Mean OH concentration

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On this page we track the evolution of the mean OH concentration in GEOS-Chem. This value is an indicator of how "hot" the chemistry is. Please also see the related topic about the methyl chloroform lifetime in GEOS-Chem.

Computation of the mean OH diagnostic

The mean OH diagnostic in GEOS-Chem is computed in diag_pl_mod.f.

Routine DO_DIAG_OH sums up the tropospheric air mass and mass-weighted OH mass after each call to the chemistry solver. The summing happens in these lines of code:

  ! Sum air mass term into AIR_MASS array
  XAIRMASS        = AIRDENS(JLOOP)    * VOLUME(JLOOP)
  AIR_MASS(I,J,L) = AIR_MASS(I,J,L)   + XAIRMASS

  ! Sum OH mass term into OH_MASS array
  XOHMASS         = CSPEC(JLOOP,IDOH) * XAIRMASS
  OH_MASS(I,J,L)  = OH_MASS(I,J,L)    + XOHMASS

where the arrays contain the following quantities:

  JLOOP             = 1-D array index for SMVGEAR
  I,J,L             = 3-D array indices
  AIRDENS(JLOOP)    = air density [molec/cm3]
  VOLUME(JLOOP)     = grid box volume [cm3]
  AIR_MASS(I,J,L)   = air mass [molec air]
  CSPEC(JLOOP,IDOH) = OH concentration [molec OH/cm3]  
  OH_MASS(I,J,L)    = mass-weighted OH = OH mass * air mass [molec OH/cm3 * molec air]

After the GEOS-Chem simulation finishes, the mean OH value is printed out in subroutines PRINT_MEAN_OH:

  ! Total Mass-weighted OH [molec OH/cm3] * [molec air]
  SUM_OHMASS = SUM( OH_MASS )

  ! Atmospheric air mass [molec air]
  SUM_MASS   = SUM( AIR_MASS ) 
         
  ! Divide OH [molec OH/cm3 * molec air] by [molec air] and report as [1e5 molec/cm3]
  OHCONC = ( SUM_OHMASS / SUM_MASS ) / 1d5

  ! Write value to log file
  WRITE( 6, '(/,a)' ) REPEAT( '=', 79 ) 
  WRITE( 6, *       ) 'ND23: Mass-Weighted OH Concentration'
  WRITE( 6, *       ) 'Mean OH = ', OHCONC, ' [1e5 molec/cm3]' 
  WRITE( 6, '(  a)' ) REPEAT( '=', 79 ) 
        

Typical values vary between 105 - 115 molec/cm3.

--Bob Y. 15:12, 11 February 2010 (EST)

Evolution of mean OH in GEOS-Chem

Plot of mean OH evolution

Here is a plot of the mean OH concentration from several recent GEOS–Chem 1-year benchmark simulations. The mean OH is an indicator how the chemistry mechanism is performing. Typical values are 10–12 x 105 molecules cm-1.

GEOS-Chem-Mean OH.png

--Bob Y. 12:41, 17 January 2014 (EST)

Table of mean OH values

The following table chronicles the evolution of the mean OH value from several different GEOS-Chem simulations. All benchmark simulations were conducted at 4 x 5 resolution unless noted otherwise.

Benchmark Met Fields & Year Mean OH
[105 molec cm-3]
Change from
previous version
[105 molec cm-3]
Important updates in this benchmark simulation References
GEOS-Chem version 10
v10-01i-Run0 GEOS-FP 2013 11.125 0.033 (0.298%)
v10-01h-Run0 GEOS-FP 2013 11.092 -0.751 (-6.341%)
v10-01e-Run1 GEOS-FP 2013 11.843 -0.042 (-0.353%)
v10-01c-Run1 GEOS-FP 2013 11.885 -0.665 (-5.299%)
v10-01c-Run0 GEOS-FP 2013 12.550 -0.139 (-1.095%)
GEOS-Chem version 9
v9-02r-geosfp-Run1 GEOS-FP 2013 12.689 0.300 (2.421%)
v9-02r-geosfp-Run0 GEOS-FP 2013 12.389 -0.537 (-4.154%)


v9-02r-geos5-Run0 GEOS-5.1.0 2005 12.926 0.356
(2.832%)
v9-02l-Run0 GEOS-5.1.0 2005 12.570 0.332
(2.713%)
v9-02j-Run0 GEOS-5.1.0 2005 12.238 -0.234
(-1.876%)
v9-02g-Run0 GEOS-5.1.0 2005 12.472 0.969
(8.424%)
v9-02f-Run0 GEOS-5.1.0 2005 11.503 0.079
(0.692%)
v9-02b-Run0 GEOS-5.1.0 2005 11.424 0.068
(0.599%)
v9-01-03r-Run1 GEOS-5.1.0 2005 11.356 -0.502
(-4.233%)
v9-01-03r-Run0 GEOS-5.1.0 2005 11.858 -0.077
(-0.645%)
v9-01-03e-Run0 GEOS-5.1.0 2005 11.935 -0.397
(-3.219%)
v9-01-02-Run1 GEOS-5.1.0 2005 12.332 +0.099
(+0.809%)
v9-01-02-Run0 GEOS-5.1.0 2005 12.233 -0.009
(-0.074%)
v9-01-01-Run1 GEOS-5.1.0 2005 12.242 +0.377
(+3.177%)
v9-01-01-Run0 GEOS-5.1.0 2005 11.865 +0.798
(+7.2%)
GEOS-Chem version 8
v8-02-04-Run2 GEOS-5.1.0 2005 11.067 +0.019
(+0.17%)
  • Linoz stratospheric ozone chemistry used instead of SYNOZ scheme
v8-02-04-Run1 GEOS-5.1.0 2005 11.048 +0.598
(+5.72%)
  • MEGAN hybrid model with MODIS-derived LAI
v8-02-04-Run0 GEOS-5.1.0 2005 10.450 -1.362
(-11.53%)
  • MEGAN hybrid model with AVHRR-derived LAI
  • EPA/NEI2005 emissions
  • Non-local PBL mixing scheme
v8-02-01-Run0 GEOS-5.1.0 2005 11.812 +0.713
(+6.42%)
  • Updated chemical mechanism: globchem.dat
  • Updated photolysis rxn rates: jv_spec.dat, ratj.d
NOTE: there was a bug in near IR photolysis of HNO4 and HCHO in the jv_spec.dat and ratj.d files. This was finally resolved in v8-02-04. We recommend all users of v8-02-01, v8-02-02, and v8-02-03 to use these updated jv_spec.dat and ratj.d files.
v8-01-04-Run2 GEOS-5.1.0 2005 11.099 +0.805
(+7.82%)
v8-01-04-Run1 GEOS-5.0.1 2005 10.294 -0.395
(-3.69%)
  • Various emissions updates with regional overwrites
  • Aaron van Donkelaar et al scale factors for 2005
  • Switched from linear to random cloud overlap in FAST-J
v8-01-04-Run0 GEOS-5.0.1 2005 10.689 -1.351
(-11.22%)
v8-01-01-Run1 GEOS-5.0.1 2005 12.040 +0.034
(+0.28%)
  • Switched aerosol thermodynamical equilibrium scheme from ISORROPIA I to RPMARES
v8-01-01-Run0 GEOS-5.0.1 2005 12.006 -0.141
(-1.16%)
  • First simulation with GEOS-5 met data
GEOS-Chem version 7
v7-04-13-Run GEOS-4 2005 12.147 -0.669
(-5.22%)
v7-04-12-Run2 GEOS-4 2005 12.816 +1.053
(+8.95%)
  • Original non-near-land OTD/LIS local scaling
v7-04-12-Run1 GEOS-4 2005 11.763 -0.68
(-5.5%)
  • Ancient lightning scheme
v7-04-02-MEGAN GEOS-4 2001 12.44 -0.11
(-0.87%)
  • First benchmark w/ MEGAN biogenic emissions
v7-04-02-NOMEGAN GEOS-4 2001 12.55 +0.01
(+0.08%)
  • Switched fossil fuel scale year from 1995 to 1998
  • Last benchmark w/ the older GEIA biogenic emissions
v7-04-02-Base GEOS-4 2001 12.54 +0.67
(+5.6%)
  • 43 tracer simulation (no secondary organic aerosols)
  • Last 1-yr benchmark with fossil fuel scale year = 1995
v7-02-03-Run1 GEOS-4 2001 11.87 +1.39
(+13.26%)
  • Secondary organic aerosols (50 tracers)
  • GEOS-4 met fields
v7-02-03-Run0 GEOS-3 2001 10.48 ---
  • Secondary organic aerosols (50 tracers)
  • GEOS-3 met fields

--Bob Y. 12:13, 3 October 2013 (EDT)
--Melissa Sulprizio (talk) 21:23, 28 May 2015 (UTC)

Additional documentation

GEOS-Chem version 8

GEOS-Chem version 7

--Bob Y. 09:32, 23 February 2010 (EST)