| The work presented in this dissertation comprises two major objectives. The first objective has been to carry out an investigation of the production of N2O from reactions of electronically and vibrationally excited atmospheric trace species with N2 (using tunable diode laser absorption spectroscopy as the N2O detection method). The second objective of this study has been to accurately investigate the kinetics of the important stratospheric reaction O(3P) + NO2 → O2 + NO (k1) (using the technique of laser flash photolysis-resonance fluorescence). Investigation of N2O production from the collisional deactivation of electronically excited NO 2 and OH by N2 and from the interaction of nascent O 3 with N2 have resulted in upper limit quantum yields which render all three processes as insignificant sources of atmospheric N 2O. The following expression adequately describes the observed temperature dependence of the rate coefficient for the reaction O(1D) + N2 + M → N2O + M (k2) in its third order low-pressure limit over the temperature range 220–324 K: k2,0(T) = (2.72 ± 0.08) × 10−36 (T/300)−(0.92 ± 0.37) cm6 molecule−2 s−1, where the uncertainties represent precision at the 2σ level. The accuracy of the reported rate coefficients is estimated to range from 30 to 40%. Preliminary calculations indicate that reaction 2 represents a source of about 0.2 Tg N2O per year to the atmosphere (i.e., about 1% of the currently estimated global source budget of N 2O). This is the first suggested mechanism that generates N2O photochemically in the atmosphere that is capable of explaining the altitude dependence of the N2O isotopic signature. The following Arrhenius expression adequately describes the observed temperature dependence of the rate coefficient for reaction 1: k1(T ) = (4.21 ± 0.25) × 10−12 exp{lcub}(273 ± 18)/T{rcub} cm3 molecule−1 s−1, where the uncertainties represent precision at the 2σ level. The accuracy of the reported values for k 1(T) is estimated to be ±6% over the entire temperature range investigated (221–425 K). Incorporation of our kinetics results for reaction 1 into models of stratospheric chemistry would lead to somewhat lower mid-stratospheric ozone levels than would be obtained using results of previous studies. |
