Chlorofluoromethanes in the Environment

Rowland, F. S.; Molina, Mario J.

doi:10.1002/9781118782132.ch1

Cited by 16 publications

(15 citation statements)

References 85 publications

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“…The simplest modification of the C-F bond is its transformation to the simple C-H bond (hydrodefluorination, HDF), a process that has been mainly limited to fluoroarenes, with very few examples referring to trifluoromethylarenes and other perfluoroalkyl groups 1,[22][23][24][25][26] . HDF is an interesting process not only because of the fundamental importance on the C-F bond activation chemistry involved but also because of the potential applications in the activation and disposal of the chlorofluorocarbons, considered as 'super greenhouse gases' [27][28][29][30][31] . Metal hydrido complexes are often chosen for HDF, but C-F activation can produce stable fluoride complexes, which may hamper catalytic turnover 4,15 .…”

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confidence: 99%

Hydrodefluorination of carbon–fluorine bonds by the synergistic action of a ruthenium–palladium catalyst

2013

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Catalytic hydrodefluorination of organic molecules is a major organometallic challenge, owing to the strength of C-F sigma bonds, and it is a process with multiple industrial applications. Here we report a new heterodimetallic ruthenium-palladium complex based on a triazolyldi-ylidene ligand. The complex is remarkably active in the hydrodefluorination of aromatic and aliphatic carbon-fluorine bonds under mild reaction conditions. We observe that both metals are required to promote the reaction process. The overall process implies that the palladium fragment facilitates the C-F activation, whereas the ruthenium centre allows the reduction of the substrate via transfer hydrogenation from isopropanol/sodium t-butoxide. The activity of this heterodimetallic complex is higher than that shown by a mixture of the related homodimetallic complexes of ruthenium and palladium, demonstrating the catalytic benefits of the heterodimetallic complex linked by a single-frame ligand.

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confidence: 99%

Hydrodefluorination of carbon–fluorine bonds by the synergistic action of a ruthenium–palladium catalyst

2013

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“…Although the proportion of ozone in the atmosphere is low, it filters certain wavelengths of incoming solar ultraviolet (UV) light [1] and protects humans from UV. In 1974, some scientists discovered that anthropogenically released chemicals such as chlorofluorocarbons (CFCs) and other chlorine-containing volatile gases have a potentially damaging effect on ozone in the stratosphere [2,3]. The destruction of the ozone layer has been located and scientifically discussed.…”

Section: Introductionmentioning

confidence: 99%

Investigating the Temporal and Spatial Variability of Total Ozone Column in the Yangtze River Delta Using Satellite Data: 1978–2013

Chen

et al. 2014

Remote Sensing

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Abstract:The objective of this work is to analyze the temporal and spatial variability of the total ozone column (TOC) trends over the Yangtze River Delta, the most populated region in China, during the last 35 years using remote sensing-derived TOC data. Due to the lack of continuous and well-covered ground-based TOC measurements, little is known about the Yangtze River Delta. TOC data derived from the Total Ozone Mapping Spectrometer (TOMS) for the period 1978-2005 and Ozone Monitoring Instrument (OMI) for the period 2004-2013 were used in this study. The spatial, long-term, seasonal, and short-term variations of TOC in this region were analyzed. For the spatial variability, the latitudinal variability has a large range between 3% and 13%, and also represents an annual cycle with maximum in February and minimum in August. In contrast, the longitudinal variability is not significant and just varies between 2% and 4%. The long-term variability represented a notable decline for the period 1978-2013. The ozone depletion was observed significantly during 1978-1999, with linear trend from (−3.2 ± 0.7) DU/decade to (−10.5 ± 0.9) DU/decade. As for seasonal variability, the trend of TOC shows a distinct seasonal pattern, with maximum in April or May and minimum in October or November. The short-term analysis demonstrates the day-to-day changes as well as the six-week system persistence of the TOC. The results OPEN ACCESSRemote Sens. 2014, 6 12528 can provide comprehensive descriptions of the TOC variations in the Yangtze River Delta and benefit climate change research in this region.

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“…Branch (2b) of the ozone photodissociation reaction absorbs strongly at wavelengths < 310 nm, and filters out the biologically damaging solar UVB radiation (280 to 320 nm) that would otherwise reach the Earth's surface. This science was of little interest to international policymakers until the realization that ozone could also be destroyed globally in a catalytic cycle by chlorine initially released in the upper stratosphere by photodissociation of human-made chlorofluorocarbons (Rowland and Molina, 1975). This, and the later discovery of the Antarctic ozone "hole" (Farman et al, 1985), led to much more intensive study of the upper atmosphere through measurements of the relevant oxygen, hydrogen, nitrogen, chlorine and bromine species, laboratory measurements of their reaction rates, and computational modeling of the chemistry and dynamics of the stratosphere using these data.…”

Section: Introductionmentioning

confidence: 99%

Diurnal variations of stratospheric ozone measured by ground-based microwave remote sensing at the Mauna Loa NDACC site: measurement validation and GEOSCCM model comparison

et al. 2014

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Abstract. There is presently renewed interest in diurnal variations of stratospheric and mesospheric ozone for the purpose of supporting homogenization of records of various ozone measurements that are limited by the technique employed to being made at certain times of day. We have made such measurements for 19 years using a passive microwave remote sensing technique at the Mauna Loa Observatory (MLO) in Hawaii, which is a primary station in the Network for Detection of Atmospheric Composition Change (NDACC). We have recently reprocessed these data with hourly time resolution to study diurnal variations. We inspected differences between pairs of the ozone spectra (e.g., day and night) from which the ozone profiles are derived to determine the extent to which they may be contaminated by diurnally varying systematic instrumental or measurement effects. These are small, and we have reduced them further by selecting data that meet certain criteria that we established. We have calculated differences between profiles measured at different times: morning-night, afternoon-night, and morning-afternoon and have intercompared these with like profiles derived from the Aura Microwave Limb Sounder (Aura-MLS), the Upper Atmosphere Research Satellite Microwave Limb Sounder (UARS-MLS), the Superconducting Submillimeter-Wave Limb-Emission Sounder (SMILES), and Solar Backscatter Ultraviolet version 2 (SBUV/2) measurements. Differences between averages of coincident profiles are typically < 1.5 % of typical nighttime values over most of the covered altitude range with some exceptions. We calculated averages of ozone values for each hour from the Mauna Loa microwave data, and normalized these to the average for the first hour after midnight for comparison with corresponding values calculated with the Goddard Earth Observing System Chemistry Climate Model (GEOSCCM). We found that the measurements and model output mostly agree to better than 1.5 % of the midnight value, with one noteworthy exception: The measured morning-night values are significantly (2-3 %) higher than the modeled ones from 3.2 to 1.8 hPa (∼ 39-43 km), and there is evidence that the measured values are increasing compared to the modeled values before sunrise in this region.

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Chlorofluoromethanes in the Environment

Cited by 16 publications

References 85 publications

Hydrodefluorination of carbon–fluorine bonds by the synergistic action of a ruthenium–palladium catalyst

Hydrodefluorination of carbon–fluorine bonds by the synergistic action of a ruthenium–palladium catalyst

Investigating the Temporal and Spatial Variability of Total Ozone Column in the Yangtze River Delta Using Satellite Data: 1978–2013

Diurnal variations of stratospheric ozone measured by ground-based microwave remote sensing at the Mauna Loa NDACC site: measurement validation and GEOSCCM model comparison

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