README_mech Chemical Mechanism Updates 20 Sep 2002 Arlene Fiore (amf@io.harvard.edu) Jennifer Logan (jal@io.harvard.edu) Bob Yantosca (bmy@io.harvard.edu) NOTE: The following information is also included at the top of the GEOS-CHEM chemical mechanism file "chem.dat". Updated for GEOS-CHEM version 4.27: =================================== NOTE: The large change in the methylchloroform lifetime occurs because OH has decreased due to updates to the chemical mechanism. The most important change is the faster rate constant for O(1D) + N2 as recommended by Ravishankara et al., 2002. amf 1/4/02 added near-IR photolysis of HNO4, J-value is 1e-5 s-1 according to Roehl et al., 2002. Change is hardwired in calcrate.f. this J-value is added to that previously calculated by fast-J for the photolysis reaction HNO4 -> HO2 + NO2. Note: this reaction is handled similarly to the O3 + hv -> 2OH reaction. It is flagged with a "B" in chem.dat, that is picked up by the variable NKHNO4 in the code. amf 1/3/02 changed pressure dependence (only N2 part) of JO3 -> 2OH in calcrate.f to be in accordance with the new rate constant for O(1D) + N2 recommended by Heard, personal communication, 2002. temperature dependence of this reaction remains unchanged. old: 1.8e-11exp(110/T) new: 2.14e-11exp(110/T) this corresponds to a room temperature rate constant of 3.1e-11 rather than the previous 2.6e-11. amf 1/2/02 changed yield of alkyl nitrates from isoprene oxidation to ~12% according to Sprengnether et al., 2002 ? up from 4% yield recommended by Chen et al., 1998. They claim Chen et al results could be systematically low due to GC method. They have ascertained that their results are not influenced by interferences from RO +NO2 or ROONO2 change occurs in fyrno3.f -> code was changed back to the algorithm used by Larry Horowitz that calculates the yield depending on temp & pressure. This results in a yield of 12-16% over the U.S., and 11-19% range from 52S to 52N. Updated for GEOS-CHEM version 4.25: =================================== README for mechanism update as recommended by tyndall et al: (amf, 8/2001) see end of file for additional reactions updated based on these new recommendations see also other readmes for what was done in previous (8/99) updates to model. Tyndall et al., Atmospheric Chemistry of small organic peroxy radicals, JGR 106, 12157-12182, june 16, 2001. ================================================================================ rxn # rxn old A tyndall A k(298) old Ea/R Tyndall Ea/R ================================================================================ 52 MO2 + HO2 3.8e-13 4.1e-13 5.2e-12 800 750 Add temperature dependence & second branch to this reaction as found by Elrod et al, 2001, "Direct Kinetics Study of the Temperature Dependence of the CH2O Branching Channel for the CH3O2 + HO2 Reaction" John Wiley & Sons, Inc. correspondence: elrod@hope.edu (Matthew) Beta = k7a/k7b where k7a = MO2+HO2 -> MP + O2 k7b = MO2+HO2 -> CH2O + H2O + O2 ln(beta) = 6.21 - 1160/T => beta = 498e-2 exp (-1160/T) beta -> CH2O production branch 1/beta -> MP branch : 1/beta = 2e-3 exp(1160/T) 53 MO2 + MO2 2.5e-13 9.5e-14 3.5e-13 190 390 Beta: temperature dependent branching ratio MO2+MO2 -> MOH + CH2O + O2 19. 26.2 -1130 -1130 MO2+MO2 -> 2CH2O+2HO2 .05 .04 1130 1130 51 MO2 + NO 3.0e-12 2.8e-12 7.7e-12 280 300 Nitrate path assumed not important here. tyndall recommends < .005 formation. x MO2 + NO2 forms methyl peroxynitrate, which is apparently thermally unstable 29 MO2 + O3 ADDED: MO2 + O3 -> CH2O + HO2 + 2O2 3.0e-16 1e-17 -1000 note: this reaction did not have any previous number - was arbitrarily assigned 29. 448 ETO2 + NO* 2.6e-12 2.7e-12 8.9e-12 365 350 note: our mechanism considers that there is a 0% yield of ethyl nitrate tyndall recommends a 1.4% yield. 485 ETO2 + HO2* 7.5e-13 7.4e-13 7.8e-12 700 700 x ETO2 + NO2 forms ethyl peroxynitrate: thermally unstable 490 MCO3 + HO2 4.5e-13 4.3e-13 1.4e-11 1000 1040 Beta: temperature dependent branching ratio MCO3+HO2 -> ACTA + O3 -- tyndall: average results from crawford & moortgat 330. 37. -1430 -660 MCO3+HO2 -> MAP + O2 .00303 .027 1430 660 716 MCO3 + MO2 new recommended branching ratios: ka/k = .9; kb/k = .1 new recommended k = 2e-12 exp (500/T) k(298)=1.1e-11 MCO3+MO2 -> CH2O+MO2+HO2 8.45E-13 1.8e-12 640 500 MCO3+MO2 -> ACTA + CH2O 4.55e-13 2.0e-13 640 500 715 MCO3 + MCO3** 2.9e-12 2.5e-12 1.4e-11 500 500 444 MCO3 + NO** 5.3e-12 8.1e-12 2.0e-11 360 270 442 MCO3 + NO2 k0 9.7e-29 8.5e-29 8.5e-29 5.6 6.5 kinf 9.3e-12 1.1e-11 1.1e-11 1.50 1.0 442 PAN decomp the Equilibrium (K) expression is used in chem.dat K 9e-29 9.3e-29 14000 14000 472 ATO2 + HO2 1.9e-13 8.6e-13 9.0e-12 1300 700 note: tyndall forms CH3C(O)CH2OOH -> this must split and go to MCO3 + MO2, which are the products in chem.dat ?? 478 ATO2 + MO2 9.7e-14 7.5e-13 4.0e-12 0 500 note:tyndall has 3 branches, which form MCO3+ CH2O +HO2 CH3C(O)CH2OH+ CH2O CH3C(O)CHO + CH3OH Branching ratios: k15a/k15 = .3; k15b/k15 = .2, k15c/k15 = .5 chem.dat: forms .4HO2 + .1 CH2O + .1 MCO3 + .4 MGLY + .25 MEK + .75 CH2O + .25MOH + .25 ROH + .5 HO2 new products: .3MCO3 + .3 CH2O + .3HO2 .2HAC + .2 CH2O .5 MGLY + .5 MOH 453 ATO2 + NO 2.7e-12 2.8e-12 8.0e-12 360 300 note: it says MGLY does not form, yet it's in our products list... products were: 0.960 NO2 0.770 HO2 0.190 CH2O 0.190 MCO3 0.040 R4N2 0.770 MGLY Keep the assumption of a 4% branching rate to alkyl nitrate formation - no recommendation is made in tyndall except that Sehested reported substantial yields of nitrate. Thus change to: 0.96 NOx + 0.96 CH2O + 0.96 MCO3 + .04 R4N2 (changed to this as of 8/20) ATO2 + NO2 forms acetonyl peroxynitrate which is much less stable than PAN, (weak OO-NO2 bond) and is not an imp NOy reservoir in the free trop. ------------------------------------------------------------------------------ ADDITIONAL REACTIONS THAT DEPEND ON THOSE UPDATED: *Species reacting with NO, HO2 at same rate as ETO2 + NO,HO2: (apply this rate to all higher peroxy radicals for which we do not have measured rates) 450 RO2 + NO 2.7e-12 2.7e-12 360 350 applies to: A3O2, PO2 453 RO2 + NO 2.7e-12 2.7e-12 360 350 applies to: R4O2,R4N1,KO2,RIO2,RIO1,IAO2,ISN1,VRO2,MRO2,MVN2,MAN2,B3O2, INO2,PRN1 486 RO2 + HO2 1.9e-13 7.4e-13 1300 700 applies to: A3O2,PO2 472 RO2 + HO2 1.9e-13 7.4e-13 1300 700 applies to: R4O2,R4N1,KO2,RIO2,RIO1,IAO2,ISN1,VRO2,MRO2,MVN2,MAN2,B3O2, INO2,PRN1 ** Species reacting with NO,MCO3,HO2 at same rate as MCO3 + NO,MCO3,HO2 RCO3,GCO3,MAO3,GLCO3 491 RCO3 + HO2 same as MCO3 + HO2 466 RCO3 + NO same as MCO3 + NO 722 RCO3 + MCO3 same as MCO3 + MCO3 OTHER REACTIONS THAT DEPEND ON THOSE UPDATED: 471 RO2 primary + MO2 old k = 6.85e-13 Following isa's notes (based on madronich & calvert) K(RO2+MO2) = 2*sqrt(k(MO2+MO2)*k(RO2+RO2)) k(RO2+RO2) = 2.5e-13 (isa - atkinson 97) k(MO2+MO2) = 3.5e-13 at 298K (tyndall recommendation) => new K(RO2 + MO2) = 5.92e-13 478 RO2 secondary + MO2 also following Isa's notes (see update.0899 in /r/terra/user/bnd/MECHANISM) old k = 9.7e-14 same calculation as in 471 but with k(RO2+RO2) = 5.00e-15 k(MO2+MO2) = 3.5e-13 => new K(RO2 secondary + MO2) = 8.37e-14 597 & 598 MCO3 + A3O2,PO2 (primary radicals) from isa - from villenave 98: k = 1e-11cm3 molec-1 at 298 use temperature dependence from MCO3 + MO2 (see above) Isa's method of determining branching ratios was from averaging the the branching ratios between radical & molecular channels for MCO3+MCO3 and RO2+RO2. Since these reactions proceed similarly to MCO3 + MO2, apply the new branching ratios for MCO3 + MO2, which are .9 radical, .1 molecular, and update the temperature dependence. Temperature dependence changed from exp(640/T) to exp(500/T) Keeping rate constant at 298K equal to 1e-11 means that A factor is 1.87e-12 So, for radical branch, .9*1.87e-12 -> 1.68e-12*exp(500/T) for molecular branch,.1*1.87e-12 -> 1.87e-13*exp(500/T) info for 597*598 also applies to 718&719, 720&721, 632&633: 718 & 719: MCO3 + RO2 R4O2,ATO2,KO2,RIO2,RIO1,IAO2,ISN1,VRO2,MRO2,B3O2,R4N1, MVN2,MAN2,INO2,PRN1 720 & 721: MCO3 + ETO2 632 & 633: RCO3 + MO2, GCO3+MO2, MAO3+MO2, GLCO3+MO2 ----------------------------------------------------------------------------- Update other PANs (PPN,PMN,GPAN,GLPAN) to the high pressure limit of MCO3 + MO2 as recommended by Atkinson 92. 464 old: 464 A 1 1.20E-11 9.00E-01 0 new: 464 A 1 1.10E-11 1.00E+00 0 RCO3 + NO2 -> PPN GCO3 + NO2 -> GPAN MAO3 + NO2 -> PMN GLCO3 +NO2 -> GLPAN 465 thermal decomposition reaction PPN,GPAN, GLPAN Take high pressure decomposition rate of PAN from Tyndall et al: 2.8e16 exp(-13580/T) 503 thermal decomposition of PMN -- same as 465.