Trend Analyses of the Abundances of Atmospheric Molecules

TREND ANALYSES OF THE ABUNDANCES OF ATMOSPHERIC MOLECULES Anton M. Fernando B.S. November 2011, University of Colombo, Sri Lanka M.S. May 2014, Old Dominion University Old Dominion University, 2020 Director: Dr. Peter Bernath A new linelist for the A3Π−X3Σ− electronic transition of NH has been prepared using line positions from the literature and calculated line intensities. High level ab initio calculations were performed with the MOLPRO program to obtain the A − X transition dipole moment function. Potential energy curves and line strengths were calculated with Le Roy’s RKR1 and LEVEL programs. Line intensities and Einstein A values were calculated with Western’s PGOPHER program after converting the Hund’s case (b) output of LEVEL to Hund’s case (a) input needed for PGOPHER. The HermanWallis effect is included in the Einstein A calculations of the bands for the levels with v′ = 0− 2 and v′′ = 0− 6. Spectra of pure isobutane were recorded at high temperature in the CH stretching region (2700-3100 cm) by high resolution Fourier transform spectroscopy. Isobutane absorption cross sections were determined for six temperatures from 273 K to 723 K. Integrated cross sections were compared with cross section data from the Pacific Northwest National Laboratory (PNNL) database. Near global ozone isotopologue distributions have been determined from infrared solar occultation measurements of the Atmospheric Chemistry Experiment (ACE) satellite mission. ACE measurements are made with a high resolution Fourier transform spectrometer (ACE-FTS). Annual and seasonal latitudinal fractionation (δ value) distributions of the ozone isotopologues OOO, OOO and OOO were obtained. Asymmetric ozone (OOO) shows higher fractionation compared to symmetric ozone (OOO). The maximum ozone fractionation occurs in the tropical stratosphere as expected from the contribution of photolysis to the enrichment of heavy isotopologues. An enhancement of the heavy ozone isotopologues is also seen in the upper stratosphere of the Antarctic polar vortex. A new version of ACE-FTS routine data product (4.0) provides near global VMR altitude profiles of low altitude CO2 on a 1 km grid from 5-18 km. An initial evaluation of these data has been carried out for the years 2004-2017 and for the month May in the 55◦-70◦S latitude range. The ACE-FTS data has been compared with ground-based measurements at Macquarie Island, the South Pole, the CarbonTracker 2017 model and G. Toon’s empirical model. Trends agree, but ACE-FTS data has a low bias at 5.5 and 6.5 km in altitude. The Montreal Protocol banned the production of major ozone depleting substances such as chlorofluorocarbons (CFCs) to protect the Earth’s ozone layer. These halogenated compounds are inert in the troposphere and ultimately converted to HCl in the upper atmosphere. Therefore, by measuring stratospheric HCl concentrations, the effectiveness of the Montreal Protocol can be evaluated. After banning the production of CFCs, the increased production and emissions of CFC-replacement hydrofluorocarbons (HFCs) has caused a dramatic increase in their atmospheric abundances. Although these HFCs do not contribute directly to the depletion of the ozone layer because they contain no chlorine, they are powerful greenhouse gases with large global warming potentials. In January 2019, the Kigali Amendment to the Montreal Protocol came into force to phase out long-lived HFCs. The two most abundant HFCs in the atmosphere, HFC-134a (CF3CH2F) and HFC-23 (CHF3), are measured from orbit by ACE-FTS. These measurements will be useful for monitoring the Kigali Amendment to the Montreal Protocol. A trend analysis of the ACE-FTS near-global measurements confirms the rapid increase in HFC-134a (4.9±0.1 ppt per year) and HFC-23 (0.75±0.02 ppt per year) volume mixing ratios (VMRs). A trend analysis has been carried out for HCl volume mixing ratio profiles provided by ACE-FTS as well; and the upper stratospheric HCl VMR time series of ACE-FTS shows a linear trend of -4.8±0.2%/decade for 2004-2017, highlighting the continuing success of the Montreal Protocol.