Satellite Limb Observations of Stratospheric NOx

The trace gases NO and NO2, collectively called NOx, are critical components of the stratosphere. NOx has become a key contributor to the destruction of the ozone layer since the Montreal Protocol of 1997 successfully reduced emissions of chlorine based ozone depleting substances. It is therefore important to monitor stratospheric NOx concentrations so that we can assess their impact on the ozone layer. The work in this thesis falls into two categories: improvements to the NO2 measurement record from satellite limb profiling instruments, and applications of the NO2 measurements to answer questions about the state of the atmosphere.\n\n An extended time series, spanning from 1984 to 2018, was created by combining observations from the Stratospheric Aerosol and Gas Experiment (SAGE) II with observations from the Optical Spectrograph and InfraRed Imager System (OSIRIS). \n These combined data were used to show that stratospheric NOx has been increasing at a rate of 10%/decade in the tropical lower stratosphere. The construction of the merged data illuminated some biases between the SAGE II and OSIRIS data. This led to the development of a scaling factor for the SAGE retrieval that accounts for changes in chemistry with the position of the sun. This scaling was applied to NO2 retrievals from SAGE III on the International Space Station (ISS). The result was a reduction in the bias between SAGE III/ISS and OSIRIS NO2 by up to 20% at altitudes below 30 km.\n Improvements to the spectral resolution fitting and cloud filtering in the OSIRIS NO2 retrieval were also made, resulting in improved agreement between NO2 observations from OSIRIS, SAGE III/ISS, and the Atmospheric Chemistry Experiment - Fourier Transform Spectrometer (ACE-FTS). These updated data were then used to show that smoke from large wildfires can enter the stratosphere and initiate a series of chemical reactions that can lead to ozone destruction. The NO2 observations were also used to show that the Asian summer monsoon (ASM) results in a NO2 minimum and a NOx maximum in the upper troposphere and lower stratosphere. This provides insight on the chemistry of the ASM that is important for evaluating the performance of chemistry-climate models in that region.

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