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

[X]=number concentration of a compound X

diffusionconvectionadvectionchemistry t

X

t

X

t

X

t

X

t

X

Description I

« Box model »

N species - N equations

Chemical transport model (CTM)N x N1 x N2 x N3 equationsN1=number of longitudesN2=number of latitudesN3=number of altitudesoperator splitting-less accurate solvers

XJYXkBAkt

XX

21

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

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

][][

Xt

X

Advection Semi-Lagrangian scheme : suitable for large timesteps

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(~][

r

XK

rt

X rr

Diffusion equation in 3 dimensions:

Kxx, Kyy, Kzz are the zonal, meridional and vertical diffusion coefficients, solve with a implicit Eulerian scheme in each direction

Description III

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

Description IV

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dzzXzzt

X

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

Deep convection : Treated as an 1-dimensional process

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XPt

X

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

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

Wash-out parameterization : uses large-scale and convenctive precipitation from ECMWF, 3-d cloud cover fields and much more under construction

Heterogeneous reactions on sulphate aerosols N2O5 + SO4 2 HNO3 + SO4, NO3+SO4 HNO3+SO4, HO2+SO40.5 H2O2+SO4, (cloud droplets) N2O5 2HNO3 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

The reactive carbon cycle (units: Tg C/year)

COCO2 CH2O CH4

OH OH, hv OH

1100 570 360

85 30

deposition deposition

NMVOC (non-methane volatile organic compounds)

700100

50

200

80250

OH,O3

100340 deposition

SOA

CO2

Global total : 27 Tg N/yr, source: EDGAR v3.3

Bottom-up emissions

Global total : 8 Tg N/yr, Yienger and Levy, 1995

Global total : 3 Tg N/yr, Price et al, 1997, Pickering et al, 1998

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

Bottom-up biogenic emissions

IMAGES results : CO Mixing ratio

NOx : role, surces and sinks

NO2 O3 RO2

NO

OH HO2

CO, VOC, O3

O3

+

2HNO3

NO3

N2O5

O3 +

H2O

+

HNO3

+ O O3

Total NOx emissions for 2000: 43 Tg N

Anthropogenic61%

Soil19%

Pyrogenic11%

Lightning7%

Aircrafts2%

Annually averaged modelled vs.

observed NOx column - 2003

SCIAMACHY NO2 column

HCHO chemistry, sources and sinks

CH4

OH

HCHO

HO2

CH3O2

NMVOC

RO2

CH3OOHOH OH

NO

OH

CO+2HO2

CO+H2

CO+HO2+H2O

deposition

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

Annually averaged prior NMVOC

emissions from biomass burning

and biogenic sources - 2003

Annually averaged modelled vs.

observed HCHO column - 2003

SCIAMACHY HCHO column

Impact of NMVOCs on O3 mixing ratios

July 1997

without NMVOCs with NMVOCs