Global isoprene emissions estimated using MEGAN, ECMWF analyses and a detailed canopy environment model J.-F. Müller1, T. Stavrakou1, S. Wallens1, I. De Smedt1, M. Van Roozendael1, M. J. Potosnak2, J. Rinne3, B. Munger4, A. Goldstein5, and A. B. Guenther6 1Belgian Institute for Space Aeronomy, Brussels, Belgium 2Desert Research Institute, Reno, NV, USA 3Department of Physics, University of Helsinki, Finland 4Harvard University, Cambridge, MA, USA 5University of California, Berkeley, CA, USA 6National Center for Atmospheric Research, Boulder, CO, USA
Abstract. 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 calculation of leaf temperature and visible
radiation fluxes. The calculation is driven by meteorological fields – air temperature,
cloud cover, downward solar irradiance, windspeed, volumetric soil moisture in 4 soil layers –
provided by analyses 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 Niño events. The emission inventory is evaluated against
flux measurement campaigns at Harvard forest (Massachussets) and Tapajós 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 calculated by a chemistry and transport
model (CTM) with HCHO distributions retrieved from space provides useful insights on tropical
isoprene emissions. For example, the relatively low emissions calculated over Western Amazonia
(compared to the corresponding estimates in the inventory of Guenther
et al., 1995)
are validated by the excellent agreement found between the CTM and HCHO data over this region.
The parameterized impact of the soil moisture stress on isoprene emissions is found to
reduce the model/data bias over Australia, but it leads to underestimated emissions near the end
of the dry season over subtropical Africa.
Citation: Müller, J.-F., Stavrakou, T., Wallens, S., De Smedt, I., Van Roozendael, M., Potosnak, M. J., Rinne, J., Munger, B., Goldstein, A., and Guenther, A. B.: Global isoprene emissions estimated using MEGAN, ECMWF analyses and a detailed canopy environment model, Atmos. Chem. Phys., 8, 1329-1341, doi:10.5194/acp-8-1329-2008, 2008.