GEOS-Chem chemistry mechanisms
On this page, we provide an overview of the chemistry mechanisms used in GEOS-Chem.
Overview of chemical mechanisms
The following table provides links to information about the available chemistry mechanisms in GEOS-Chem. Please contact the relevant GEOS-Chem Working Group for more information.
1The benchmark simulation is used for 1-month and 1-year benchmarks. It uses the Standard chemistry mechanism, but includes both the simple SOA and complex SOA species.
--Melissa Sulprizio (talk) 17:02, 22 February 2019 (UTC)
Chemistry updates
Updated isoprene and monoterpene chemistry
This update was included in v11-02c and approved on 21 Sep 2017.
Developers:
- Katie Travis (MIT, formerly Harvard)
- Jenny Fisher (U. Wollongong)
- Christopher Chan Miller (Smithsonian Astrophysical Observatory, formerly Harvard)
- Eloise Marais (U. Birminghan, formerly Harvard)
This document compiled by Katie Travis and Josh Cox describes the updated isoprene and monoterpene chemistry to be included in GEOS-Chem v11-02c (also see the list of modifications below). These updates include the monoterpene nitrate scheme and aqueous isoprene uptake and were originally implemented for simulation of the SEAC4RS data.
References
- Chan Miller, C., D.J.Jacob, E.A. Marais, K. Yu, K.R. Travis, P.S. Kim, J.A. Fisher, L. Zhu, G.M. Wolfe, F.N. Keutsch, J. Kaiser, K.-E. Min, S.S. Brown, R.A. Washenfelder, G. Gonzalez Abad, and K. Chance, Glyoxal yield from isoprene oxidation and relation to formaldehyde: chemical mechanism, constraints from SENEX aircraft observations, and interpretation of OMI satellite data, Atmos. Chem. Phys., 17, 8725-8738, https://doi.org/10.5194/acp-17-8725-2017, 2017. PDF
- Fisher, J.A., D.J. Jacob, K.R. Travis, P.S. Kim, E.A. Marais, C. Chan Miller, K. Yu, L. Zhu, R.M. Yantosca, M.P. Sulprizio, J. Mao, P.O. Wennberg, J.D. Crounse, A.P. Teng, T.B. Nguyen, J.M. St. Clair, R.C. Cohen, P. Romer, B.A. Nault, P.J. Wooldridge, J.L. Jimenez, P. Campuzano-Jost, D.A. Day, P.B. Shepson, F. Xiong, D.R. Blake, A.H. Goldstein, P.K. Misztal, T.F. Hanisco, G.M. Wolfe, T.B. Ryerson, A. Wisthaler, and T. Mikoviny. Organic nitrate chemistry and its implications for nitrogen budgets in an isoprene- and monoterpene-rich atmosphere: constraints from aircraft (SEAC4RS) and ground-based (SOAS) observations in the Southeast US. Atmos. Chem. Phys., 16, 2961-2990, 2016. PDF
- Marais, E. A., D. J. Jacob, J. L. Jimenez, P. Campuzano-Jost, D. A. Day, W. Hu, J. Krechmer, L. Zhu, P. S. Kim, C. C. Miller, J. A. Fisher, K. Travis, K. Yu, T. F. Hanisco, G. M. Wolfe, H. L. Arkinson, H. O. T. Pye, K. D. Froyd, J. Liao, V. F. McNeill, Aqueous-phase mechanism for secondary organic aerosol formation from isoprene: application to the southeast United States and co-benefit of SO2 emission controls, Atmos. Chem. Phys., 16, 1603-1618, 2016. PDF
- Travis, K. R., D. J. Jacob, J. A. Fisher, P. S. Kim, E. A. Marais, L. Zhu, K. Yu, C. C. Miller, R. M. Yantosca, M. P. Sulprizio, A. M. Thompson, P. O. Wennberg, J. D. Crounse, J. M. St. Clair, R. C. Cohen, J. L. Laughner, J. E. Dibb, S. R. Hall, K. Ullmann, G. M. Wolfe, J. A. Neuman, and X. Zhou, Why do models overestimate surface ozone in the Southeast United States, Atmos. Chem. Phys., 16, 13561-13577, doi:10.5194/acp-16-13561-2016, 2016. PDF, Supplement
--Melissa Sulprizio (talk) 18:06, 12 July 2017 (UTC)
Modifications to the original updates
The following modifications were made to the original updates listed in the above document following conversations with the developers. These modifications were included in v11-02c.
(1) Restore H2O2 Henry's law constant for wet deposition. Daniel Jacob wrote:
- For wetdep of H2O2 we should restore the old Henry’s law constant of 8.3E4exp[7400(1/T – 1/298)] because as Dylan points out that’s the physical value. For drydep of H2O2 we can keep the value of 5E7 as parameterized by Nguyen to fit his drydep data.
(2) HC187 is advected
(3) The following species have different names from the original document:
- API is now MTPA (for consistency with existing SOA scheme)
- APIO2 is now PIO2 (for consistency with PAN updates added in v11-02a)
- LIM is now LIMO (for consistency with existing SOA scheme)
- PMN is now NPMN and IPMN (PMN from non-isoprene and isoprene sources; from aqueous isoprene uptake updates)
- ONITAam is now IONITA (Jenny Fisher recommended we change the names - they were originally daytime/nighttime species, but changed to isop/monot)
- ONITApm is now MONITA (Jenny Fisher recommended we change the names - they were originally daytime/nighttime species, but changed to isop/monot)
(4) Fix typos in the original document
Orig: ISNOHOO + MO2 = 0.660PROPNN + 0.700GLYX + 1.200HO2 + 0.750CH2O + 0.040ISN1OG
Rate = 2.00e-13
v11-02c: ISNOHOO + MO2 = 0.660PROPNN + 0.700GLYX + 1.200HO2 + 0.750CH2O + 0.250MOH + 0.040ISN1OG
Rate = 2.06e-13
Orig: ISOPNB + OH = ISOPNBO2 + 0.100IEPOX + 0.100NO2
v11-02c: ISOPNB + OH = 0.900ISOPNBO2 + 0.100IEPOX + 0.100NO2
Orig: HONIT + OH = NO3 + HKET
v11-02c: HONIT + OH = NO3 + HAC
Orig: HONIT + hv = HKET + NO2
v11-02c: HONIT + hv = HAC + NO2
(5) Completely replace RIP with RIPA, RIPB, RIPD and IEPOX with IEPOXA, IEPOXB, IEPOXD
Orig: RIP + hv = 0.985OH + 0.985HO2 + 0.710CH2O + 0.425MVK + 0.285MACR + 0.275HC5 + 0.005LVOC v11-02c: RIPA + hv = 0.985OH + 0.985HO2 + 0.710CH2O + 0.425MVK + 0.285MACR + 0.275HC5 + 0.005LVOC RIPB + hv = 0.985OH + 0.985HO2 + 0.710CH2O + 0.425MVK + 0.285MACR + 0.275HC5 + 0.005LVOC RIPD + hv = 0.985OH + 0.985HO2 + 0.710CH2O + 0.425MVK + 0.285MACR + 0.275HC5 + 0.005LVOC Orig: ISOPND + OH = 0.100IEPOX + 0.900ISOPNDO2 +0.100NO2 v11-02c: ISOPND + OH = 0.100IEPOXD + 0.900ISOPNDO2 +0.100NO2 Orig: ISOPNB + OH = 0.900ISOPNBO2 + 0.100IEPOX + 0.100NO2 v11-02c: ISOPNB + OH = 0.900ISOPNBO2 + 0.067IEPOXA + 0.033IEPOXB + 0.100NO2 Orig: IEPOX = SOAIE : HET(ind_IEPOX,1); v11-02c: IEPOXA = SOAIE : HET(ind_IEPOXA,1); IEPOXB = SOAIE : HET(ind_IEPOXB,1); IEPOXD = SOAIE : HET(ind_IEPOXD,1);
(6) Add LVOC to RIP channels
Orig: RIPA + OH = 0.750 RIO2 + 0.250 HC5 + 0.125 (OH + H2O) v11-02c: RIPA + OH = 0.750 RIO2 + 0.245 HC5 + 0.125 (OH + H2O) + 0.005 LVOC Orig: RIPA + OH = 0.850 OH + 0.578 IEPOXA + 0.272 IEPOXB + 0.150 HC5OO v11-02c: RIPA + OH = 0.850 OH + 0.578 IEPOXA + 0.272 IEPOXB + 0.145 HC5OO + 0.005 LVOC Orig: RIPB + OH = 0.480 RIO2 + 0.520 HC5 + 0.26 (OH + H2O) v11-02c: RIPB + OH = 0.480 RIO2 + 0.515 HC5 + 0.26 (OH + H2O) + 0.005 LVOC Orig: RIPD + OH = 0.250 RIO2 + 0.750 HC5 + 0.375 (OH + H2O) v11-02c: RIPD + OH = 0.250 RIO2 + 0.745 HC5 + 0.375 (OH + H2O) + 0.005 LVOC Orig: RIPD + OH = 0.500 OH + 0.500 IEPOXD + 0.500 HC5OO v11-02c: RIPD + OH = 0.500 OH + 0.500 IEPOXD + 0.495 HC5OO + 0.005 LVOC The only reaction that wont have LVOC as a product is RIPB + OH = OH + IEPOXA + IEPOXB.
--Melissa Sulprizio (talk) 16:26, 7 September 2017 (UTC)
Stratospheric chemistry
GEOS-Chem was historically developed as a model of tropospheric chemistry and composition. The above-mentioned chemistry mechamisms in GEOS-Chem v9-01-03 and in GEOS-Chem v9-02 only solve the chemical reaction matrix within the troposphere. In order to prevent tropospheric species from accumulating in the stratosphere and being transported back into the troposphere, we have implemented the following simple stratospheric chemistry schemes:
- Linoz stratospheric ozone chemistry
- Application of monthly-mean prod/loss rates archived from the GMI model
Linoz only applied to ozone. The simple linearized stratospheric chemistry, which uses production and loss rates archived from the GMI model, is applied to all other species. (NOTE: The user has the option to disable Linoz and use the archived GMI prod/loss rates for ozone, but this is typically not done.)
In GEOS-Chem v10-01 we added the Unified tropospheric-stratospheric Chemistry eXtension (UCX) mechanism into GEOS-Chem. UCX was developed by Seb Eastham and Steven Barrett at the MIT Laboratory for Aviation and the Environment. This mechanism combines the existing GEOS-Chem "NOx-Ox-HC-aerosol" mechanism with several new stratospheric species and reactions.
--Bob Y. 12:11, 1 October 2013 (EDT)
--Melissa Sulprizio (talk) 17:18, 26 May 2015 (UTC)
Correcting ozone from the height of the lowest model level to 10m
This update is slated for inclusion in GEOS-Chem v11-02e.
Katie Travis created a diagnostic to correct daytime ozone values from the lowest model layer, ~60m, to 10m.
C(zC) = (1-Ra(z1,zC)vd(z1))C(z1) Eq. 1
where Ra(z1,zC) is the aerodynamic resistance between z1 and zC, and vd(z1) is the ozone deposition velocity at z1, and C(z1) is the ozone concentration at z1.
Ra(z1,zC) is calculated to the lowest model level in drydep_mod.F. We recalculate Ra using z1 = 10 m, which is the height of the CASTNET measurement for ozone. The new Ra is added to the diagnostic array AD_RA and passed to diag49.F for use in Equation 1.
This new diagnostic is called O3@10m-$, and can be called with tracer 539 in ND49 in input.geos.
References
- Travis, K.R., D.J. Jacob, C.A. Keller, S. Kuang, J. Lin, M.J. Newchurch, A.M. Thompson, Resolving ozone vertical gradients in air quality models, Atmos. Chem. Phys. Disc.,2017.
- Zhang, L., D.J. Jacob, E.M. Knipping, N. Kumar, J.W. Munger, C.C. Carouge, A. van Donkelaar, Y. Wang, and D. Chen, Nitrogen deposition to the United States: distribution, sources, and processes, Atmos. Chem. Phys., 12, 4,539-4,4554, 2012.
--Melissa Sulprizio (talk) 22:26, 17 November 2017 (UTC)
Analytical tools
Process analysis diagnostics
Barron Henderson (U. Florida) has created a software package for process analysis diagnostics. He writes:
Process-based Analysis examines the change in each species due to each process and reaction. Models predict atmospheric state, which in a time-series can be used to create net-change of each species. What this cannot tell us, is which processes led to that change. To supplement state (or concentration), GEOS-Chem has long archived emissions and employed advanced diagnostics to predict gross chemical production or loss. Process Analysis goes a step further archiving grid-cell budgets for each species, and decomposing gross production/loss into individual reaction contributions. Process Analysis extensions are currently available in CAMx, WRF-Chem, CMAQ, and now GEOS-Chem. This allows for direct comparisons of models at a fundamental, process level.
To obtain this software, please contact Barron Henderson directly.
--Bob Y. 12:26, 1 October 2013 (EDT)
Linking GEOS-Chem to CMAQ
Barron Henderson has created Python software that will let you translate GEOS-Chem output to the proper speciation for input to CMAQ. Please see our Linking GEOS-Chem to CMAQ wiki page for more information.
--Bob Y. (talk) 16:46, 26 October 2015 (UTC)
Previous issues that have now been resolved
Centralizing chemistry time step
This update was tested in the 1-month benchmark simulation v9-01-02q and approved on 18 Oct 2011.
Please see the full discussion on the Centralized chemistry time step wiki page.
--Bob Y. 16:01, 4 November 2011 (EDT)
Acetone photolysis
This discussion has been moved to our FAST-J photolysis mechanism wiki page.
--Bob Y. 15:20, 20 May 2014 (EDT)
Issues that have been since rendered obsolete by newer code updates
Most of the issues described below pertained to the SMVGEAR chemical solver (which was replaced by FlexChem in v11-01) and/or the FAST-J photolysis mechanism (which was replaced by FAST-JX in v10-01).
NIT should be converted to molec/cm3 in calcrate.F
SMVGEAR was removed from GEOS-Chem v11-01 and higher versions. The code in calcrate.F will be replaced by the KPP master equation file.
In calcrate.F, we have:
! Nitrate effect; reduce the gamma on nitrate by a
! factor of 10 (lzh, 10/25/2011)
IF ( N == 8 ) THEN
TMP1 = State_Chm%Tracers(IX,IY,IZ,IDTSO4) +
& State_Chm%Tracers(IX,IY,IZ,IDTNIT)
TMP2 = State_Chm%tracers(IX,IY,IZ,IDTNIT)
IF ( TMP1 .GT. 0.0 ) THEN
XSTKCF = XSTKCF * ( 1.0e+0_fp - 0.9e+0_fp
& *TMP2/TMP1 )
ENDIF
ENDIF
Here NIT is added to SO4 but NIT is in different units than SO4. This unit difference can be traced to the definition of IDTRMB, which is only nonzero for species that are in the SMVGEAR mechanism. Since NIT is not a SMVGEAR species, IDTRMB = 0 for NIT and it is therefore skipped in the unit conversion from kg --> molec/cm3 in partition.F.
This issue was discovered during the implementation of FlexChem. In GEOS-Chem v11-01g and later versions, units of NIT are properly accounted for in routine HETN2O5 (found in gckpp_HetRates.F90).
--Melissa Sulprizio (talk) 20:25, 12 September 2016 (UTC)
--Bob Yantosca (talk) 20:27, 31 January 2017 (UTC)
rate of HNO4
SMVGEAR was removed from GEOS-Chem v11-01 and higher versions. The globchem.dat file is now replaced by the KPP master equation file.
Ellie Browne found a typo in the globchem.dat (GEOS-Chem v8-02-01 and beyond)
A 73 9.52E-05 3.2E+00 -10900 1 P 0.60 0. 0.
1.38E+15 1.4E+00 -10900 0 0.00 0. 0.
HNO4 + M
=1.000HO2 +1.000NO2 + +
This should be corrected as:
A 73 9.52E-05 3.4E+00 -10900 1 P 0.60 0. 0.
1.38E+15 1.1E+00 -10900 0 0.00 0. 0.
HNO4 + M
=1.000HO2 +1.000NO2 + +
The difference is within 2%.
--J Mao. 19:04, 30 Aug 2010 (EDT)
--Bob Yantosca (talk) 20:29, 31 January 2017 (UTC)
near-IR photolysis of HNO4
This update was added to GEOS-Chem v8-02-04.
SMVGEAR was removed from GEOS-Chem v11-01 and higher versions. The globchem.dat file is now replaced by the KPP master equation file. Also, FAST-JX has now replaced FAST-J photolysis.
1. Since FastJX already takes this into account with cross section data at 574nm, we do not need to redo this in calcrate.f. We can therefore comment out this entire IF block:
!---------------------------------------------------------------------
! Prior to 10/27/09:
! FastJX has taken near-IR photolysis into account with
! cross section at 574nm, so we don't need to add 1e-5 anymore.
! According to Jimenez et al., "Quantum yields of OH, HO2 and
! NO3 in the UV photolysis of HO2NO2", PCCP, 2005, we also
! changed the branch ratio from 0.67(HO2)/0.33(OH) to 0.95/0.05
! This will put most weight of near-IR photolysis on HO2 channel.
! (jmao, bmy, 10/27/09)
!
!!==============================================================
!! HARDWIRE addition of 1e-5 s-1 photolysis rate to
!! HNO4 -> HO2+NO2 to account for HNO4 photolysis in near-IR --
!! see Roehl et al. 'Photodissociation of peroxynitric acid in
!! the near-IR', 2002. (amf, bmy, 1/7/02)
!!
!! Add NCS index to NKHNO4 for SMVGEAR II (gcc, bmy, 4/1/03)
!!==============================================================
!IF ( NKHNO4(NCS) > 0 ) THEN
!
! ! Put J(HNO4) in correct spot for SMVGEAR II
! PHOTVAL = NKHNO4(NCS) - NRATES(NCS)
! NKN = NKNPHOTRT(PHOTVAL,NCS)
!
! DO KLOOP=1,KTLOOP
! RRATE(KLOOP,NKN)=RRATE(KLOOP,NKN) + 1d-5
! ENDDO
!ENDIF
!---------------------------------------------------------------------
2. We need to change the branch ratio of HNO4 photolysis in ratj.d. Change these lines from:
13 HNO4 PHOTON OH NO3 0.00E+00 0.00 33.3 HO2NO2 14 HNO4 PHOTON HO2 NO2 0.00E+00 0.00 66.7 HO2NO2
to:
13 HNO4 PHOTON OH NO3 0.00E+00 0.00 5.0 HO2NO2 14 HNO4 PHOTON HO2 NO2 0.00E+00 0.00 95.0 HO2NO2
This is based on Jimenez et al. (Quantum yields of OH, HO2 and NO3 in the UV photolysis of HO2NO2, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 2005) shows that HO2 yield should be 0.95 and OH yield should be 0.05 for wavelength above 290nm.
This way all the near-IR photolysis will have most weight on HO2 channel(Stark et al., Overtone dissociation of peroxynitric acid (HO2NO2): Absorption cross sections and photolysis products, JOURNAL OF PHYSICAL CHEMISTRY A, 2008).
This update has now been added to the chemistry mechanism documentation file.
--J Mao. 11:00, 26 Oct 2009 (EDT)
--Bob Y. 16:08, 4 November 2011 (EDT)
yield of isoprene nitrates
This update was added to GEOS-Chem v8-03-02 as a post-release patch, and standardized in GEOS-Chem v9-01-01.
SMVGEAR was removed from GEOS-Chem v11-01 and higher versions. The globchem.dat file is now replaced by the KPP master equation file.
Fabien Paulot found a problem in current chemistry scheme. In GEOS-Chem v8-02-01 and beyond, isoprene nitrates are produced twice: one through channel A and one through 10% loss in channel B. This makes the loss of NOx larger than it should be (18.7% vs. 10%) and also reduces the yield of MVK/MACR/CH2O by about 13%.
A 453 2.70E-12 0.0E+00 350 1 B 0.00 0. 0.
5.00E+00 0.0E+00 0 0 0.00 0. 0.
RIO2 + NO
=0.900NO2 +0.900HO2 +0.340IALD +0.340MVK
+0.220MACR +0.560CH2O + +
A 453 2.70E-12 0.0E+00 350 1 A 0.00 0. 0.
5.00E+00 0.0E+00 0 0 0.00 0. 0.
RIO2 + NO
=1.000HNO3 + + +
So it should be corrected as (no channel A):
A 453 2.70E-12 0.0E+00 350 0 0 0.00 0. 0.
RIO2 + NO
=0.900NO2 +0.900HO2 +0.340IALD +0.340MVK
+0.220MACR +0.560CH2O + +
D 453 2.70E-12 0.0E+00 350 1 A 0.00 0. 0.
5.00E+00 0.0E+00 0 0 0.00 0. 0.
RIO2 + NO
=1.000HNO3 + + +
--J Mao. 18:04, 30 Aug 2010 (EDT)
--Bob Yantosca (talk) 20:31, 31 January 2017 (UTC)
Potential issue with reading restart.cspec file
This update was tested in the 1-month benchmark simulation v9-01-02c and approved on 21 Jul 2011.
The binary-punch format restart.cspec.YYYYMMDDhh file is slated to be replaced by a netCDF-format restart file, starting in GEOS-Chem v11-01 and higher versions. But during a transition period, you can still request binary-punch format output.
Jingqiu Mao discovered a mis-indexing problem when using the restart.cspec.YYYYMMDDhh file. Please see this wiki post for more information.
--Bob Y. 16:02, 4 November 2011 (EDT)
--Bob Yantosca (talk) 20:33, 31 January 2017 (UTC)
GLCO3, GLPAN bug in standard mechanism
This update was tested in the 1-month benchmark simulation v9-01-03a and approved on 08 Dec 2011.
SMVGEAR was removed from GEOS-Chem v11-01 and higher versions. The globchem.dat file is now replaced by the KPP master equation file.
Fabien Paulot wrote:
- I think there is a relatively serious bug in the standard chemistry. GLPAN and GLCO3 are set to inactive but their production and loss reactions are active. As a result they never reach equilibrium and this results in an artificial loss of NOx.
- If this is the only cause of the imbalance between sources and sinks of NOx in my simulations, this would account for ~5% of NOy losses. I don't see that problem in a simulation with a different chemistry that among other changes does not feature those reactions. So hopefully that's it.
- To fix the error, I made the following modifications in globchem.dat:
- I set GLPAN and GLCO3 rxns from active to dead. These rxns were causing an artificial loss of NOx.
- I have physically removed GLCO3, GLP, GLPAN, GPAN, ISNO3, MNO3, O2CH2OH, MVN2 and their associated reactions.
- I have made GLYX active. I'm not sure why it's not active by default.
- and to ratj.d:
- I deleted photolysis reactions for MNO3 and GLP, since these species have also now been deleted in globchem.dat
--Bob Y. 14:51, 10 November 2011 (EST)
--Melissa Payer 10:49, 15 December 2011 (EST)
--Bob Yantosca (talk) 20:35, 31 January 2017 (UTC)
Bug in routine ARSL1K
This update was tested in the 1-month benchmark simulation v9-01-03m and approved on 06 Jun 2012.
SMVGEAR was removed from GEOS-Chem v11-01 and higher versions. The ARSL1K routine was replaced by an equivalent function in KPP's rate law library.
A bug in routine ARSL1K became problematic in the implementation of Justin Parrella's tropospheric bromine chemistry mechanism for GEOS-Chem v9-01-03. In the bromine chemistry mechanism, a sticking coefficient of 0.0 is passed to the routine ARSL1K for non-sulfate, non-sea salt aerosol. The IF statement modified in GEOS-Chem v8-02-04 resulted in the reaction rate being set to the default value of 1.0d-3. A 1-month benchmark for July 2005 indicated that the simulated BrO was a little more than twice the expected zonal mean. Modifying the default value from 1.0d-3 to 1.0d-30 resulted in reasonable simulated BrO values.
Mat Evans wrote:
- I've re-run two 2 month simulation [using GEOS-Chem v9-01-02]. One with the error handling value of 1e-3 (standard) and one with it being 1e-30. There are 5127 time and space points where the model traps the problem and invokes the 1e-3 or 1e-30 value. There are 30*24*2*37*72*46 (roughly 200 million) time and space points when the error could have occurred so we are looking at a relatively infrequent event.
- The simulations show virtually no difference between the two simulations.
- mean and stddev ratio of all grid boxes with and without the fix are shown below
NOx 0.999996 0.000409291
Ox 1.00000 1.27233e-05
O3 1.00000 1.52284e-05
PAN 0.997849 0.0111997
CO 1.00000 4.21768e-06
ALK4 0.990514 0.0351941
ISOP 0.999979 0.0108033
H2O2 0.992067 0.0264659
DST1 1.00000 0.00000
HO2 0.999996 0.00309464
OH 1.00003 0.00767954
- So although there are some differences they are very minor. For completeness we should put this in as a bug fix (make the error value 1d-30 rather than 1d-3). But it is not a major problem.
--Melissa Payer 17:52, 14 May 2012 (EDT)
--Bob Yantosca (talk) 20:35, 31 January 2017 (UTC)