Dry deposition

This page describes the current dry deposition scheme used in GEOS-Chem.

Overview

Here is a description of the GEOS-Chem dry deposition scheme from several journal articles:

From Section 4 of Alexander et al [2005]:

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. [2001] 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 [1989] as described by Wang et al. [1998].

From Section 2.4 of Bey et al [2001]:

Dry deposition of oxidants and water soluble species is computed using a resistance-in-series model based on the original formulation of Wesely [1989] 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 [1998]:

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 [1989] 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 [1990] and Jacob et al [1992], 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 [1989]. Dry deposition of CO and hydrocarbons is negligibly small and not included in the model [Mueller and Brasseur, 1995].

Aerosol dry deposition

Havala Pye reexamined the code, and she found that there are three routines basically using the Zhang et al.(2001) scheme:

1. AERO_SFCRSII: Aerodynamic resistance for seasalt tracers. Hygroscopic growth is accounted for. Implemented by Rokjin Park ~ 2004? Used for: SALA, SALC, SO4S, NITS
2. DUST_SFCRSII: Aerodynamic resistance of dust aerosol tracers. No hygroscopic growth. Implemented by bec ~2005? Used for: DST1, DST2, DST3, DST4
3. ADUST_SFCRSII: Aerodynamic resistance of non-size resolved aersosols. No hygroscopic growth. Based on DUST_SRFCRSII and activated by Pye 2007. Assume particle diameter is 0.5 microns, density is 1.5 g/cm3 (1500 kg/m3). Used for all other aerosols that are not listed above (aerosols are indicated by a T/F flag in INIT_DRYDEP called AIROSOL).

This was briefly mentioned in Pye et al. (2009) paper.

Reference

1. Pye, H. O. T., H. Liao, S. Wu, L. J. Mickley, D. J. Jacob, D. K. Henze, and J. H. Seinfeld (2009), Effect of changes in climate and emissions on future sulfate-nitrate-ammonium aerosol levels in the United States, Journal of Geophysical Research: Atmospheres, 114(D1), D01205, doi:10.1029/2008JD010701.
2. Zhang, L. M., S. L. Gong, J. Padro, and L. Barrie (2001), A size-segregated particle dry deposition scheme for an atmospheric aerosol module, Atmos. Environ., 35(3), 549-560, doi:10.1016/s1352-2310(00)00326-5.

Source code and data

The source code of the various routines are located in drydep_mod.f.

1. Routine DO_DRYDEP is the main driver for the dry deposition. This calls various setup subroutines.
2. Routine DEPVEL (which is called by DO_DRYDEP) computes dry deposition dry deposition velocities in [m/s].
3. Dry deposition frequencies [1/s] for all species are computed in DO_DRYDEP, after the call to DEPVEL.

In GEOS-Chem v10-01 and higher versions, the following changes were made to how dry deposition is applied:

1. Dry deposition is now applied to all tracers in module GeosCore/mixing_mod.F90. Prior to this, dry deposition had been applied in several locations throughout the code, which was confusing and prone to error.
2. Dry deposition fluxes (i.e. category DRYD-FLX) are now archived to the ND44 diagnostic in module GeosCore/mixing_mod.F90. Furthermore, drydep fluxes are now archived with units of molec/cm2/s for all GEOS-Chem simulations. In prior GEOS-Chem versions, some simulations (in particular Rn-Pb-Be) had archived drydep fluxes in units of kg/s.
3. Routines DRYFLX and DRYFLXRnPbBe have now been removed from module GeosCore/drydep_mod.F90. The equivalent functionality is now provided by GeosCore/mixing_mod.F90.

Input values for dry deposition

Here we list some of the various input values used by the dry deposition routines. Full citations may be found in the references section below.

Land cover parameters

The land cover input variables for the GEOS-Chem dry deposition module are listed in the table below:

Variable	Read from	Description	Values	Reference
DRYCOEFF	Olson_1992_Drydep_inputs.nc	Local dependence of stomal resistance on the intensity I of light impinging the leaf; this is expressed as a mutliplicative factor I/(I+b) to the stomatal resistance where b = 50 W m-2 (equation (7) of Baldocchi et al. [1987])	-0.358, 3.02, 3.85, -0.0978, -3.66, 12, 0.252, -7.8, 0.226, 0.274, 1.14, -2.19, 0.261, -4.62, 0.685, -0.254, 4.37, -0.266, -0.159, -0.206	Baldocchi et al, AE, 1987.
IDRYDEP	Olson_1992_Drydep_inputs.nc	Indices for the 11 dry deposition land types	1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11	Wesely, AE 1989; Jacob et al., JGR 1990, 1992.
IOLSON	Olson_1992_Drydep_inputs.nc	Indices for the 72 Olson land types	1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74	Wesely, AE 1989; Jacob et al., JGR 1990, 1992.
IDEP	Olson_1992_Drydep_inputs.nc	Indices that map each of the 72 Olson land types to the corresponding dry deposition land type	11, 10, 5, 1, 1, 1, 2, 1, 8, 1, 1, 1, 1, 1, 1, 1, 5, 1, 1, 1, 3, 3, 3, 3, 2, 2, 2, 3, 2, 2, 4, 4, 2, 6, 1, 1, 9, 4, 4, 4, 5, 5, 5, 5, 5, 9, 5, 5, 5, 5, 8, 8, 5, 7, 6, 2, 2, 2, 2, 2, 3, 3, 3, 5, 5, 11, 11, 11, 11, 8, 1, 8, 9, 11	Wesely, AE 1989; Jacob et al., JGR 1990, 1992.
IWATER	Olson_1992_Drydep_inputs.nc	Indices of the Olson land types denoting water (i.e. ocean/lake/ice) surfaces	1, 66, 67, 68, 69, 74	Wesely, AE 1989; Jacob et al., JGR 1990, 1992.
IZO	Olson_1992_Drydep_inputs.nc	Roughness heights (1e-4 m) for each of the 72 Olson land types	10, 25000, 100, 1000, 1000, 1000, 10000, 1000, 10, 1000, 1000, 1000, 1000, 1000, 1000, 1000, 1000, 1, 1000, 1000, 10000, 10000, 10000, 10000, 10000, 10000, 10000, 10000, 1000, 10000, 1000, 1000, 2000, 10000, 1000, 1000, 100, 1000, 1000, 1000, 100, 100, 100, 100, 100, 100, 1000, 1000, 1000, 1000, 10, 10, 100, 50, 10000, 2000, 2000, 2000, 2000, 2000, 10000, 10000, 10000, 2000, 50, 100, 100, 100, 100, 10, 1, 1, 500, 10	Wesely, AE 1989; Jacob et al., JGR 1990, 1992.

Aerodynamic resistances

The aerodynamic resistances (IRI, IRLU, IRAC, IRGSS, IRGSO, IRCLS, IRCLO) and maximum deposition velocity for aerosol (IVSMAX) for each of the 11 dry deposition land types are read from this file:

• v9-01-03 and higher: Olson_1992_Drydep_inputs.nc
• Prior to v9-01-03: drydep.table

and have the following values:

DD type	Description	IRI [s m-1]	IRLU [s m-1]	IRAC [s m-1]	IRGSS [s m-1]	IRGSO [s m-1]	IRCLS [s m-1]	IRCLO [s m-1]	IVSMAX [10-2 cm s-1]	Reference
1	Snow/Ice	9999	9999	0	100	3500	9999	1000	100	Wesely, AE, 1989
2	Deciduous forest	200	9000	2000	500	200	2000	1000	100	Wesely, AE, 1989
3	Coniferous forest	400	9000	2000	500	200	2000	1000	100	Wesely, AE, 1989
4	Agricultural land	200	9000	200	150	150	2000	1000	100	Wesely, AE, 1989
5	Shrub/grassland	200	9000	100	350	200	2000	1000	100	Wesely, AE, 1989
6	Amazon forest	200	1000	2000	200	200	9999	9999	100	Jacob & Wofsy, JGR 1990
7	Tundra	200	4000	0	340	340	9999	9999	100	Jacob et al., JGR 1992
8	Desert	9999	9999	0	1000	400	9999	9999	10	Wesely, AE, 1989
9	Wetland	200	9000	300	0	1000	2500	1000	100	Wesely, AE, 1989
10	Urban	9999	9999	100	400	300	9999	9999	100	Wesely, AE, 1989
11	Water	9999	9999	0	0	2000	9999	9999	10	Wesely, AE, 1989

--Bob Yantosca (talk) 17:43, 21 July 2016 (UTC)

OVOCs dry deposition

This update was tested in the 1-month benchmark simulation v9-01-03c and approved on 19 Dec 2011.

These parameters are defined in the GEOS-Chem species database.

Species	H*(moles L-1 atm-1 )	f0	Reference
NO2	0.01	0.1
Ox	0.01	1.0
PAN	3.6	0.1
HNO3	1.0d+14	0.0
H2O2	1.0d+5	1.0
PMN	as PAN
PPN	as PAN
PYPAN	as PAN
ISN2	as HNO3
R4N2	as PAN
CH2O	6.0e+3	change from 0 to 1.0
GLYX	3.6d+5	change from 0 to 1.0
MGLY	3.7d+3	change from 0 to 1.0
GLYC	4.1d+4	change from 0 to 1.0
MPAN,GPAN, GLPAN	as PAN
N2O5	as HNO3
HCOOH	1.67d+5	change from 0 to 1.0
ACTA	1.14d+4	change from 0 to 1.0
ISOPND	1.7d+4	0.0
ISOPNB	1.7d+4	0.0
MVKN+MACRN	1.7d+4	0.0
PROPNN	1.0d+3	0.0	NITROOXYACETONE IN SANDER TABLE
RIP	as H2O2
IEPOX	as H2O2
MAP	8.4d+2	1.0
MVK	4.4d1	change from 0 to 1.0	from R.Sander
MACR	6.5d0	change from 0 to 1.0	from R.Sander
SO2	1.0d+5	0.0

Reference: Karl, T., Harley, P., Emmons, L., Thornton, B., Guenther, A., Basu, C., Turnipseed, A., and Jardine, K.: Efficient Atmospheric Cleansing of Oxidized Organic Trace Gases by Vegetation, Science, 330, 816-819, 10.1126/science.1192534, 2010.

Code updates

Cold-temperature dry deposition updates

This update was included in GEOS-Chem 12.6.0, which was released on 18 Oct 2019.

Viral Shah implemented the following updates in drydep_mod.F:

• Set HNO3 bulk surface resistance to 1 s/m
• Limit increases in Rc at low temperature to a factor of 2

The reference for these updates is

Jaeglé, L., Shah, V.,et al., Nitrogen oxides emissions, chemistry, deposition, and export over the Northeast United States during the WINTER aircraft campaign, J Geophys Res: Atmospheres, 123, https://doi.org/10.1029/2018JD029133, 2018.

--Melissa Sulprizio (talk) 18:00, 27 June 2019 (UTC)

Simple parameterization for CO2 dependence of stomatal resistance

This update was included in GEOS-Chem 12.6.0, which was released on 18 Oct 2019.

Anthony Wong and Amos Tai have developed code to apply CO2 effect on stomatal conductance according to Franks et a. (2013) equation. This feature is implemented as an option in the Deposition Menu of input.geos and is off by default:

------------------------+------------------------------------------------------ 
%%% DEPOSITION MENU %%% :
Turn on Dry Deposition? : T
Turn on Wet Deposition? : T
Turn on CO2 Effect?     : F
CO2 level               : 600.0
Reference CO2 level     : 380.0
------------------------+------------------------------------------------------

References:

• Franks, Peter J., et al., Sensitivity of plants to changing atmospheric CO2 concentration: from the geological past to the next century, New Phytologist, 197.4, 1077-1094, 2013.

--Melissa Sulprizio (talk) 17:40, 27 June 2019 (UTC)

Bug in computation of aerodynamic resistance RA

This fix was included in v11-02a and approved on 12 May 2017.

Brian Boys wrote:

In module GeosCore/drydep_mod.F, I discovered a bug in the subroutine DEPVEL. For the calculation of aerodynamic resistance RA under very stable atmospheric conditions (line 1811), the integration of the stability function phi_h (aka dimensionless vertical temperature gradient) from the roughness length to grid box center doesn't take into account the discontinuity occurring at z/L = 1 where phi_h switches from 1 + 5(z/L) to 5 + z/L (Holtslag, 1993). The result is too high of a value for the integral of phi_h and subsequently RA.

A straightforward solution is to calculate RA under stable conditions (L>0) using an integral form of the stability function, such as equation (12) of Holtslag, 1988. I implemented these changes in drydep_mod.F (from GCv 10-01, public release). To see the effect of the bug, namely a discontinuity in RA, refer to Figure 1, which plots RA as a function of stability (1/L).

I've also attached two scatter plots comparing outputted RA (GCv10-01, geosfp, 2x2.5, 2012/11/01) from the base model and an updated simulation employing the bug-fix as described above--please refer to Figure 2 (linear comparison):

and Figure 3 (logarithmic comparison):

Updates to dry deposition when using the Olson 2001 land map

This update was validated in the 1-month benchmark simulation GEOS-Chem v10-01a and approved on 05 Feb 2014.

It was discovered that ozone in the eastern US in GEOS-Chem v9-02 was too high when using the Olson 2001 land map. Patrick Kim implemented the following updates to correct this issue:

1. Force the use of MODIS LAI from 2008 if the last year is beyond 2008. There is a large difference in the 2009 file that still needs to be investigated.

In routine Init_Modis_Lai (modis_lai_mod.F90):

   IF ( USE_OLSON_2001 ) THEN
      I_MODIS     = 1440             ! For Olson 2001, use MODIS LAI
      J_MODIS     = 720              ! on the 0.25 x 0.25 native grid
      MODIS_START = 2005             ! First year of MODIS data  
      MODIS_END   = 2008             ! Force to 2008 (skim, 1/29/14)

2. Change the internal resistance for coniferous forests to match the internal resistance for deciduous forests.

In routine READ_DRYDEP_INPUTS (drydep_mod.F):

     !----------------------------------------
     ! VARIABLE: IRI
     !----------------------------------------

     ! Variable name
     v_name = "IRI"

     ! Read IRI from file
     st1d   = (/ 1         /)
     ct1d   = (/ NDRYDTYPE /)
     CALL NcRd( IRI, fId, TRIM(v_name), st1d, ct1d )

     ! Read the IRI:units attribute
     a_name = "units"
     CALL NcGet_Var_Attributes( fId,TRIM(v_name),TRIM(a_name),a_val )

     ! If using Olson 2001 land map, replace IRI for coniferous forests
     ! with IRI for deciduous forests (skim, mps, 2/3/14)
     IF ( USE_OLSON_2001 ) THEN
        IRI(3) = 200
     ENDIF

     ! Echo info to stdout
     IF ( am_I_Root ) THEN
        WRITE( 6, 130 ) TRIM(v_name), TRIM(a_val)
     ENDIF

Updates to facilitate grid-independent operation

This update was tested in the 1-month benchmark simulation v9-01-03jand approved on 17 Apr 2012.

A number of structural updates were made to the dry deposition routines in order to remove bottlenecks that would have prevented grid-independent functionality. These include:

1. Introduction of a new module to read Olson land map data from native resolution and to regrid to the currently-selected model resolution. The regridding is done in such a way so as to preserve backwards compatibility and to populate the existing arrays (IREG, ILAND, IUSE, FRCLND) in the same manner as before.
2. Introduction of a new module to read MODIS LAI data from native resolution and regrid to the current resolution in a consistent manner.
3. Removal of obsolete variables:
   1. From Headers/CMN_VEL_mod.F: IJREG, IJUSE, IJLAND
   2. From GeosCore/drydep_mod.F: NNNTYPE, NNNVEGTYPE
4. Replacement of obsolete ASCII input files with netCDF files.

--Bob Y. 15:35, 17 December 2012 (EST)

Update dry deposition to use local surface pressure

This update was tested in the 1-month benchmark simulation v9-01-03d and approved on 12 Jan 2012.

Lyatt Jaeglé wrote:

The only difference comes from the pressure value (PRESS variable) used in the dry deposition code to calculate the diffusivity of a molecule in air. Pressure comes into play in the mean free path calculation in DIFFG. For some reason the pressure was set at a constant value of 1500hPa (I do not know why this value was chosen in the first place, any ideas?). When I was going over the dry deposition code for sea salt I had replaced this fixed value with local sea level pressure (SLP). I think that it makes sense to use the actual local pressure instead of this fixed value. The overall effect is small.

--Melissa Payer 11:19, 11 January 2012 (EST)

Aerosol dry deposition velocities over snow and ice surfaces

This update was tested in the 1-month benchmark simulation v9-01-02i and approved on 15 Aug 2011.

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. [1983]; Duan et al. [1988]; Nilsson and Rannik [2001]). In GEOS-Chem v9-01-02 we have imposed a dry deposition velocity of 0.03 cm/s for all aerosols over snow and ice surfaces.

This update affects the following aerosol tracers: SO4s, NITs, DST1, DST2, DST3, DST4, SALA, SALC.

References

1. 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
2. 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.
3. Brutsaert, W., Evaporation into the Atmosphere, Reidel, 1982.
4. Businger, J.A., et al., Flux-profile relationships in the atmospheric surface layer, J. Atmos. Sci., 28, 181-189, 1971.
5. 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
6. Corbitt, E. S., How does the current implementation of dry deposition work in GEOS-Chem?, Graduate Student Forum Talk, 20 Oct 2011. PDF
7. Duan, B., Fairall, C.W., and Thomson, D.W., Eddy correlation measurements of the dry deposition of particles in wintertime, J. Appl. Met., 27, 642-652, 1988.
8. Dwight, H.B., Tables of integrals and other mathematical data, MacMillan, 1957.
9. 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.
10. 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.
11. 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.
12. Gerber, H. E. (1985), Relative-humidity parameterization of the Navy aerosol model (NAM), NRL Rep. 8956, Natl. Res. Lab., Washington, D. C., 1985.
13. Guenther, A., et al, A global model of natural volatile organic compound emissions, J. Geophys. Res., 100, 8873-8892, 1995.
14. Hicks, B.B., and P.S. Liss, Transfer of SO2 and other reactive gases across the air-sea interface, Tellus, 28, 348-354, 1976.
15. Ibrahim, M., Barrie, L.A., and Fanaki, F., An experimental and theoretical investigation of the dry deposition of particles to snow, pine trees, and artificial collectors, Atmos. Environ., 17, 781-788, 1983.
16. 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.
17. Jacob, D.J., et al, Deposition of ozone to tundra, J. Geophys. Res., 97, 16473-16479, 1992.
18. Jacob, D.J, et al, Summertime photochemistry of the troposphere at high northern latitudes, J. Geophys. Res., 98, 14,797-14,816, 1993.
19. 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.
20. Levine, I.N., Physical Chemistry, 3rd ed., McGraw-Hill, New York, 1988.
21. 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.
22. 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.
23. Nilsson, E.D. and Rannik, U. Turbulent aerosol fluxes over the Arctic Ocean: 1. Dry deposition over sea and pack ice, J. Geophys. Res, 106, 32,125-32,137, 2001.
24. 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
25. Pye, H. O. T., H. Liao, S. Wu, L. J. Mickley, D. J. Jacob, D. K. Henze, and J. H. Seinfeld (2009), Effect of changes in climate and emissions on future sulfate-nitrate-ammonium aerosol levels in the United States, J. Geophys. Res., 114(D1), D01205, doi:10.1029/2008JD010701.
26. 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.
27. 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
28. 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.
29. Wesely, M. L., Parameterization of surface resistance to gaseous dry deposition in regional-scale numerical models, Atmos. Environ., 23, 1293-1304, 1989.
30. 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.
31. Zhang, L. M., S. L. Gong, J. Padro, and L. Barrie (2001), A size-segregated particle dry deposition scheme for an atmospheric aerosol module, Atmos. Environ., 35(3), 549-560, doi:10.1016/s1352-2310(00)00326-5.

--Bob Y. 15:24, 19 February 2010 (EST)