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An automated gas chromatograph/mass spectrometer is described for the routine field monitoring of the CFC replacement compounds, the hydrofluorocarbons (HFCs) and hydrochlorofluorocarbons (HCFCs). Detection limits of 0.5 pptv are achieved by concentration of a 2-L air sample onto a three-stage adsorbent-filled microtrap. The microtrap is cooled to subambient temperatures (-50 °C) using Peltier thermoelectric devices, without a postdesorption cryofocussing step, thereby eliminating the need for liquid cryogens. The enriched air sample is thermally desorbed by direct ohmic heating of the microtrap, and compounds are separated on a 100-m, 5-µthick film high-resolution capillary column. Individual hydrohalocarbons are determined by selected ion masses for quantitation. The instrument is designed to operate automatically at a remote atmospheric research station providing ~2-h replicate air and calibration analyses.The chemical industry is presently replacing the ozonedepleting chlorofluorocarbons (CFCs) with a group of hydrofluorocarbons (HFCs) and hydrochlorofluorcarbons (HCFCs), referred to collectively as hydrohalocarbons. These compounds contain carbon-hydrogen bonds that are subject to destruction in the lower atmosphere through reaction with hydroxyl radicals. This destruction mechanism shortens their atmospheric lifetimes, thereby reducing their potential for ozone depletion.1™3 However, the replacement hydrohalocarbons, like their CFC predecessors, absorb radiation in the 8-12-«m region of the spectrum and therefore contribute to global warming. Model calculations indicate that the potential impact of these compounds as greenhouse gases is ~1 order of magnitude less than the CFCs.4 Since the long-term environmental effects of these hydrohalocarbons

h i g h l i g h t sPhotochemical production from monoterpenes gives 64% to the global acetone sources. The tropospheric life-time of acetone is found to be 18 days. Higher acetone is found over the forested regions throughout the summer. Good agreement between model and measurement data for acetone is found. a b s t r a c tThe impact of including a more detailed VOC oxidation scheme (CRI v2-R5) with a multi-generational approach for simulating tropospheric acetone is investigated using a 3-D global model, STOCHEM-CRI. The CRI v2-R5 mechanism contains photochemical production of acetone from monoterpenes which account for 64% (46.8 Tg/yr) of the global acetone sources in STOCHEM-CRI. Both photolysis and oxidation by OH in the troposphere contributes equally (42%, each) and dry deposition contributes 16% of the atmospheric sinks of acetone. The tropospheric life-time and the global burden of acetone are found to be 18 days and 3.5 Tg, respectively, these values being close to those reported in the study of Jacob et al. (2002). A dataset of aircraft campaign measurements are used to evaluate the inclusion of acetone formation from monoterpenes in the CRI v2-R5 mechanism used in STOCHEM-CRI. The overall comparison between measurements and models show that the parameterised approach in STOCHEM-NAM (no acetone formation from monoterpenes) underpredicts the mixing ratios of acetone in the atmosphere. However, using a detailed monoterpene oxidation mechanism forming acetone has brought the STOCHEM-CRI into closer agreement with measurements with an improvement in the vertical simulation of acetone. The annual mean surface distribution of acetone simulated by the STOCHEM-CRI shows a peak over forested regions where there are large biogenic emissions and high levels of photochemical activity. Year-long observations of acetone and methanol at the Mace Head research station in Ireland are compared with the simulated acetone and methanol produced by the STOCHEM-CRI and found to produce good overall agreement between model and measurements. The seasonal variation of model and measured acetone levels at Mace Head, California, New Hampshire and Minnesota show peaks in summer and dips in winter, suggesting that photochemical production may have the strongest effect on its seasonal trend.

Ground‐based in situ measurements of 1,1‐difluoroethane (HFC‐152a, CH3CHF2) which is regulated under the Kyoto Protocol are reported under the auspices of the AGAGE (Advanced Global Atmospheric Gases Experiment) and SOGE (System of Observation of halogenated Greenhouse gases in Europe) programs. Observations of HFC‐152a at five locations (four European and one Australian) over a 10 year period were recorded. The annual average growth rate of HFC‐152a in the midlatitude Northern Hemisphere has risen from 0.11 ppt/yr to 0.6 ppt/yr from 1994 to 2004. The Southern Hemisphere annual average growth rate has risen from 0.09 ppt/yr to 0.4 ppt/yr from 1998 to 2004. The 2004 average mixing ratio for HFC‐152a was 5.0 ppt and 1.8 ppt in the Northern and Southern hemispheres, respectively. The annual cycle observed for this species in both hemispheres is approximately consistent with measured annual cycles at the same locations in other gases which are destroyed by OH. Yearly global emissions of HFC‐152a from 1994 to 2004 are derived using the global mean HFC‐152a observations and a 12‐box 2‐D model. The global emission of HFC‐152a has risen from 7 Kt/yr to 28 Kt/yr from 1995 to 2004. On the basis of observations of above‐baseline elevations in the HFC‐152a record and a consumption model, regional emission estimates for Europe and Australia are calculated, indicating accelerating emissions from Europe since 2000. The overall European emission in 2004 ranges from 1.5 to 4.0 Kt/year, 5–15% of global emissions for 1,1‐difluoroethane, while the Australian contribution is negligible at 5–10 tonnes/year, <0.05% of global emissions.