Thesis (Ph. D.)--Columbis University, 1923. / Vita.

Methyl bromide (CH3Br) and methyl chloride (CH3Cl) are two halocarbons that are unique in that they play a significant role in stratospheric ozone destruction, and are mainly produced by natural systems. The current average tropospheric mixing ratios are 7.9 pptv CH3Br and 550 pptv CH3Cl (WMO, 2007). Although CH3Br and CH3Cl are present in such low concentrations, their atmospheric life times are sufficiently long that they can be transported to the stratosphere via the tropical tropopause at the equator. This process takes approximately six months.

No description available.

Soil salinity is a serious environmental stress threatening productivity of major crops worldwide. Among the various biotic and abiotic strategies that exist, transgenic technologies provide a promising avenue to reduce yield losses in crops under saline environments. Recently, transgenic technology involving the TMT gene encoding thiol methyltransferase enzyme has been suggested as an effective solution for engineering a chloride detoxification capability into a high value crops to improve tolerance against chloride ion toxicity under saline environments. This proposed mechanism, however, results in the emission of methyl chloride (CH3Cl) from plants, which has deleterious effects on stratospheric ozone. This study was performed to examine the relationship between salt tolerance and chloride volatilizing capacity of transgenic plants containing TMT gene as well as to explore the possibility of generating transgenic rice crop containing TMT gene for salinity tolerance. To achieve these objectives, transgenic tobacco plants containing TMT gene were grown in comparison with wild type tobacco plants under three levels of sodium chloride (NaCl) salinity (0, 100 and 200 mM), three levels of soil water content (40%, 60% and 80% of the field capacity) and their tolerance to NaCl and water stress was studied. Plant growth parameters recorded included plant height, number of leaves, leaf area, stem dry weight, leaf dry weight, root dry weight, plant dry biomass and root/shoot ratio. Similarly, both types of plants were exposed to five levels of NaCl concentrations (0, 50, 100, 150 and 200 mM) and three levels of soil water content (40%, 60% and 80% of the field capacity), and the quantity of CH3Cl emitted was recorded. Significant decrease in plants growth parameters of both types of plants were recorded upon exposure to salinity and water stress. Under 100 mM NaCl, however, transgenic plants showed better tolerance to salinity by suffering less reduction in growth parameters compared to wild type plants. Under 200 mM NaCl, growth of both types of plants was completely inhibited. The interactive effects of salinity and water stress were more pronounced in wild type plants than in transgenic plants. Results also showed that all engineered plants acquired an ability to efficiently transform chloride ion to CH3Cl, and the rate of such transformation was higher under greater NaCl and soil water content compared to lower NaCl concentrations and soil water content. In order to explore the possibility of generating a transgenic food crop using TMT gene, a hypothetical transgenic rice crop was grown over 27 million hectares of the saline coastal areas of south and southeast Asia and the possible emission of CH3Cl from such ecosystem was inferred based on the CH3Cl emission data obtained from transgenic tobacco plants. The estimates showed that the possible CH3Cl emission from such ecosystem would be 219.21 Gg which is equivalent to 5.36 % of the global atmospheric emissions of CH3Cl.

Soil salinity is a serious environmental stress threatening productivity of major crops worldwide. Among the various biotic and abiotic strategies that exist, transgenic technologies provide a promising avenue to reduce yield losses in crops under saline environments. Recently, transgenic technology involving the TMT gene encoding thiol methyltransferase enzyme has been suggested as an effective solution for engineering a chloride detoxification capability into a high value crops to improve tolerance against chloride ion toxicity under saline environments. This proposed mechanism, however, results in the emission of methyl chloride (CH3Cl) from plants, which has deleterious effects on stratospheric ozone. This study was performed to examine the relationship between salt tolerance and chloride volatilizing capacity of transgenic plants containing TMT gene as well as to explore the possibility of generating transgenic rice crop containing TMT gene for salinity tolerance. To achieve these objectives, transgenic tobacco plants containing TMT gene were grown in comparison with wild type tobacco plants under three levels of sodium chloride (NaCl) salinity (0, 100 and 200 mM), three levels of soil water content (40%, 60% and 80% of the field capacity) and their tolerance to NaCl and water stress was studied. Plant growth parameters recorded included plant height, number of leaves, leaf area, stem dry weight, leaf dry weight, root dry weight, plant dry biomass and root/shoot ratio. Similarly, both types of plants were exposed to five levels of NaCl concentrations (0, 50, 100, 150 and 200 mM) and three levels of soil water content (40%, 60% and 80% of the field capacity), and the quantity of CH3Cl emitted was recorded. Significant decrease in plants growth parameters of both types of plants were recorded upon exposure to salinity and water stress. Under 100 mM NaCl, however, transgenic plants showed better tolerance to salinity by suffering less reduction in growth parameters compared to wild type plants. Under 200 mM NaCl, growth of both types of plants was completely inhibited. The interactive effects of salinity and water stress were more pronounced in wild type plants than in transgenic plants. Results also showed that all engineered plants acquired an ability to efficiently transform chloride ion to CH3Cl, and the rate of such transformation was higher under greater NaCl and soil water content compared to lower NaCl concentrations and soil water content. In order to explore the possibility of generating a transgenic food crop using TMT gene, a hypothetical transgenic rice crop was grown over 27 million hectares of the saline coastal areas of south and southeast Asia and the possible emission of CH3Cl from such ecosystem was inferred based on the CH3Cl emission data obtained from transgenic tobacco plants. The estimates showed that the possible CH3Cl emission from such ecosystem would be 219.21 Gg which is equivalent to 5.36 % of the global atmospheric emissions of CH3Cl.

No description available.

The ocean is both a source and a sink for atmospheric methyl bromide (CH3Br) and methyl chloride (CH3Cl). It plays a significant role in their global biogeochemical cycling. In response to the Montreal Protocol, the atmospheric CH3Br is declining and the saturation state of CH3Br in the surface ocean is becoming more positive. Results from two large-scale transect studies in the eastern Pacific and the eastern Atlantic suggest that the ocean became near equilibrium with atmospheric CH3Br in 2010. Results from a "top-down" two-box model indicate that, if the remaining anthropogenic emissions are eliminated, atmospheric CH3Br is likely to drop to the pre-industrial level and the ocean would become a net source to atmospheric CH3Br. This study also represents an effort to improve current understanding of the oceanic and atmospheric budgets of CH3Cl. The global net sea-to-air flux of CH3Cl was estimated at 335 (210 ? 480) Gg yr-1 with improved parameterizations on the solubility, seasonal saturation anomaly ? (sea surface temperature, wind speed) relationships and the use of an updated parameterization on gas transfer velocity. For the first time, we estimated the gross oceanic emission and gross oceanic uptake rates of CH3Cl in the surface ocean, which was 700 (490 to 920) Gg yr^-1 and -370 (-440 to -280) Gg yr^-1, respectively. The ocean accounts for 10 - 19 % in the global CH3Cl emission and 6 - 9 % in its global sinks. Methane (CH4) is a potent greenhouse gas, which has a warming potential 72 times that of carbon dioxide over a 20 year time horizon. Gas hydrates are the largest CH4 reservoir in the planet. How much CH4 is transported from marine gas hydrates to the atmosphere is under debate. In this study, we investigated CH4 fluxes over three deepwater hydrocarbon seeps in the northern Gulf of Mexico using continuous air-sea flux measurements. Extrapolating the highest daily flux from this study to other deepwater seeps in the northern Gulf of Mexico suggests that CH4 fluxes to the atmosphere from the deepwater hydrocarbon seeps in this region are an insignificant source to atmospheric CH4 budget.

Thesis (Ph. D.)--University of Michigan, 1931. / "By C.S. Schoepfle and J.D. Ryan." Reprinted from the Journal of the American Chemical Society, v. 52, 1930 and v. 54, 1932.

Thesis (M.S.)--University of Michigan, 1957.

CH3Br and CH3Cl (methyl halides) are the most abundant natural vectors of bromine and chlorine into the stratosphere and play an important role in stratospheric ozone destruction. The current knowledge of their respective natural sources is incomplete leading to large uncertainties in their global budgets. Beside the issue of quantification, characterisation of possible sources is needed to assist modelling of future environmental change impacts on these sources and hence the stratosphere. This study describes measurements conducted at two temperate salt marsh and three temperate forest sites in Scotland, and one tropical rainforest site in Malaysian Borneo to quantify and characterise natural methyl halide producing processes in these respective ecosystems. Measurements were conducted with static enclosure techniques, and methyl halide fluxes were calculated from the concentration difference between blank/background and afterenclosure samples. Methyl halide concentrations were determined via oxygen-doped GCECD with a custom-built pre-concentration unit. External factors such as photosyntheticallyactive radiation (PAR), total solar radiation, air temperature, soil temperature, internal chamber temperature and soil moisture were recorded in parallel to the enclosures to determine possible dependencies. Salt marsh studies were carried out at Heckie’s Hole in East Lothian, and Hollands Farmin East Dumfriesshire for 2 years. The study subjects were salt marsh plants that were enclosed during daylight hours in transparent enclosures for 10min each at 2–4 week intervals throughout the year. Parallel to this monitoring programme, systematic manipulation experiments and diurnal studies were carried out to learn more about the possible influence of potential drivers such as sunlight and temperature. Mean annual net fluxes ( standard deviation (sd)) were 300 44 ngm-2 h-1 for CH3Br and 660 270 ngm-2 h-1 for CH3Cl, with fluxes of both gases following a diurnal as well as an annual cycle, being lowest during winter nights and highest during summer days. A possible link between variations of daytime fluxes over the course of a year and changes in temperature was found. CH3Cl and CH3Br fluxes were positively correlated to each other and average fluxes of CH3Cl were linked to dry mass of certain species such as Puccinellia maritima, Aster tripolium, Juncus gerardi and Plantago maritima as found at the different measurement locations. No link between methyl halide fluxes and total halogen content or halogen concentration of the enclosed vegetation was found. Work in temperate forests was carried out for over one year at Fir Links, a mixed beech/ sycamore forest in East Lothian, and on one occasion each in Griffin Forest, a sitka spruce plantation in Perthshire, and finally the Hermitage of Braid, a mixed woodland park in Edinburgh. The study subject was leaf and needle litter which was enclosed in opaque 12 L containers for 10min–24h. During enclosure, internal chamber temperature was recorded, and leaf/needle litter water content was determined after enclosure. Combined average CH3Br and CH3Cl fluxes from temperate forest litter were 4.3 10-3 ngg-1 h-1 and 0.91 ngg-1 h-1, respectively. Average fluxes measured from leaf and needle litter were comparable in magnitude and CH3Br and CH3Cl were positively correlated. However no correlation of methyl halide fluxes to either temperature or litter water content was observed. Work at Danum Valley inMalaysian Borneo focused on flux measurements from both trees and leaf litter in a tropical dipterocarp forest. Fluxes from tropical trees were measured with transparent branch chambers at 20min enclosure times whilst methyl halide fluxes from leaf litter were measured with opaque 12 L containers at 24h enclosure times. Mean CH3Br and CH3Cl fluxes from branch enclosures were 0.53 ngg-1 h-1 and 27 ngg-1 h-1, respectively, and CH3Br and CH3Cl fluxes from tropical leaf litter were 1.4 10-3 ngg-1 h-1 and 2.3 ngg-1 h-1 respectively. Again fluxes of CH3Br and CH3Cl were positively correlated but no direct environmental driver for flux variations was found. The magnitude of methyl halide fluxes was species specific with individuals of the genus Shorea generally producing large amounts of methyl halide. Tropical rainforests were confirmed to be potentially the largest single natural source of CH3Cl. Global estimates were derived from extrapolating measured fluxes from the respective global land cover areas. These estimates suggest that the ecosystems examined in this study could account for over 1/3 of global CH3Cl production and up to 13%of global CH3Br production in nature. The ratio of CH3Br to CH3Cl emissions for these ecosystems is likely to be dependent on the abundance of bromine in the plant material with higher bromine content boosting CH3Br production and suppressing CH3Cl production. For this reason salt marshes are only a very minor source of CH3Cl.