HR: 15:00h
 AN: A23D-05    [Abstracts]
 TI: Potential Excited NO2 Chemistry Could Increase Tropospheric O3 Production Rates and Stratospheric NOX/NOY Ratio
 AU: * Prasad, S S
 EM: ssp@CreativeResearch.org
 AF: Creative Research Enterprises, 6354 Camino del Lago, Pleasanton, CA 94566, United States
AB: Potential reaction of electronically excited NO2 (A,2B1,2B2) with O2, NO2 (A, 2B1,2B2) + O2 → NO + O3 (R1) could increase the probability of NO2 reverting to NO while producing O3 and reduce the probability of being lost to the HNO3 reservoir. This would increase O3 production efficiency and the stratospheric NOX/NOY ratio. It is important to investigate this matter, since air pollution affects climate mostly through the radiative forcing of O3. The reaction NO2+O2 → NO+O3 is expected to occur with a rate coefficient of 5x10-12 exp(-50,550/RT) cm3 s-1, assuming reversibility of reaction holds for the well known reaction NO+O3 → NO2+O2 that occurs with a rate coefficient of 3x10-12 exp(-3,000/RT) cm3 s-1. In the atmosphere in local thermodynamic equilibrium (LTE), therefore, reaction of NO2 (X 2A1) with O2 would be totally insignificant. However, due to the presence of solar photons the atmosphere is not in LTE. Excited NO2 having internal electronic energy in excess of the 50.6 kcal mole-1 activation energy (due, for example, to the absorption of solar photons) could significantly react with O2, especially if it is in the non-dissociative state. The NO2(A, 2B1, 2B2) produced by NO2 (X 2A1) + hν (≤ 500 nm) can therefore drive the reaction (R1). Note that in reaction (R1) the excitation energy is in the reactant that transfers the O atom. Thus, the reaction is more likely than not. Data on the quenching of NO2 fluorescence by N2 and O2 [Myer et al., J. Chem.Phys., 44, 718, 1966] provide some support for the reaction (R1). In Myer et al. experiment fluorescence from electronically excited NO2(A, 2B1, 2B2) was produced by the absorption of &lamda; = 435.8 nm photons by NO2 (X 2A1). The N2 and O2 molecules quenched this fluorescence with rate constant of, respectively, 3.1 x 10-11 cm3 s-1 and 3.4 x 10-11 cm3 s-1. The quenching rate coefficient increases with the molecular complexity of the quencher (such as H2O a polar molecule with many degrees of freedom). However, the more efficient quenching by O2 relative to N2 (which are of comparable complexity) suggests a reactive channel in the case of O2. What fraction of the quenching by O2 is reactive cannot be deduced from the quenching data. However, the previous paragraph supports the conjecture k1 = 5.0 x 10-12 cm3 s-1. Assuming that the conjecture holds for excited NO2 produced by photons 400 ≤ λ ≤ 500 nm, the probability of the reaction (R1) is seen to be about 10% of the photodissociation. Details will be given in the presentation at the meeting. In summary, inclusion of the reaction pair (R1) could increase the O3 production efficiency and rate by about 10%.
DE: 0340 Middle atmosphere: composition and chemistry
 DE: 0365 Troposphere: composition and chemistry
 SC: Atmospheric Sciences [A]
 MN: 2007 Joint Assembly