Carbon monoxide (CO) is present in the troposphere as a product of fossil fuel combustion, biomass burning and the oxidation of volatile hydrocarbons. It is the principal sink of the hydroxyl radical (OH), thereby affecting the concentrations of greenhouse gases such as CH4 and O3. Consequently, CO has an atmospheric lifetime of 1-3 months, making it a good tracer for studying the long range transport of pollution. Satellite observations present a valuable tool to investigate tropospheric CO. The Atmospheric InfraRed Sounder (AIRS), onboard the Aqua satellite, is sensitive to tropospheric CO in ~50 of its 2378 channels. This sensitivity to CO, combined with the daily global coverage provided by AIRS, makes AIRS a potentially useful instrument for observing CO sources and transport. An optimal estimation retrieval scheme has been developed for AIRS, to provide CO profiles from near-surface altitudes to 150 hPa. Through a validation study, using CO profiles from in-situ aircraft measurements, this retrieval scheme has been shown to provide CO observations with strong correlations to in situ measurements. Compared to the operational AIRS v4 CO product this retrieval scheme is shown to provide total column CO retrievals with a reduced bias relative to the in situ measurements (~ -10% to ~ -1%). In addition, the optimal estimation retrieval is shown to provide improved estimation and characterization of the retrieval errors. Further validation work has been carried out through comparison with the established CO observations from the MOPITT instrument, onboard the Terra satellite. Good agreement (correlation coefficient > 0.9, and bias < 1.0 ppbv) between the instruments is observed in the mid-troposphere. At this level, the optimal estimation scheme is shown to remove a positive bias of ~10 ppbv, relative to MOPITT, that is present in the AIRS v4 CO product. The AIRS instrument is also shown to be less sensitive to CO in the lower troposphere than MOPITT. AIRS is also demonstrated to provide fewer pieces of independent information about the vertical structure of CO at tropical latitudes, where higher thermal contrast increases the sensitivity of MOPITT. Through time series analysis, the capability of AIRS to detect seasonal trends in CO is demonstrated. The potential of AIRS to be used to track, both horizontal and vertical, CO transport is explored. AIRS is shown to be capable of tracking horizontal transport, and to have potential to track vertical transport when combined with another satellite sensor.

Stratosphere Troposphere exchange (STE) is important to study as it controls the chemical composition of the upper troposphere/lower stratosphere (UTLS) and thus the radiative balance of this region. STE also controls the transport of chemicals into the stratosphere which are vital to ozone depletion. The troposphere and the stratosphere have specific chemical characteristics and the transition region between these regions displays characteristics of both. Ozone and water vapour concentrations can be used as tracers for the characteristics of the troposphere and stratosphere. This thesis develops measures in tracer space, which allow the determination of the strength and depth of atmospheric mixing between the troposphere and the stratosphere in extratropical regions. The application of entropy as a measure of atmospheric mixing as introduced by Patmore and Toumi [2006], is improved in this study. This is a measure of how the ozone and water vapour mixing ratios vary as a result of mixing. An additional metric to give further information on the form of the mixing line in tracer space is also developed. This measure uses the ozone and water vapour mixing ratios at the boundaries of the transition region (BO3 and BH2O). This study uses data from ozonesondes and hygrometers, along with satellite data from the Atmospheric Infrared Sounder (AIRS). The ozone product from AIRS is also validated as part of this study. The entropy, BO3 and BH2O measures from this study, are successfully shown to detect regions of enhanced mixing in comparison studies. A key comparison shows that the measures developed in this study are able to produce comparable conclusions to higher resolution aircraft data, with regards to mixing. The separation of entropy, BO3 and BH2O, into different categories allows mixing processes to be assigned to some of the categories. Mixing is shown to have geographic preference, with some regions having significantly more mixing. Some categories have preference with regards to their location either poleward or equatorward of the jet stream. In addition, some information as to the direction of the vertical transport, whether stratosphere to troposphere or vice versa, is obtained.

Stratosphere Troposphere exchange (STE) is important to study as it controls the chemical composition of the upper troposphere/lower stratosphere (UTLS) and thus the radiative balance of this region. STE also controls the transport of chemicals into the stratosphere which are vital to ozone depletion. The troposphere and the stratosphere have specific chemical characteristics and the transition region between these regions displays characteristics of both. Ozone and water vapour concentrations can be used as tracers for the characteristics of the troposphere and stratosphere. This thesis develops measures in tracer space, which allow the determination of the strength and depth of atmospheric mixing between the troposphere and the stratosphere in extratropical regions. The application of entropy as a measure of atmospheric mixing as introduced by Patmore and Toumi [2006], is improved in this study. This is a measure of how the ozone and water vapour mixing ratios vary as a result of mixing. An additional metric to give further information on the form of the mixing line in tracer space is also developed. This measure uses the ozone and water vapour mixing ratios at the boundaries of the transition region (BO3 and BH2O). This study uses data from ozonesondes and hygrometers, along with satellite data from the Atmospheric Infrared Sounder (AIRS). The ozone product from AIRS is also validated as part of this study. The entropy, BO3 and BH2O measures from this study, are successfully shown to detect regions of enhanced mixing in comparison studies. A key comparison shows that the measures developed in this study are able to produce comparable conclusions to higher resolution aircraft data, with regards to mixing. The separation of entropy, BO3 and BH2O, into different categories allows mixing processes to be assigned to some of the categories. Mixing is shown to have geographic preference, with some regions having significantly more mixing. Some categories have preference with regards to their location either poleward or equatorward of the jet stream. In addition, some information as to the direction of the vertical transport, whether stratosphere to troposphere or vice versa, is obtained.

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