IMAGES: Intermediate model for the annual and global evolution of species

1. IMAGES: Intermediate model for the annual and global evolution of species • Description of the model • The reactive carbon cycle • Bottom-up inventories • Model results for CO • NOx chemistry, modelled NOx columns, comparison with SCIAMACHY NO2 columns • Modelling HCHO, comparison with measurements

2. Description I [X]=number concentration of a compound X « Box model » N species - N equations Chemical transport model (CTM) N x N1 x N2 x N3 equations N1=number of longitudes N2=number of latitudes N3=number of altitudes operator splitting-less accurate solvers • Extends from the surface to the pressure level of 44 mbar, 40 vertical levels, and 5x5 degree horizontal resolution • Provides the distribution of 48 chemical species (including non-oxygenated organic e.g. C2H6, C2H4, oxygenated e.g. PAN, MPAN, CH3COOOH, carbonyls e.g. HCHO, CHOCHO, CH3CHO, etc., peroxyradicals e.g. CH3O2, etc.) • Short-lived species are not transported in the model

3. Description II • The vertical resolution is higher near the surface • Equation 1 is solved numerically by an operator-splitting technique • Time step = 1 day, except for the three first days of each month : diurnal cycle calculation • Advection is driven by monthly mean climatological fields from ECMWF  short-term wind variability not taken into account – mixing associated with wind variability is comprised in the diffusion term • Turbulent mixing in the PBL  diffusion term • Vertical transport associated with deep convection Advection  Semi-Lagrangian scheme : suitable for large timesteps

4. Description III Diffusion equationin 3 dimensions:Kxx, Kyy, Kzz are the zonal, meridional and vertical diffusion coefficients, solve with a implicit Eulerian scheme in each direction • Horizontal diffusion coefficients : proportional to the deviations of wind fields • Vertical diffusion coefficient : depends on the PBL height • Kxx = 106-107 m2/s at mid-latitudes, much smaller values in the tropics, Kyy = factor of two lower than Kxx • Kzz values are sufficiently high to allow for rapid exchanges of mass between the surface and the free troposphere

5. Description IV Deep convection : Treated as an 1-dimensional process • Assumption : Ascending motions transport air from the boundary layer to the free troposphere, while subsidence transports air from each level to the adjacent lower level only  derive probabilities from the updraft densities • Use updraft fluxes from the ECMWF analyses Chemistry : P is the photochemical production and beta the loss rate For transported species, the quasi-steady state approximation is used, or an Eulerian appoximation when beta is close to zero, for short-lived equilibrium is assumed, iterative procedure

6. Description V • 48 long-lived and 20 short-lived species • ~200 chemical reactions, ~30 photolytic reactions (Muller and Stavrakou, 2005) • Water vapor, pressure and temperature are specified from ECMWF data • Lumping is used to reduce the number of species, e.g. the peroxy radicals formed from ISOP+OH are lumped into one species (MIM is used) • J’s are interpolated from values calculated offline using a radiative model • J’s depend on the sza, ozone column, surface albedo, T, clouds, and z Heterogeneous reactions on sulphate aerosols N2O5+ SO4  2 HNO3 + SO4, NO3+SO4 HNO3+SO4, HO2+SO40.5 H2O2+SO4, (cloud droplets) N2O5 2HNO3  under construction Wash-out parameterization : uses large-scale and convenctive precipitation from ECMWF, 3-d cloud cover fields and much more  under construction • The model is parallelized with OpenMP at 95%. It runs on 2,4,8, and 16 cpus. On the 5x5 grid : 20 min for 1-year simulation

7. The reactive carbon cycle (units: Tg C/year) deposition deposition 85 30 OH OH, hv OH CH2O CO2 CO CH4 1100 570 360 CO2 340 deposition 100 OH,O3 80 NMVOC(non-methane volatile organic compounds) 250 SOA 200 50 700 100

8. Bottom-up emissions Global total : 27 Tg N/yr, source: EDGAR v3.3

9. Global total : 8 Tg N/yr, Yienger and Levy, 1995 Global total : 3 Tg N/yr, Price et al, 1997, Pickering et al, 1998

11. Bottom-up biogenic emissions • MEGAN model coupled with the MOHYCAN canopy model • driven by ECMWF fields and accounts for leaf age, soil moisture stress, and past temperature radiation levels (Muller et al., 2008) • http://www.aeronomie.be/tropo/inventory.html

12. IMAGES results : CO Mixing ratio

13. NOx : role, surces and sinks + O  O3 NO3 O3 NO2 NO + RO2 O3 + + N2O5 H2O CO, VOC, O3 OH HO2 2HNO3 O3 HNO3

14. Annually averaged modelled vs. observed NOx column - 2003 SCIAMACHY NO2 column

15. HCHO chemistry, sources and sinks • The most abundant carbonyl in the atmosphere • Short-lived - lifetime on the order of a few hours • Directly emitted from fossil fuel combustion and biomass burning • Also formed as a high-yield secondary product in the CH4, and NMVOC oxidation NMVOC CH4 HO2 OH OH CH3OOH CH3O2 RO2 OH NO HCHO OH CO+2HO2 CO+HO2+H2O CO+H2 deposition

16. Annually averaged prior NMVOC emissions from biomass burning and biogenic sources - 2003

17. Annually averaged modelled vs. observed HCHO column - 2003 SCIAMACHY HCHO column

18. Impact of NMVOCs on O3 mixing ratios July 1997 without NMVOCs with NMVOCs