Climate Change 2001:
Working Group I: The Scientific Basis
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4.4.2 The OxComp Workshop

In the SAR, the chapter on atmospheric chemistry included two modelling studies: PhotoComp (comparison of ozone photochemistry in box models) and Delta-CH4 (methane feedbacks in 2-D and 3-D tropospheric chemistry models). These model studies established standard model tests for participation in IPCC. They resulted in a consensus regarding the CH4 feedback and identified the importance (and lack of uniform treatment) of NMHC chemistry on tropospheric O3 production. This synthesis allowed for the SAR to use the CH4-lifetime feedback and a simple estimate of tropospheric O3 increase due solely to CH4. The SAR noted that individual CTMs had calculated an impact of changing NOx and CO emissions on global OH and CH4 abundances, but that a consensus on predicting future changes in O3 and OH did not exist.

Since 1995, considerable research has gone into the development and validation of tropospheric CTMs. The IPCC Special Report on Aviation and the Global Atmosphere (Derwent and Friedl, 1999) used a wide range of global CTMs to predict the enhancement of tropospheric O3 due to aircraft NOx emissions. The results were surprisingly robust, not only for the hemispheric mean O3 increase, but also for the increase in global mean OH reported as a decrease in the CH4 lifetime. The current state-of-modelling in global tropospheric chemistry has advanced since PhotoComp and Delta-CH4 in the SAR and now includes as standard a three-dimensional synoptic meteorology and treatment of non-methane hydrocarbon chemistry. A survey of recent CTM-based publications on the tropospheric O3 budget, collected for this report, is discussed in Section 4.5.

This assessment, building on these developments, organised a workshop to compare CTM results for a few, well-constrained atmospheric simulations. An open invitation, sent out in March 1999 to research groups involved in 3-D global tropospheric chemistry modelling, invited participation in this reportís assessment of change in tropospheric oxidative state through a model intercomparison and workshop (OxComp). This workshop is an IPCC-focused follow-on to the Global Integration and Modelling (GIM) study (Kanakidou et al., 1999). The infrastructure for OxComp (ftp site, database, graphics, and scientific support) was provided by the University of Oslo group, and the workshop meeting in July 1999 was hosted by the Max Planck Institute for Meteorology (MPI) Hamburg. Participating models are described by publications in peer-reviewed literature as summarised in Table 4.10; all include 3-D global tropospheric chemistry including NMHC; and assessment results are based on models returning a sufficient number of OxComp cases. The two goals of OxComp are (i) to build a consensus on current modelling capability to predict changes in tropospheric OH and O3 and (ii) to develop a useful parametrization to calculate the greenhouse gases (including tropospheric O3 but not CO2) using the IPCC emissions scenarios.

Table 4.10: Chemistry-Transport Models (CTM) contributing to the OxComp evaluation of predicting tropospheric O3 and OH.
CTM Institute Contributing authors References
GISS GISS Shindell /Grenfell Hansen et al. (1997b)
HGEO Harvard U. Bey / Jacob Bey et al. (1999)
HGIS Harvard U. Mickley / Jacob Mickley et al. (1999)
IASB IAS/Belg. Mülller Müller and Brasseur (1995, 1999)
KNMI KNMI/Utrecht van Weele Jeuken et al. (1999), Houweling et al. (2000)
MOZ1 NCAR/CNRS Hauglustaine / Brasseur Brasseur et al. (1998b), Hauglustaine et al. (1998)
MOZ2 NCAR Horowitz/ Brasseur Brasseur et al. (1998b), Hauglustaine et al. (1998)
MPIC MPI/Chem Kuhlmann / Lawrence Crutzen et al. (1999), Lawrence et al. (1999)
UCI UC Irvine Wild Hannegan et al. (1998), Wild and Prather (2000)
UIO U. Oslo Berntsen Berntsen and Isaksen (1997), Fuglestvedt et al. (1999)
UIO2 U. Oslo Sundet Sundet (1997)
UKMO UK Met Office Stevenson Collins et al. (1997), Johnson et al. (1999)
ULAQ U. L. Aquila Pitari Pitari et al. (1997)
UCAM U. Cambridge Plantevin /Johnson Law et al. (1998, 2000) (TOMCAT)

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