IT is well established that chlorine- and bromine-containing molecules are primarily responsible for stratospheric ozone depletion. Nitrogen oxides also participate in chemical cycles that lead to…

This is a $750,457.93 grant awarded by the National Aeronautics and Space Administration (NASA) to Harvard University for a research project focused on improving laboratory data and reducing uncertainties related to the kinetics and spectroscopy of reactions involving inorganic halogens and nitrogen oxides. The objective is to better understand atmospheric chemistry processes that impact stratospheric ozone depletion. The work involves conducting a series of experiments over a range of temperatures using techniques like broadband cavity-enhanced absorption spectroscopy. This research directly supports NASA's solicitation for laboratory studies on the atmospheric transformations of trace species involved in ozone chemistry. The project also aligns with the activities of the NASA Panel for Data Evaluation, of which the principal investigator is a member. The award does not have a set-aside designation.

IT is well established that chlorine- and bromine-containing molecules are primarily responsible for stratospheric ozone depletion. Nitrogen oxides also participate in chemical cycles that lead to catalytic destruction of ozone, as well as interact in coupled cycles with halogen and hydrogen radicals that serve to suppress ozone losses at high NOX levels. Given the atmospheric importance of reactions involving inorganic halogens and nitrogen oxides, accurate laboratory data for the kinetics and spectroscopy of these reactions are essential for minimizing the uncertainty in photochemical models, better interpreting the wealth of atmospheric field data already collected, and more accurately projecting future ozone changes. In the recent literature, several important recommended values in the JPL data evaluation pertaining to the kinetics and spectroscopy of reactions involving bromine, chlorine, and nitrogen oxides have been explicitly challenged or called out for further study. The focus of this proposal is to provide improved laboratory data on these and other reactions that have significant uncertainties in the latest JPL evaluation (JPL-15), specifically: the rate constant of the BRONO2 formation reaction (BRO+NO2+m), the absorption cross sections of BRONO2, the kinetics of CL atom reactions with O3 and no (along with CL+CH4 for reference), and the rate constant of the no+O3 reaction. Most notable is the approximate 100% uncertainty on the recommended rate constant for BRONO2 formation at cold temperatures in JPL-15. This, along with uncertainties in the BRONO2 absorption cross sections, directly impacts determinations of the total amount and partitioning of inorganic bromine in the stratosphere, as well as the abundance of very short-lived (VSL) bromine compounds. In this project, we will study the kinetics and spectroscopy of the reactions listed above in a series of experiments over a range of temperatures relevant to the atmosphere. The objective of the proposed work is to significantly reduce uncertainties in the rate constants and cross sections and employ new detection techniques and experimental methods. A primary detection method utilized here is broadband cavity-enhanced absorption spectroscopy (bbceas) in the UV-VIS spectral range, which provides a sensitive and selective method for detection of molecules in this study. Single pass and multi-pass absorption cells are also employed, and atomic resonance fluorescence is used for highly sensitive detection of halogen atoms. This proposal is directly responsive to NASA s solicitation for laboratory kinetic and photochemical studies over a range of earth s temperature and pressure that describe the atmospheric transformations of trace species involved in ozone chemistry. This proposal also supports the activities of the NASA panel for data evaluation, which is stated to be an area of particular interest, and the PI of the proposal is a member of the panel.