The Tropospheric Lifetimes of Halocarbons and Their Reactions with OH Radicals: an Assessment Based on the Concentration of CO-14

Chemical reaction with hydroxyl radicals formed in the troposphere from ozone photolysis in the presence of methane, carbon monoxide and nitrogen oxides provides an important removal mechanism for halocarbons containing C-H and C = C double bonds. The isotropic distribution in atmospheric carbon monoxide was used to quantify the tropospheric hydroxyl radical distribution. Here, this methodology is reevaluated in the light of recent chemical kinetic data evaluations and new understandings gained in the life cycles of methane and carbon monoxide. None of these changes has forced a significant revision in the CO-14 approach. However, it is somewhat more clearly apparent how important basic chemical kinetic data are to the accurate establishment of the tropospheric hydroxyl radical distribution

An analysis of the likely success of policy actions under uncertainty: recovery from acidification across Great Britain

In the context of wider debates about the role of uncertainty in environmental science and the development of environmental policy, we use a Generalised Likelihood Uncertainty Estimate (GLUE) approach to address the uncertainty in both acid deposition model predictions and in the sensitivity of the soils to assess the likely success of policy actions to reduce acid deposition damage across Great Britain. A subset of 11,699 acid deposition model runs that adequately represented observed deposition data were used to provide acid deposition distributions for 2005 and 2020, following a substantial reduction in SO2 and NOx emissions. Uncertain critical loads data for soils were then combined with these deposition data to derive estimates of the accumulated exceedance (AE) of critical loads for 2005 and 2020. For the more sensitive soils, the differences in accumulated exceedance between 2005 and 2020 were such that we could be sure that they were significant and a meaningful environmental improvement would result. For the least sensitive soils, critical loads were largely met by 2020, hence uncertainties in the differences in accumulated exceedance were of little policy relevance. Our approach of combining estimates of uncertainty in both a pollution model and an effects model, shows that even taking these combined uncertainties into account, policy-makers can be sure that the substantial planned reduction in acidic emissions will reduce critical loads exceedances. The use of accumulated exceedance as a relative measure of environmental protection provides additional information to policy makers in tackling this ‘wicked problem’

Halocarbon ozone depletion and global warming potentials

Concern over the global environmental consequences of fully halogenated chlorofluorocarbons (CFCs) has created a need to determine the potential impacts of other halogenated organic compounds on stratospheric ozone and climate. The CFCs, which do not contain an H atom, are not oxidized or photolyzed in the troposphere. These compounds are transported into the stratosphere where they decompose and can lead to chlorine catalyzed ozone depletion. The hydrochlorofluorocarbons (HCFCs or HFCs), in particular those proposed as substitutes for CFCs, contain at least one hydrogen atom in the molecule, which confers on these compounds a much greater sensitivity toward oxidation by hydroxyl radicals in the troposphere, resulting in much shorter atmospheric lifetimes than CFCs, and consequently lower potential for depleting ozone. The available information is reviewed which relates to the lifetime of these compounds (HCFCs and HFCs) in the troposphere, and up-to-date assessments are reported of the potential relative effects of CFCs, HCFCs, HFCs, and halons on stratospheric ozone and global climate (through 'greenhouse' global warming)

RETROCAM: A Versatile Optical Imager for Synoptic Studies

We present RETROCAM, an auxiliary CCD camera that can be rapidly inserted into the optical beam of the MDM 2.4m telescope. The speed and ease of reconfiguring the telescope to use the imager and a straightforward user interface permit the camera to be used during the course of other observing programs. This in turn encourages RETROCAM's use for a variety of monitoring projects.Comment: 6 pages, 6 figures, Accepted by A

Atmospheric chemistry regimes in intercontinental air traffic corridors:Ozone versus NOx sensitivity

This study focusses on the environmental consequences of aircraft NOx emissions and their role and impact on ozone formation in the upper troposphere and lower stratosphere (UTLS). We use a global chemistry transport/box model approach to quantify the impacts of NOx on UTLS ozone over time scales of hours and over distance scales appropriate to air traffic corridors and aircraft flight paths. An important feature of our study has been to provide a marked contrast to the coarse spatial resolution of the global model studies typically employed to assess the impacts of aviation NOx on UTLS ozone. Real operational aviation routing data are used to quantify the NOx impacts on ozone at 235 locations on 21 flight paths. The NOx impact on ozone in the intercontinental air traffic corridors is strongest in the great circle routes from North America and Europe into Asia and weakest in the trans-polar routes. The NOx impacts identified with the CTM/box model combination are significantly smaller compared with those identified in the current global models typically used to assess aviation NOx impacts. Further research is required to confirm our assessment of those flight paths that appear to show greatest NOx – O3 impacts and those the least and extend our analyses into the tropics and southern hemisphere

Analysis of UK and European NOx and VOC emission scenarios in the Defra model intercomparison exercise

This is a PDF file of an unedited manuscript that has been accepted for publication. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertainSimple emission scenarios have been implemented in eight United Kingdom air quality models with the aim of assessing how these models compared when addressing whether photochemical ozone formation in southern England was NOx- or VOC-sensitive and whether ozone precursor sources in the UK or in the Rest of Europe (RoE) were the most important during July 2006. The suite of models included three Eulerian-grid models (three implementations of one of these models), a Lagrangian atmospheric dispersion model and two moving box air parcel models. The assignments as to NOx- or VOC-sensitive and to UK- versus RoE-dominant, turned out to be highly variable and often contradictory between the individual models. However, when the assignments were filtered by model performance on each day, many of the contradictions could be eliminated. Nevertheless, no one model was found to be the 'best' model on all days, indicating that no single air quality model could currently be relied upon to inform policymakers robustly in terms of NOx- versus VOC-sensitivity and UK- versus RoE-dominance on each day. It is important to maintain a diversity in model approaches.Peer reviewedFinal Accepted Versio