## 3.10. Application of a reaction mechanism

There are several reaction mechanisms, which describe chemical transformation occurring in the atmosphere. These can differ from each other depending on what type of detailed description is needed. One of these mechanisms is the CBM Leeds (Table 3.1, Heard et al., 1998), which describe the photochemical air pollution formation in the troposphere. Elementary reactions in the mechanism are either thermal or photochemical reactions. We can construct a set of ordinary differential equations (ODEs) from a reaction mechanism, which describes the temporal variation of chemical species. These ODEs can be solved by various numerical methods with appropriate initial conditions. Figures 3.4–3.11 show the variation of different compounds involved in the mechanism in winter and summer.

Table 3.1: CBM Leeds mechanism

 Reactions Reaction rate coefficients ( k i ) NO2 + hν → NO+O k1=1.45·10–2×exp(–0.4/ cosϕz) (R1) O + O2. M → O3 k2=1.4·103×exp(1175/ Tk) (R2) O3 + NO → NO2 k3=1.8·10–12×exp(–1370/ Tk) (R3) O + NO2 → NO k4=9.3×10–12 (R4) O3 + NO2 → NO3 k5=1.2·10–13×exp(–2450/ Tk) (R5) O3 + hν → O k6=7.865·10–4×exp(–0.4/ cosϕz) (R6) O3 + hν → O1D k7=2.0·10–4×exp(–1.4/ cosϕz) (R7) O1D (+M) → O k8=1.9·108×exp(390/ Tk) (R8) O1D + H2O → OH + OH k9=2.2·10–10 (R9) O3+HO2 → OH k10=1.4·10–14×exp(–580/ Tk) (R10) NO3 + hν → 0.89(NO2+O) + 0.11NO k11=4.91·10–1×exp(–0.4/ cosϕz) (R11) NO3 + NO → NO2 + NO2 k12=1.3·10–11×exp(250/ Tk) (R12) NO3 + NO2 (+M) → N2O5 k13=5.3·10–13×exp(256/ Tk) (R13) N2O5 + H2O → HNO3 + HNO3 k14=1.3·10–21 (R14) N2O5 + NO3 → NO2 k15=3.5·1014×exp(–10897/ Tk) (R15) NO + NO → NO2 + NO2 k16=1.8·10–20×exp(530/ Tk) (R16) OH + NO (+M) → HONO k17=4.5·10–13×exp(806/ Tk) (R17) HONO + hν → OH + NO k18=2.86·10–3×exp(–0.4/ cosϕz) (R18) OH + NO2 (+M) → HNO3 k19=1.0·10–12×exp(713/ Tk) (R19) HO2 + NO → OH + NO2 k20=3.7·10–12×exp(240/ Tk) (R20) HO2 + HO2 → H2O2 k21=5.9·10–14×exp(1150/ Tk) (R21) HO2 + HO2 + H2O → H2O2 k22=2.2·10–38×exp(5800/ Tk) (R22) OH + CO → HO2 k23=2.2·10–13 (R23) FORM + OH → HO2 + CO k24=1.0·10–11 (R24) FORM + hν → 2 HO2 + CO k25=5.40·10–5×exp(–0.79/ cosϕz) (R25) FORM + hν → CO k26=6.65·10–5×exp(–0.6/ cosϕz) (R26) ALD2 + OH → C2O3 k27=7.0·10–12 (R27) ALD2 + hν → MEO2 + HO2 + CO k28=1.35·10–5×exp(–0.94/ cosϕz) (R28) C2O3 + NO → NO2 + MEO2 k29=5.4·10–12×exp(250/ Tk) (R29) C2O3 + NO2 → PAN k30=8.0·10–20×exp(5500/ Tk) (R30) PAN → C2O3 + NO2 k31=9.4·1016×exp(–14000/ Tk) (R31) MEO2 + NO → FORM + HO2 + NO2 k32=4.2·10–12×exp(180/ Tk) (R32) MEO2 + C2O3 → MEO2 + FORM + HO2 k33=3.0·10–12 (R33) C2O3 + C2O3 → 2 MEO2 k34=2.5·10–12 (R34) MEO2 + HO2 → 0.77(FORM + HO2 + OH) k35=7.5·10–14×exp(1300/ Tk) (R35) C2O3 + HO2 → 0.79(MEO2 + OH) k36=6.5·10–12 (R36) OH → MEO2 k37=1.1·102×exp(–1710/ Tk) (R37) PAR + OH → –NO + 0.87 NO2 + 0.77 ROR + 0.1(HO2 + ALD2) k38=8.1·10–13 (R38) ROR → 1.1 ALD2 + 0.94 NO2 + 0.96 HO2 + 0.2(KET-NO-PAR) + 0.02 ROR k39=1.05·1015×exp(–8000/ Tk) (R39) ROR → KET + HO2 k40=1.6·103 (R40) KET + hν → C2O3 + 0.95(NO2 + HO2 + ALD2)-NO k41=4.35·10–6×exp(–0.4/ cosϕz) (R41) OH + OLE → MEO2 + ALD2 k42=5.2·10–12×exp(504/ Tk) (R42) O3 + OLE → 0.5 ALD2 + 0.52 FORM + 0.12 CO + 0.17 HO2 + 0.22 MEO2 + 0.1 OH k43=1.4·10–14×exp(–2105/ Tk) (R43) OH + ETH → –NO + NO2 + 1.56 FORM +HO2 + 0.22 ALD2 k44=2.0·10–12×exp(411/ Tk) (R44) O3 + ETH → FORM k45=1.25·10–14×exp(–2633/ Tk) (R45) OH + TOL → 0.08(–NO + NO2) + 0.36 CRES + 0.44 HO2 + 0.56 TO2 k46=2.13·10–12×exp(322/ Tk) (R46) TO2 + NO → 0.9(NO2 + OPEN+ HO2) k47=8.1·10–12 (R47) TO2 → HO2 + CRES k48=4.2 (R48) OH + CRES → 0.22 NO2 + 0.61 NO + 0.3 OPEN k49=4.1·10–11 (R49) NO3 + CRES → –NO2 k50=2.2·10–11 (R50) OH + XYL → 0.7 HO2 + 0.5 (–NO + NO2) + 0.2 CRES + 0.8 MGLY + 1.1 PAR + 0.3 TO2 k51=1.66·10–11×exp(116/ Tk) (R51) OH + OPEN → –NO + NO2 + C2O3 + 2(HO2 + CO) + FORM k52=3.0–11 (R52) OPEN + hν → C2O3 + CO + HO2 k53=4.88·10–4×exp(–0.79/ cosϕz) (R53) O3 + OPEN → 0.03 (–NO + NO2 + ALD2) + 0.62 C2O3 + 0.7(FORM + CO) + 0.08 OH + + 0.75 HO2 + 0.2 MGLY k54=5.43·10–17×exp(–500/ Tk) (R54) OH + MGLY → NO + NO2 + C2O3 k55=1.7·10–11 (R55) MGLY + hν → C2O3 + CO + HO2 k56=5.2·10–4×exp(–0.79/ cosϕz) (R56) O + ISOP → 0.49 HO2 + 0.44 ALD2 + 0.6 OLE + 0.25(–NO + NO2 + CO) + 0.15 KET + 0.45 PAR + 0.05(MEO2 + C2O3) K57=1.82·10–11 (R57) OH + ISOP → –NO + 0.87 (NO2 + HO2) + FORM + OLE) + 0.58 (KET + PAR) + 0.29 ALD2 k58=9.6·10–11 (R58) O3 + ISOP → FORM + 0.45 ALD2 + 0.65 OLE + 0.35 CO + 0.2(PAR+KET) k59=1.2·10–17 (R59)

Figure 3.4: Results of the numerical simulations using CBM Leeds mechanism – variation of ozone in summer and winter time

Figure 3.5: Results of the numerical simulations using CBM Leeds mechanism – variation of OH radical in summer and winter time

Figure 3.6: Results of the numerical simulations using CBM Leeds mechanism – variation of HO2 radical in summer and winter time.

Figure 3.7: Results of the numerical simulations using CBM Leeds mechanism – variation of TO2 species in summer and winter time.

Figure 3.8: Results of the numerical simulations using CBM Leeds mechanism – variation of NOx in summer time.

Figure 3.9: Results of the numerical simulations using CBM Leeds mechanism – variation of NOx in winter time.

Figure 3.10: Results of the numerical simulations using CBM Leeds mechanism – variation of TOL (toluene) species in summer and winter time.

Figure 3.11: Results of the numerical simulations using CBM Leeds mechanism – variation of XYL (xylol) species in summer and winter time.

References

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Heard A.C., Pilling M.J., and Tomlin A.S.. 1998. Mechanism reduction techniques applied to tropospheric chemistry In: Atmospheric Environment. 32. 1059-1073.

Jacob, D.J.. 1999. Introduction to Atmospheric Chemistry. Princeton University Press.

Mészáros E.. 1977. The Basics of Atmospheric Chemistry, (In Hungarian). Akadémiai Kiadó.

Pilling M.J. and Seakin P.W.. 1995. Reaction Kinetics (Oxford Science Publications). Oxford University Press, USA.

Seinfeld J.H. and Pandis S.N.. 2006. Atmospheric Chemistry and Physics: From Air Pollution to Climate Change. Wiley.