Difference between revisions of "Sea salt aerosols"
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Also see [http://acmg.seas.harvard.edu/geos/wiki_docs/emissions/BeckySeaSaltFixAnalyticalSolution.pdf this document by Becky Alexander] which describes the analytical solution in more detail. | Also see [http://acmg.seas.harvard.edu/geos/wiki_docs/emissions/BeckySeaSaltFixAnalyticalSolution.pdf this document by Becky Alexander] which describes the analytical solution in more detail. | ||
− | ''''' | + | '''''[mailto:t.d.fairlie@nasa.gov Duncan Fairlie] replied:''''' |
:Thanks for taking a look at this. I will look at your code corrections and integrate them into my dust code. | :Thanks for taking a look at this. I will look at your code corrections and integrate them into my dust code. |
Revision as of 18:55, 25 February 2010
Contents
Overview
The reference document for the GEOS-Chem sea salt simulation is Alexander et al [2005].
Updates to sea salt emissions algorithm
Updated hygroscopic growth factors
Becky Alexander recommends new hygroscopic growth factors for sea salt aerosols. For more information, please see her post on the discussion page.
Modification of size bins for coarse mode aerosols
Lyatt Jaeglé wrote:
- I think that we should change the dry size bins for the coarse mode aerosols in input.geos. Instead of using:
Online SEASALT AEROSOLS : T => SALA radius bin [um]: 0.1 0.5 => SALC radius bin [um]: 0.5 10.0
- we should use a smaller upper cut for the dry radius of the coarse mode aerosols (up to 4 microns dry size ==> 8-10 microns radius for wet sea salt).
Online SEASALT AEROSOLS : T => SALA radius bin [um]: 0.1 0.5 => SALC radius bin [um]: 0.5 4.0
- The first two changes lead to a factor of 2 decrease in total sea-salt emissions (from ~8000 Tg/yr to ~4300 Tg/yr using GEOS-4 winds for 2003 2x2.5). The last change leads to another reduction by 40% in emissions. However the total burden of sea-salt aerosols (~12.5 Tg) remains nearly unchanged compared to the old formulation (~13.7 Tg) because of the strong non-linearity of the dry deposition velocity at sizes > 2 microns. Indeed the lifetime of coarse mode sea-salt aerosols (0.5-4um vs 0.5-10um) increases by a factor of almost 3.
- Here is a summary of the changes:
- Old formulation in GEOS-Chem (2x2.5 GEOS-4 winds 2003)
0.1-0.5 um 0.5-10 um Total: 0.1-10 um Emissions (Tg/yr) 106 7865 7970 Dry deposition (Tg/yr) 4.7 5012 5016 Wet deposition (Tg/yr) 102 2859 2955 Burden (Tg) 0.73 13.01 13.74 Lifetime (hours) 60 14 15
- New formulation, includes the following changes:
- Changing BETHA from 1.0 to 2.0 (as described on the GEOS-Chem v8-02-04 wiki page)
- Changing LOG to LOG10 in the expression for sea salt base emissions (as described on GEOS-Chem v8-02-04 wiki page)
- Capping of the coarse sea salt aerosol bin size at 4um
0.1-0.5 um 0.5-4 um Total: 0.1-4 um Emissions (Tg/yr) 92 2633 2725 Dry deposition (Tg/yr) 4 689 693 Wet deposition (Tg/yr) 87 1944 2031 Burden (Tg) 0.63 11.92 12.55 Lifetime (hours) 60 40 40
- I am also including calculations for a 3rd bin size 4-10 microns
4-10 um Emissions (Tg/yr) 1544 Dry deposition (Tg/yr) 1156 Wet deposition (Tg/yr) 387 Burden (Tg) 1.6 Lifetime (hours) 9
- While these larger aerosols (4-10 microns dry size) add another 50% to the emissions, they only contribute to 12% of the burden because of their short lifetime. So if we want to stick to 2 size bins, I think that it's fine to neglect these larger aerosols and limit the upper cut of the coarse mode sea-salt aerosols to 4 microns.
- The overall sea-salt emissions ~3000 Tg/year is now similar to what other studies found when applying the Monahan formula: Monahan (1986), Spillane et al. (1986), Gong et al. (1998), Penner et al. (2001), etc... This is also within the range recommended by Lewis & Schwartz.
- I also tried the Gong (2003) formulation which leads to a factor of ~2 decrease in emissions of accumulation mode aerosols but little change to the coarse mode aerosols. I am in the process of evaluating the sea-salt formulation against comparisons to cruise sea-salt observations from PMEL and find that both Gong (2003) and Monahan tend to overestimate sea-salt emissions at the high wind speeds in mid-latitudes and underestimate emissions in subtropical warmer waters. I am working on updating the Gong formulation based on SST.
- Note that the optical properties currently used in the GEOS-Chem (jv_spec.dat) assume log-normal size distributions that lead to effective radii that are too large for coarse mode aerosols: ~9 microns at 50% RH! Based on observed sea-salt size distributions, this should be much smaller ~ 1-2 microns. This correction leads to larger AODs due to sea-salt. I think that Colette and Randall are working on updating jv_spec.dat and I will send them my recommendations.
--Bob Y. 10:56, 23 November 2009 (EST)
References
- 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
--Bob Y. 15:29, 19 February 2010 (EST)
Known issues
Double-substitution bug in routine GET_ALK
Becky Alexander wrote:
- The code in GET_ALK (in routine seasalt_mod.f) as it is now is wrong. I did a substitution twice by mistake, that should have been applied only once. This is calculated for both accumulation and coarse mode seasalt, for both SO2 and HNO3, so there are 4 places in the code that must be fixed.
- The correct code should be as follows:
!---------------------------------- ! SO2 uptake onto fine particles !---------------------------------- ! calculate gas-to-particle rate constant for uptake of ! SO2 onto fine sea-salt aerosols [Jacob, 2000] analytical solution CONST1 = 4.D0/(V*GAMMA_SO2) A1 = (RAD1/DG)+CONST1 B1 = (RAD2/DG)+CONST1 !----------------------------------------------------------------------------- ! Prior to 7/18/08: ! Becky Alexander's fix to remove double-substitution (bec, bmy, 7/18/08) ! Remove these lines: ! TERM1A = (((B1/DG)**2)+(2.0D0*CONST1*B1/DG)+(CONST1**2)) - ! & (((A1/DG)**2)+(2.0D0*CONST1*A1/DG)+(CONST1**2)) ! TERM2A = 2.D0*CONST1*(((B1/DG)+CONST1)-((A1/DG)+CONST1)) ! TERM3A = (CONST1**2)*(LOG((B1/DG)+CONST1) - ! & LOG((A1/DG)+CONST1)) ! KT1 = 4.D0*PI*N1*(DG**2)*(TERM1A - TERM2A + TERM3A) !----------------------------------------------------------------------------- TERM1A = ((B1**2)/2.0d0) - (((A1**2)/2.0d0) TERM2A = 2.D0*CONST1*(B1-A1) TERM3A = (CONST1**2)*LOG(B1/A1) KT1 = 4.D0*PI*N1*(DG**3)*(TERM1A - TERM2A + TERM3A) !---------------------------------- ! SO2 uptake onto coarse particles !---------------------------------- ! calculate gas-to-particle rate constant for uptake of ! SO2 onto coarse sea-salt aerosols [Jacob, 2000] analytical solution CONST2 = 4.D0/(V*GAMMA_SO2) A2 = (RAD2/DG)+CONST2 B2 = (RAD3/DG)+CONST2 !------------------------------------------------------------------------------ ! Prior to 7/18/08: ! Becky Alexander's fix to remove double-substitution (bec, bmy, 7/18/08) ! Remove these lines: ! TERM1B = (((B2/DG)**2)+(2.0D0*CONST2*B2/DG)+(CONST2**2)) - ! & (((A2/DG)**2)+(2.0D0*CONST2*A2/DG)+(CONST2**2)) ! TERM2B = 2.D0*CONST2*(((B2/DG)+CONST2)-((A2/DG)+CONST2)) ! TERM3B = (CONST2**2)*(LOG((B2/DG)+CONST2) - ! & LOG((A2/DG)+CONST2)) ! KT2 = 4.D0*PI*N2*(DG**2)*(TERM1B - TERM2B + TERM3B) !------------------------------------------------------------------------------ TERM1B = ((B2**2)/2.0d0) - (((A2**2)/2.0d0) TERM2B = 2.D0*CONST2*(B2-A2) TERM3B = (CONST2**2)*LOG(B2/A2) KT2 = 4.D0*PI*N2*(DG**3)*(TERM1B - TERM2B + TERM3B) KT = KT1 + KT2 !---------------------------------- ! HNO3 uptake onto fine particles !---------------------------------- ! calculate gas-to-particle rate constant for uptake of ! HNO3 onto fine sea-salt aerosols [Jacob, 2000] analytical solution CONST1N = 4.D0/(V*GAMMA_HNO3) A1N = (RAD1/DG)+CONST1N B1N = (RAD2/DG)+CONST1N !----------------------------------------------------------------------------- ! Prior to 7/18/08: ! Becky Alexander's fix to remove double-substitution (bec, bmy, 7/18/08) ! Remove these lines: ! TERM1AN = (((B1N/DG)**2)+(2.0D0*CONST1N*B1N/DG)+(CONST1N**2)) - ! & (((A1N/DG)**2)+(2.0D0*CONST1N*A1N/DG)+(CONST1N**2)) ! TERM2AN = 2.D0*CONST1N*(((B1N/DG)+CONST1N)-((A1N/DG)+CONST1N)) ! TERM3AN = (CONST1N**2)*(LOG((B1N/DG)+CONST1N) - ! & LOG((A1N/DG)+CONST1N)) ! KT1N = 4.D0*PI*N1*(DG**2)*(TERM1AN - TERM2AN + TERM3AN) !----------------------------------------------------------------------------- TERM1AN = ((B1N**2)/2.0d0) - (((A1N**2)/2.0d0) TERM2AN = 2.D0*CONST1N*(B1N-A1N) TERM3AN = (CONST1N**2)*LOG(B1N/A1N) KT1N = 4.D0*PI*N1*(DG**3)*(TERM1AN - TERM2AN + TERM3AN) !---------------------------------- ! HNO3 uptake onto coarse particles !---------------------------------- ! calculate gas-to-particle rate constant for uptake of ! HNO3 onto coarse sea-salt aerosols [Jacob, 2000] analytical solution CONST2N = 4.D0/(V*GAMMA_HNO3) A2N = (RAD2/DG)+CONST2N B2N = (RAD3/DG)+CONST2N !----------------------------------------------------------------------------- ! Prior to 7/18/08: ! Becky Alexander's fix to remove double-substitution (bec, bmy, 7/18/08) ! Remove these lines: ! TERM1BN = (((B2N/DG)**2)+(2.0D0*CONST2N*B2N/DG)+(CONST2N**2)) - ! & (((A2N/DG)**2)+(2.0D0*CONST2N*A2N/DG)+(CONST2N**2)) ! TERM2BN = 2.D0*CONST2N*(((B2N/DG)+CONST2N)-((A2N/DG)+CONST2N)) ! TERM3BN = (CONST2N**2)*(LOG((B2N/DG)+CONST2N) - ! & LOG((A2N/DG)+CONST2N)) ! KT2N = 4.D0*PI*N2*(DG**2)*(TERM1BN - TERM2BN + TERM3BN) !----------------------------------------------------------------------------- TERM1BN = ((B2N**2)/2.0d0) - (((A2N**2)/2.0d0) TERM2BN = 2.D0*CONST2N*(B2N-A2N) TERM3BN = (CONST2N**2)*LOG(B2N/A2N) KT2N = 4.D0*PI*N2*(DG**3)*(TERM1BN - TERM2BN + TERM3BN)
Please make the fix in your version, or you may download it from ftp://ftp.as.harvard.edu/pub/geos-chem/patches/v8-01-01/seasalt_mod.f_w_getalk_fix.
Also see this document by Becky Alexander which describes the analytical solution in more detail.
Duncan Fairlie replied:
- Thanks for taking a look at this. I will look at your code corrections and integrate them into my dust code.
- Since we're looking back at the analytical solution, I think the last line should read
Kt = 4.pi.N.D(cubed)[ ] ,
- the extra factor of D coming from
dr = D.dx,
- and the limits of the integral
( r=[a,b] )
- become
X = [a/D+c, b/D+c]
- I'll recheck my math, and look back at the code.....
NOTE: This fix was standardized into GEOS-Chem v8-01-02 and higher versions.
--Bob Y. 16:25, 22 February 2010 (EST)