Organohalogen emissions from saline environments – spatial extrapolation using remote sensing as most promising tool

Abstract

Abstract. Due to their negative water budget most recent semi-/arid regions are characterized by vast evaporates (salt lakes and salty soils). We recently identified those hypersaline environments as additional sources for a multitude of volatile halogenated organohalogens (VOX). These compounds can affect the ozone layer of the stratosphere and play a key role in the production of aerosols. A remote sensing based analysis was performed in the Southern Aral Sea basin, providing information of major soil types as well as their extent and spatial and temporal evolution. VOX production has been determined in dry and moist soil samples after 24 h. Several C1-and C2 organohalogens have been found in hyper-saline topsoil profiles, including CH 3 Cl, CH 3 Br, CHBr 3 and CHCl 3 . The range of organohalogens also includes trans-1,2-dichloroethene (DCE), which is reported here to be produced naturally for the first time. Using MODIS time series and supervised image classification a daily production rate for DCE has been calculated for the 15 000 km 2 ranging research area in the southern Aralkum. The applied laboratory setup simulates a short-term change in climatic conditions, starting from dried-out saline soil that is instantly humidified during rain events or flooding. It describes the general VOX production potential, but allows only for a rough estimation of resulting emission loads. VOX emissions are expected to increase in the future since the area of salt affected soils is expanding due to the regressing Aral Sea. Opportunities, limits and requirements of satellite based rapid change detection and salt classification are discussed.

Formation mechanisms of trichloromethyl-containing compounds in the terrestrial environment: A critical review

“…Although most of these organohalogens have been discovered in the marine environment, various chemical and biological processes producing organohalogens have been identified in the terrestrial environment as well. The presence of volatile and non-volatile trihalomethyl compounds (especially trichloromethane, trichloroacetic acid, trichloroacetyl-containing compounds -the model compounds of this review) in unpolluted terrestrial environments has been shown in for example temperate forests, grasslands and peatlands (Hoekstra et al, 1999;Haselmann et al, 2000a;Dimmer et al, 2001;McCulloch, 2003;Peters, 2003;Albers et al, 2010a), boreal forests (Hellén et al, 2006), wet tundra (Rhew et al, 2008b), subtropical shrub lands and hypersaline arid soil (Kotte et al, 2012), salt marshes (Rhew et al, 2008a) and rice paddies (Khalil et al, 1990). The frequent detection of trichloromethyl compounds in soils and groundwater in absence of other anthropogenic contaminants suggests strongly that these halogenated compounds are produced naturally by biogeochemical processes (Laturnus et al, 2000;Albers et al, 2010a;Hunkeler et al, 2012).…”

Thermolytic degradation of methylmethionine and implications for its role in DMS and MeCl formation in hypersaline environments

“…This can be explained by the higher organic matter content in soils. Based on a 24-h production time under moist conditions and elevated summer temperatures leading to topsoil temperatures of up to 55 8C, [29] a soil density of 1.3 g cm À3 and 1-cm soil depth, our data are extrapolated to high MeCl production rates of 650 mmol m À2 day À1 . For comparison, Rhew et al [6] found similarly large MeCl fluxes from salt marshes of up to 570 mmol m À2 day À1 , but production was related to plant activity.…”

“…A rewetting and drying-out cycle is typical for SW Australian salt lakes. Kotte et al [29] reported high emissions of MeCl and MeBr from dry samples of similar environments in south Russia and Namibia. But areas of regressing (salt) lakes such as the Aral Sea could also contribute to thermolytic emissions.…”

Halogenated hydrocarbon formation in a moderately acidic salt lake in Western Australia – role of abiotic and biotic processes

“…A few years later, the organohalogen emissions from salt lakes and salt-affected soils were investigated on a broader scale by combining microcosm experiments and remote sensing. [28] For an area of 15 000 km 2 in the southern Aral Sea basin, fluxes of 16 873 g day À1 in the cover area for C 2 H 2 Cl 2 (dichloroethene) were estimated. Recently, it was shown that pH-neutral to alkaline hypersaline lake sediments from Western Australia also contribute to the global emissions of halogenated hydrocarbons and that biotic processes dominate the emissions.…”