Tropospheric Chemistry Modelling Group

Global three-dimensional chemical transport model of the troposphere

The IMAGES global chemistry-transport model stimulates the concentrations of 132 trace species at a resolution of 2°x2.5°, and at 40 sigma-pressure levels between the Earth's surface and the lower stratosphere (44 hPa). Meteorology is obtained from ERA-Interim analyses of the European Center of Medium-Range Weather Forecasts (ECMWF) for the year of the simulation (2007).

Details about the model can be found in previously published work:

The chemistry is solved by the fourth order Rosenbrock solver of the Kinetic Preprocessor software tool (KPP, Sandu et al., 2006). The model time step for the forward simulations is taken equal to 4 h. The effects of diurnal variations are accounted for through correction factors calculated from a detailed model run with a 20 min time step. This diurnal cycle simualtion accounts for diurnal variations in the photolysis and kinetic rates, in the meteorological fields, and in the emissions.


The model uses anthropogenic emissions from the EDGAR 3.2 FT2000 inventory for year 2000, overwritten by the REAS (Ohara et al., 2007) inventory over Asia, and EMEP emissions over Europe. Over the US, the EDGAR emission is scaled to the National Emission Inventory (NEI) values for each year.

The seasonality of anthropogenic emissions accounts for:

  1. a temperature dependence of vehicle emissions from the MOBILE 6 algorithm (Giannelli et al., 2002)
  2. the seasonal variation of residential heating

In MOBILE 6, the effect of cold starts on CO road transport emissions is accounted for by a correction factor applied for temperatures lower than 18°C, equal to 1 + (18 - T) x 0.05, with T the temperature in Celsius. Road emissions of NOx are only slightly temperature-dependent, a correction factor equal to 1 + (24 - T) x 0.0072 being applied only for temperatures above 24°C. The sectoral split of anthropogenic emissions is obtained from EDGAR. The seasonal variation of heating emissions is estimated by assuming that these emissions are proportional to the number of heating degree-days, with a threshold of 18°C.

Diurnal and weekly profiles of CO,NOx and VOC anthropogenic emissions for OECD countries are obtained from Jenkin et al. (2000). A diurnal cycle is also applied to biomass burning emissions (Stavrakou et al., 2009a) as well as to lightning emissions, assumed to follow the diurnal cycle of convective updraft fluxes.

Model runs include a spin-up time of 4 months.