Abstract. The Antarctic ozone hole arises from ozone destruction driven by elevated levels of ozone destroying ("active") chlorine in Antarctic spring. These elevated levels of active chlorine have to be formed first and then maintained throughout the period of ozone destruction. It is a matter of debate how this maintenance of active chlorine is brought about in Antarctic spring, when the rate of formation of HCl (considered to be the main chlorine deactivation mechanism in Antarctica) is extremely high. Here we show that in the heart of the ozone hole (16-18 km or 85-55 hPa, in the core of the vortex), high levels of active chlorine are maintained by effective chemical cycles (referred to as HCl null cycles hereafter). In these cycles, the formation of HCl is balanced by immediate reactivation, i.e. by immediate reformation of active chlorine. Under these conditions, polar stratospheric clouds sequester HNO 3 and thereby cause NO 2 concentrations to be low. These HCl null cycles allow active chlorine levels to be maintained in the Antarctic lower stratosphere and thus rapid ozone destruction to occur. For the observed almost complete activation of stratospheric chlorine in the lower stratosphere, the heterogeneous reaction HCl + HOCl is essential; the production of HOCl occurs via HO 2 + ClO, with the HO 2 resulting from CH 2 O photolysis. These results are important for assessing the impact of changes of the future stratospheric composition on the recovery of the ozone hole. Our simulations indicate that, in the lower stratosphere, future increased methane concentrations will not lead to enhanced chlorine deactivation (through the reaction CH 4 + Cl −→ HCl+CH 3 ) and that extreme ozone destruction to levels below ≈ 0.1 ppm will occur until mid-century.
Abstract. The Antarctic ozone hole arises from ozone destruction driven by elevated levels of ozone destroying ("active") chlorine in Antarctic spring. These elevated levels of active chlorine have to be formed first and then maintained throughout the period of ozone destruction. It is a matter of debate, how this maintenance of active chlorine is brought about in Antarctic spring, when the rate of formation of HCl (considered to be the main chlorine deactivation mechanism in Antarctica) is extremely high.
5Here we show that in the heart of the ozone hole (16-18 km or 100-70 hPa, in the core of the vortex), high levels of active chlorine are maintained by effective chemical cycles (referred to as HCl null-cycles hereafter). In these cycles, the formation of HCl is balanced by immediate reactivation, i.e. by immediate reformation of active chlorine. Under these conditions, polar stratospheric clouds sequester HNO 3 and thereby cause NO 2 concentrations to be low. These HCl null-cycles allow active chlorine levels to be maintained in the Antarctic lower stratosphere and thus rapid ozone destruction to occur. For the observed 10 almost complete activation of stratospheric chlorine in the lower stratosphere, the heterogeneous reaction HCl + HOCl, the production of HOCl via HO 2 + ClO, with the HO 2 resulting from CH 2 O photolysis, is essential. These results are important for assessing the impact of changes of the future stratospheric composition on the recovery of the ozone hole. Our simulations indicate that, in the lower stratosphere, future increased methane concentrations will not lead to enhanced chlorine deactivation (through the reaction CH 4 + Cl −→ HCl + CH 3 ) and that extreme ozone destruction to levels below ≈ 0.1 ppm will occur until 15 mid-century.
Lehmann (2018) The relevance of reactions of the methyl peroxy radical (CH 3 O 2) and methylhypochlorite (CH 3 OCl) for Antarctic chlorine activation and ozone loss, Tellus B:
Due to rising population and industrialization, two-thirds of the world’s population may suffer water scarcity by 2025. Biodesalination is a promising sustainable practice targeting salt removal from seawater by micro-organisms, using lower energy consumption and resulting in less environmental impact. This study examined the evolution of biodesalination from 2007 to 2022 by applying bibliometric analysis. A scoping review was also conducted through content analysis of biodesalination publications. Using the Scopus database, the research trends, major contributors in the field, and recent advancements were identified. The study investigated a total of 80 peer-reviewed journal articles in the field of biodesalination. Results of the bibliometric analysis revealed that publications peaked in 2022 and citations in 2021, with values of 14 and 473, respectively. Results also revealed that the research trend in biodesalination is leaning towards the use of microbial desalination cells. Furthermore, advancements in the field focused on enhancing the nutrient medium to yield better growth rates for algae and cyanobacteria and improve desalination efficiencies to up to 40%. Other modifications focused on introducing microbial strains with increased salinity tolerance. Finally, an outline of future research potential was presented, focusing on nutrient medium modifications, specifically the substitution of chloride and sodium salts in the medium with nitrate and potassium minerals.
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