We have developed a chemical mechanism describing the tropospheric degradation of chlorine containing very short‐lived substances (VSLS). The scheme was included in a global atmospheric model and ...used to quantify the stratospheric injection of chlorine from anthropogenic VSLS ( ClyVSLS) between 2005 and 2013. By constraining the model with surface measurements of chloroform (CHCl3), dichloromethane (CH2Cl2), tetrachloroethene (C2Cl4), trichloroethene (C2HCl3), and 1,2‐dichloroethane (CH2ClCH2Cl), we infer a 2013 ClyVSLS mixing ratio of 123 parts per trillion (ppt). Stratospheric injection of source gases dominates this supply, accounting for ∼83% of the total. The remainder comes from VSLS‐derived organic products, phosgene (COCl2, 7%) and formyl chloride (CHClO, 2%), and also hydrogen chloride (HCl, 8%). Stratospheric ClyVSLS increased by ∼52% between 2005 and 2013, with a mean growth rate of 3.7 ppt Cl/yr. This increase is due to recent and ongoing growth in anthropogenic CH2Cl2—the most abundant chlorinated VSLS not controlled by the Montreal Protocol.
Key Points
Stratospheric Cl from short‐lived chemicals has increased significantly
Increasing Cl due to rapid growth in surface emissions of CH2Cl2
COCl2 and HCl from VSLS make a nonzero contribution to stratospheric Cl
Volcanoes are very strong sources of sulphur, acids and other gases, as well as particles, that are of atmospheric relevance. Some gases only behave as passive tracers, others affect the formation, ...growth or chemical characteristics of aerosol particles and many lead to adverse effects on vegetation and human health when deposited in the vicinity of volcanoes. In this article the main effects of volcanic emissions on atmospheric chemistry are discussed, with a focus on sulphur and halogen compounds, and to a smaller extent on climate. We primarily focus on quiescent degassing but the main effects of explosive eruptions on the troposphere and stratosphere are covered as well. The key distinction between chemistry in magmatic and hydrothermal settings and the atmosphere is that the atmosphere is oxidising whereas the chemistry is typically reducing in the former cases due to very low oxygen concentrations. Rapid catalytic cycles involving radicals are a further characteristic of atmospheric chemistry. Most reaction cycles involve the photolysis of molecules as a key part of the reaction chains. Recent measurements of halogen radicals in volcanic plumes showed that volcanic plumes are chemically very active. We explain the formation mechanism of halogen oxides in plumes as well as their relevance for the atmosphere.
We present a comprehensive chemical mechanism for gas-phase iodine, to be used for modelling tropospheric chemistry. The mechanism has been compiled from evaluated data and individual literature ...studies, where available; a number of key processes have not been studied experimentally or theoretically and in these cases estimations have been made. The uncertainty associated with these assumptions is evaluated. We analyze the mechanism using a box-model under a variety of boundary layer scenarios – representative of environments where iodine species have been observed – to study the response of the chemical system to changes in the kinetic parameters of selected reactions. We focus in particular on key species such as IO, OIO, INO3 and I2Oy and the impact of iodine chemistry on ozone formation and HOx levels. The results indicate that the chemical system is most sensitive to reactions leading to comparatively stable iodine compounds, which should be a focus of future laboratory studies.
► Assembled gas-phase inorganic iodine chemical mechanism. ► Analyzed mechanism using box-model under different scenarios. ► Response of mechanism to changes in kinetic parameters of selected reactions. ► Mechanism most sensitive to reactions forming stable iodine species. ► Laboratory studies of some key reactions are urgently needed.
Current understanding of the behaviour of sea breezes in the offshore environment is limited but rapidly requires improvement due, not least, to the expansion of the offshore wind energy industry. ...Here we report on contrasting characteristics of three sea‐breeze types on five coastlines around the southern North Sea from an 11 year model‐simulated climatology. We present and test an identification method which distinguishes sea‐breeze types which can, in principle, be adapted for other coastlines around the world. The coherence of the composite results for each type demonstrates that the method is very effective in resolving and distinguishing characteristics and features. Some features, such as jets and calm zones, are shown to influence offshore wind farm development areas, including the sites of the proposed wind farms up to 200 km offshore. A large variability in sea‐breeze frequency between neighbouring coastlines of up to a factor of 3 is revealed. Additionally, there is a strong association between sea‐breeze type on one coastline and that which may form coincidentally on another nearby. This association can be as high as 86% between, for example, the North Norfolk and East Norfolk coasts. We show, through associations between sea‐breeze events on coastlines with contrasting orientations, that each coastline can be important for influencing the wind climate of another. Furthermore, we highlight that each sea‐breeze type needs separate consideration in wind power resource assessment and that future larger turbines will be more sensitive to sea‐breeze impacts.
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