Sea salt aerosols
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Revision as of 15:59, 23 November 2009 by Bmy (Talk | contribs) (→Modification of size bins for coarse mode aerosols)
Contents
Updates to sea salt emissions algorithm
= Updated hygroscopic
Please see the dis GEOS-Chem_v8-02-04#Updated_hygroscopic_growth_factors_for_sea-salt
Bug fixes in seasalt_mod.f
Please see [[this discussion
Modification of size bins for coarse mode aerosols
Lyatt Jaeglé (jaegle@atmos.washington.edu) 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)
Double-substitution bug in routine GET_ALK
Becky Alexander (beckya@u.washington.edu) 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 (t.d.fairlie@nasa.gov) 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 has been incorporated into GEOS-Chem v8-01-02.
--Bob Y. 16:15, 7 August 2008 (EDT)