A new insight into the climatic impact of volcanic explosion: A lesson from the sulfur stable isotopes

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Ozone and Stratospheric Chemistry

International audienceThe stratosphere is the atmospheric layer comprised between 8–18 km for its lower altitudes and 40–60 km for its upper altitudes, which correspond more or less to the stratospheric ozone layer thickness. In this part of the atmosphere, intense UV radiations from the sun fuel an active and energetic photochemical reactor leading to the formation of two important by-products: the ozone molecule (O3), an oxygen allotrope, and heat that mostly originates from absorption of UV radiation by ozone. While heat causes a strong vertical stability of the air mass in the stratosphere (stratified atmosphere), large concentrations of ozone form a UV-protective shield allowing the development of life on the Earth’s surface. The intense UV radiations combined with the ozone concentration generate a distinct stratospheric chemistry where nitrogen, oxygen, and halogen compounds are highly coupled in cycles that maintain the chemical stability of this UV-protective atmospheric laye

Major influence of BrO on the NO_x and nitrate budgets in the Arctic spring, inferred from Δ¹⁷O(NO₃^–) measurements during ozone depletion events

International audienceThe triple oxygen isotopic composition of atmospheric inorganic nitrate was measured in samples collected in the Arctic in springtime at Alert, Nunavut and Barrow, Alaska. The isotope anomaly of nitrate (Δ17O = δ17O – 0.52δ18O) was used to probe the influence of ozone (O3), bromine oxide (BrO), and peroxy radicals (RO2) in the oxidation of NO to NO2, and to identify the dominant pathway that leads to the production of atmospheric nitrate. Isotopic measurements confirm that the hydrolysis of bromine nitrate (BrONO2) is a major source of nitrate in the context of ozone depletion events (ODEs), when brominated compounds primarily originating from sea salt catalytically destroy boundary layer ozone. They also show a case when BrO is the main oxidant of NO into NO2

Laboratory study of nitrate photolysis in Antarctic snow. II. Isotopic effects and wavelength dependence

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Regional characteristics of atmospheric sulfate formation in East Antarctica imprinted on 17 O-excess signature

International audience17O-excess (Δ17O = δ17O − 0.52 × δ18O) of sulfate trapped in Antarctic ice cores has been proposed as a potential tool for assessing past oxidant chemistry, while insufficient understanding of atmospheric sulfate formation around Antarctica hampers its interpretation. To probe influences of regional specific chemistry, we compared year-round observations of Δ17O of non-sea-salt sulfate in aerosols (Δ17O(SO42−)nss) at Dome C and Dumont d'Urville, inland and coastal sites in East Antarctica, throughout the year 2011. Although Δ17O(SO42−)nss at both sites showed consistent seasonality with summer minima (∼1.0‰) and winter maxima (∼2.5‰) owing to sunlight-driven changes in the relative importance of O3 oxidation to OH and H2O2 oxidation, significant intersite differences were observed in austral spring–summer and autumn. The cooccurrence of higher Δ17O(SO42−)nss at inland (2.0‰ ± 0.1‰) than the coastal site (1.2‰ ± 0.1‰) and chemical destruction of methanesulfonate (MS–) in aerosols at inland during spring–summer (October–December), combined with the first estimated Δ17O(MS–) of ∼16‰, implies that MS– destruction produces sulfate with high Δ17O(SO42−)nss of ∼12‰. If contributing to the known postdepositional decrease of MS– in snow, this process should also cause a significant postdepositional increase in Δ17O(SO42−)nss over 1‰, that can reconcile the discrepancy between Δ17O(SO42−)nss in the atmosphere and ice. The higher Δ17O(SO42−)nss at the coastal site than inland during autumn (March–May) may be associated with oxidation process involving reactive bromine and/or sea-salt particles around the coastal region

High-resolution sulfur isotopic composition measurements of volcanic sulfate from Toba candidate eruptions preserved in EDML and EDC Antarctic ice cores

Multiple peaks in sulfate concentration in ice cores have been identified as potential candidates for the ~74 ka Toba supereruption. The sulfur isotopic composition of sulfate preserved in two EPICA Antarctic ice cores, EDML and EDC, for 11 of the candidates has been analysed at high temporal resolution for mass-independent fractionation (MIF) using multi-collector inductively coupled plasma mass spectrometry. S-MIF signals preserved in volcanic sulfate are indicative of stratospheric eruptions due to sulfur aerosols being exposed to ultraviolet radiation when erupted into and above the ozone layer and subsequently undergoing photochemical reactions. Sulfur aerosols in the stratosphere will have longer residence times than those in the troposphere and will scatter incoming solar radiation. This data set includes the eruption, sample type, depths, ages (using the AICC2012 age model), sulfate concentration (determined by ion chromatography) and isotopic composition data (δ34S, δ33S, Δ33S) and their associated errors