Constraints on Arctic Atmospheric Chlorine Production through Measurements and Simulations of Cl2 and ClO.
07 Nov 2016-Environmental Science & Technology (American Chemical Society)-Vol. 50, Iss: 22, pp 12394-12400
TL;DR: The ClO measurements and simulations are consistent with Cl2 being the dominant Cl atom source in the Arctic boundary layer, and simulated Cl atom concentrations, up to ∼1 × 106 molecules cm-3, highlight the importance of chlorine chemistry in the degradation of volatile organic compounds, including the greenhouse gas methane.
Abstract: During springtime, unique halogen chemistry involving chlorine and bromine atoms controls the prevalence of volatile organic compounds, ozone, and mercury in the Arctic lower troposphere. In situ measurements of the chlorine monoxide radical, ClO, and its precursor, Cl2, along with BrO and Br2, were conducted using chemical ionization mass spectrometry (CIMS) during the Bromine, Ozone, and Mercury Experiment (BROMEX) near Barrow, Alaska, in March 2012. To our knowledge, these data represent the first ClO measurements made using CIMS. A maximum daytime ClO concentration of 28 ppt was observed following an early morning peak of 75 ppt of Cl2. A zero-dimensional photochemistry model was constrained to Cl2 observations and used to simulate ClO during a 7-day period of the field campaign. The model simulates ClO within the measurement uncertainty, and the model results highlight the importance of chlorine chemistry participation in bromine radical cycling, as well as the dependence of halogen chemistry on NOx ...
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Cites background from "Constraints on Arctic Atmospheric C..."
...Halides from sea salt are the major source of reactive halogen species in polar regions, but the substrate upon which halogen activation occurs remains an open question (e.g., Abbatt, Thomas, et al., 2012; Custard et al., 2016, 2017; Saiz-Lopez & von Glasow, 2012; Simpson et al., 2007)....
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TL;DR: This study provides a breakthrough in quantitatively constraining bromine chemistry in the polar atmosphere, where this chemistry connects the rapidly changing surface to pollutant fate.
Abstract: Bromine atoms play a central role in atmospheric reactive halogen chemistry, depleting ozone and elemental mercury, thereby enhancing deposition of toxic mercury, particularly in the Arctic near-surface troposphere. However, direct bromine atom measurements have been missing to date, due to the lack of analytical capability with sufficient sensitivity for ambient measurements. Here we present direct atmospheric bromine atom measurements, conducted in the springtime Arctic. Measured bromine atom levels reached 14 parts per trillion (ppt, pmol mol−1; 4.2 × 108 atoms per cm−3) and were up to 3–10 times higher than estimates using previous indirect measurements not considering the critical role of molecular bromine. Observed ozone and elemental mercury depletion rates are quantitatively explained by the measured bromine atoms, providing field validation of highly uncertain mercury chemistry. Following complete ozone depletion, elevated bromine concentrations are sustained by photochemical snowpack emissions of molecular bromine and nitrogen oxides, resulting in continued atmospheric mercury depletion. This study provides a breakthrough in quantitatively constraining bromine chemistry in the polar atmosphere, where this chemistry connects the rapidly changing surface to pollutant fate.
61 citations
Cites background or methods from "Constraints on Arctic Atmospheric C..."
...This examination employs an unprecedented suite of halogen and mercury measurements, including direct measurements of Br, along with Br2, BrO, HOBr, Cl2, ClO, O3, and mercury (Hg 0 and HgII) (23–26)....
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...This inlet design has been used to measure surface-active gases including HNO3 (52), NH3 (53), BrO (27, 49), HOBr (26, 48), and ClO (24)....
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...For a measurement cycle of 10.6 s, m/z 206 (Br), m/z 287 (Br2), 197 (Cl2), 224 (BrO), 178 (ClO), and 225 (HOBr) were monitored for 500 ms each, with a 5% duty cycle for each mass....
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...Hydrated I clusters [I·(H2O)n ] were used as the reagent ion to measure Br [m/z 206 (I(79)Br) and 208 (I(81)Br)], Br2 [m/z 287 (I(79)Br(81)Br) and 289 (I(81)Br(81)Br)], BrO [m/z 222 (I(79)BrO) and 224 (I(81)BrO)], HOBr [m/z 223 (IHO(79)Br) and 225 (IHO(81)Br)], Cl2 [m/z 197 (I(35)Cl(35)Cl) and 199 (I(35)Cl(37)Cl)], and ClO [m/z 178 (I(35)ClO) and 180 (I(37)ClO)], with isotope ratios used for verification of ion identities (24, 48, 50)....
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...The calibrations for BrO (relative sensitivity to Br2: 0.5 ± 0.1) (49), ClO (relative sensitivity to Cl2: 0.3 ± 0.1) (24), and HOBr (relative sensitivity to Br2: 0.5 ± 0.1) (48) are described in previous studies....
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TL;DR: Modeling shows that observed I2 levels are able to significantly increase ozone depletion rates, while also producing iodine monoxide (IO) at levels recently observed in the Arctic, implying that I2 is likely a dominant source of iodine atoms inThe Arctic.
Abstract: During springtime, the Arctic atmospheric boundary layer undergoes frequent rapid depletions in ozone and gaseous elemental mercury due to reactions with halogen atoms, influencing atmospheric composition and pollutant fate. Although bromine chemistry has been shown to initiate ozone depletion events, and it has long been hypothesized that iodine chemistry may contribute, no previous measurements of molecular iodine (I2) have been reported in the Arctic. Iodine chemistry also contributes to atmospheric new particle formation and therefore cloud properties and radiative forcing. Here we present Arctic atmospheric I2 and snowpack iodide (I−) measurements, which were conducted near Utqiaġvik, AK, in February 2014. Using chemical ionization mass spectrometry, I2 was observed in the atmosphere at mole ratios of 0.3–1.0 ppt, and in the snowpack interstitial air at mole ratios up to 22 ppt under natural sunlit conditions and up to 35 ppt when the snowpack surface was artificially irradiated, suggesting a photochemical production mechanism. Further, snow meltwater I− measurements showed enrichments of up to ∼1,900 times above the seawater ratio of I−/Na+, consistent with iodine activation and recycling. Modeling shows that observed I2 levels are able to significantly increase ozone depletion rates, while also producing iodine monoxide (IO) at levels recently observed in the Arctic. These results emphasize the significance of iodine chemistry and the role of snowpack photochemistry in Arctic atmospheric composition, and imply that I2 is likely a dominant source of iodine atoms in the Arctic.
59 citations
TL;DR: An increase in emission of CO2 from terrestrial and aquatic ecosystems due to the effects of global warming, such as droughts and thawing of permafrost soils, fuels a positive feedback on global warming.
Abstract: Global change influences biogeochemical cycles within and between environmental compartments (i.e., the cryosphere, terrestrial and aquatic ecosystems, and the atmosphere). A major effect of global change on carbon cycling is altered exposure of natural organic matter (NOM) to solar radiation, particularly solar UV radiation. In terrestrial and aquatic ecosystems, NOM is degraded by UV and visible radiation, resulting in the emission of carbon dioxide (CO2) and carbon monoxide, as well as a range of products that can be more easily degraded by microbes (photofacilitation). On land, droughts and land-use change can reduce plant cover causing an increase in exposure of plant litter to solar radiation. The altered transport of soil organic matter from terrestrial to aquatic ecosystems also can enhance exposure of NOM to solar radiation. An increase in emission of CO2 from terrestrial and aquatic ecosystems due to the effects of global warming, such as droughts and thawing of permafrost soils, fuels a positive feedback on global warming. This is also the case for greenhouse gases other than CO2, including methane and nitrous oxide, that are emitted from terrestrial and aquatic ecosystems. These trace gases also have indirect or direct impacts on stratospheric ozone concentrations. The interactive effects of UV radiation and climate change greatly alter the fate of synthetic and biological contaminants. Contaminants are degraded or inactivated by direct and indirect photochemical reactions. The balance between direct and indirect photodegradation or photoinactivation of contaminants is likely to change with future changes in stratospheric ozone, and with changes in runoff of coloured dissolved organic matter due to climate and land-use changes.
54 citations
TL;DR: In this paper, the authors present the first simultaneous direct measurements of Br2, Cl2, and BrCl in snowpack interstitial air, as well as the first measured emission rates of both Br2 and Cl2 out of the snowpack into the atmosphere.
Abstract: Atmospheric bromine and chlorine atoms have a significant influence on the pathways of atmospheric chemical species processing. The photolysis of molecular halogens and subsequent reactions with ozone, mercury, and hydrocarbons are common occurrences in the Arctic boundary layer during spring, following polar sunrise. While it was recently determined that Br2 is released from the sunlit surface snowpack, the source(s) and mechanisms of Cl2 and BrCl production have remained unknown. Current efforts to model Arctic atmospheric composition are limited by the lack of knowledge of the sources and emission rates of these species. Here, we present the first simultaneous direct measurements of Br2, Cl2, and BrCl in snowpack interstitial air, as well as the first measured emission rates of Br2 and Cl2 out of the snowpack into the atmosphere. Using chemical ionization mass spectrometry, Br2, Cl2, and BrCl were observed to be produced within the tundra surface snowpack near Utqiaġvik, AK, during Feb 2014, following ...
42 citations
References
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TL;DR: According to Henry's law, the equilibrium ratio between the abundances in the gas phase and in the aqueous phase is constant for a dilute solution as discussed by the authors, and a compilation of 17 350 values of Henry's Law constants for 4632 species, collected from 689 references is available at http://wwwhenrys-law.org
Abstract: Many atmospheric chemicals occur in the gas phase as well as in liquid cloud droplets and aerosol particles Therefore, it is necessary to understand the distribution between the phases According to Henry's law, the equilibrium ratio between the abundances in the gas phase and in the aqueous phase is constant for a dilute solution Henry's law constants of trace gases of potential importance in environmental chemistry have been collected and converted into a uniform format The compilation contains 17 350 values of Henry's law constants for 4632 species, collected from 689 references It is also available at http://wwwhenrys-laworg
1,935 citations
University of California, Riverside1, University of Leeds2, University of Cambridge3, Max Planck Society4, National Institute of Standards and Technology5, Commonwealth Scientific and Industrial Research Organisation6, Imperial College London7, École Polytechnique Fédérale de Lausanne8, University of Göttingen9
TL;DR: In this article, the IUPAC Subcommittee on GasKinetic Data Evaluation for Atmospheric Chemistry presented the first in the series, presenting kinetic and photochemical data evaluated by the committee.
Abstract: . This article, the first in the series, presents kinetic and photochemical data evaluated by the IUPAC Subcommittee on GasKinetic Data Evaluation for Atmospheric Chemistry. It covers the gas phase and photochemical reactions of Ox, HOx, NOx and SOx species, which were last published in 1997, and were updated on the IUPAC website in late 2001. The article consists of a summary sheet, containing the recommended kinetic parameters for the evaluated reactions, and five appendices containing the data sheets, which provide information upon which the recommendations are made.
1,612 citations
TL;DR: In this paper, the authors focus on recent ground-level observations from the Canadian baseline station at Alert (82.5° N, 62.3° W) and from aircraft that show that ozone destruction is occurring under the Arctic surface radiation inversion during March and April as the Sun rises.
Abstract: There is increasing evidence that at polar sunrise sunlight-induced changes in the composition of the lower Arctic atmosphere (0–2 km) are taking place that are important regarding the tropospheric cycles of ozone, bromine, sulphur oxides1, nitrogen oxides2 and possibly iodine3. Here we focus on recent ground-level observations from the Canadian baseline station at Alert (82.5° N, 62.3° W) and from aircraft that show that ozone destruction is occurring under the Arctic surface radiation inversion during March and April as the Sun rises. The destruction might be linked to catalytic reactions of BrOx radicals and the photochemistry of bromoform, which appears to have a biological origin in the Arctic Ocean. This may clarify previously unexplained regular springtime occurrences of ozone depletion at ground level in a 10-year data record at Barrow, Alaska4, as well as peaks in aerosol bromine observed throughout the Arctic in March and April3. Current information does not allow us to offer more than a speculative explanation for the chemical mechanisms leading to these phenomena.
939 citations
University of Alaska Fairbanks1, University of East Anglia2, National Institute of Water and Atmospheric Research3, British Antarctic Survey4, McGill University5, Environment Canada6, University of Bremen7, University of York8, Heidelberg University9, University of Southern Denmark10, University of Leeds11, University of Hamburg12, Earth System Research Laboratory13, Max Planck Society14, Purdue University15, University College Cork16
TL;DR: In the polar regions, unique photochemistry converts inert halide salt ions (e.g. Br−) into reactive halogen species that deplete ozone in the boundary layer to near zero levels as discussed by the authors.
Abstract: . During springtime in the polar regions, unique photochemistry converts inert halide salt ions (e.g. Br−) into reactive halogen species (e.g. Br atoms and BrO) that deplete ozone in the boundary layer to near zero levels. Since their discovery in the late 1980s, research on ozone depletion events (ODEs) has made great advances; however many key processes remain poorly understood. In this article we review the history, chemistry, dependence on environmental conditions, and impacts of ODEs. This research has shown the central role of bromine photochemistry, but how salts are transported from the ocean and are oxidized to become reactive halogen species in the air is still not fully understood. Halogens other than bromine (chlorine and iodine) are also activated through incompletely understood mechanisms that are probably coupled to bromine chemistry. The main consequence of halogen activation is chemical destruction of ozone, which removes the primary precursor of atmospheric oxidation, and generation of reactive halogen atoms/oxides that become the primary oxidizing species. The different reactivity of halogens as compared to OH and ozone has broad impacts on atmospheric chemistry, including near complete removal and deposition of mercury, alteration of oxidation fates for organic gases, and export of bromine into the free troposphere. Recent changes in the climate of the Arctic and state of the Arctic sea ice cover are likely to have strong effects on halogen activation and ODEs; however, more research is needed to make meaningful predictions of these changes.
581 citations
TL;DR: In this paper, the authors proposed a mechanism based on known aqueous phase chemistry, which rapidly converts HBr, HOBr and BrNO3 back to Br and BrO radicals.
Abstract: NEAR-TOTAL depletion of the ozone in surface air is often observed in the Arctic spring, coincident with high atmospheric concentrations of inorganic bromine1–5. Barrie et al.1 suggested that the ozone depletion was due to a catalytic cycle involving the radicals Br and BrO (ref. 6); however, these species are rapidly converted to the nonradical species HBr, HOBr and BrNO3, quenching ozone loss. McConnell et al.7 proposed that cycling of inorganic bromine between aerosols and the gas phase could maintain sufficiently high levels of Br and BrO to destroy ozone, but they did not specify a mechanism for aerosol-phase production of active bromine species. Here we propose such a mechanism, based on known aqueous-phase chemistry, which rapidly converts HBr, HOBr and BrNO3 back to Br and BrO radicals. This mechanism should be particularly efficient in the presence of the high concentrations of sulphuric acid aerosols observed during ozone depletion events3.
444 citations