| 1. |
- Aeppli, Christoph, et al.
(author)
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Direct compound-specific stable chlorine isotope analysis of organic compounds with quadrupole GC/MS using standard isotope bracketing
- 2010
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In: Analytical Chemistry. - Columbus, OH : American Chemical Society. - 0003-2700 .- 1520-6882. ; 82:1, s. 420-426
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Journal article (peer-reviewed)abstract
- A method has been developed for the direct determination of the stable chlorine isotope composition (delta(37)Cl) of organochlorines that eliminates sample preparation, achieves precision comparable to earlier techniques while improving the sensitivity, and makes use of benchtop gas chromatography-quadrupole mass spectrometry instruments (GCqMS). The method is based on the use of multiple injections (n = 8-10) of the sample, bracketed by a molecularly identical isotopic standard with known delta(37)Cl, determined using off-line thermal ionization mass spectrometry (TIMS). Mass traces of two isotopologues differing by one chlorine isotope were used to calculate delta(37)Cl values. Optimization of mass spectrometry and peak integration parameters as well as method validation was achieved using tetrachloroethene (PCE), p,p'-dichlorodiphenyltrichloroethane (DDT), and pentachlorophenol (PCP), spanning a delta(37)Cl range of -5.5 to +3.2 per thousand vs SMOC. Injecting 1.6-1100 pmol resulted in standard deviations (1sigma) of 0.6-1.3 per thousand, and the delta(37)Cl results agreed with values independently measured with TIMS. The method was tested by determining the Rayleigh fractionation during evaporation of pure liquid PCE, resulting in a chlorine isotopic enrichment factor of epsilon(Cl) = -1.1 +/- 0.4 per thousand. Furthermore, position-specific delta(37)Cl analysis based on analysis of DDT mass fragments was evaluated. The GCqMS-delta(37)Cl method offers a simplified yet sensitive approach for compound-specific chlorine isotope analysis.
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| 2. |
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| 3. |
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| 4. |
- Aeppli, Christoph, et al.
(author)
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Use of Cl and C Isotopic Fractionation to Identify Degradation and Sources of Polychlorinated Phenols : Mechanistic Study and Field Application
- 2013
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In: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 47:2, s. 790-797
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Journal article (peer-reviewed)abstract
- The widespread use of chlorinated phenols (CPs) as a wood preservative has led to numerous contaminated sawmill sites. However, it remains challenging to assess the extent of in situ degradation of CPs. We evaluated the use of compound-specific chlorine and carbon isotope analysis (Cl- and C-CSLA) to assess CP biotransformation. In a laboratory system, we measured isotopic fractionation during oxidative 2,4,6-trichlorophenol dechlorination by representative soil enzymes (C. fumago chloroperoxidase, horseradish peroxidase, and laccase from T. versicolor). Using a mathematical model, the validity of the Rayleigh approach to evaluate apparent kinetic isotope effects (AKIE) was confirmed. A small but significant Cl-AKIE of 1.0022 +/- 0.0006 was observed for all three enzymes, consistent with a reaction pathway via a cationic radical species. For carbon, a slight inverse isotope effect was observed (C-AKIE = 0.9945 +/- 0.0019). This fractionation behavior is clearly distinguishable from reported reductive dechlorination mechanisms. Based on these results we then assessed degradation and apportioned different types of technical CP mixtures used at two former sawmill sites. To our knowledge, this is the first study that makes use of two-element CSIA to study sources and transformation of CPs in the environment.
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| 5. |
- Bikkina, Srinivas, et al.
(author)
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Air quality in megacity Delhi affected by countryside biomass burning
- 2019
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In: Nature Sustainability. - : Springer Science and Business Media LLC. - 2398-9629. ; 2:3, s. 200-205
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Journal article (peer-reviewed)abstract
- South Asian megacities are strong sources of regional air pollution. Delhi is a key hotspot of health-and climate-impacting black carbon (BC) emissions, affecting environmental sustainability in densely populated northern India. Effective mitigation of BC impact is hampered by highly uncertain emission source estimates. Here, we use dual-carbon isotope fingerprints (delta C-13/Delta C-14) of BC to constrain the seasonal source variability in Delhi. These measurements show that lower BC concentrations in summer are predominantly from fossil fuel sources (similar to 83%). However, large-scale open burning of post-harvest crop residue/wood in nearby rural regions is contributing to severe haze pollution in Delhi during winter and autumn (similar to 42 +/- 17%). Hence, the common conception that megacities affect their surroundings is here amended or seasonally reversed. Therefore, to combat the severe air pollution problems in Delhi and the environmental quality of northern India, current urban efforts need to be complemented with countryside regional mitigation.
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| 6. |
- Budhavant, Krishnakant, et al.
(author)
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Black carbon aerosols over Indian Ocean have unique source fingerprint and optical characteristics during monsoon season
- 2023
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In: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 120:8
-
Journal article (peer-reviewed)abstract
- Effects of aerosols such as black carbon (BC) on climate and buildup of the monsoon over the Indian Ocean are insufficiently quantified. Uncertain contributions from various natural and anthropogenic sources impede our understanding. Here, we use observations over 5 y of BC and its isotopes at a remote island observatory in northern Indian Ocean to constrain loadings and sources during little-studied monsoon season. Carbon-14 data show a highly variable yet largely fossil (65 ± 15%) source mixture. Combining carbon-14 with carbon-13 reveals the impact of African savanna burning, which occasionally approach 50% (48 ± 9%) of the total BC loadings. The BC mass-absorption cross-section for this regime is 7.6 ± 2.6 m2/g, with higher values during savanna fire input. Taken together, the combustion sources, longevity, and optical properties of BC aerosols over summertime Indian Ocean are different than the more-studied winter aerosol, with implications for chemical transport and climate model simulations of the Indian monsoon.
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| 7. |
- Budhavant, Krishnakant, et al.
(author)
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Changing optical properties of Black Carbon and Brown Carbon aerosols during long-range transport from the Indo-Gangetic Plain to the equatorial Indian Ocean
-
Other publication (other academic/artistic)abstract
- Atmospheric aerosols strongly influence the global climate by their light absorption (e.g., black carbon, BC, brown carbon, BrC) and scattering (e.g., sulfate) properties. This study presents simultaneous measurements of ambient aerosol light absorption properties and chemical composition from three large-footprint South Asian receptor sites during the South Asian Pollution Experiment (SAPOEX) in December 2017 - March 2018. The BC mass absorption cross-section (BC-MAC678) values increased from 3.5 ± 1.3 at the Bhola Climate Observatory-Bangladesh (i.e., located at exit outflow of Indo-Gangetic Plain) to 6.4 ± 1.3 at the two regional receptor observatories at Maldives Climate Observatory-Hanimaadhoo (MCOH) and Maldives Climate Observatory-Gan (MCOG), an increase of 80%. This likely reflects a scavenging fractionation resulting in a population of finer BC with higher MAC678 having higher longevity. At the same time, the BrC-MAC365 decreased by a factor of three from the IGP exit to the equatorial Indian Ocean, likely due to photochemical bleaching of organic chromophores. The high chlorine-to-sodium ratio at the near-source-region BCOB suggests a significant contribution of chlorine from anthropogenic activities. This particulate Cl- has the potential to convert into Cl-radicals that can affect the oxidation capacity of the polluted air. Moreover, Cl- is shown to be near-fully consumed during the long-range transport. The results of this synoptic study over the large South Asian scale contribute rare observational constraints on optical properties of ambient BC (and BrC) aerosols over regional scales away from emission sources. It also contributes significantly to understanding the ageing effect of the optical and chemical properties of aerosols as the pollution from the Indo-Gangetic Plain disperses over the tropical ocean.
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| 8. |
- Budhavant, Krishnakant, et al.
(author)
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Enhanced Light-Absorption of Black Carbon in Rainwater Compared With Aerosols Over the Northern Indian Ocean
- 2020
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In: Journal of Geophysical Research - Atmospheres. - 2169-897X .- 2169-8996. ; 125:2
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Journal article (peer-reviewed)abstract
- Black carbon (BC) aerosols affect climate, especially in high aerosol loading regions such as South Asia. A key uncertainty for the climate effects of BC is the evolution of light-absorbing properties in the atmosphere. Here, we present a year-round comparison of the mass absorption cross section (MAC; 678 nm) of BC in air (PM10) and rain, for samples collected at the Maldives Climate Observatory at Hanimaadhoo. We develop a filter-loading correction scheme for estimating BC absorption on filters used in high-volume samplers. The year-round average MAC(678) of BC in the rain is almost twice (13.3 +/- 4.2 m(2)/g) compared to the PM10 aerosol (7.2 +/- 2.6 m(2)/g). A possible explanation is the elevated ratio of organic carbon (OC) to BC observed in rain particulate matter (9.4 +/- 6.3) compared to in the aerosols (OC/BC 2.6 +/- 1.4 and water-insoluble organic carbon/BC 1.2 +/- 0.8), indicating a coating-enhancement effect. In addition to BC, we also investigated the MAC(365) of water-soluble brown carbon in PM10 (0.4 +/- 0.4 m(2)/g, at 365 nm). In contrast to BC, MAC(365)brown carbon relates to air mass history, showing higher values for samples from air originating over the South Asian landmass. Furthermore, calculated washout ratios are much lower for BC compared to OC and inorganic ions such as sulfate, implying a longer atmospheric lifetime for BC. The wet deposition flux for BC during the high loading winter was 3 times higher than during the wet summer, despite much less precipitation in the winter.
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| 9. |
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| 10. |
- Carrizo, Daniel, et al.
(author)
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Compound-specific bromine isotope compositions of one natural and six = dustrially synthesised organobromine substances
- 2011
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In: Environmental Chemistry. - 1448-2517 .- 1449-8979. ; 8:2, s. 127-132
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Journal article (peer-reviewed)abstract
- AB The stable bromine isotopic composition (delta(81)Br) was determined for six industrially synthesised brominated organic compounds (BOCs) and one natural BOC by gas-chromatography multi-collector inductively coupled plasma mass spectrometry (GC-mcICP-MS). The delta(81)Br compositions of brominated benzenes, phenols (both natural and industrial), anisoles, and naphthalenes were constrained with the standard differential measurement approach using as reference a monobromobenzene sample with an independently determined delta(81)Br value (-0.39 parts per thousand v. Standard Mean Ocean Bromide, SMOB). The delta(81)Br values for the industrial BOCs ranged from -4.3 to -0.4 parts per thousand. The average delta(81)Br value for the natural compound (2,4-dibromophenol) was 0.2 +/- 1.6% (1 s.d.), and for the identical industrial compound (2,4-dibromophenol) -1.1 +/- 0.9 parts per thousand (1 s.d.), with a statistically significant difference of similar to 1.4 (P<0.05). The delta(81)Br of four out of six industrial compounds was found to be significantly different from that of the natural sample. These novel results establish the bromine isotopic variability among the industrially produced BOCs in relation to a natural sample.
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| 11. |
- Dasari, Sanjeev, et al.
(author)
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Observation-constrained atmospheric lifetime and emission fluxes of black carbon aerosols over South Asia
-
Other publication (other academic/artistic)abstract
- Black carbon (BC) aerosols cause climate perturbation and affect air quality/human health. In densely populated South Asia—where the warming effect of BC is estimated to be ~ orders of magnitude higher than the global average—model simulations underestimate the wintertime atmospheric abundance of BC relative to surface observations. Two possible explanations for this model-observation offset are ill-constrained regional emission fluxes and atmospheric BC lifetime (τBC). Here, we combine hourly-resolved BC and carbon monoxide (CO) measurements for three successive winters from a South Asian receptor site—the Maldives Climate Observatory at Hanimaadhoo (MCOH)—in inverse frameworks, to assess the impact of emissions fluxes and lifetimes on ambient BC concentrations. The average ΔBC/ΔCO ratio (background corrected) at MCOH of 14±5 ng m-3 ppb-1 is found to be 2-3 times higher than in the East Asian outflow (range: 2 to 8 ng m-3 ppb-1). A BC transport efficiency of ~86% suggests low influence of wet scavenging processes during the dry South Asian winter period. Using statistical time series analysis, the τBC for dry wintertime South Asia is estimated to be 8±0.5 days, which is higher than commonly used in models. By coupling air mass back trajectories, lifetimes, and the ΔBC/ΔCO time-series data within an inverse modelling framework, we provide an observation-based “top-down” BC emission flux for South Asia estimated to be ~2.4±1 Tg/year. This is significantly higher than estimates from current “bottom-up” emission inventories (EIs). Taken together, this study suggests that to reconcile long-standing BC model-observation offsets in South Asia, existing emission estimates may need to be more than doubled in magnitude.
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| 12. |
- Dasari, Sanjeev, 1989-, et al.
(author)
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Observational Evidence of Large Contribution from Primary Sources for Carbon Monoxide in the South Asian Outflow
- 2022
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In: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 56:1, s. 165-174
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Journal article (peer-reviewed)abstract
- South Asian air is among the most polluted in the world, causing premature death of millions and asserting a strong perturbation of the regional climate. A central component is carbon monoxide (CO), which is a key modulator of the oxidizing capacity of the atmosphere and a potent indirect greenhouse gas. While CO concentrations are declining elsewhere, South Asia exhibits an increasing trend for unresolved reasons. In this paper, we use dual-isotope (δ13C and δ18O) fingerprinting of CO intercepted in the South Asian outflow to constrain the relative contributions from primary and secondary CO sources. Results show that combustion-derived primary sources dominate the wintertime continental CO fingerprint (fprimary ∼ 79 ± 4%), significantly higher than the global estimate (fprimary ∼ 55 ± 5%). Satellite-based inventory estimates match isotope-constrained fprimary-CO, suggesting observational convergence in source characterization and a prospect for model–observation reconciliation. This “ground-truthing” emphasizes the pressing need to mitigate incomplete combustion activities for climate/air quality benefits in South Asia.
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| 13. |
- Dasari, Sanjeev, et al.
(author)
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Photochemical degradation affects the light absorption of water-soluble brown carbon in the South Asian outflow
- 2019
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In: Science Advances. - : American Association for the Advancement of Science (AAAS). - 2375-2548. ; 5:1
-
Journal article (peer-reviewed)abstract
- Light-absorbing organic aerosols, known as brown carbon (BrC), counteract the overall cooling effect of aerosols on Earth's climate. The spatial and temporal dynamics of their light-absorbing properties are poorly constrained and unaccounted for in climate models, because of limited ambient observations. We combine carbon isotope forensics (delta C-13) with measurements of light absorption in a conceptual aging model to constrain the loss of light absorptivity (i.e., bleaching) of water-soluble BrC (WS-BrC) aerosols in one of the world's largest BrC emission regions-South Asia. On this regional scale, we find that atmospheric photochemical oxidation reduces the light absorption of WS-BrC by similar to 84% during transport over 6000 km in the Indo-Gangetic Plain, with an ambient first-order bleaching rate of 0.20 +/- 0.05 day(-1) during over-ocean transit across Bay of Bengal to an Indian Ocean receptor site. This study facilitates dynamic parameterization of WS-BrC absorption properties, thereby constraining BrC climate impact over South Asia.
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| 14. |
- Dasari, Sanjeev, et al.
(author)
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Source Quantification of South Asian Black Carbon Aerosols with Isotopes and Modeling
- 2020
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In: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 54:19, s. 11771-11779
-
Journal article (peer-reviewed)abstract
- Black carbon (BC) aerosols perturb climate and impoverish air quality/ human health-affecting similar to 1.5 billion people in South Asia. However, the lack of source-diagnostic observations of BC is hindering the evaluation of uncertain bottom-up emission inventories (EIs) and thereby also models/policies. Here, we present dual-isotope-based (Delta C-14/delta C-13) fingerprinting of wintertime BC at two receptor sites of the continental outflow. Our results show a remarkable similarity in contributions of biomass and fossil combustion, both from the site capturing the highly populated highly polluted Indo-Gangetic Plain footprint (IGP; Delta C-14-f(biomass) = 50 +/- 3%) and the second site in the N. Indian Ocean representing a wider South Asian footprint (52 +/- 6%). Yet, both sites reflect distinct delta C-13-fingerprints, indicating a distinguishable contribution of C-4-biomass burning from peninsular India (PI). Tailored-model-predicted seasonaveraged BC concentrations (700 +/- 440 ng m(-3)) match observations (740 +/- 250 ng m(-3)), however, unveiling a systematically increasing model-observation bias (+19% to -53%) through winter. Inclusion of BC from open burning alone does not reconcile predictions (f(biomass) = 44 +/- 8%) with observations. Direct source-segregated comparison reveals regional offsets in anthropogenic emission fluxes in EIs, overestimated fossil-BC in the IGP, and underestimated biomass-BC in PI, which contributes to the model-observation bias. This ground-truthing pinpoints uncertainties in BC emission sources, which benefit both climate/air-quality modeling and mitigation policies in South Asia.
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| 15. |
- Ek, Caroline, et al.
(author)
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Using Compound-Specific and Bulk Stable Isotope Analysis for Trophic Positioning of Bivalves in Contaminated Baltic Sea Sediments
- 2018
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In: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 52:8, s. 4861-4868
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Journal article (peer-reviewed)abstract
- Stable nitrogen isotopes (delta N-15) are used as indicators of trophic position (TP) of consumers. Deriving TP from delta N-15 of individual amino acids (AAs) is becoming popular in ecological studies, because of lower uncertainty than TP based on bulk delta N-15 (TPbulk). This method would also facilitate biomagnification studies provided that isotope fractionation is unaffected by toxic exposure. We compared TPAA and TPbulk estimates for a sediment-dwelling bivalve from two coastal sites, a pristine and a contaminated. Chemical analysis of PCB levels in mussels, sediments, and pore water confirmed the expected difference between sites. Both methods, but in particular the TPAA underestimated the actual TP of bivalves. Using error propagation, the total uncertainty related to the analytical precision and assumptions in the TP calculations was found to be similar between the two methods. Interestingly, the significantly higher intercept for the regression between T-AA, and TPbulk in the contaminated site compared to the pristine site indicates a higher deamination rate due to detoxification as a result of chronic exposure and a higher N-15 fractionation. Hence, there is a need for controlled experiments on assumptions underlying amino acid-specific stable isotope methods in food web and bimagnification studies.
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| 16. |
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| 17. |
- Fang, Wenzheng, et al.
(author)
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Combined influences of sources and atmospheric bleaching on light absorption of water-soluble brown carbon aerosols
- 2023
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In: npj Climate and Atmospheric Science. - 2397-3722. ; 6:1
-
Journal article (peer-reviewed)abstract
- Light-absorbing Brown Carbon (BrC) aerosols partially offset the overall climate-cooling of aerosols. However, the evolution of BrC light-absorption during atmospheric transport is poorly constrained. Here, we utilize optical properties, ageing-diagnostic delta C-13-BrC and transport time to deduce that the mass absorption cross-section (MACWS-BrC) is decreasing by similar to 50% during long-range oversea transport, resulting in a first-order bleaching rate of 0.24 day(-1) during the 3-day transit from continental East Asia to a south-east Yellow Sea receptor. A modern C-14 signal points to a strong inverse correlation between BrC light-absorption and age of the source material. Combining this with results for South Asia reveals a striking agreement between these two major-emission regions of rapid photobleaching of BrC with a higher intrinsic absorptivity for BrC stemming from biomass burning. The consistency of bleaching parameters constrained independently for the outflows of both East and South Asia indicates that the weakening of BrC light absorption, thus primarily related to photochemical processes rather than sources, is likely a ubiquitous phenomenon.
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| 18. |
- Fang, Wenzheng, et al.
(author)
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Divergent Evolution of Carbonaceous Aerosols during Dispersal of East Asian Haze
- 2017
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In: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 7
-
Journal article (peer-reviewed)abstract
- Wintertime East Asia is plagued by severe haze episodes, characterized by large contributions of carbonaceous aerosols. However, the sources and atmospheric transformations of these major components are poorly constrained, hindering development of efficient mitigation strategies and detailed modelling of effects. Here we present dual carbon isotope (delta C-13 and Delta C-14) signatures for black carbon (BC), organic carbon (OC) and water-soluble organic carbon (WSOC) aerosols collected in urban (Beijing and BC for Shanghai) and regional receptors (e.g., Korea Climate Observatory at Gosan) during January 2014. Fossil sources (>50%) dominate BC at all sites with most stemming from coal combustion, except for Shanghai, where liquid fossil source is largest. During source-to-receptor transport, the delta C-13 fingerprint becomes enriched for WSOC but depleted for water-insoluble OC (WIOC). This reveals that the atmospheric processing of these two major pools are fundamentally different. The photochemical aging (e.g., photodissociation, photooxidation) during formation and transport can release CO2/CO or short-chain VOCs with lighter carbon, whereas the remaining WSOC becomes increasingly enriched in delta C-13. On the other hand, several processes, e.g., secondary formation, rearrangement reaction in the particle phase, and photooxidation can influence WIOC. Taken together, this study highlights high fossil contributions for all carbonaceous aerosol sub-compartments in East Asia, and suggests different transformation pathways for different classes of carbonaceous aerosols.
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| 19. |
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| 20. |
- Holmstrand, Henry, et al.
(author)
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Chlorine isotope evidence for the anthropogenic origin of tris-(4-chlorophenyl)methane
- 2010
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In: Applied Geochemistry. - : Elsevier BV. - 0883-2927 .- 1872-9134. ; 25:9, s. 1301-1306
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Journal article (peer-reviewed)abstract
- Compound-specific Cl-isotope analysis was performed on the persistent and bioaccumulating compound tris-(4-chlorophenyl)methane (4,4',4 ''-TCPMe, referred to as TCPMe in this study) to elucidate whether its main source is natural or anthropogenic. Blubber from the Baltic grey seal (Halichoerus grypus) was extracted by continuous acetonitrile partitioning, and the TCPMe was isolated from the extract by preparative-capillary gas chromatography. Chlorine isotope analysis was subsequently performed by sealed-tube combustion in conjunction with thermal-ionization mass spectrometry (TIMS). The delta Cl-37 of TCPMe was -3.5 +/- 0.5 parts per thousand, similar to the previously reported delta Cl-37 of technical grade p,p'-DDT (referred to as DDT in this study). The data is not consistent with a putative marine natural source of TCPMe, as enzymatic (biotic) production is reported to give values of delta Cl-37 < - 10 parts per thousand. The delta Cl-37-TCPMe data thus supports the hypothesis that TCPMe is produced as a byproduct during DDT synthesis and is released to the environment through the same pathways as DDT. It is also consistent with tris-(4-chlorophenyl)methanol as the primary biotransformation product of TCPMe.
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| 21. |
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| 22. |
- Holmstrand, Henry, et al.
(author)
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Compound-specific bromine isotope analysis of brominated diphenyl ethers using gas chromatography multiple collector/inductively coupled plasma mass spectrometry
- 2010
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In: Rapid Communications in Mass Spectrometry. - : Wiley. - 0951-4198 .- 1097-0231. ; 24:14, s. 2135-2142
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Journal article (peer-reviewed)abstract
- The bromine isotope composition is potentially diagnostic in both degradation monitoring and source apportionment of organobromines in the environment. A method for compound-specific bromine isotope analysis (delta Br-81) based on gas chromatography multiple collector inductively coupled plasma mass spectrometry (GC/ICPMS) was developed for common brominated diaromatic compounds. Brominated diphenyl ethers (BDEs) in Bromkal 70-5DE, a technical flame-retardant mixture containing mainly BDEs #47, #99 and #100, were used as test substances, with standard bracketing for the samples achieved through co-injected monobromobenzene (MBB) with a known delta Br-81 of -0.39 parts per thousand vs. Standard Mean Ocean Bromine (SMOBr). Three different heated transfer lines were constructed and tested to achieve efficient conduction of the BDEs from the gas chromatograph to the ICPMS instrument. The MBB was analyzed with a precision of 0.4 parts per thousand (1 s, n = 18). The precision for BDEs was 1.4-1.8 parts per thousand (1 s, n = 10-12 depending on the congener). The lower precision for the BDEs than for MBB may reflect the heat required to prevent condensation of the analytes in ICP torch assembly. The use of an internal standard of similar chemical structure to the analytes alleviates this problem, as illustrated by a difference of 0.3 +/- 0.7 parts per thousand (1 s, n = 6) between the (delta Br-81 values of co-injected methoxy BDE-47 and BDE-47 extracted from whale blubber. Improvements in precision and accuracy may be achieved by the use of a more efficient heating of the torch assembly in conjunction with a set of internal standards that match the target compounds.
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| 23. |
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| 24. |
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| 25. |
- Holmstrand, Henry, 1974-
(author)
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Compound-specific stable chlorine isotope analysis : A versatile tool for investigating biochemical and geochemical processes of organochlorine substances
- 2006
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Doctoral thesis (other academic/artistic)abstract
- Chlorinated organic compounds (OCls) from anthropogenic sources are generally considered to be a class of chemicals with high potential for ecotoxicity, including infamous substances such as polychlorinated biphenyls (PCB), dichloro-dibenzo-trichloroethane (DDT) and polychlorinated dibenzo-p-dioxins (PCDD). OCls are also produced naturally, sometimes at the same order of magnitude as anthropogenic compounds. The scope of this thesis was to develop and apply a method for isotope analysis of OCls, as a part of compound-specific chlorine isotope analysis (CSIA-δ37Cl) of trace level compounds. Isotope analysis of chlorine was performed with sealed-tube combustion and thermal-ionization mass spectrometry (TIMS), in order to improve the analytical sensitivity by a factor 20 relative to conventional techniques. Chlorine isotope signatures of organochlorines (δ37Cl-OCl) can be used for source apportionment in the natural vs. anthropogenic spectrum. CSIA-δ37Cl was tested as a tool to resolve the origin of putatively natural PCDD found in ball clay from the Mississippi Embayment, USA. Combined with results from 14C analysis, the δ37Cl-PCDD was consistent with a natural abiotic formation of PCDD. Reactions involving the scission of a chemical bond to a molecular chlorine substituent will induce a shift in the δ37Cl-OCl of the remaining reactant. This concept was used to calculate the undegraded fraction of DDT in the Baltic marine environment (~7% DDT remaining) based on δ37Cl-OCl measurements of DDT harvested from seal blubber. Hence, it is suggested that CSIA-δ37Cl may be very useful in studies of fate and origin of OCls in the environment, and that further applications of the technique are warranted.
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| 26. |
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| 27. |
- Horst, Axel, et al.
(author)
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Compound-specific bromine isotope analysis of methyl bromide using gas chromatography hyphenated with inductively coupled plasma multiple-collector mass spectrometry
- 2011
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In: Rapid Communications in Mass Spectrometry. - : Wiley. - 0951-4198 .- 1097-0231. ; 25:17, s. 2425-2432
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Journal article (peer-reviewed)abstract
- Methyl bromide is the most important natural bromine contributor to stratospheric ozone depletion, yet there are still large uncertainties regarding quantification of its sources and sinks. The stable bromine isotope composition of CH(3)Br is potentially a powerful tool to apportion its sources and to study both its transport and its reactive fate. A novel compound-specific method to measure (81)Br/(79)Br isotope ratios in CH3Br using gas chromatography hyphenated with inductively coupled plasma multiple-collector mass spectrometry (GC/MCICPMS) was developed. Sample amounts of >40 ng could bemeasured with a precision of 0.1 parts per thousand (1 sigma, n=3). The method results are reproducible over the long term as shown with 36 analyses acquired over 3 months, yielding a standard deviation ( 1s) better than 0.4 parts per thousand. This new method demonstrates for the first time Br isotope ratio determination in gaseous brominated samples. It is three orders of magnitude more sensitive than previously existing isotope ratio mass spectrometry methods for Br isotope determination of other organobromines, thus allowing applications towards ambient atmospheric samples.
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| 28. |
- Horst, Axel, et al.
(author)
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Stable bromine isotopic composition of atmospheric CH3Br
- 2013
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In: Tellus. Series B, Chemical and physical meteorology. - : Stockholm University Press. - 0280-6509 .- 1600-0889. ; 65, s. 21040-
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Journal article (peer-reviewed)abstract
- Tropospheric methyl bromide (CH3Br) is the largest source of bromine to the stratosphere and plays an important role in ozone depletion. Here, the first stable bromine isotope composition (delta Br-81) of atmospheric CH3Br is presented. The delta Br-81 of higher concentration Stockholm samples and free air subarctic Abisko samples suggest a source/background value of -0.04 +/- 0.28 parts per thousand ranging up to +1.75 +/- 0.12 parts per thousand. The Stockholm delta Br-81 versus concentration relationship corresponds to an apparent isotope enrichment factor of -4.7 +/- 3.7 parts per thousand, representing the combined reaction sink. This study demonstrates the scientific potential of atmospheric delta Br-81 measurements, which in the future may be combined with other isotope systems in a top-down inverse approach to further understand key source and sink processes of methyl bromide.
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| 29. |
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| 30. |
- Horst, Axel, et al.
(author)
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Stable bromine isotopic composition of methyl bromide released from plant matter
- 2014
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In: Geochimica et Cosmochimica Acta. - : Elsevier BV. - 0016-7037 .- 1872-9533. ; 125, s. 186-195
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Journal article (peer-reviewed)abstract
- Methyl bromide (CH3Br) emitted from plants constitutes a natural source of bromine to the atmosphere, and is a component in the currently unbalanced global CH3Br budget. In the stratosphere, CH3Br contributes to ozone loss processes. Studies of stable isotope composition may reduce uncertainties in the atmospheric CH3Br budget, but require well-constrained isotope fingerprints of the source end members. Here we report the first measurements of stable bromine isotopes (delta Br-81) in CH3Br from abiotic plant emissions. Incubations of both KBr-fortified pectin, a ubiquitous cell-stabilizing macromolecule, and of a natural halophyte (Salicornia fruticosa), yielded an enrichment factor (epsilon) of -2.00 +/- 0.23 parts per thousand (1 sigma, n = 8) for pectin and -1.82 +/- 0.02 parts per thousand (1 sigma, n = 4) for Salicornia (the relative amount of the heavier Br-81 was decreased in CH3Br compared to the substrate salt). For short incubations, and up to 10% consumption of the salt substrate, this isotope effect was similar for temperatures from 30 up to 300 degrees C. For longer incubations of up to 90 h at 180 degrees C the delta Br-81 values increased from -2 parts per thousand to 0 parts per thousand for pectin and to -1 parts per thousand for Salicornia. These delta Br-81 source signatures of CH3Br formation from plant matter combine with similar data for carbon isotopes to facilitate multidimensional isotope diagnostics of the CH3Br budget.
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| 31. |
- Ivansson, Milena Edith, 1986-
(author)
-
Stable chlorine isotope analysis of chlorinated acetic acids
- 2016
-
Licentiate thesis (other academic/artistic)abstract
- Chlorinated acetic acids (CAAs) constitute a group of polar organic compounds that are ubiquitous in the environment. Their environmental occurrence has been extensively studied but their sources are still not well constrained. Isotopic characterization of compounds found in the environment can provide additional information and allow their source apportionment. Previous studies indicate, however, that CAAs of industrial and natural origin may not be distinguishable by stable carbon isotope analysis only. This thesis presents an analytical method for stable chlorine isotope analysis of CAAs using gas chromatography/quadruple mass spectrometry (GC/qMS), for which systems are found in most laboratories. The method was cross-calibrated with an offline reference method and allows the determination of chlorine isotope signatures of CAAs with sample amounts as small as 10 pmol with good precisions of <1 ‰. With this method CAAs can be isotopically characterized at environmental relevant concentrations, in contrast to conventional offline methods were large sample requirements limit the application. This new method enables multi-element stable isotope analysis of CAAs and may help to identify and quantify sources of CAAs to the environment.
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| 32. |
- Ledesma, Matias, et al.
(author)
-
Nitrogen isotope composition of amino acids reveals trophic partitioning in two sympatric amphipods
- 2020
-
In: Ecology and Evolution. - : Wiley. - 2045-7758. ; 10:19, s. 10773-10784
-
Journal article (peer-reviewed)abstract
- According to ecological theory, two species cannot occupy the same niche. Using nitrogen isotope analyses (delta N-15) of amino acids, we tested the extent to which two sympatric deposit-feeding amphipods,Monoporeia affinisandPontoporeia femorata, partition their trophic resources. We found that trophic position (TP) and resynthesis index ( n-ary sumation V; a proxy for degradation status of ingested material prior to assimilation by the consumer) differ between species. The surface-feedingM. affinishad higher TP and intermediate n-ary sumation V, both pointing to a large contribution of metazoans in its diet.P. femorata, which feeds in the subsurface layers, had lower TP and a bimodal distribution of the n-ary sumation V values, supporting previous experimental evidence of a larger feeding niche. We also evaluated whether TP and n-ary sumation V values have consequences for amphipod fecundity and embryo viability and found that embryo viability inM. affiniswas negatively linked to TP. Our results indicate that the amino acid-delta N-15 data paired with information about reproductive status are useful for detecting differences in the trophic ecology of sympatric amphipods.
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| 33. |
- Miska, Milena E., et al.
(author)
-
Stable chlorine isotope analysis of chlorinated acetic acids using gas chromatography/quadrupole mass spectrometry
- 2015
-
In: Rapid Communications in Mass Spectrometry. - : Wiley. - 0951-4198 .- 1097-0231. ; 29:24, s. 2341-2348
-
Journal article (peer-reviewed)abstract
- RationaleThe environmental occurrence of chlorinated acetic acids (CAAs) has been extensively studied, but the sources and transport are still not yet fully understood. A promising approach for source apportionment and process studies is the isotopic characterization of target compounds. We present the first on-line stable chlorine isotope analysis of CAAs by use of gas chromatography/quadrupole mass spectrometry (GC/qMS). MethodsFollowing approved procedures for concentration analysis, CAAs extracted into MTBE were methylated to GC-amenable methyl esters (mCAAs). These mCAAs were then analyzed by GC/qMS for their stable chlorine isotope composition using a sample/standard-bracketing approach (CAA standards in the range Cl-37 -6.3 to -0.2 , Standard Mean Ocean Chloride). ResultsCross-calibration of the herein presented method with off-line reference methods (thermal ionization and continuous-flow GC isotope ratio mass spectrometry; TI-MS and CF-GC/IRMS, respectively) shows good agreement between the methods (regression slope for GC/qMS vs reference method data sets: 0.92 +/- 0.29). Sample amounts as small as 10 pmol Cl can herewith be analyzed with a precision of 0.1 to 0.4 parts per thousand. ConclusionsThis method should be useful for environmental studies of CAAs at ambient concentrations in precipitations (<0.06 to 100nmolL(-1)), surface waters (<0.2 to 5nmolL(-1)) and soil (<0.6 to 2000nmolkg(-1) dry soil) where conventional off-line methods cannot be applied.
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| 34. |
- Norström, Elin, et al.
(author)
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Late Quaternary vegetation dynamics and hydro-climate in the Drakensberg, South Africa
- 2014
-
In: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 105, s. 48-65
-
Journal article (peer-reviewed)abstract
- Abstract A multi-proxy study of a sediment sequence from Braamhoek wetland, covering the last c. 16,000 years, reveals a record of regional climate and vegetation dynamics in the Drakensberg region, South Africa, including signals from both the organic sediment fraction (fossil pollen, charcoal, n-alkane abundance, n-alkane δ13C, TOC) and the inorganic fraction (mineral magnetic properties). The reconstruction, supported by a robust chronology, indicates two major periods of increased regional wetness during the late Pleistocene to early Holocene phase (c. 13,800–12,600 cal yr BP; c. 10,200–8500 cal yr BP) and one during the late Holocene (c. 2000 cal yr BP to present). Drier conditions are recorded during the Younger Dryas (c. 12,600–11,300 cal yr BP) and mid-Holocene (c. 7000–2000 cal yr BP). A major decline in fynbos vegetation during the early Holocene suggests a shift towards warmer temperatures and possibly towards less pronounced winter rains in eastern South Africa from c. 8500 cal yr BP. Comparison with records from interior of South Africa show relatively high inter-site variability, however, the Braamhoek moisture proxies do co-vary with the speleothem isotope records from Makapansgat, suggesting a similar hydro-climate evolution in eastern and interior parts of the summer rainfall region during the studied period. On multi-millennial time scales, an inverse hydro-climatological pattern is evident between these two South African records and reconstructions from tropical locations in southeast Africa. Such a rainfall dipole between eastern tropical and southern Africa, has previously been identified on shorter time scales, i.e. on inter-annual to millennial scales. The Braamhoek study suggests that a similar dipole pattern is acting also on a multi-millennial perspective. These long-term precipitation anomalies are tentatively coupled to teleconnections from multi-millennial changes in the dynamics of the Indian Ocean Dipole (IOD) and El Niño-Southern Oscillation (ENSO).
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| 35. |
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| 36. |
- Rosqvist, Håkan, et al.
(author)
-
Development of an innovative methodology for monitoring of in situ remediation of chlorinated solvents – the MIRACHL-project
- 2018
-
In: ; , s. 112-112
-
Conference paper (peer-reviewed)abstract
- BackgroundDense Non Aqueous Phase Liquids (DNAPL) such as chlorinated solvents are common pollutants stemming from different types of industries including dry cleaning facilities, and reports on cases showing serious risk to soil and ground water are frequent on a global scale. DNAPLs are especially problematic as they are denser than water and move down through the groundwater, not always following the groundwater flow but are mainly driven by gravitational forces. Difficulties associated with remediation activities of DNAPLs are many, especially delineation of the source plume, and understanding of the migration of contaminated groundwater in the underground.Therefore, the Swedish national environmental authority, (SEPA) has called for new and innovative in-situ remediation techniques.The MIRACHL-project (monitoring of in situ remediation of chlorinated hydrocarbon contaminants - http://mirachl.com/) are focused on developing new and innovative methods for better understanding of the transport and fate of chlorinated solvents in soil and groundwater. The MIRACHL-project combine three methods; i)geoelectrical imaging by the geophysical method Direct Current resistivity and Induced Polarisation (DCIP), ii)Physical and BioGeochemical Characterisation (PBGC) and iii)the method Compound-specific isotope analysis (CSIA). The MIRACHL-project, based at the Engineering Geology at Lund University, is a collaborative project including several other universities and other relevant organizations, In particular, the collaboration on field sites with the Geological Survey of Sweden (SGU) is of great importance.AimIn the MIRACHL project we develop an integrated methodology based on threemethods, i.e., Direct Current resistivity and Induced Polarisation (DCIP), Physical and BioGeochemical Characterisation (PBGC) and the method Compound-specific isotope analysis (CSIA), to better understand and map in situ remediation processes. A combination of continuous geo-electrical observations during the decontamination, together with the analysis of biogeochemistry and isotope fractionation, provides opportunities to follow transport and fate of chlorinated solvents during different types of in-situ remediation processes.The MIRACHL-project started in 2016 and will continue until 2022. In 2017, theMIRACHL methodology was established at two sites in collaboration with SGU, i.e., in Hagfors and Alingsås. At both site contaminations coming from dry cleaning facilities are in focus. The geology and hydrogeology is very different at these sites and the presentation will show the status in mapping and monitoring the ongoing remediation at the sites.ConclusionInitial studies performed at a site in Kristianstad (Färgaren 3) show the combination of DCIP, PBGC, and CSIA are promising methodology for mapping of transport and fate of chlorinated solvents. We will present on-going research on two sites where contamination from chlorinated solvents are in focus, i.e, contamination due to dry cleaning activities in Hagfors and Alingsås.
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| 37. |
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| 38. |
- Steinbach, Julia, et al.
(author)
-
Source apportionment of methane escaping the subsea permafrost system in the outer Eurasian Arctic Shelf
- 2021
-
In: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 118:10
-
Journal article (peer-reviewed)abstract
- The East Siberian Arctic Shelf holds large amounts of inundated carbon and methane (CH4). Holocene warming by overlying seawater, recently fortified by anthropogenic warming, has caused thawing of the underlying subsea permafrost. Despite extensive observations of elevated seawater CH4 in the past decades, relative contributions from different subsea compartments such as early diagenesis, subsea permafrost, methane hydrates, and underlying thermogenic/ free gas to these methane releases remain elusive. Dissolved methane concentrations observed in the Laptev Sea ranged from 3 to 1,500 nM (median 151 nM; oversaturation by similar to 3,800%). Methane stable isotopic composition showed strong vertical and horizontal gradients with source signatures for two seepage areas of delta C-13-CH4 = (-42.6 +/- 0.5)/(-55.0 +/- 0.5) % and delta D-CH4 = (-136.8 +/- 8.0)/(-158.1 +/- 5.5) %, suggesting a thermogenic/ natural gas source. Increasingly enriched delta C-13-CH4 and delta D-CH4 at distance from the seeps indicated methane oxidation. The Delta C-14-CH4 signal was strongly depleted (i.e., old) near the seeps (-993 +/- 19/-1050 +/- 89%). Hence, all three isotope systems are consistent with methane release from an old, deep, and likely thermogenic pool to the outer Laptev Sea. This knowledge of what subsea sources are contributing to the observed methane release is a prerequisite to predictions on how these emissions will increase over coming decades and centuries.
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| 39. |
- Thornton, Brett F., et al.
(author)
-
A High-Volume Cryosampler and Sample Purification System for Bromine Isotope Studies of Methyl Bromide
- 2013
-
In: Journal of Atmospheric and Oceanic Technology. - 0739-0572 .- 1520-0426. ; 30:9, s. 2095-2107
-
Journal article (peer-reviewed)abstract
- A system was developed for collecting from the ambient atmosphere the methyl halides CH3Cl and CH3Br in quantities sufficient for chlorine and bromine isotope analysis. The construction and operation of the novel cryogenic collection system (cryosampler) and sample purification system developed for this task are described. This study demonstrates the capability of the cryosampler by quantifying the CH3Cl and CH3Br collected from atmospheric samples and the nonfractionating bromine isotope fingerprint of CH3Br from synthetic air samples of controlled composition. An optimized cryosampler operation time of 4 h at a flow rate of 15 L min(-1) is applied to yield the nearly 40 ng required for subsequent Br-81-CH3Br analyses. The sample purification system is designed around a packed column gas chromatography-quadropole-mass spectrometry (GCqMS) system with three additional cryotraps and backflushing capacity. The system's suitability was tested by observing both the mass recovery and the lack of Br-81 isotope fractionation induced during sample purification under varying flow rates and loading scenarios. To demonstrate that the entire system samples and dependably delivers CH3Br to the isotope analysis system without inducing isotope fractionation, diluted synthetic air mixtures prepared from standard gases were processed through the entire system, yielding a Br-81-CH3Br of +0.03 parts per thousand +/- 0.10 parts per thousand relative to their starting composition. Finally, the combined cryosampler-purification and analysis system was applied to demonstrate the first-ever Br-81-CH3Br in the ambient atmosphere with two samples collected in the autumn of 2011, yielding -0.08 parts per thousand +/- 0.43 parts per thousand and +1.75 parts per thousand +/- 0.13 parts per thousand versus standard mean ocean bromide for samples collected at a suburban Stockholm, Sweden, site.
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| 40. |
- Thornton, Brett F., et al.
(author)
-
Methyl chloride and methyl bromide emissions from baking : an unrecognized anthropogenic source
- 2016
-
In: Science of the Total Environment. - : Elsevier BV. - 0048-9697 .- 1879-1026. ; 551, s. 327-333
-
Journal article (peer-reviewed)abstract
- Methyl chloride and methyl bromide (CH3Cl and CH3Br) are the largest natural sources of chlorine and bromine, respectively, to the stratosphere, where they contribute to ozone depletion. We report the anthropogenic production of CH3Cl and CH3Br during breadbaking, and suggest this production is an abiotic process involving the methyl ester functional groups in pectin and lignin structural polymers of plant cells. Wide variations in baking styles allow only rough estimates of this flux of methyl halides on a global basis. A simple model suggests that CH3Br emissions from breadbaking likely peaked circa 1990 at approximately 200 tonnes per year (about 0.3% of industrial production), prior to restrictions on the dough conditioner potassium bromate. In contrast, CH3Cl emissions from breadbaking may be of similar magnitude as acknowledged present-day CH3Cl industrial emissions. Because the mechanisms involve functional groups and compounds widely found in plant materials, this type of methyl halide production may occur in other cooking techniques as well.
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| 41. |
- Vonk, Jorien E., et al.
(author)
-
Distinguishing between old and modern permafrost sources in the northeast Siberian land-shelf system with compound-specific delta H-2 analysis
- 2017
-
In: The Cryosphere. - : Copernicus GmbH. - 1994-0416 .- 1994-0424. ; 11:4, s. 1879-1895
-
Journal article (peer-reviewed)abstract
- Pleistocene ice complex permafrost deposits contain roughly a quarter of the organic carbon (OC) stored in permafrost (PF) terrain. When permafrost thaws, its OC is remobilized into the (aquatic) environment where it is available for degradation, transport or burial. Aquatic or coastal environments contain sedimentary reservoirs that can serve as archives of past climatic change. As permafrost thaw is increasing throughout the Arctic, these reservoirs are important locations to assess the fate of remobilized permafrost OC. We here present compound-specific deuterium (delta H-2) analysis on leaf waxes as a tool to distinguish between OC released from thawing Pleistocene permafrost (ice complex deposits; ICD) and from thawing Holocene permafrost (from near-surface soils). Bulk geochemistry (%OC; delta C-13; % total nitrogen, TN) was analyzed as well as the concentrations and delta H-2 signatures of long-chain n-alkanes (C-21 to C-33) and midto long-chain n-alkanoic acids (C-16 to C-30) extracted from both ICD-PF samples (n = 9) and modern vegetation and Ohorizon (topsoil-PF) samples (n = 9) from across the northeast Siberian Arctic. Results show that these topsoil-PF samples have higher %OC, higher OC/TN values and more depleted delta(COC)-C-13 values than ICD-PF samples, suggesting that these former samples trace a fresher soil and/or vegetation source. Whereas the two investigated sources differ on the bulk geochemical level, they are, however, virtually indistinguishable when using leaf wax concentrations and ratios. However, on the molecular isotope level, leaf wax biomarker delta H-2 values are statistically different between topsoil PF and ICD PF. For example, the mean delta H-2 value of C-29 n-alkane was -246 +/- 13% (mean +/- SD) for topsoil PF and -280 +/- 12 parts per thousand for ICD PF. With a dynamic isotopic range (difference between two sources) of 34 to 50 parts per thousand; the isotopic fingerprints of individual, abundant, biomarker molecules from leaf waxes can thus serve as endmembers to distinguish between these two sources. We tested this molecular delta H-2 tracer along with another source-distinguishing approach, dual-carbon (delta C-13-Delta C-14) isotope composition of bulk OC, for a surface sediment transect in the Laptev Sea. Results show that general offshore patterns along the shelfslope transect are similar, but the source apportionment between the approaches vary, which may highlight the advan-tages of either. This study indicates that the application of delta H-2 leaf wax values has potential to serve as a complementary quantitative measure of the source and differential fate of OC thawed out from different permafrost compartments.
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| 42. |
- Wiegert, Charline, 1980-, et al.
(author)
-
Carbon and Chlorine Isotope Fractionation During Microbial Degradation of Tetra- and Trichloroethene
- 2013
-
In: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 47:12, s. 6449-6456
-
Journal article (peer-reviewed)abstract
- Two-dimensional compound-specific isotope analysis (2D-CSIA), combining stable carbon and chlorine isotopes, holds potential for monitoring of natural attenuation of chlorinated ethenes (CEs), in contaminated soil and groundwater. However, interpretation of 2D-CSIA data sets is challenged by a shortage of experimental Cl isotope enrichment factors. Here, isotope enrichments factors for C and Cl (i.e., epsilon(C) and epsilon(Cl)) were determined for biodegradation of tetrachloroethene (PCE) and trichloroethene (TCE) using microbial enrichment cultures from a heavily CE-contaminated aquifer. The obtained values were epsilon(C) = -5.6 +/- 0.7 parts per thousand (95% CI) and epsilon(Cl) = -2.0 +/- 0.5 parts per thousand for PCE degradation and epsilon(C) = -8.8 +/- 0.2 parts per thousand and epsilon(Cl) = -3.5 +/- 0.5 parts per thousand for TCE degradation. Combining the values for both epsilon(C) and epsilon(Cl) yielded mechanism-diagnostic epsilon(Cl)/epsilon(C) ratios of 0.35 +/- 0.11 and 0.37 +/- 0.11 degradation of PCE and TCE, respectively. Application of the obtained epsilon(C) and epsilon(Cl) values to a previously investigated field site gave similar estimates for the fraction of degraded contaminant as in the previous study, but with a reduced uncertainty in assessment of the natural attenuation. Furthermore, 16S rRNA gene clone library analyses were performed on three samples from the PCE degradation experiments. A species closely related to Desulfitobacterium aromaticivorans UKTL dominated the reductive dechlorination process. This study contributes to the development of 2D-CSIA as a tool for evaluating remediation strategies of CEs at contaminated sites.
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| 43. |
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| 44. |
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| 45. |
- Wiegert, Charline, 1980-, et al.
(author)
-
Dual carbon chlorine stable isotope investigation of sources and fate of chlorinated ethenes in contaminated groundwater
- 2012
-
In: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 46:20, s. 10918-10925
-
Journal article (peer-reviewed)abstract
- Chlorinated ethenes (CEs) are ubiquitous groundwater contaminants, yet there remains a need for a method to efficiently monitor their in situ degradation. We report here the first field application of combined stable carbon and chlorine isotope analysis of tetrachloroethene (PCE) and trichloroethene (TCE) to investigate their biodegradation in a heavily contaminated aquifer. The two-dimensional Compound Specific Isotope Analysis (2D-CSIA) approach was facilitated by a recently developed gas chromatography-quadrupole mass spectrometry (GCqMS) method for delta Cl-37 determination. Both C and Cl isotopes showed evidence of ongoing PCE transformation. Applying published C isotope enrichment factors (epsilon(C)) enabled evaluation of the extent of in situ PCE degradation (11-78%). We interpreted C and Cl isotopes using a numerical reactive transport model along a 60-m flow path. It revealed that combined PCE and TCE mass load was dechlorinated by less than 10%, and that cis-dichloroethene was not further dechlorinated. Furthermore, the 2D-CSIA approach allowed estimation of Cl isotope enrichment factors epsilon(Cl) (-7.8 to -0.8 parts per thousand) and characteristic epsilon(Cl)/epsilon(C) values (0.42-1.12) for reductive PCE dechlorination at this field site. This investigation demonstrates the benefit of 2D-CSIA to assess in situ degradation of CEs and the applicability of Cl isotope fractionation to evaluate PCE and TCE dechlorination.
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| 46. |
- Wild, Birgit, et al.
(author)
-
Nitrous Oxide Dynamics in the Siberian Arctic Ocean and Vulnerability to Climate Change
- 2023
-
In: Journal of Geophysical Research - Biogeosciences. - 2169-8953 .- 2169-8961. ; 128:5
-
Journal article (peer-reviewed)abstract
- Nitrous oxide (N2O) is a strong greenhouse gas and stratospheric ozone-depleting substance. Around 20% of global emissions stem from the ocean, but current estimates and future projections are uncertain due to poor spatial coverage over large areas and limited understanding of drivers of N2O dynamics. Here, we focus on the extensive and particularly data-lean Arctic Ocean shelves north of Siberia that experience rapid warming and increasing input of land-derived nitrogen with permafrost thaw. We combine water column N2O measurements from two expeditions with on-board incubation of intact sediment cores to assess N2O dynamics and the impact of land-derived nitrogen. Elevated nitrogen concentrations in water column and sediments were observed near large river mouths. Concentrations of N2O were only weakly correlated with dissolved nitrogen and turbidity, reflecting particulate matter from rivers and coastal erosion, and correlations varied between river plumes. Surface water N2O concentrations were on average close to equilibrium with the atmosphere, but varied widely (N2O saturation 38%-180%), indicating strong local N2O sources and sinks. Water column N2O profiles and low sediment-water N2O fluxes do not support strong sedimentary sources or sinks. We suggest that N2O dynamics in the region are influenced by water column N2O consumption under aerobic conditions or in anoxic microsites of particles, and possibly also by water column N2O production. Changes in biogeochemical and physical conditions will likely alter N2O dynamics in the Siberian Arctic Ocean over the coming decades, in addition to reduced N2O solubility in a warmer ocean.
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| 47. |
- Winiger, Patrik, et al.
(author)
-
Source apportionment of circum-Arctic atmospheric black carbon from isotopes and modeling
- 2019
-
In: Science Advances. - : American Association for the Advancement of Science (AAAS). - 2375-2548. ; 5:2
-
Journal article (peer-reviewed)abstract
- Black carbon (BC) contributes to Arctic climate warming, yet source attributions are inaccurate due to lacking observational constraints and uncertainties in emission inventories. Year-round, isotope-constrained observations reveal strong seasonal variations in BC sources with a consistent and synchronous pattern at all Arctic sites. These sources were dominated by emissions from fossil fuel combustion in the winter and by biomass burning in the summer. The annual mean source of BC to the circum-Arctic was 39 +/- 10% from biomass burning. Comparison of transport-model predictions with the observations showed good agreement for BC concentrations, with larger discrepancies for (fossil/biomass burning) sources. The accuracy of simulated BC concentration, but not of origin, points to misallocations of emissions in the emission inventories. The consistency in seasonal source contributions of BC throughout the Arctic provides strong justification for targeted emission reductions to limit the impact of BC on climate warming in the Arctic and beyond.
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| 48. |
- Åkesson, Sofia, et al.
(author)
-
Characterizing natural degradation of tetrachloroethene (PCE) using a multidisciplinary approach
- 2020
-
In: Ambio: a Journal of the Human Environment. - : Springer Science and Business Media LLC. - 0044-7447 .- 1654-7209. ; 50, s. 1074-1088
-
Journal article (peer-reviewed)abstract
- A site in mid-western Sweden contaminated with chlorinated solvents originating from a previous dry cleaning facility, was investigated using conventional groundwater analysis combined with compound-specific isotope data of carbon, microbial DNA analysis, and geoelectrical tomography techniques. We show the value of this multidisciplinary approach, as the different results supported each interpretation, and show where natural degradation occurs at the site. The zone where natural degradation occurred was identified in the transition between two geological units, where the change in hydraulic conductivity may have facilitated biofilm formation and microbial activity. This observation was confirmed by all methods and the examination of the impact of geological conditions on the biotransformation process was facilitated by the unique combination of the applied methods. There is thus significant benefit from deploying an extended array of methods for these investigations, with the potential to reduce costs involved in remediation of contaminated sediment and groundwater.
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| 49. |
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| 50. |
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