Difference between revisions of "Sea salt aerosols"

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The GEOS-Chem sea salt simulation is in the process of being updated following [http://www.atmos-chem-phys.net/11/3137/2011/acp-11-3137-2011.html ''Jaegle et al.''<nowiki> [2011]</nowiki>]. The reference document for the GEOS-Chem sea salt simulation prior to version v9.xx.x is [http://acmg.seas.harvard.edu/publications/alexander2005.pdf ''Alexander et al'' <nowiki>[2005]</nowiki>].
 
The GEOS-Chem sea salt simulation is in the process of being updated following [http://www.atmos-chem-phys.net/11/3137/2011/acp-11-3137-2011.html ''Jaegle et al.''<nowiki> [2011]</nowiki>]. The reference document for the GEOS-Chem sea salt simulation prior to version v9.xx.x is [http://acmg.seas.harvard.edu/publications/alexander2005.pdf ''Alexander et al'' <nowiki>[2005]</nowiki>].
  
== Recent Updates to sea salt emissions and deposition ==
+
== Recent Updates to sea salt simulation ==
 +
=== SST dependent sea salt emissions ===
 +
=== Updates to sea salt deposition ===
 +
=== Updates to hygroscopic growth ===
  
 
== Prior Updates to sea salt emissions algorithm ==
 
== Prior Updates to sea salt emissions algorithm ==
 +
  
 
=== Updated hygroscopic growth factors ===
 
=== Updated hygroscopic growth factors ===

Revision as of 17:03, 24 May 2011

Overview

The GEOS-Chem sea salt simulation is in the process of being updated following Jaegle et al. [2011]. The reference document for the GEOS-Chem sea salt simulation prior to version v9.xx.x is Alexander et al [2005].

Recent Updates to sea salt simulation

SST dependent sea salt emissions

Updates to sea salt deposition

Updates to hygroscopic growth

Prior 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:
  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

  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

--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)