Trace gases in the atmosphere: Laser ionization of atmospherically relevant species, and the generation of chlorine dioxide (OClO), dichlorine oxide (Cl(2)O), and the asymmetric chlorine oxide dimer (ClClO(2)) by heterogeneous reactions of chlorine oxide

The detection and quantification of atmospheric species, specifically trace gases, is key to understanding both their formation and removal processes. Two important trace gases are NO and NO2, for which reliable detection techniques exist. However, these detection techniques do not generate independent signals for NO and NO2; the detection of NO2 generally requires its conversion to NO. The first topic covered is the development of a technique based on laser ionization mass spectrometry capable of generating independent signals for NO and NO2.; The chemistry of the stratospheric ozone layer, particularly radical-catalyzed ozone depletion cycles, has been a subject of research for nearly thirty years. The discovery of the Antarctic ozone hole brought attention to the chemistry of the chlorine radical. It has been determined that nearly 25% of ozone depletion in the Antarctic is due to a reaction of ClO and BrO, which produces Br and Cl radicals, and also OClO. This reaction is generally accepted as the only source of OClO in the stratosphere. However, modeled abundances of OClO are as much as 30% lower that measured abundances. Thus there is a missing source of OClO in current models. The second topic covered is the generation of OClO (and other chlorine oxides) from the reaction of ClO radicals with various surfaces.; The final topic covered is the application of picosecond laser pulses to the laser ionization of two atmospherically relevant species, methyl bromide and NO. There is much uncertainty in the current methyl bromide budget, as approximately 40% of methyl bromide sources are unknown. One problem could be the lack of a real-time measurement technique, as the detection of methyl bromide is laboratory bound. Methyl bromide possesses a dissociative first excited state, thus most laser excitation results in fragmentation of the parent methyl bromide molecule. Picosecond laser pulses have been demonstrated to ionize molecules through dissociative states, because the molecule absorbs a second photon before it can dissociate. Thus, picosecond laser pulses were applied to methyl bromide in an effort to develop a real-time detection technique.