Formulation and evaluation of IMS, an interactive three-dimensional tropospheric chemical transport Model 1. Model emission schemes and transport processes

In part one of this series of papers on a new integrated modelling system(IMS),the interactive three-dimensional chemical transport model (CTM),we presenta detailed description of the interactive emission scheme for biogenic speciesand outlinethe datasets used for anthropogenic species. In addition, we describe thetransportscheme employed in this model.The biogenic emission schemes incorporate the high-resolution Olson World Ecosystem data (Olson, 1992),the satellite-sensedterrestrial vegetation data from AVHRR (A Very High Resolution Radiometer) (Brown et al., 1985),and the CZCS (Coastal Zone Color Scanner) data (Erickson and Eaton, 1993).These datasetsprovide seasonal variations in surface biogenic emissions.The emission schemesare tested against other estimates (e.g., GEIA) and equilibrium emissions. A comparison of terrestrial biogenic fluxes,both the spatial and temporal (seasonal) variation of modelled surfacenet primary production, is consistent with the geographicalvariations of the global vegetation index (GVI) distribution derived fromAVHRR.The annual net primary production is 76000 Tg C yr−1, whichcompares wellwith the 40500–78000 Tg C yr−1 estimated by Melilloet al. (1993).This indicates that the model works well in capturing spatial andseasonal variations in the terrestrial vegetation. The modelled surface vegetation fluxes are verified against data from Guenther et al. (1995). While thecomparison shows agenerally good agreement in terms of the temporal and spatial distributionsof isoprene (530 Tg yr−1), large discrepancies are seen overthetropical locations which often exhibit strong seasonality in rainfalland very small variation in temperature. These differences indicatethata large difference in the estimation between an empirical relation and an LSMcalculation occursif an area in which seasonal distribution of rainfall is the main factor whichdeterminesthe type of vegetation. In this paper, we assess(results are discussed in following papers)the role of changing surface biogenic distributions insurface-to-atmosphere biogenic fluxes (both ocean-to-atmosphere and land-to-atmosphere).