WMO Cloud Modeling Workshop - Case 5, Part 2

Part 2. A box model simulation. Part 2 is a simulation of simple sulfur oxidation with initial aerosol specified. The case is intended to examine predictions of bulk vs. size-resolved chemistry, including pH and modification of aerosol= size distributions.

Simulation.

For two of the simulations (1 and 2), please use the simple mechanism= shown below. For the optional simulations (3 and 4), you may use your own sulfur-oxidation mechanism.

Please run the following simulations:

1. Simple chemistry as listed here, multiple size bins= [Required]

2. Simple chemistry as listed here, one size bin at 10 micrometer diameter= [Required]

3. Any chemistry mechanism, multiple size bins= [Optional]

4. Any chemistry mechanism, one size bin at 10 micrometer diameter= [Optional]

Table 1. Mechanism

					k₂₉₈	-E/R
S(IV)	O₃	-->	S(VI)	k₀	2.4e+04
				k₁	3.7e+05	-5.53e+03
				k₂	1.5e+09	-5.28e+03
S(IV)	H₂O₂	-->	S(VI)	k₃	7.45e+07	-4.43e+03 =20
				k₄	13

Rate expressions are as follows:

[O₃(aq)](k₀[SO₂(aq= )] + k₁[HSO₃^-] + k₂[SO₃²^-])

k₃[H₂O₂(aq)][H⁺][HSO₃^-] / (1+ k₄[H⁺])

Reaction rates should be implemented as

k = k₂₉₈ exp [E/R (1/298 - 1/T)]

The units of k are liters(water) mole^-1 s^-1

Table 2. Equilibria

			K₂₉₈	- Delta H/R
O₃(g)	<-->	O₃(aq)	1.13e-02	2.54e+03
H₂O₂(g)	<-->	H₂O₂(aq)	7.45e+04	7.30e+03
HNO₃(g)	<-->	HNO₃(aq)	2.1e+05	See Table 4
CO₂(g)	<-->	CO₂(aq)	3.4e-02	2.44e+03
SO₂(g)	<-->	SO₂(aq)	1.23e+00	3.15e+03
<-->	NH₃(aq)	6.2e+01	4.11e+03

Equilibrium constants should be implemented as:

K_H = K₂₉₈ exp[- Delta H/R(1/T-1/298)]

Units are M atm^-1, where M = mol / L H₂O

Table 3. Accommodation Coefficients (Most of these have not been updated from Lelieveld and Crutzen, 1991; see Case 5, Part I).

O₃	5.3e-04
H₂O₂(g)	1.8e-02
HNO₃(g)	5.0e-02
CO₂(g)	5.0e-02
SO₂(g)	3.5e-02
NH₃(g)	5.0e-02

Table 4. Dissociation Constants

				K₂₉₈	- Delta H/R
H₂O₂(aq)	<-->	HO₂^-	H⁺	2.2e-12	-3.73e+03
CO₂(aq)	<-->	HCO₃^-	H⁺	4.3e-07	-1.00e+03
HCO₃^-	<-->	CO₃^2-	H⁺	4.68e-11	-1.76e+03
SO₂(aq)	<-->	HSO₃^-	H⁺	1.3e-02	1.96e+03
HSO₃^-	<-->	SO₃^2-	H⁺	6.6e-08	1.50e+03
NH₃(aq)	<-->	NH₄⁺	OH^-	1.7e-05	-4.50e+02
HNO₃(aq)	<-->	NO₃^-	H⁺	1.54e+01	*8.70e+03

* value for HNO₃(g) <--> NO₃^-+ H⁺

Dissociation constants should be implemented as:

K =3D K₂₉₈ exp[- Delta H/R(1/T-1/298)]

Units are M, where M =3D mol / L H₂O

Initial Conditions

Thermodynamic variables:

Parcel begins at altitude = 600 m, pressure = 950 mbar, temperature = 12 C = 285.2 K

Relative humidity, RH, is 95%, and aerosol initial water content is in equilibrium with this RH

Updraft velocity: 50 cm s^-1(treat as an adiabatic parcel)

Cloud base (RH=100%) is at 698 m

Cloud base temperature: 284.2 K

Cloud base pressure: 939 mbar

Cloud base density: 1.15e-03 g cm^-3

At 1200 m above cloud base, adiabatic cloud water mixing ratio = 2.17 g kg^-1

If you choose to run your own chemical mechanism for simulations 3 and 4, set the time of the run to noon for purposes of computing photolysis rates. Use the photolysis rates given for the box model simulation= (Part I of Case 5 for the cloud modeling workshop) where possible.

The concentrations given below are at the initial parcel T and P (P = 950 mbar), for conversion purposes.

Initial gas phase concentrations:

SO₂	200 pptv
NH₃	100 pptv
H₂O₂	500 pptv
Total= HNO₃	100 pptv
O₃	50 ppb (50,000= pptv)
CO₂	360 ppmv

Initial particulate mass concentration (ammonium bisulfate):

SO₄^2-	2 micrograms m^-³
NH₄⁺	0.375 micrograms m^-³

Initial dry aerosol number size distribution (monomodal):

D_g = 0.08 micrometer

Sigma_g = 2.0

N = 566 cm^-3

Particle density, Rho_p = 1.8 g cm^-3

The above are the parameters for a lognormal fit,= where

dN/dlnDp = N/[(2 PI)^0.5 ln Sigma_g] exp [-A/B]

A = (ln Dp ln D_g)²

B = 2 ln² Sigma_g

Total aerosol mass, M = (PI/6) Rho_p N = (D_g exp(1.5 ln²= Sigma_g))³

If you are running simulation (2) or (4) and need a single particle= size to initialize ion concentrations in the single drop size, please use= the mode diameter (0.08 micrometers).

Simulation

For each of the four suggested simulations:

Simulate particle microphysics and chemistry from cloud base to 1200 m above cloud base (40 minutes)

Report the requested results for in-cloud conditions (e.g.,= pH)

Evaporate water to report final gases and particulate masses (see= below)

Results

We request to have results in ASCII files (preferably columns). We hope= to show results from different groups on the same plot. Thus, if can= submit your results to us by July 15, 2000, then we will have time to do= these plots.

Report time-dependent results for pH, with time resolution no coarser than= 1 minute. For size-resolved models, report the LWC-weighted overall pH at each time.

Provide the following order of results:

Time (s)

overall pH

pH in bin 1

pH in bin 2

...

pH in bin N

For size-dependent models, also provide as functions of time, with the= same time resolution as used for pH, the size (drop diameter, Dd, in= microns) and LWC (in g water / kg air) in each bin, so the bin-dependent pH= may be interpreted:

Time (s)

Dd in bin 1

Dd in bin 2

...

Dd in bin N


Time (s)	LWC in bin 1	LWC in bin 2	...	LWC in bin N

You may provide the above information in three separate files if you= wish. Just be sure to label what the file contains.

Provide the following at the end of the simulation (40 min), evaporating= water or reporting=20total gas + aqueous concentrations:

Final SO₂, in pptv

Final H₂O₂, in pptv

Final O₃, in pptv

For particulate S(VI), particulate NH₄⁺, and particulate NO₃^-, tabulate the following at the end of the simulation, in units of micrograms m^-3 air:

Bin	Lower Dp (microns)	Upper Dp (microns)	S(VI), initial	S(VI), final
1	Dp_1,L	Dp_1,U
...	...	...	...	...
N	Dp_N,L	Dp_N,U

Bin	Lower Dp (microns)	Upper Dp (microns)	NH₄⁺, initial	NH₄⁺, final
1	Dp_1,L	Dp_1,U
...	...	...	...	...
N	Dp_N,L	Dp_N,U

Bin	Lower Dp (microns)	Upper Dp (microns)	NO₃^-, initial	NO₃^-, final
1	Dp_1,L	Dp_1,U
...	...	...	...	...
N	Dp_N,L	Dp_N,U