The Experts below are selected from a list of 234 Experts worldwide ranked by ideXlab platform
S J Deverel - One of the best experts on this subject based on the ideXlab platform.
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Methyl halide and chloroform emissions from a subsiding sacramento san joaquin delta island converted to rice fields
Atmospheric Environment, 2011Co-Authors: M A H Khan, Robert C. Rhew, M Whelan, K Zhou, S J DeverelAbstract:Net fluxes of Methyl Halides and chloroform were measured from recently converted rice fields on Twitchell Island, California, using field- and laboratory-based incubations. A stable isotope tracer method was used to demonstrate that the net emissions of CH3Cl and CH3Br during the growing season were predominantly the result of large gross production rates, with gross consumption rates being relatively minor. In agreement with prior studies, the production rates for Methyl Halides differed significantly at different rice plant growth phases. The Twitchell Island rice field, however, had production rates of CH3Cl during the growth phases that were higher than rates reported at commercial rice fields, presumably because of higher soil chloride concentrations. Laboratory soil incubations showed that the non-flooded rice field soils acted as a small net sink for CH3Cl and as small net sources for CH3Br, CH3I and CHCl3. Despite the higher CH3Cl emissions during the growing season, the overall emissions of halomethanes from the conversion of all potential islands in the San Joaquin Delta to rice paddies is predicted to be an insignificant source of halomethanes.
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Methyl halide and chloroform emissions from a subsiding Sacramento–San Joaquin Delta island converted to rice fields
Atmospheric Environment, 2011Co-Authors: M A H Khan, Robert C. Rhew, M Whelan, K Zhou, S J DeverelAbstract:Net fluxes of Methyl Halides and chloroform were measured from recently converted rice fields on Twitchell Island, California, using field- and laboratory-based incubations. A stable isotope tracer method was used to demonstrate that the net emissions of CH3Cl and CH3Br during the growing season were predominantly the result of large gross production rates, with gross consumption rates being relatively minor. In agreement with prior studies, the production rates for Methyl Halides differed significantly at different rice plant growth phases. The Twitchell Island rice field, however, had production rates of CH3Cl during the growth phases that were higher than rates reported at commercial rice fields, presumably because of higher soil chloride concentrations. Laboratory soil incubations showed that the non-flooded rice field soils acted as a small net sink for CH3Cl and as small net sources for CH3Br, CH3I and CHCl3. Despite the higher CH3Cl emissions during the growing season, the overall emissions of halomethanes from the conversion of all potential islands in the San Joaquin Delta to rice paddies is predicted to be an insignificant source of halomethanes.
Robert C. Rhew - One of the best experts on this subject based on the ideXlab platform.
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Methyl halide and chloroform emissions from a subsiding sacramento san joaquin delta island converted to rice fields
Atmospheric Environment, 2011Co-Authors: M A H Khan, Robert C. Rhew, M Whelan, K Zhou, S J DeverelAbstract:Net fluxes of Methyl Halides and chloroform were measured from recently converted rice fields on Twitchell Island, California, using field- and laboratory-based incubations. A stable isotope tracer method was used to demonstrate that the net emissions of CH3Cl and CH3Br during the growing season were predominantly the result of large gross production rates, with gross consumption rates being relatively minor. In agreement with prior studies, the production rates for Methyl Halides differed significantly at different rice plant growth phases. The Twitchell Island rice field, however, had production rates of CH3Cl during the growth phases that were higher than rates reported at commercial rice fields, presumably because of higher soil chloride concentrations. Laboratory soil incubations showed that the non-flooded rice field soils acted as a small net sink for CH3Cl and as small net sources for CH3Br, CH3I and CHCl3. Despite the higher CH3Cl emissions during the growing season, the overall emissions of halomethanes from the conversion of all potential islands in the San Joaquin Delta to rice paddies is predicted to be an insignificant source of halomethanes.
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Methyl halide and chloroform emissions from a subsiding Sacramento–San Joaquin Delta island converted to rice fields
Atmospheric Environment, 2011Co-Authors: M A H Khan, Robert C. Rhew, M Whelan, K Zhou, S J DeverelAbstract:Net fluxes of Methyl Halides and chloroform were measured from recently converted rice fields on Twitchell Island, California, using field- and laboratory-based incubations. A stable isotope tracer method was used to demonstrate that the net emissions of CH3Cl and CH3Br during the growing season were predominantly the result of large gross production rates, with gross consumption rates being relatively minor. In agreement with prior studies, the production rates for Methyl Halides differed significantly at different rice plant growth phases. The Twitchell Island rice field, however, had production rates of CH3Cl during the growth phases that were higher than rates reported at commercial rice fields, presumably because of higher soil chloride concentrations. Laboratory soil incubations showed that the non-flooded rice field soils acted as a small net sink for CH3Cl and as small net sources for CH3Br, CH3I and CHCl3. Despite the higher CH3Cl emissions during the growing season, the overall emissions of halomethanes from the conversion of all potential islands in the San Joaquin Delta to rice paddies is predicted to be an insignificant source of halomethanes.
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gross production exceeds gross consumption of Methyl Halides in northern california salt marshes
Geophysical Research Letters, 2010Co-Authors: Robert C. Rhew, Olivier MazeasAbstract:[1] Coastal salt marshes are sources of CH3Br and CH3Cl to the atmosphere, but the wide range of reported emission rates illustrates the need to understand better the factors controlling net fluxes. Here we demonstrate the use of a stable isotope tracer method to separately evaluate gross production and consumption fluxes to determine their relative roles in the overall net flux. At two salt marshes in northern California, gross production exceeds gross consumption at all measured sites, leading to a large net source overall. Emission rates are within the range observed at other temperate salt marshes. By evaluating the consumption component separately, we explain how a typical salt marsh source might convert into a temporary net sink by exposing the ecosystem to uncharacteristically high concentrations of Methyl Halides. This circumstance may account for the reported net uptake of Methyl chloride during the growing season at a coastal salt marsh in China.
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Genetic control of Methyl halide production in Arabidopsis.
Current biology : CB, 2003Co-Authors: Robert C. Rhew, Eric S Saltzman, Lars Østergaard, Martin F. YanofskyAbstract:Methyl chloride (CH(3)Cl) and Methyl bromide (CH(3)Br) are the primary carriers of natural chlorine and bromine, respectively, to the stratosphere, where they catalyze the destruction of ozone, whereas Methyl iodide (CH(3)I) influences aerosol formation and ozone loss in the boundary layer. CH(3)Br is also an agricultural pesticide whose use is regulated by international agreement. Despite the economic and environmental importance of these Methyl Halides, their natural sources and biological production mechanisms are poorly understood. Besides CH(3)Br fumigation, important sources include oceans, biomass burning, tropical plants, salt marshes, and certain crops and fungi. Here, we demonstrate that the model plant Arabidopsis thaliana produces and emits Methyl Halides and that the enzyme primarily responsible for the production is encoded by the HARMLESS TO OZONE LAYER (HOL) gene. The encoded protein belongs to a group of Methyltransferases capable of catalyzing the S-adenosyl-L-methionine (SAM)-dependent Methylation of chloride (Cl(-)), bromide (Br(-)), and iodide (I(-)) to produce Methyl Halides. In mutant plants with the HOL gene disrupted, Methyl halide production is largely eliminated. A phylogenetic analysis with the HOL gene suggests that the ability to produce Methyl Halides is widespread among vascular plants. This approach provides a genetic basis for understanding and predicting patterns of Methyl halide production by plants.
M A H Khan - One of the best experts on this subject based on the ideXlab platform.
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Methyl halide and chloroform emissions from a subsiding sacramento san joaquin delta island converted to rice fields
Atmospheric Environment, 2011Co-Authors: M A H Khan, Robert C. Rhew, M Whelan, K Zhou, S J DeverelAbstract:Net fluxes of Methyl Halides and chloroform were measured from recently converted rice fields on Twitchell Island, California, using field- and laboratory-based incubations. A stable isotope tracer method was used to demonstrate that the net emissions of CH3Cl and CH3Br during the growing season were predominantly the result of large gross production rates, with gross consumption rates being relatively minor. In agreement with prior studies, the production rates for Methyl Halides differed significantly at different rice plant growth phases. The Twitchell Island rice field, however, had production rates of CH3Cl during the growth phases that were higher than rates reported at commercial rice fields, presumably because of higher soil chloride concentrations. Laboratory soil incubations showed that the non-flooded rice field soils acted as a small net sink for CH3Cl and as small net sources for CH3Br, CH3I and CHCl3. Despite the higher CH3Cl emissions during the growing season, the overall emissions of halomethanes from the conversion of all potential islands in the San Joaquin Delta to rice paddies is predicted to be an insignificant source of halomethanes.
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Methyl halide and chloroform emissions from a subsiding Sacramento–San Joaquin Delta island converted to rice fields
Atmospheric Environment, 2011Co-Authors: M A H Khan, Robert C. Rhew, M Whelan, K Zhou, S J DeverelAbstract:Net fluxes of Methyl Halides and chloroform were measured from recently converted rice fields on Twitchell Island, California, using field- and laboratory-based incubations. A stable isotope tracer method was used to demonstrate that the net emissions of CH3Cl and CH3Br during the growing season were predominantly the result of large gross production rates, with gross consumption rates being relatively minor. In agreement with prior studies, the production rates for Methyl Halides differed significantly at different rice plant growth phases. The Twitchell Island rice field, however, had production rates of CH3Cl during the growth phases that were higher than rates reported at commercial rice fields, presumably because of higher soil chloride concentrations. Laboratory soil incubations showed that the non-flooded rice field soils acted as a small net sink for CH3Cl and as small net sources for CH3Br, CH3I and CHCl3. Despite the higher CH3Cl emissions during the growing season, the overall emissions of halomethanes from the conversion of all potential islands in the San Joaquin Delta to rice paddies is predicted to be an insignificant source of halomethanes.
Lester Andrews - One of the best experts on this subject based on the ideXlab platform.
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Methylidyne complexes prepared by reactions of laser ablated os atoms with methane Methyl Halides and ethane observation of the c h and os h stretching absorptions
Organometallics, 2008Co-Authors: Hangook Cho, Lester AndrewsAbstract:Simple Os carbyne complexes (HC≡OsH3, HC≡OsH2F, HC≡OsH2Cl, HC≡OsH2Br, and CH3C≡OsH3) are produced in reactions of laser-ablated Os atoms with small alkanes and Methyl Halides via oxidative C−H insertion and α-hydrogen migration. The diagnostic Methylidyne C—H stretching absorptions of HC≡OsH3 and its halide derivatives are observed about 200 cm−1 above the precursor C—H stretching bands, and the frequencies are consistent with s character in hybridization in the C—H bond. The Methylidyne complexes all have computed Cs structures, and particularly the HC≡OsH3 and CH3C≡OsH3 complexes have two equivalent shorter and one longer Os—H bonds, parallel to the case of Re in similar complexes. The strong unique Os—H stretching absorption at an exceptionally low frequency is traced to the stretching mode of the long Os—H bond and antibonding character in the doubly occupied HOMO.
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infrared spectra of Methylidynes formed in reactions of re atoms with methane Methyl Halides Methylene Halides and ethane Methylidyne c h stretching absorptions bond lengths and s character
Inorganic Chemistry, 2008Co-Authors: Hangook Cho, Lester AndrewsAbstract:Rhenium carbyne complexes (HC≡ReH3, HC≡ReH2X, HC≡ReHX2, [X = F, Cl, and Br] and CH3C≡ReH3) are produced by reactions of laser-ablated Re atoms with methane, Methyl Halides, Methylene Halides, and e...
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infrared spectra of the ch3 mx and ch2 mhx complexes formed by reactions of laser ablated group 3 metal atoms with Methyl Halides
Journal of Physical Chemistry A, 2007Co-Authors: Hangook Cho, Lester AndrewsAbstract:Reactions of laser-ablated group 3 metal atoms with Methyl Halides have been carried out in excess of Ar during condensation and the matrix infrared spectra studied. The metals are as effective as other early transition metals in providing insertion products (CH 3 -MX) and higher oxidation state Methylidene complexes (CH 2 -MHX) (X = F, Cl, Br) following α-hydrogen migration. Unlike the cases of the group 4-6 metals, the calculated Methylidene complex structures show little evidence for agostic distortion, consistent with the previously studied group 3 metal Methylidene hydrides, and the C-M bond lengths of the insertion and Methylidene complexes are comparable to each other. However, the C-Sc bond lengths are 0.013, 0.025, and 0.029 A shorter for the CH 2 -ScHX complexes, respectively, and the spin densities are consistent with weak C(2p)-Sc(3d) πbonding. The present results reconfirm that the number of valence electrons on the metal is important for agostic interaction in simple Methylidene complexes.
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Formation of Grignard Species from the Reaction of Methyl Halides with Laser-Ablated Magnesium Atoms. A Matrix Infrared Study of CH3MgF, CH3MgCl, CH3MgBr, and CH3MgI
Journal of the American Chemical Society, 1998Co-Authors: William D. Bare, Lester AndrewsAbstract:Magnesium atoms generated by laser ablation were reacted with Methyl Halides diluted (0.5% to 0.1%) in argon. Reaction products were trapped in a cryogenic argon matrix and analyzed by infrared spectroscopy. The primary reaction product, isolated Grignard molecule CH3MgX, and the secondary reaction products MgX, MgX2, MgH, MgH2, CH4, C2H6, CH2X, CH3MgCH3, XMgCH2, HMgCH3, and HMgCH2X were identified by isotopic (13C, D, and 26Mg) substitution and by correlation with B3LYP and BP86 isotopic frequency calculations. This investigation reports the first experimental evidence for the fluoride Grignard species, CH3MgF. Infrared absorptions were also observed for associated Grignard species.
M Whelan - One of the best experts on this subject based on the ideXlab platform.
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Methyl halide and chloroform emissions from a subsiding sacramento san joaquin delta island converted to rice fields
Atmospheric Environment, 2011Co-Authors: M A H Khan, Robert C. Rhew, M Whelan, K Zhou, S J DeverelAbstract:Net fluxes of Methyl Halides and chloroform were measured from recently converted rice fields on Twitchell Island, California, using field- and laboratory-based incubations. A stable isotope tracer method was used to demonstrate that the net emissions of CH3Cl and CH3Br during the growing season were predominantly the result of large gross production rates, with gross consumption rates being relatively minor. In agreement with prior studies, the production rates for Methyl Halides differed significantly at different rice plant growth phases. The Twitchell Island rice field, however, had production rates of CH3Cl during the growth phases that were higher than rates reported at commercial rice fields, presumably because of higher soil chloride concentrations. Laboratory soil incubations showed that the non-flooded rice field soils acted as a small net sink for CH3Cl and as small net sources for CH3Br, CH3I and CHCl3. Despite the higher CH3Cl emissions during the growing season, the overall emissions of halomethanes from the conversion of all potential islands in the San Joaquin Delta to rice paddies is predicted to be an insignificant source of halomethanes.
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Methyl halide and chloroform emissions from a subsiding Sacramento–San Joaquin Delta island converted to rice fields
Atmospheric Environment, 2011Co-Authors: M A H Khan, Robert C. Rhew, M Whelan, K Zhou, S J DeverelAbstract:Net fluxes of Methyl Halides and chloroform were measured from recently converted rice fields on Twitchell Island, California, using field- and laboratory-based incubations. A stable isotope tracer method was used to demonstrate that the net emissions of CH3Cl and CH3Br during the growing season were predominantly the result of large gross production rates, with gross consumption rates being relatively minor. In agreement with prior studies, the production rates for Methyl Halides differed significantly at different rice plant growth phases. The Twitchell Island rice field, however, had production rates of CH3Cl during the growth phases that were higher than rates reported at commercial rice fields, presumably because of higher soil chloride concentrations. Laboratory soil incubations showed that the non-flooded rice field soils acted as a small net sink for CH3Cl and as small net sources for CH3Br, CH3I and CHCl3. Despite the higher CH3Cl emissions during the growing season, the overall emissions of halomethanes from the conversion of all potential islands in the San Joaquin Delta to rice paddies is predicted to be an insignificant source of halomethanes.