Retrospective Isotopic Analysis of Summertime Urban Atmospheric Sulfate in South Asia Using Improved Source Constraints

The emissions of sulfur dioxide (SO2), a harmful atmospheric pollutant, are on the rise in South Asia. Sulfate, formed from the oxidation of SO2, often comprises 10%–67% of aerosol mass and has a profound impact on climate, air quality/human health, and the environment. The potential drivers of sulfate-linked urban air pollution in South Asian megacitiesfacing a choking air pollution crisisremain poorly understood due to a lack of systematic observations. Here, we conducted stable S-isotope (δ34S) fingerprinting of sulfate aerosols in summertime megacity Delhi in South Asia to evaluate the potential drivers. With newly developed region-specific isotopic endmembers in this study, a statistical source apportionment of urban atmospheric sulfate was feasible. Results show that coal combustion (80 ± 12%) and oil combustion (14 ± 11%), followed by road dust (4 ± 3%) and biomass burning (2 ± 2%), were major contributors to atmospheric sulfate in summertime Delhi. Retrospective analysis showed a marked isotopic shift in stable sulfate isotopic composition in summertime megacity Delhi wherein the average δ34S value was 4 ± 1‰ in 2015 and 2 ± 1‰ in 2021, respectively. This was evidently linked to changes in the dominant fuel type as sulfate sourced from coal combustion (oil combustion) significantly increased ∼ 20% (decreased ∼ 20%) during this period. With no clear increase in the number of thermal power plants in and around Delhi, we speculate that the substantial increase in coal-derived sulfate could plausibly be linked to a rise in the informal industries such as brick production and food and agricultural product processing operations, whose SO2 emissions remain challenging to estimate. While further observations from the region are warranted, the findings here suggest that the continued dependence on coal in developing nations of South Asia could be one of the reasons for rising SO2 levels

Oxygen and nitrogen isotopic fractionations during human respiration

International audienceBoth oxygen and nitrogen isotope compositions (δ 18 O and δ 15 N) of exhaled air from 10 individuals were measured. Results show linear relations between isotope variation and the fraction of O 2 used during the respiration process. The isotopic influence of physiological parameters such as smoking habits, age, haemoglobin count, oxygen fixation rate or physical exercise was assessed. Among them, only smoking habits do not have any effect on δ 18 O. δ 15 N differences between inhaled and exhaled air may indicate an active (but minor) role for nitrogen during the human respiration process. Nevertheless, nitrogen fractionation is homogenous among all the individuals, which is coherent with the fact that nitrogen metabolism is controlled by the intestinal bacterial activity.Les compositions isotopiques en oxygène et azote (O et N) de l'air expiré par 10 sujets ont été mesurées. Les résultats montrent des relations linéaires entre les fractionnements isotopiques et la fraction d'oxygène utilisée lors de la respiration. L'influence isotopique de paramètres physiologiques tels que le tabagisme, le taux d'hémoglobine, le taux de fixation de l'oxygène ou l'exercice physique est analysée. Seul le tabagisme semble n'avoir aucun effet sur le O. Les différences de N entre l'air inspiré et expiré pourraient indiquer un rôle actif (mineur) de l'azote durant la respiration. Néanmoins, le fractionnement en azote est homogène pour l'ensemble des sujets, en accord avec le fait que son métabolisme est lié à l'activité bactérienne intestinale

Strontium isotope geochemistry of alluvial groundwater: a tracer for groundwater resources characterisation

International audienceThis study presents strontium isotope and major ion data of shallow groundwater and river water from the Ile du Chambon catchment, located on the Allier river in the Massif Central (France). There are large variations in the major-element contents in the surface- and groundwater. Plotting of Na vs. Cl contents and Ca, Mg, NO3, K, SO4, HCO3, Sr concentrations reflect water–rock interaction (carbonate dissolution for Ca, Mg, HCO3 and Sr because the bedrock contains marly limestones), agricultural input (farming and fertilising) and sewage effluents (for NO3, K, SO4), although some water samples are unpolluted. Sr contents and isotope ratios (87Sr/86Sr vary from 0.70892 to 0.71180 along the hydrological cycle) in the groundwater agree with previous work on groundwater in alluvial aquifers in the Loire catchment. The data plot along three directions in a 87Sr/86Sr v. 1/Sr diagram as a result of mixing, involving at least three geochemical signatures–Allier river water, and two distinct signatures that might be related to different water-rock interactions in the catchment. Mixing proportions are calculated and discussed. The alluvial aquifer of the Ile du Chambon catchment is considered, within the Sr isotope systematic, in a larger scheme that includes several alluvial aquifers of the Loire Allier catchment. Keywords: : Loire river, major and trace elements, Sr isotopic ratio, alluvial aquifer, hydrolog

Boron isotope ratio (delta B-11) measurements in water framework directive monitoring programs: comparison between double focusing sector field ICP and thermal ionization mass spectrometry

International audienceThe aim of our research was to compare delta B-11 measurements performed with thermal ionization mass spectrometry (TIMS) and sector field-inductively coupled plasma-mass spectrometry (SF-ICP-MS) and evaluate the feasibility of implementing stable isotope methods in European water framework directive (WFD) monitoring programs. The comparison was based on delta B-11 measurements of 192 ground-and surface water samples and 15 leachates of nitrate pollution source materials (organic and mineral fertilisers). The precision of delta B-11 measurements attainable with SF-ICP-MS, 2 sigma= +/- 2.6 parts per thousand; (n = 192), is as expected lower than the precision achieved by TIMS, 2 sigma= +/- 0.3 parts per thousand (n=183). However the ease of use, rapidity and availability of SF-ICP-MS on one hand and the observed variability in delta B-11 in ground-and surface water on the other (from -3.4 to +37 parts per thousand), demonstrates that using SF-ICP-MS as an isotopic screening method would promote the use of isotopic methodology for WFD monitoring. Based on the results of the different case studies it is shown that retrieving precise information on the identification of pollution sources from delta B-11 values requires reaching the best analytical precision and accuracy possible. Hence, the superior precision of TIMS advantages tracing of nitrate pollution sources. However for some cases, e. g. trying to decipher contributions between sources with really distinct delta B-11 signatures (e.g. manure and sewage effluent), SF-ICP-MS results lead to the same conclusions and can therefore be used as a first approachable screening method for the determination of delta B-11 in WFD monitoring programs

Petrological and geochemical characterization of Ge-bearing coals from the eastern Rhodopes, Bulgaria

The coals from Pchelarovo and Vulce Pole are perhydrogenated coals showing high sulphur content (3.2 - 6.2 wt%) and significant Ga and Ge contents (0 - 480 ppm) in organic matter (OM). The coals from Medenbuk could be perhydrogenated coals modified by weathering processes. They show low sulphur content (1.5 wt%), high homogeneous Ge contents in OM (~2500 ppm) and an unusual enrichment in Ge (up to 0.8 wt%) and V (2.8 wt%) in weathered zones of framboïdal pyrite. Sulphur isotopic study of pyrite and organic sulphur provides evidence of bacterial reduction of dominantly seawater sulphates. However taking account the geological context of the three basins, the introduction of volcanic fluids in the basins of Pchelarovo and Vulce Pole during their forma-tion cannot be excluded

Mineralogical and isotopic record of biotic and abiotic diagenesis of the Callovian-Oxfordian clayey formation of Bure (France)

International audienceThe Callovian-Oxfordian (COx) clayey unit is being studied in the Eastern part of the Paris Basin at depths between 400 and 500 m depth to assess of its suitability for nuclear waste disposal. The present study combines new mineralogical and isotopic data to describe the sedimentary history of the COx unit. Petrologic study provided evidence of the following diagenetic mineral sequence: (1) framboidal pyrite and micritic calcite, (2) iron-rich euhedral carbonates (ankerite, sideroplesite) and glauconite (3) limpid calcite and dolomite and celestite infilling residual porosity in bioclasts and cracks, (4) chalcedony, (5) quartz/calcite. Pyrite in bioturbations shows a wide range of δ34S (−38‰ to +34.5‰), providing evidence of bacterial sulphate reduction processes in changing sedimentation conditions. The most negative values (−38‰ to −22‰), measured in the lower part of the COx unit indicate precipitation of pyrite in a marine environment with a continuous sulphate supply. The most positive pyrite δ34S values (−14‰ up to +34.5‰) in the upper part of the COx unit indicate pyrite precipitation in a closed system. Celestite δ34S values reflect the last evolutionary stage of the system when bacterial activity ended; however its deposition cannot be possible without sulphate supply due to carbonate bioclast dissolution. The 87Sr/86Sr ratio of celestite (0.706872-0.707040) is consistent with deposition from Jurassic marine-derived waters. Carbon and oxygen isotopic compositions of bulk calcite and dolomite are consistent with marine carbonates. Siderite, only present in the maximum clay zone, has chemical composition and δ18O consistent with a marine environment. Its δ13C is however lower than those of marine carbonates, suggesting a contribution of 13C-depleted carbon from degradation of organic matter. δ18O values of diagenetic chalcedony range between +27‰ and +31‰, suggesting precipitation from marine-derived pore waters. Late calcite crosscutting a vein filled with chalcedony and celestite, and late euhedral quartz in a limestone from the top of the formation have lower δ18O values (not, vert, similar+19‰), suggesting that they precipitated from meteoric fluids, isotopically close to present-day pore waters of the formation. Finally, the study illustrates the transition from very active, biotic diagenesis to abiotic diagenesis. This transition appears to be driven by compaction of the sediment, which inhibited movement of bacterial cells by reduction of porosity and pore sizes, rather than a lack of inorganic carbon or sulphates

Combustibles, fuels and their combustion products: A view through carbon isotopes

International audienceStable (i.e. non-radioactive) carbon-isotope composition (δ13C) in fuels has been extensively used as an indicator of the processes leading to the generation of their parent crude-oil. With the example of those used in Paris (France), this preliminary study isotopically characterizes fuels and combustibles, as well as the isotopic relations existing with their combustion by-products, i.e. gases (CO2) and particles (bulk carbon). Results show that δ13C in fuels is clearly related to their physical state, with natural gas being strongly depleted in 13C while coal yields the highest δ13C, and liquid fuels display intermediate values. This relation is also valid for combustion gases, although δ13C values of combustion particles form a homogeneous range within which no clear distinction is observed. Combustion processes are accompanied by carbon-isotope fractionation (noted Δ13C) resulting from the combustion being incomplete. Carbon-isotope fractionation is strictly negative (Δ13C = −1.3‰) during the formation of combustion gases, but generally positive in particle formation even if values close to zero are observed. Using simple mixing equations for describing the closed system formed by fuel, CO2 and carbonaceous particles, we discuss the carbon budget for spark-ignition (unleaded gasoline) and diesel engines. Stable carbon isotopes corroborate the already-proved superior efficiency of diesel combustion mode compared with spark ignition, as carbon is preferentially transformed into CO2

Lead isotopes decipher multiple origins within single PM 10 samples in the atmosphere of Paris

International audienceThe atmospheric concentration of lead (Pb) in France has strongly decreased since its legal reduction in gasoline in 2000. Pb-isotope ratios are effective tracers of its origin. Pb in atmospheric particulate matter with a diameter 90 % (mass) of the bulk Pb and aggregates on pre-existing particles in the atmosphere. Characterisation of the emissions from different pollution sources, however, indicates that Pb is entirely contained in the labile fraction. Our results show that, in air, the intrinsic fraction is consistently more radiogenic (the degree of enrichment being greater in summer), hinting at different origins. The labile fraction clearly identifies industrial activity as its main source, but the intrinsic fraction may result from either a different industrial-pollution source or, more likely, from a natural end-member (i.e. pre-industrial sediment)

Nitrogen isotopes: Tracers of origin and processes affecting PM10 in the atmosphere of Paris

International audienceNitrogen in atmospheric particles in an urban environment is the result of complex primary and secondary processes, which renders identifying its origin somewhat complicated. Using the example of PM10 in the atmosphere of Paris (France), it is shown that the use of stable nitrogen-isotope compositions (δ15N) alleviates this difficulty and provides clear information on the sources of primary and possibly of secondary nitrogen. Characterization of emissions of the different types of emitters in the city (road traffic, waste incinerators and heating sources) shows that these are clearly discriminated by specific isotope signatures. δ15N is particularly useful in showing that a substantial portion of the nitrogen is the result of secondary reactions, reactions that are different in summer and winter, as are the corresponding pollution sources. While it is unclear, among point sources, what the winter source of primary nitrogen is, road traffic appear to be the source of primary nitrogen in summer. Identification of the sources of the secondary nitrogen strongly depends on the nitrogen isotope fractionations (Δ15N) associated to atmospheric conversion of NOx to nitrate, but hypothesises presented here hint at the possible corresponding pollution sources

Assessing the Environmental Impact of Geothermal Power Utilization Using Isotope Ratios (C, N, S, Pb) in Moss (Rhacomitrium Lanuginosum)

ABSTRACT Conventional geothermal power plants are sources of industrial waste including spent fluids and non-condensable gases. Increasingly spent fluids are being re-injected in to the geothermal systems reducing significantly the environmental impact of power production and sustaining pressure within the system. While efforts are afoot to sequester some of the non-condensable gases (e.g. CO2 and H 2 S) a significant portion of the gases are currently vented to the atmosphere. Little is known of the effects of long term exposures to low levels of hydrogen sulfide. However, it has been suggested that H 2 S plays a role in the decline of vegetation around the geothermal power plant in Hellisheiði. In this study we examine the stable isotopic composition of woolly fringe moss (Rhacomitrium lanuginosum) from lava-fields around geothermal power plants in south-west Iceland. A sample suite originally collected for trace element analysis was analyzed for the isotopic composition of sulfur (S), nitrogen (N), carbon (C) and lead (Pb). The isotope ratio of sulfur varies by about 16 per mil and is controlled by binary mixing, with the most probable end members being i) hydrothermal/magmatic ("mantle-derived") sulfur and ii) marine-derived sulfur. The isotopic composition of N ( 15 N) varies from -10.3 to -6.0 (‰ PDB). The more enriched (less negative -values) samples are more variable in terms of N content and are have comparatively high Pb content. The isotopic composition of C ( 13 C) varies from -26.1 to -23.0 (‰ PDB). The more enriched samples have typically lower C content possibly reflecting addition of dust (carbon free) to the samples. The dust may contribute Pb to the moss samples. The change in discrimination for the heavy isotopes ( 15 N and 13 C) may be a result of environmental factors such as reduced precipitation or due to an increased anthropogenic influence. The results do not support the contention that geothermal H 2 S is responsible for the decline in vegetation around geothermal power plants. Other inputs are suggested by the data, including locally derived bedrock dust (e.g. construction activities), possibly heavy traffic (car exhaust, road dust) or other environmental factors such as reduced precipitation