G. Nickless

Calculated trends and the atmospheric abundance of 1,1,1,2‐tetrafluoroethane, 1,1‐dichloro‐1‐fluoroethane, and 1‐chloro‐1,1‐difluoroethane using automated in‐situ gas chromatography‐mass spectrometry measurements recorded at Mace Head, Ireland, from October 1994 to March 1997

The first in-situ measurements by automated gas chromatograph-mass spectrometer are reported for 1,1,1,2-tetrafluoroethane (HFC-134a), 1,1-dichloro-1-fluoroethane, (HCFC-141b), and 1-chloro-1,1-difluoroethane, (HCFC-142b). These compounds are steadily replacing the chlorofluorocarbons (CFCs) as refrigerants, foam-blowing agents, and solvents. The concentrations of all three compounds are shown to be rapidly increasing in the atmosphere, with 134a increasing at a rate of 2.05±0.02 ppt yr−1 over the 30 months of observations. Similarly, 141b and 142b increased at rates of 2.49±0.03 and 1.24±0.02 ppt yr−1, respectively, over the same period. The concentrations recorded at the atmospheric research station at Mace Head, Ireland, on January 1, 1996, the midpoint of the time series, were 3.67 ppt (134a), 7.38 ppt (141b), and 8.78 ppt (142b). From these observations we optimally estimate the HCFC and HFC emissions using a 12-box global model and OH concentrations derived from global 1,1,1-trichloroethane (CCl3CH3) measurements. Comparing two methods of estimating emissions with independent industry estimates shows satisfactory agreement for 134a and 141b, while for 142b, industry estimates are less than half those required to explain our observations.

Analysis of replacement chlorofluorocarbons using carboxen microtraps for isolation and preconcentration in gas chromatography-mass spectrometry

Abstract A microtrap containing a mixture of Carboxen 1000/1003 has successfully been developed for trapping and preconcentrating the very volatile replacement chlorofluorocarbons (CFCs) (fluorinated hydrofluorocarbons and hydrochlorofluorocarbons) from sample volumes of several litres. We have shown that a mixture of replacement CFCs can be quantitatively adsorbed and desorbed when a Carboxen-filled microtrap is held at −50°C, thus negating the need for cryotrapping, or cryofocussing using liquid nitrogen. The adsorbed compounds are rapidly desorbed by the direct ballistic heating of the microtrap to a temperature of 260°C in about 4 s. The application of these microtraps in the automated GC-MS analysis of the replacement CFCs and other environmentally important trace gases is presently under development in our laboratories for eventual deployment in remote atmospheric monitoring stations.

Evaluation of Carboxen carbon molecular sieves for trapping replacement chlorofluorocarbons

Abstract A method has been developed for trapping and preconcentrating the very volatile replacement chlorofluorocarbons (hydrofluorocarbons and hydrochlorofluorocarbons) using microtraps filled with Carboxen, a carbon molecular sieve type material, without the need for extensive cryotrapping using liquid nitrogen. We present here the adsorption characteristics of four Carboxen materials, Carboxen 569, 1000, 1001, and 1002, used to trap a range of replacement chlorofluorocarbons varying in boiling point from −48.4 to −9.8°C. The application of these traps for the automated analysis of trace gases in atmospheric and environmental chemistry could prove extremely useful.

Analysis of chlorofluorocarbon replacement compounds by capillary gas chromatography

Abstract Several thick film wall-coated open tubular and porous-layer open tubular (PLOT) type capillary columns have been investigated for the separation of wi

Stable carbon isotope analysis of selected halocarbons at parts per trillion concentration in an urban location

Environmental Context. Halocarbons can have significant effects on the atmosphere and the environment, particularly with regard to ozone depletion and climate change impacts. The determination of isotopic concentrations for selected halocarbon species should provide useful information to identify and constrain halocarbon sources and sinks within the urban environment. In the present study, a new instrumental method is described to determine these isotope ratios for selected halocarbons and the resultant data are interpreted in terms of local sources and sinks. Abstract. δ13C values of a suite of halocarbons have been determined in an urban background site in Bristol, UK. A novel mobile preconcentration system, based on the use of multi-adsorbent sample tubes, has been developed for trapping relatively large-volume air samples in potentially remote areas. An Adsorption Desorption System–Gas Chromatography–Electron Capture Detector was used to measure the mixing ratios of the selected halocarbon species, while a Gas Chromatography–Combustion–Isotope Ratio Mass Spectrometer was used to determine δ13C values. For the species with strong local sources, the variation of isotope ratios has been observed over the experimental period. Some of the results reported in the present study differ from previously reported values and reasons for this are discussed. The reporting of different δ13C values for selected halocarbons from different areas in the present study suggests that δ13C values may be used to determine the relative magnitudes of anthropogenic and biogenic sources.

Separation of hydrohalocarbons and chlorofluorocarbons using a cyclodextrin gas solid chromatography capillary column

Abstract Chromatographic analysis of very volatile hydrohalocarbons and chlorofluorocarbons has proved to be a difficult task due to the generally poor retention of these compounds on commercially available wall coated open tubular capillary columns. Although porous layer open tubular (PLOT) capillary columns coated with alumina/KCl, or alumina/Na 2 SO 4 provide adequate resolution for this class of compound they induce dehydrochlorination of certain hydrohalocarbons. More recently PLOT columns coated with Porapak porous polymer materials Q, S and U have been shown to provide inadequate resolution and high column bleed at the high column temperatures required for separation. We present results from the analysis of mixtures of hydrohalocarbons, chlorofluorocarbons, halocarbons, and halons, using a commercially available cyclodextrin PLOT column.

Leaf Cutter Ants: A Possible missing source of biogenic halocarbons

Environmental context. With large reductions in anthropogenic emissions of many ozone-depleting gases in response to the Montreal Protocol, gases with biogenic sources have become relatively more important in recent years. The global budgets of the biogenic halocarbons are unbalanced with known sinks outweighing sources, suggesting that additional natural sources are required to balance the budgets. In the present study, an investigation has been carried out to determine the importance of leaf cutter ants as a missing source of the biogenic halocarbons, which will reduce the discrepancy of the global budget of the halocarbons. Abstract. Leaf cutter ant colonies are shown to be a potentially significant new source of biogenic halocarbons. Fungus cultivated by these ant species may emit CH3Br, CH3I, CH3Cl, CH2Cl2 and CHCl3 in significant quantities, contributing to their respective global atmospheric budgets. The study suggests that the mixing ratios of CH3Br, CH3I, CH3Cl, CH2Cl2 and CHCl3 in the ant colony under test were significantly higher than background levels, by on average a factor of 1.5–5.0. Sampling was carried out during three stages of ant colony development (new, moderately active and highly active) and it was found that levels of these halocarbons were elevated during the active phases of the ant colony life cycle. A very rough estimate of the possible emission of CH3Br, CH3I, CH3Cl, CH2Cl2 and CHCl3 from ant colonies globally are 0.50, 0.02, 0.80, 0.15 and 0.22 Gg year–1.

Gas chromatographic determination of volatile alkenes by on-column bromination and electron-capture detection

Abstract A method is described for the GC-electron-capture detection determination of ultra trace quantities of alkenes via on-column bromination reactions. Copper bromide coated onto a non-polar solid support, Gas Chrom Q (100–120 mesh) acted as the bromine source. At a temperature of 90–110°C, steel wool may be used to remove selectively up to 90% of the bromine bleed from the reactor. The conversion efficiency of an alkene to the dibrominated derivative is extremely high, up to 90% for ethene, propene, butene and pentene. The bromination of acetylene is also possible, but is not as efficient.

Investigation of the use of oxygen doping of the electron-capture detection for determination of atmospheric halocarbons

Abstract The development of a GC-electron-capture detection instrument to determine accurately certain important trace C 1 halocarbons in a single analytical procedure from ambient air is reported. The procedure utilizes preconcentration at room temperature on an efficient microtrap filled with a commercially available adsorbent, Carboxen, followed by direct thermal desorption in a single stage on to a high-resolution capillary column. Detection is achieved with dual electron-capture detectors in series; the second being oxygen doped to dramatically enhance the sensitivity of the detector towards those halocarbons (hydrofluorochlorocarbon 22, CH 3 Cl) which normally react feebly with thermal electrons.