Atmospheric Ozone Depletion Research Articles

Photodissociation of the CH2Br radical: A theoretical study.

Bromine atom (Br) reactions lead to ozone depletion in the troposphere and stratosphere. Photodegradation of bromocarbons is one of the main sources of bromine atoms in the atmosphere. Here, we use high-level abinitio methods, including spin-orbit effects, to study the photodissociation of the CH2Br radical. All possible fragmentation pathways, namely CH2Br + hν → CH2 + Br, HCBr + H, and CBr + H2, have been analyzed. Potential-energy curves of the ground and several excited electronic states along the corresponding dissociating bond distance of each pathway have been calculated. Considering the actinic fluxes of solar irradiation in the troposphere and in the stratosphere in the relevant range of frequencies, it is found that the first five excited states of CH2Br can be accessed from the ground state. Analysis of the potential curves shows that the pathways producing CH2 + Br and HCBr + H can proceed through a fast direct dissociation mechanism, while the pathway leading to CBr + H2 involves much slower dissociation mechanisms like internal conversion between electronic states, predissociation, or tunneling through exit barriers. The main implications are that the two faster channels are predicted to be dominant, and the slower pathway is expected to be less relevant. The tropospheric and stratospheric solar actinic fluxes also allow for further dissociation of the HCBr and CBr fragments, generating additional Br atoms, provided that they survive possible collisions with other atmospheric reagents. Finally, we discuss the possible effect of each of the three CH2Br dissociation pathways on the depletion of atmospheric ozone.

An examination of the reaction pathways of XO + O → X + O2 (X = Br and I)

Kinetics and mechanism of potentially important atmospheric ozone depletion reactions XO + O → X + O2 (X = Br and I) have been explored at the ab initio level. Several minimum energy geometries and transition states are identified at the MP2 level using correlation consistent triple zeta and effective core potential basis sets and energetics are obtained at the QCISD(T)//MP2 level of theory. Possible reaction pathways are discussed on the basis of IRC calculations and changes of geometries along the reaction paths. A direct reaction mechanism as well as reaction path via transition states and equilibrium geometries are identified. For both the reactions, early transition states have been detected just after the reactions start. In case of BrO + O reaction, we obtained a transition state of Br.OO type before the product formation, whereas in case of IO + O reaction, an equilibrium geometry of I.OO type has been detected leading to the product formation. Similar to I.OO, for ClO + O reaction an equilibrium geometry of Cl.OO type was reported in literature for product formation. This anomaly for TS-Br.OO may be due the artifact of MP2 optimization method. A multi-reference approach is expected to reveal the correct picture. A detailed dynamical study of this transition state may lead to clear bond-breaking and bond-forming information, which may be helpful to predict the true reaction pathway. Heats of reaction are found to be consistent with experimental data. Bond dissociation energies of the ground state intermediate isomers to various dissociation asymptotes are also reported. This is the first theoretical report for the possible reaction pathways and may be served as a reference for future investigation using higher methodology.

The flaring TESS Objects of Interest: flare rates for all two-minute cadence TESS planet candidates

ABSTRACT Although more than 5000 TESS Objects of Interest have been catalogued, no comprehensive survey of the flare rates of their host stars exists. We perform the first flare survey of all 2250 non-retired TOIs with 2-min cadence light curves to measure or place upper limits on their flare rates. We find 93 candidates orbit flare stars and measure their flare frequency distributions. Across the sample, TOIs of ≤1.5R⊕ orbit flare stars more frequently than do TOIs of 1.5 < R< 2.75R⊕, 2.75 < R< 4R⊕, or R≥ 4R⊕. We sort all TOI host stars by their flare rate/upper limit, stellar mass, and distance to create a flare ranking metric (FRM) to determine suitability for follow-up. The FRM of each TOI is then checked against the expected signal-to-noise of atmospheric features in transmission spectroscopy to locate the most promising targets. We find 1/4 of terrestrial M-dwarf planets amenable to transmission spectroscopy orbit flare stars. However, none of the M-dwarf hosts to terrestrial planets are currently flaring at sufficient levels for >99.9 per cent atmospheric ozone depletion. We give the first upper limits on the flare rate of the host star to TOI 700 d and explore the flare rates incident on young planets such as DS Tuc Ab.

Investigation of the Presence Volatile Organic Compounds (BTEX) in the Ambient Air and Biogases Produced by a Shiraz Landfill in Southern Iran

The generation and emission of volatile organic compounds (VOCs) affects the environment and air quality, playing an important role in global warming, depletion of atmospheric ozone and emission of unpleasant odors, but also directly affect human health. This study investigated the health risks of benzene, toluene, ethylbenzene, xylene (BTEX) compounds and biogas released in and around the municipal landfill. Sampling of the VOCs was carried out by the 1501NIOSH method from 8 points over 5 months. The samples were analyzed for BTEX in the ambient air of the landfill, resulting in 0.03–18.09 ppm concentrations, while for biogases a 0.08–25.2 ppm range was found. Assessment of definite health and potential risks showed that the lifetime cancer risk (LCR) for benzene and hazard quotient (HQ) for the BTEX components in all studied sampling sites are higher than the acceptable standard. The high concentration of benzene measured in ambient air indicated that petroleum compounds containing benzene and its derivatives have the highest value in the category of BTEX compounds among all emissions. Therefore, high concentrations of volatile compounds derived from VOCs, especially benzene, should be reduced at the site with control engineering measures.

Homogeneous Ni(I)tetra Sulfonated Phthalocyanine Electrocatalyst Generated at Low Overpotential Clubbed with a Wet‐Scrubbing Column for High Efficiency NO Reduction to NH3

AbstractAlthough the degradation of NO gas to a less toxic form is a promising strategy to help solve atmospheric health and ozone depletion problems, conversion to a useful gas is a recent strategy. The generation of NH3 from NO with high efficiency per catalyst area or weight is in the early stages. In this investigation, a tetra sulfonated phthalocyanine with a Ni(II) (Ni(II)TSPc) complex was used to produce a low valent homogenous electrocatalyst Ni(I)TSPc in an alkaline medium at a lower overpotential. Ni(I)TSPc formation at a lower overpotential was demonstrated by the initial change in oxidation/reduction potential from 25 mV to −360 mV during electrolysis, peak potential change in cyclic voltammetry, and UV‐Vis spectral analysis. A potentiometric titration method used to quantify the electrogenerated Ni(I)TSPc revealed 90 % efficiency in 1 h. The decrease of Ni(I)TSPc concentration when contacting NO gas at the wet scrubber column showed that the NO removal process followed a Ni(I)TSPc (Ni(I)) mediation or mediated electrocatalytic reduction (MER) process. The NO removal efficiency reached almost 100 % at a 0.2 L/min gas flow rate of 20 ppm. The selective formation of NH3 with a maximum of 1492 μmol/g Ni(I) was achieved for the first time in the homogeneous electrocatalytic reduction process. The developed process generated NH3 from NO gas and has the potential for scale‐up.

Global Drivers on Southern Ocean Ecosystems: Changing Physical Environments and Anthropogenic Pressures in an Earth System

The manuscript assesses the current and expected future global drivers of Southern Ocean (SO) ecosystems. Atmospheric ozone depletion over the Antarctic since the 1970s, has been a key driver, resulting in springtime cooling of the stratosphere and intensification of the polar vortex, increasing the frequency of positive phases of the Southern Annular Mode (SAM). This increases warm air-flow over the East Pacific sector (Western Antarctic Peninsula) and cold air flow over the West Pacific sector. SAM as well as El Niño Southern Oscillation events also affect the Amundsen Sea Low leading to either positive or negative sea ice anomalies in the west and east Pacific sectors, respectively. The strengthening of westerly winds is also linked to shoaling of deep warmer water onto the continental shelves, particularly in the East Pacific and Atlantic sectors. Air and ocean warming has led to changes in the cryosphere, with glacial and ice sheet melting in both sectors, opening up new ice free areas to biological productivity, but increasing seafloor disturbance by icebergs. The increased melting is correlated with a salinity decrease particularly in the surface 100 m. Such processes could increase the availability of iron, which is currently limiting primary production over much of the SO. Increasing CO2is one of the most important SO anthropogenic drivers and is likely to affect marine ecosystems in the coming decades. While levels of many pollutants are lower than elsewhere, persistent organic pollutants (POPs) and plastics have been detected in the SO, with concentrations likely enhanced by migratory species. With increased marine traffic and weakening of ocean barriers the risk of the establishment of non-indigenous species is increased. The continued recovery of the ozone hole creates uncertainty over the reversal in sea ice trends, especially in the light of the abrupt transition from record high to record low Antarctic sea ice extent since spring 2016. The current rate of change in physical and anthropogenic drivers is certain to impact the Marine Ecosystem Assessment of the Southern Ocean (MEASO) region in the near future and will have a wide range of impacts across the marine ecosystem.

El vanadio, desde su descubrimiento hasta su papel en la vida

<p>El vanadio es un elemento químico con una historia peculiar y tan fascinante como su química. Fue descubierto en el municipio argentífero de Zimapán, México, por Andrés Manuel Del Río, y redescubierto en Suecia por Nils Gabriel Sefström, quien lo nombró vanadio, en honor de la diosa nórdica <em>Vanadis</em>. El vanadio<em> </em>es el elemento número 22 más abundante en la corteza terrestre, y después del molibdeno, el segundo metal de transición con mayor presencia en disolución en el ambiente marino. Forma parte de más de 200 minerales entre los que se encuentra la vanadinita, Pb<sub>5</sub>(VO<sub>4</sub>)<sub>3</sub>Cl, y recientemente se encontró en su forma nativa en sublimados de fumarolas del cráter del volcán de Colima en México. El papel del vanadio en sistemas biológicos ha despertado el interés de la comunidad científica debido a varios hechos extraordinarios. Existen organismos exóticos que lo acumulan en cantidades excepcionales como las ascidias y los hongos alucinógenos del<em> </em>género<em> Amanita</em>. Además, se encuentra en la nitrogenasa de <em>Azobacter vinelandii</em> formando parte del cofactor FeVco, componente organometálico responsable de la “fijación” del nitrógeno atmosférico; también se presenta en las enzimas vanadio haloperoxidasas, las cuales intervienen indirectamente en el agotamiento del ozono atmosférico. A pesar de que la actividad antidiabetica del vanadio ha quedado bien establecida para sus estados de oxidación +4 y +5, actualmente no existe un medicamente basado en este metal para el tratamiento de la diabetes mellitus, enfermedad que actualmente padecen casi 13 millones de mexicanos.</p>

Oxidative hydrothermal surface modification of activated carbon for sevoflurane removal

The emission of waste anaesthetic gas is a growing contributor to global warming and remains a factor in atmospheric ozone depletion. Volatile anaesthetics in medical waste gases could be removed via adsorption using suitable activated carbon materials possessing an enhanced affinity to anaesthetic molecules. In this work, the effects of surface physical and chemical properties on sevoflurane adsorption were investigated by oxidative hydrothermal surface modification of a commercial activated carbon using only distilled water. The hydrothermal surface modification was carried out at different treatment temperatures (150–300 °C) for varying durations (10–30 min), and adsorption was conducted under fixed conditions (bed depth = 10 cm, inlet concentration = 528 mg/L, and flow rate = 3 L/min). The hydrothermal treatment generally increased the BET surface area of the activated carbons. At oxidation temperatures above 200 °C, the micropore volume of the samples diminished. The relative amount of surface oxygen was enriched as the treatment temperature increased. Treatment duration did not significantly affect the introduction of relative amount of surface oxygen, except at higher temperatures. There were no new types of functional groups introduced. However, disappearance and re-formation of oxygen functional groups containing C–O structures (as in hydroxyl and ether groups) occurred when treatment temperature was increased from 150 to 200 °C, and when treatments were conducted above 200 °C, respectively. The ester/acetal groups were enriched under the temperature range studied. The findings suggested that the re-formation of surface oxygen functionalities might lead to the development of functional groups that improve sevoflurane adsorption.

Selection of pesticides to reduce human and environmental health risks: a global guideline and minimum pesticides list

Pesticides present widespread risks to human and environmental health, yet selection criteria for end-users that factor in differences in risk between compounds are scant. We developed a system to classify pesticide risks and hazards with respect to human and environmental health and produce a minimum (lower risk) pesticide list. We classified 659 pesticides by acute and chronic risks to human health (eg, respiratory and carcinogenic effects) and by environmental risks, including biomagnification and atmospheric ozone depletion and risks to aquatic life, terrestrial wildlife, and pollinators. From this analysis, we produced a guideline for selection of lower risk pesticides. The classification of highly hazardous and high-risk compounds has been tested in more than a million farm households in the tropics, and in US integrated pest management (IPM) programmes. The full classification, including the minimum pesticide list, has been used in management of the fall armyworm (Spodoptera frugiperda) throughout Africa and Asia. Our analysis developed a stand-alone guideline for selection of lower risk pesticides. When classifying pesticides in current use against the fall armyworm in Africa, our guideline identified chemicals that are effective and of lower risk to human and environmental health. We argue that a minimum (lower risk) pesticides list, which meets IPM needs, could be developed from our classification system. As far as we are aware, our analysis is the first to propose a method for implementing the idea of a minimum pesticide list and the first to outline lower risk candidate compounds. Currently accepted criteria for defining highly hazardous pesticides do not adequately protect human bystanders, aquatic life, terrestrial wildlife, and pollinators. The Sustainable Agriculture Network, the Rainforest Alliance, the US Department of Agriculture-National Institute of Food and Agriculture, the US Department of Agriculture, the Foreign Agricultural Service, the US Agency for International Development, the International Maize and Wheat Improvement Center, and the UN Food and Agriculture Organization.

Competition between the hydrogen bond and the halogen bond in a [CH3OH-CCl4] complex: a matrix isolation IR spectroscopy and computational study.

Methanol (CH3OH) is the simplest alcohol and carbon tetrachloride (CCl4) is widely used as a solvent in the chemical industry. CH3OH and CCl4 are both important volatile substances in the atmosphere and CCl4 is an important precursor for atmospheric ozone depletion. Moreover, mixtures of CH3OH and CCl4 are an important class of non-aqueous mixtures as they exhibit a large deviation from Raoult's law. The specific interaction between CH3OH and CCl4 is not yet investigated experimentally. The interaction between CH3OH and CCl4 at the molecular level can be twofold: hydrogen bond (O-HCl) and halogen bond (C-ClO) interaction. One halogen bonded minimum and two hydrogen bonded minima are identified in the dimer potential energy surface. Herein, the 1 : 1 complex of [CH3OH-CCl4] has been characterised using matrix-isolation infrared spectroscopy and electronic structure calculations to investigate the competition between hydrogen bonded and halogen bonded complexes. Vibrational spectra have been monitored in the C-Cl, C-O, and O-H stretching regions. The exclusive formation of halogen bonded 1 : 1 complexes in argon and nitrogen matrices is confirmed by a combination of experimental and simulated vibrational frequency, stabilisation energy, energy decomposition analysis, and natural bond orbital and atoms-in-molecules analyses. This investigation helps to understand the specific interactions in the [CH3OH-CCl4] mixture and also the possibilities of formation of halogen bonded atmospheric complexes that may influence the atmospheric chemical activities, and enhance aerosol formation and deposition of CCl4.

A Global Guideline for Pesticide Selection to Reduce Risks, and Establish a Minimum Pesticides List

Pesticides present widespread risks to human health, and they contribute to global biodiversity decline. Information on the relative risks posed by pesticides is difficult to obtain, and we lack procedures for pesticide selection that factor in the differences in risk between compounds. This is perpetuating problems that require urgent solution. We have classified more than 700 pesticides by acute and chronic human health risk, environmental risk including bio-magnification and atmospheric ozone depletion, and risks to aquatic life, terrestrial wildlife, and pollinators. Our analysis is presented as a guideline that can be used to encourage selection of lower risk pesticides. It also demonstrates that currently accepted criteria for defining highly hazardous pesticides fail to adequately protect human bystanders, aquatic life, terrestrial wildlife, and pollinators. When used to classify pesticides in current use against the fall armyworm, an invasive pest that is attacking maize crops in Africa, our guideline identifies effective lower-risk chemicals. This risk and hazard-based classification system has been field tested among more than a million farm households in the tropics, and in IPM programs in the United States and Africa, with success. We have isolated a lower-risk group of pesticides, from which a minimum list could be developed in order to meet most IPM needs, while limiting risks to human and environmental health. Our analysis is the first to propose a methodology to develop and refine this concept, and the first to outline candidate compounds since the minimum list was proposed through the Lancet in 2002. Funding Statement: Funding was provided by the Sustainable Agriculture Network, Rainforest Alliance, United States Department of Agriculture (USDA) National Institute of Food and Agriculture, USDA Foreign Agriculture Service, the International Maize and Wheat Improvement Center, and the UN Food and Agriculture Organization. Funding for the international review process for HHPs, pesticides requiring risk mitigation, and mitigation methods was provided by the Sustainable Agriculture Network (SAN) and Rainforest Alliance. Development and use of this classification system in the Western USA was supported by a United States Department of Agriculture Western Sustainable Agriculture Research and Extension Professional Development Program (USDA WSARE PDP) grant EW17-019, and USDA National Institute of Food and Agriculture Crop Protection and Pest Management Extension IPM Program (NIFA CPPM EIP) grant 2017-70006-27154, and a USDA NIFA CPPM Western IPM Center (WIPMC) Signature Program Sub-award SA18-4060-01 to PCJ and KM; and a USDA NIFA CPPM Applied Research and Development (ARDP) grant 2016-70006-25868 to KM. Drafting of this publication, development of the low risk (minimum) pesticide classification, and determination of PPE requirements was supported by a USDA Foreign Agriculture Service (FAS) Agreement (FX18TA- 10960R021) to PCJ, which also funded the African case study, with additional support from the International Maize and Wheat Improvement Center (CIMMYT) and the UN Food and Agriculture Organization (FAO) to PCJ. Declaration of Interests: The authors state that they do not have conflicts of interest to declare. Ethics Approval Statement: Not required.

Plant-Pesticide Interactions and the Global Chloromethane Budget.

Ecological, signaling, metabolic, and chemical processes in plant-microorganism systems and in plant-derived material may link the use of chlorinated pesticides in the environment with plant chloromethane emission. This neglected factor should be taken into account to assess global planetary budgets of chloromethane and impacts on atmospheric ozone depletion.

Nutrient limitation in two marine diatoms inhibits release of bromoform

Bromoform released from phytoplankton and kelp in the ocean is the largest known carrier of bromine to the atmosphere. The photoproducts of atmospheric bromoform catalyse ozone depletion. Laboratory investigations were conducted into the link between nutrient limitation and bromoform production using axenic cultures of two warm-water diatoms (Chaetoceros neogracile and Phaeodactylum tricornutum). During exponential growth the bromoform production was 2 000–3 000 nmol bromoform (g Chl a)−1 h−1, i.e. 10–100 times higher than earlier values for temperate and cold-water diatoms. Bromoform production decreased down to zero under CO2 and nitrate limitation for both species. These results suggest that the bromoform production could be directly related to bromoperoxidase activity (and irradiance) only during exponential growth, whereas compounds other than bromoform might be formed under nutrient limitation.

A Novel Anti-Pollution Filter for Volatile Agents During Cardiopulmonary Bypass: Preliminary Tests

Concerns regarding pollution of the operating room by volatile anesthetics and effects on atmospheric ozone depletion exist. Volatile agents commonly are used during cardiopulmonary bypass to provide anesthesia independent of any supposed myocardial protective effects. The authors' aim was to create and to assess the performance of a prototype filter for volatile agents to be connected to the cardiopulmonary bypass circuit to avoid the emission of volatile agents to the operating room, and also to the environment without causing damage to the membrane oxygenator. Observational trial. University hospital. Prototype filter for volatile agents. The prototype filter was tested in a single ex vivo experiment. The main data measured during the test were pressure drop to detect interference with the performance of the oxygenator, back pressure to detect overpressure to the outlet gas jacket of the oxygenator, analysis of exhaled sevoflurane after the membrane oxygenator, and after the filter to detect any presence of sevoflurane. The prototype filter adsorbed the sevoflurane eliminated through the outlet portion of the oxygenator. During the entire test, the back pressure remained constant (4 mmHg) and pressure drop varied from 243 mmHg to 247 mmHg. The prototype filter was considered suitable to absorb the sevoflurane, and it did not cause an overpressure to the membrane oxygenator during the test.

The photoprotective effects of 2-benzoyl-3-phenylquinoxaline 1,4-dioxide against UVB-induced damage in HaCaT cells.

With the increasing levels of atmospheric ozone depletion, there has been much concern about the causal effects of high levels of ultraviolet radiation reaching the Earth's surface on skin cancer. This has led to growing interest in identifying new active ingredients for use in commercial sunscreens. In our study, the chemical compound 2-benzoyl-3-phenylquinoxaline 1,4-dioxide (BPQ) prepared by the Beirut reaction was tested for its ability to protect a human keratinocyte cell line (HaCaT) against ultraviolet B radiation (280-315nm). We show that BPQ exhibited strong absorbance in the UVB range, with an overall absorption spectrum very similar to that of Padimate-O, a well-known active ingredient used in commercial sunscreens. HaCaT cells, which were irradiated with UVB in the presence of multiple doses of BPQ, exhibited, in a dose-dependent fashion, a significantly higher viability and lower oxidative stress levels than cells irradiated in the absence of drug. Our results show that BPQ is a potential photoprotective drug that holds great promise for use as an active ingredient in commercial sunscreens.

International Regulation of Carbon Emission

Recent years have seen an appreciable growth in the level of understanding of the dangers facing the international environment and an extensive range of environmental problems is now the subject of serious international concerns. This includes atmospheric pollution, marine pollution, global warming and ozone depletion. Such problems have an international dimension in its obvious respects. First, pollution generated from within a particular state often has a serious impact on other countries. Secondly, it is now apparent that environmental problems cannot be resolved by states acting individually. Accordingly, co-operation between polluting and polluted state is necessitated. However, the issue becomes more complicated in those cases where it is impossible to determine from which country a particular form of environment pollution has emanated. This would be the case, for example, with ozone-depletion. The international nature of pollution, both with regard to its creation and the damage caused, is now accepted as requiring an international response. The principles of State responsibility dictate that states are accountable for breaches of international law. Customary International law imposes several important fundamental obligations upon states in the area of environment protection. The view that international law supports an approach predicated upon absolute territorial sovereignty, so that a state could do as it liked irrespective of the consequences has long been discredited. Article 19 of the Energy Charter Treaty notes that contracting parties shall strive to minimise in an economically efficient manner harmful environmental impacts. In so doing, parties are to act ‘in a cost-effective manner’. Parties are to take precautionary measures to prevent or minimise environmental degradation and agree that polluter should in principle, bear the cost of pollution with due regard to the public interest and without distorting investment in the energy cycle or international trade.

Antarctic winter mercury and ozone depletion events over sea ice

During atmospheric mercury and ozone depletion events in the springtime in polar regions gaseous elemental mercury and ozone undergo rapid declines. Mercury is quicldy transformed into oxidation products, which are subsequently removed by deposition. Here we show that such events also occur during Antarctic winter over sea ice areas, leading to additional deposition of mercury. Over four months in the Weddell Sea we measured gaseous elemental, oxidized, and particulate-bound mercury, as well as ozone in the troposphere and total and elemental mercury concentrations in snow, demonstrating a series of depletion and deposition events between July and September. The winter depletions in July were characterized by stronger correlations between mercury and ozone and larger formation of particulate-bound mercury in air compared to later spring events. It appears that light at large solar zenith angles is sufficient to initiate the photolytic formation of halogen radicals. We also propose a dark mechanism that could explain observed events in air masses coming from dark regions. Br-2 that could be the main actor in dark conditions was possibly formed in high concentrations in the marine boundary layer in the dark. These high concentrations may also have caused the formation of high concentrations of CHBr3 and CH2I2 in the top layers of the Antarctic sea ice observed during winter. These new findings show that the extent of depletion events is larger than previously believed and that winter depletions result in additional deposition of mercury that could be transferred to marine and terrestrial ecosystems.

The role of open lead interactions in atmospheric ozone variability between Arctic coastal and inland sites

Abstract Boundary layer atmospheric ozone depletion events (ODEs) are commonly observed across polar sea ice regions following polar sunrise. During March-April 2005 in Alaska, the coastal site of Barrow and inland site of Atqasuk experienced ODEs (O3< 10 nmol mol-1) concurrently for 31% of the observations, consistent with large spatial scale ozone depletion. However, 7% of the time ODEs were exclusively observed inland at Atqasuk. This phenomenon also occurred during one of nine flights during the BRomine, Ozone, and Mercury EXperiment (BROMEX), when atmospheric vertical profiles at both sites showed near-surface ozone depletion only at Atqasuk on 28 March 2012. Concurrent in-flight BrO measurements made using nadir scanning differential optical absorption spectroscopy (DOAS) showed the differences in ozone vertical profiles at these two sites could not be attributed to differences in locally occurring halogen chemistry. During both studies, backward air mass trajectories showed that the Barrow air masses observed had interacted with open sea ice leads, causing increased vertical mixing and recovery of ozone at Barrow and not Atqasuk, where the air masses only interacted with tundra and consolidated sea ice. These observations suggest that, while it is typical for coastal and inland sites to have similar ozone conditions, open leads may cause heterogeneity in the chemical composition of the springtime Arctic boundary layer over coastal and inland areas adjacent to sea ice regions.

CBrF3 (Halon-1301): UV absorption spectrum between 210 and 320K, atmospheric lifetime, and ozone depletion potential

• CBrF 3 (Halon-1301) UV absorption spectrum measurement. • Evaluation of the absorption spectrum temperature dependence. • Reduced uncertainty in the model calculated Halon-1301 atmospheric lifetime and ozone depletion potential. CBrF 3 (Halon-1301) is a man-made ozone depleting substance that is a major source of bromine in the Earth’s stratosphere. Halon-1301 is predominantly removed from the atmosphere by UV photolysis in the stratosphere at wavelengths between 200 and 225 nm. The existing level of uncertainty in the Halon-1301 UV absorption spectrum temperature-dependence directly impacts the ability to model stratospheric ozone chemistry and climate change. In this work, the UV absorption spectrum of Halon-1301 between 195 and 235 nm was measured over the temperature range 210–320 K. An empirical parameterization of the spectrum and its temperature dependence is presented. The present results are critically compared with results from previous studies and the current recommendation for use in atmospheric models. A global annually averaged lifetime for Halon-1301 of 74.6 (73.7–75.5) years was calculated using a 2-D atmospheric model and the present results. The range of lifetimes given in parenthesis represents the possible values due solely to the 2 σ uncertainty in the Halon-1301 UV spectrum obtained in this work. In addition, the CBrF 3 ozone depletion potential was calculated using the 2-D model to be 18.6 (±0.1) using the UV spectrum and 2 σ uncertainty from this work.

Effects of sulfamethazine on denitrification and the associated N2O release in estuarine and coastal sediments.

Denitrification is an important pathway of nitrogen removal and nitrous oxide (N2O) production in estuarine and coastal ecosystems, and plays a significant role in counteracting aquatic eutrophication induced by excessive nitrogen loads. Estuarine and coastal environments also suffer from increasing antibiotic contamination because of the growing production and usage of antibiotics. In this study, sediment slurry incubation experiments were conducted to determine the influence of sulfamethazine (SMT, a sulphonamide antibiotic) on denitrification and the associated N2O production. Genes important for denitrification and antibiotic resistance were quantified to investigate the microbial physiological mechanisms underlying SMT's effects on denitrification. SMT was observed to significantly inhibit denitrification rates, but increasing concentrations of SMT enhanced N2O release rates. The negative exponential relationships between denitrifying gene abundances and SMT concentrations showed that SMT reduced denitrification rates by restricting the growth of denitrifying bacteria, although the presence of the antibiotic resistance gene was detected during the incubation period. These results imply that the wide occurrence of residual antibiotics in estuarine and coastal ecosystems may influence eutrophication control, greenhouse effects, and atmospheric ozone depletion by inhibiting denitrification and stimulating the release of N2O.