This page describes the current dry deposition scheme used in GEOS-Chem.
Here is a description of the GEOS-Chem dry deposition scheme from several journal articles:
From Section 4 of Alexander et al :
Dry deposition velocities for sea-salt aerosols (and sulfate formed in sea-salt aerosols) are computed with the size-dependent scheme of Zhang et al.  integrated over each model size bin and accounting for hygroscopic growth as a function of relative humidity [Gerber, 1985]. Dry deposition velocities for all other species are computed with a standard resistance-in-series scheme based on Wesely  as described by Wang et al. .
From Section 2.4 of Bey et al :
Dry deposition of oxidants and water soluble species is computed using a resistance-in-series model based on the original formulation of Wesely  with a number of modifications [Wang et al 1998]. The dry deposition velocities are calculated locally using GEOS data for surface values of momentum and sensible heat fluxes, temperature, and solar radiation.
From Section 6 of Wang et al :
We use a resistance-in-series model [Wesely and Hicks, 1977] to compute dry deposition velocities of O3, NO2, HNO3, PANs and H2O2. The deposition velocity Vi for species i is computed as:
Vi = 1 / ( Ra + Rb,i + Rc,i )
where Ra is the aerodynamic resistance to transfer to the surface, Rb,i is the boundary resistance, and Rc,i is the canopy surface resistance. Ra and Rb,i are calculated from the GCM meteorological variables [Jacob et al 1993]. Surface resistances Rc,i are based largely on the canopy model of Wesely  with some improvements, including explicit dependence of canopy stomatal resistances on LAI [Gao and Wesely, 1995] and on direct and diffuse PAR within the canopy [Baldocchi et al, 1987]. The same radiative transfer model for direct and diffuse PAR in the canopy is used as in the formulation of isoprene emissions. Surface resistances for deposition to tropical rain forest and tundra are taken from Jacob and Wofsy  and Jacob et al , respectively. The surface resistance for deposition of NO2 is taken to be the same as that of ozone [Erisman & Pul, 1994; Kramm et al, 1995; Eugster and Hesterberg, 1996] and hence lower than specified by Wesely . Dry deposition of CO and hydrocarbons is negligibly small and not included in the model [Mueller and Brasseur, 1995].
Text to be added
Source code and data
The source code of the various routines are located in drydep_mod.f. Routine DO_DRYDEP is the main driver for the dry deposition. It calls various setup routines before calling routine DEPVEL, which computes the dry deposition velocities in [m/s]. For the NOx-Ox-HC-aerosol "full-chemistry" simulation, the deposition velocities are then stored in an array and passed to the routine CALCRATE (in source file calcrate.f). CALCRATE stores the deposition velocities in the proper rate arrays, which then get passed to either the SMVGEAR or the KPP solvers. Dry deposition is thus treated as a loss reaction in the chemistry mechanism.
For more information about the data files required by the drydep scheme, please see the README file: GEOS_1x1/drydep_200203/README
--Bob Y. 10:46, 24 February 2010 (EST)
- Alexander, B., R.J. Park, D.J. Jacob, Q.B. Li, R.M. Yantosca, J. Savarino, C.C.W. Lee, and M.H. Thiemens, Sulfate formation in sea-salt aerosols: Constraints from oxygen isotopes, J. Geophys. Res., 110, D10307, 2005. PDF
- Baldocchi, D.D., B.B. Hicks, and P. Camara, A canopy stomatal resistance model for gaseous deposition to vegetated surfaces, Atmos. Environ. 21, 91-101, 1987.
- Brutsaert, W., Evaporation into the Atmosphere, Reidel, 1982.
- Businger, J.A., et al., Flux-profile relationships in the atmospheric surface layer, J. Atmos. Sci., 28, 181-189, 1971.
- Bey I., D. J. Jacob, R. M. Yantosca, J. A. Logan, B. Field, A. M. Fiore, Q. Li, H. Liu, L. J. Mickley, and M. Schultz, Global modeling of tropospheric chemistry with assimilated meteorology: Model description and evaluation, J. Geophys. Res., 106, 23,073-23,096, 2001. PDF
- Dwight, H.B., Tables of integrals and other mathematical data, MacMillan, 1957.
- Erisman, J.W, and A.V. Pul, Parameterization of surface resistance for the quantification of atmospheric deposition of acidifying pollutants and ozone, Atmos. Environ, 28, 2595-2607, 1994.
- Eugster, W. and R. Hesterberg, Transfer resistances of NO2 determined from eddy correlation flux measurements over a litter meadow at a rural site on the Swiss plateau, Atmos. Environ, 30, 1247-1254, 1996.
- Gao, W. and M.L. Wesely, Modeling gaseous dry deposition over regional scales with satellite observations, 1. Model development, Atmos. Environ, '29, 727-737, 1995.
- Gerber, H. E. (1985), Relative-humidity parameterization of the Navy aerosol model (NAM), NRL Rep. 8956, Natl. Res. Lab., Washington, D. C., 1985.
- Guenther, A., et al, A global model of natural volatile organic compound emissions, J. Geophys. Res., 100, 8873-8892, 1995.
- Hicks, B.B., and P.S. Liss, Transfer of SO2 and other reactive gases across the air-sea interface, Tellus, 28, 348-354, 1976.
- Jacob, D.J., and S.C. Wofsy, Budgets of reactive nitrogen, hydrocarbons, and ozone over the Amazon forest during the wet season, J. Geophys. Res., 95, 16737-16754, 1990.
- Jacob, D.J., et al, Deposition of ozone to tundra, J. Geophys. Res., 97, 16473-16479, 1992.
- Jacob, D.J, et al, Summertime photochemistry of the troposphere at high northern latitudes, J. Geophys. Res., 98, 14,797-14,816, 1993.
- Kramm, G. R. Dlugi, G.J. Dollard, T. Foken, N. Moelders, H. Mueller, W. Seiler, and H. Sievering, On the dry deposition of ozone and reactive nitrogen species, Atmos. Environ, 29, 3208-3231, 1995.
- Levine, I.N., Physical Chemistry, 3rd ed., McGraw-Hill, New York, 1988.
- Mueller, J-F, and G. Brasseur, IMAGES, A three-dimensional chemical transport model of the global troposphere, J. Geophys. Res., 100, 16,445-16,490, 1995.
- Munger, J.W., et al, Atmospheric deposition of reactive nitrogen oxides and ozone in a temperate deciduous forest and a sub-arctic woodland, J. Geophys. Res., in press, 1996.
- Price, H., L. Jaeglé, A. Rice, P. Quay, P.C. Novelli, R. Gammon, Global Budget of Molecular Hydrogen and its Deuterium Content: Constraints from Ground Station, Cruise, and Aircraft Observations, submitted to J. Geophys. Res., 2007
- Walcek, C.J., R.A. Brost, J.S. Chang, and M.L.Wesely, SO2, sulfate, and HNO3 deposition velocities computed using regional landuse and meteorological data, Atmos. Environ., 20, 949-964, 1986.
- Wang, Y., D.J. Jacob, and J.A. Logan, Global simulation of tropospheric O3-NOx-hydrocarbon chemistry, 1. Model formulation, J. Geophys. Res., 103, D9,10,713-10,726, 1998. PDF
- Wesely, M.L, Improved parameterizations for surface resistance to gaseous dry deposition in regional-scale numerical models, Environmental Protection Agency Report EPA/600/3-88/025, Research Triangle Park (NC), 1988.
- Wesely, M. L., Parameterization of surface resistance to gaseous dry deposition in regional-scale numerical models, Atmos. Environ., 23, 1293-1304, 1989.
- Wesely, M.L, and B.B. Hicks, Some factors that affect the deposition rates of sulfur dioxide and similar gases on vegetation, J. Air. Pollut. Control Assoc., 27, 1110-1116, 1977.
- Zhang, L., S. Gong, J. Padro, and L. Barrie, A size-segregated particle dry deposition scheme for an atmospheric aerosol module, <u<Atmos. Environ.,</u>, 35, 549–560, 2001.
--Bob Y. 15:24, 19 February 2010 (EST)
Aerosol dry deposition velocities over snow and ice surfaces
Modeled aerosol dry deposition velocities over snow and ice surfaces in the Arctic are much higher than estimated from measured values (e.g., Ibrahim et al. ; Duan et al. ; Nilsson and Rannik ). A planned update to GEOS-Chem, to be included after v9-01-01, will impose a dry deposition velocity of 0.03 cm/s for all aerosols over snow and ice surfaces.
--Jenny F. 11:08, 20 January 2011 (EST)
Dependency between dry deposition and soil NOx emissions
In GEOS-Chem there is a code dependency between the dry deposition routines soil NOx emissions routines. This is purely historical baggage that goes back to the days of the old 9-layer Harvard-GISS CTM (from which these routines were taken).
The dry deposition routine DEPVEL (in drydep_mod.f) computes a quantity called CANOPYNOX, which is the bulk surface resistance of the canopy to NOx deposition. This is computed in the following lines of code:
C** Get the bulk surface resistance of the canopy, RSURFC, from the network C** of resistances in parallel and in series (Fig. 1 of Wesely ) DTMP1=1.D0/RIXX DTMP2=1.D0/RLUXX DTMP3=1.D0/(RAC(LDT)+RGSX) DTMP4=1.D0/(RDC+RCLX) RSURFC(K,LDT) = 1.D0/(DTMP1 + DTMP2 + DTMP3 + DTMP4) C Save the within canopy depvel of NOx, used in calculating the C canopy reduction factor for soil emissions. ! Remove hardwire for CANOPYNOX (bmy, 1/24/03) IF ( K == DRYDNO2 ) THEN CANOPYNOX(IJLOOP,LDT)=DTMP1+DTMP2+DTMP3+DTMP4 ENDIF
However, the CANOPYNOX variable is not defined within drydep_mod.f, but is found instead within the soil NOx emissions code header file commsoil.h:
REAL*8 CANOPYNOX(MAXIJ,NTYPE) !track NOx within canopy dry dep.
and is then also used within the soil NOx emissions function SOILCRF, as follows:
IF ((XLAI(IREF,JREF,K).GT.0.D0).AND. & (CANOPYNOX(IJLOOP,K).GT.0.D0))THEN VFNEW=VFNEW*SQRT(WINDSQR/9.D0*7.D0/XLAI(IREF,JREF,K))* * (SOILEXC(2)/SOILEXC(NN)) SOILCRF=CANOPYNOX(IJLOOP,K)/(CANOPYNOX(IJLOOP,K) * +VFNEW) ELSE SOILCRF=0.D0 END IF
This is not necessarily a problem as long as dry deposition is always turned on whenever you are doing a full-chemistry simulation that requires soil NOx emissions. In the driver routine main.f, dry deposition is always done before emissions. However, this is bad coding style and a potential source of error. (This also must be corrected for the GEOS-Chem column code, in which all inputs must come thru the argument list.)
In the new soil NOx emissions code being developed by Rynda Hudman (much of which is based on the GEOS-Chem column code being developed by Bob Yantosca and Philippe Le Sager), there is a new module called canopy_nox_mod.f. This module computes the CANOPYNOX quantity independently of routine DEPVEL in drydep_mod.f, which allows for a totally clean separation between dry deposition routines and emissions routines.
At present, the new canopy_nox_mod.f is not available in the standard mainline GEOS-Chem code. It is slated to be incorporated with the soil NOx emissions update.
--Bob Y. 13:51, 18 February 2010 (EST)