Atmospheric Chemistry and Physics Global Isoprene Emissions Estimated Using Megan, Ecmwf Analyses and a Detailed Canopy Environment Model

The global emissions of isoprene are calculated at 0.5 resolution for each year between 1995 and 2006, based on the MEGAN (Model of Emissions of Gases and Aerosols from Nature) version 2 model (Guenther et al., 2006) and a detailed multi-layer canopy environment model for the cal- culation of leaf temperature and visible radiation fluxes. The calculation is driven by meteorological fields - air temper- ature, cloud cover, downward solar irradiance, windspeed, volumetric soil moisture in 4 soil layers - provided by anal- yses of the European Centre for Medium-Range Weather Forecasts (ECMWF). The estimated annual global isoprene emission ranges between 374 Tg (in 1996) and 449 Tg (in 1998 and 2005), for an average of ca. 410 Tg/year over the whole period, i.e. about 30% less than the standard MEGAN estimate (Guenther et al., 2006). This difference is due, to a large extent, to the impact of the soil moisture stress factor, which is found here to decrease the global emissions by more than 20%. In qualitative agreement with past studies, high annual emissions are found to be generally associated with El Ni˜ no events. The emission inventory is evaluated against flux measurement campaigns at Harvard forest (Massachus- sets) and Tapaj ´ os in Amazonia, showing that the model can capture quite well the short-term variability of emissions, but that it fails to reproduce the observed seasonal variation at the tropical rainforest site, with largely overestimated wet season fluxes. The comparison of the HCHO vertical columns calcu- lated by a chemistry and transport model (CTM) with HCHO

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