IMAGES: Intermediate model for the annual and global evolution of species Description of the model...
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Transcript of IMAGES: Intermediate model for the annual and global evolution of species Description of the model...
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
)][
(~][
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
')']()[',(][
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
][][
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