of strong separation are not confirmed by other measurements. What would suffice is an external CO2 input of about $8\\times 10^{-4}\\,\\mathrm{mol\\,m^{-2}\\,s^{-1}}$, comparable to diffuse volcanic emissions measured on Earth, so the paper concludes that volcanic degassing is the most plausible origin.","pith_inferences":["The reality of the $\\sim 5\\,\\mathrm{ppm\\,m^{-1}}$ gradient is the load-bearing observation; an independent re-analysis of the VeGa-2 descent data, or a new in-situ profile below 7 km, would settle whether the volcanic explanation is required at all.","If diffuse crustal degassing is the cause, the same flux should leave detectable marks elsewhere, such as local enrichments of trace volcanic gases or thermal anomalies, though the paper does not model those signatures.","The terrestrial flux comparison suggests a testable scaling: because Earth's volcanic CO2 output has varied over geologic time, Venus's gradient strength might likewise vary with resurfacing epoch, so a present-day measurement could be an upper bound rather than a steady-state value.","The paper's own balance implies that a sustained flux at the required level cannot be recycled by escape or chemistry, so the mechanism needs either a buffering reservoir in the crust or a short-lived current episode of degassing."],"forward_implications":["If the proposed gradient is real, molecular diffusion and phase separation cannot account for it, so future models of Venus's deep atmosphere should not invoke fluid separation as the explanation.","Sustaining the gradient requires a crustal CO2 flux on the order of $8\\times 10^{-4}\\,\\mathrm{mol\\,m^{-2}\\,s^{-1}}$, a value consistent with diffuse volcanic degassing seen in terrestrial volcanic systems.","The deep-atmosphere nitrogen gradient, if confirmed, would be evidence of present-day volcanic or crustal activity on Venus, independent of the debate over catastrophic versus steady resurfacing.","An outgassing rate near $10^{-3}\\,\\mathrm{mol\\,m^{-2}\\,s^{-1}}$ would double the mass of Venus's atmosphere in under 10,000 years, so the fate of the released CO2 is an unsolved problem the paper leaves open."],"supporting_citations":[{"why":"Proposed the ~5 ppm m^-1 nitrogen gradient and gives the dynamical homogenization timescale that any proposed mechanism must beat.","marker":"Lebonnois & Schubert 2017"},{"why":"Supplies the equation of state for supercritical CO2-N2 used to compute fugacity coefficients, partial molar volumes, and the compressibility factor.","marker":"Duan et al. 1996"},{"why":"Derives the steady-state diffusive flux equation coupling concentration, pressure, and thermal diffusion that the paper integrates.","marker":"Ghorayeb & Firoozabadi 2000"},{"why":"Provides the VeGa-2 pressure-temperature profile used as the input path for all integrations and simulations.","marker":"Lorenz et al. 2018"},{"why":"Supplies the molecular force-field parameters used in the molecular dynamics simulations from which the diffusion coefficients are extracted.","marker":"Potoff & Siepmann 2001"},{"why":"Measured diffuse CO2 emissions at Yellowstone, including Roaring Mountain fluxes comparable to the required Venusian flux.","marker":"Werner & Brantley 2003"},{"why":"Measured CO2 release from the Katla volcanic system, providing a second terrestrial diffuse-degassing comparison.","marker":"Ilyinskaya et al. 2018"},{"why":"Reports the laboratory CO2-N2 separation that the paper re-examines and finds unsupported by other experiments and theory.","marker":"Hendry et al. 2013"}],"fun_headline_variants":["Venus nitrogen gradient likely volcanic, not intrinsic","Venus deep nitrogen slope traced to volcanic CO2","Venus N2 gradient: volcanic outgassing best fit","Venus nitrogen mystery explained by volcanic CO2"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The load-bearing premise is that the VeGa-2 measurements really show a nitrogen gradient of about $\\sim 5\\,\\mathrm{ppm\\,m^{-1}}$ in the lowest 7 km; the paper states this conditional and does not independently re-derive the gradient from the raw probe data, so if that gradient is an artifact of the measurement or its processing, the entire explanatory problem and the volcanic conclusion collapse.","fun_headline_variants_meta":{"raw":{"variants":["Venus nitrogen gradient likely volcanic, not intrinsic","Venus deep nitrogen slope traced to volcanic CO2","Venus N2 gradient: volcanic outgassing best fit","Venus nitrogen mystery explained by volcanic CO2"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000205,"raw_usage":{"total_tokens":1444,"prompt_tokens":1049,"completion_tokens":395,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":665,"completion_tokens_details":{"reasoning_tokens":332}},"tokens_in":665,"tokens_out":395,"duration_ms":466747,"temperature":1.0,"reasoning_tokens":332,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-14T11:57:24.822108+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Re-analyze the VeGa-2 descent measurements of atmospheric composition below 7 km with full instrumental calibration and independently reconstruct the nitrogen altitude profile; if the recovered gradient is much smaller than $\\sim 5\\,\\mathrm{ppm\\,m^{-1}}$, the volcanic-flux explanation is unnecessary. Alternatively, a lander measuring surface CO2 flux directly would test the required $8\\times 10^{-4}\\,\\mathrm{mol\\,m^{-2}\\,s^{-1}}$; finding a flux orders of magnitude lower would falsify the degassing scenario.","supporting_citations":[{"cited_title":"2017, Nat","cited_arxiv_id":null,"evidence_quote":"Proposed the ~5 ppm m^-1 nitrogen gradient and gives the dynamical homogenization timescale that any proposed mechanism must beat."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Supplies the equation of state for supercritical CO2-N2 used to compute fugacity coefficients, partial molar volumes, and the compressibility factor."},{"cited_title":"2000, AlChE J., 46, 883","cited_arxiv_id":null,"evidence_quote":"Derives the steady-state diffusive flux equation coupling concentration, pressure, and thermal diffusion that the paper integrates."},{"cited_title":"D., Crisp, D., & Huber, L","cited_arxiv_id":null,"evidence_quote":"Provides the VeGa-2 pressure-temperature profile used as the input path for all integrations and simulations."},{"cited_title":"2003, Icarus, 4, 1061","cited_arxiv_id":null,"evidence_quote":"Measured diffuse CO2 emissions at Yellowstone, including Roaring Mountain fluxes comparable to the required Venusian flux."},{"cited_title":"2018, Geophys","cited_arxiv_id":null,"evidence_quote":"Measured CO2 release from the Katla volcanic system, providing a second terrestrial diffuse-degassing comparison."},{"cited_title":"N., , Wickramathilaka, M., Espanani, R., & Jacoby, W","cited_arxiv_id":null,"evidence_quote":"Reports the laboratory CO2-N2 separation that the paper re-examines and finds unsupported by other experiments and theory."}],"review_version":1}