HR: 1340h
AN: A43A-0874 [Abstracts]
TI: Possible Excited NO2 Chemistry Has Potential to Increase Tropospheric Ozone 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:
Possible reaction of electronically excited NO2 (A, 2B1,2B2) with O2,
~~~~NO2 (A, 2B1,2B2) + O2 ~→ ~ NO + O3
~~~~~~~~~~~~~~~~~~~~~~~~~~~~ (R1)
has ~ potential to 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 tropospheric 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 λ = 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: 0300 ATMOSPHERIC COMPOSITION AND STRUCTURE
DE: 0345 Pollution: urban and regional (0305, 0478, 4251)
DE: 0365 Troposphere: composition and chemistry
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting