Results from peroxy radical measurements taken at two marine boundary layer sites (Mace Head and Weybourne) in 2002 are discussed. Previous peroxy radical measurements at Mace Head, Cape Grim and Weybourne are compared to the recent data to provide a broader picture of the oxidative capacity of the marine boundary layer. A seasonal comparison between summer and winter peroxy radical measurement at Weybourne reveals a peroxy radical diurnal cycle with a maximum at midday in summer, and a diurnal cycle with maxima during the night in winter. Winter peroxy radical levels were often as high as those during the day in summer. Care must be taken when calculating ozone-production values from peroxy radical data in winter, owing to the non-attainment of an NO-NO2 photostationary state. In winter, this could lead to an exaggeration in the calculation of ozone production. However, when the photostationary state was achieved, winter ozone production levels were often as high as in summer. Peroxy radical measurements at the NAMBLEX campaign at Mace Head provide insights into the photochemistry of the marine boundary layer, and a detailed picture of the effect of NOx and VOCs on peroxy radical and ozone production. Peroxy radicals were found to be linearly dependent on NOx, as well as VOC loading. Night-time peroxy radical formation was driven by a mixture of ozone-alkene and NO3-alkene reactions, with a strong dependence on NO3 when high NOx levels reach the site. Mace Head was seen to have a greater peroxy radical sensitivity to NOx and, subsequently, NOx influences ozone production more than at other marine boundary layer sites, leading to high ozone levels at the site during high NOx episodes.

In this thesis, atmospheric limb-emission spectra measured by two Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) instruments, the MIPAS balloon-borne version 2 (MIPAS-B2) and MIPAS on Envisat (MIPAS-E), have been used to successfully detect PAN in the UT by virtue of its characteristic infrared spectral signature for the first time.;This is achieved using new infrared laboratory reference cross-sections for PAN also obtained in this thesis. This spectral reference dataset represents improved room temperature cross-sections (<4% uncertainty at the 95% confidence level) for PAN in the spectral range 550-2200 cm -1 and the measurement of low temperature (down to 250 K) and nitrogen broadened (up to 300 mb) cross-sections appropriate to the UT for the first time.;Analysis of spectra measured by the MIPAS-B2 instrument over the Mediterranean Sea region in April 1998 and May 1999 has yielded PAN concentrations as high as 350 parts per trillion by volume (pptv) in the UT using an iterative spectral fitting and residual analysis method developed in this thesis.;The detection of PAN was also achieved using this method for spectra measured by the MIPAS-E instrument during April 2003 for the Mediterranean Sea and East China Sea regions. Back trajectories of airmasses observed by MIPAS-E indicate that very high PAN concentrations (up to 668 pptv) detected over the East China Seas may be indicative of pollution outflow from Asia. Limits of detection for PAN in the UT are estimated to be as low as 40 pptv.

In this thesis, measurements of tropospheric carbon monoxide (CO) obtained by the Measurements of Pollution in the Troposphere (MOPITT) instrument are investigated. The MOPITT instrument and measurement techniques are discussed, and recent results from the MOPITT validation campaign are presented.;MOPITT phase I retrieved CO profile measurements are compared to in situ data obtained during the ACTO campaign. These comparison suggest that MOPITT CO profiles may possess a positive bias throughout the troposphere. The results also demonstrate the need to take into account the effects of vertical resolution and the influence of the a priori on MOPITT retrieved profiles through the use of the retrieval averaging kernels.;Comparisons of MOPITT and TOMCAT model CO profiles are also presented. The results suggest that MOPITT profiles are biased high compared to the model, and that these biases vary greatly from location to location. Simulations conducted using MOPITT operational averaging kernels to investigate the ability of the MOPITT instrument to measure layer enhancements of CO are then discussed. It is shown that MOPITT is sensitive to layer enhancements, although it is not always possible to determine the altitude of such enhancements. The seasonal cycle in MOPITT CO profile data is derived and compared to that of six CMDL surface measuring sites. A method for detecting long range transport events with anomalous CO using a regional analysis, which achieves limited success, is presented. Finally, an investigation of the combined use of the differing sensitivity of MOPITT between day and night in order to gain extra vertical information from MOPITT data is discussed. This is the first such study of its kind and the results are encouraging. Analysis shows that by examining the difference between day and night MOPITT retrieved 'surface' data it is possible, in a number of regions and seasons, to obtain further information on the vertical structure of CO. The results are validated using the TOMCAT model to represent the 'real' atmosphere. Examinations of day-night differences in phase I MOPITT data suggest that it is possible to use these differences to identify CO source regions such as biomass burning and industrialised regions.

A three-dimensional (3-D) chemical transport model (CTM) has been used to study the tropospheric chemistry and troposphere-stratosphere transport of biogenic very short-lived species (VSLS). Calculations have been performed in order to quantify their contribution to stratospheric bromine loading and also the relative importance of the source gas injection (SGI) and product gas injection (PGI) pathways. Simulations with a chemistry-climate model (CCM) have also been performed to assess the impact of VSLS on stratospheric ozone (03) and how their transport to the stratosphere may respond to climate change. Five brominated VSLS were considered in this work; bromoform (CHBr3), dibromomethane (CH2Br2), dibromochloromethane (CHBr2Cl), bromodichloromethane (CHBrC12) and bromochloromethane (CH2BrCl). The CTM shows these gases contribute ~5 parts per trillion (pptv) of inorganic bromine (BryvSLS) to the stratosphere, representing ~25% of total stratospheric bromine in 2009. SGI accounts for between ~69-75% of this supply, with the remainder from PG!. The longest lived organic product gas (PG) from CHBr3 and CH2Br2 degradation is carbonyl dibromide (CBr20). Its tropospheric lifetime with respect to photolysis is ~7 days. It is unlikely that organic PGs make a significant contribution to the total PGI from VSLS. The CTM performs reasonably well in reproducing tropospheric VSLS observations from a number of aircraft campaigns. In the tropical tropopause layer (TTL), CH2Br2 is overestimated when vertical transport is diagnosed from the meteoro- logical analyses. An improved agreement is obtained when vertical transport is calculated using diabatic heating rates, resulting in slower transport through the TTL. CCM runs show during periods of background aerosol loading, the impact of BryvSLS on mid-latitude 03 is small. The impact is larger in polar regions, where BryvSLS enhances the BrO-ClO loss cycle, resulting in a reduction of up to ~15 Dobson units (DU) of the total 03 column over Antarctica. The CCM has also been used to diagnose the potential response of SGI to climate change. For 2000, the modelled SGI is ~1.7 pptv, lower than the CTM estimate but still in good agreement with observations. For 2100, the CCM estimate increases to ~1.9 and ~2.7 pptv when the model is forced with Intergovernmental Panel on Climate Change (IPCC) representative concentration pathways (RC Ps) 4.5 and 8.5, respectively. The increase is due to enhanced tropical deep convection, reducing transport time-scales in the upper troposphere, particularly over the tropical Western Pacific region.

Aerosol can provide a sink for gas-phase species though heterogeneous reactions. This thesis examines these heterogeneous reactions in the troposphere, with a focus on reactive uptake of N20S and H02. Model sensitivity to the rate of uptake of N20 (as manifest by γN20S ) is found to be highly regional and seasonal. Due to the impact of photolysis and the location of emissions (of NO x and aerosol), heterogeneous chemistry is generally a greater driver of chemistry for the northern extra-tropics. The northern extra-tropics show significant and enhanced sensitivity to γN20S at lower values of γN20S than other regions, as NOx loss through the heterogeneous reaction is limited by production of N03. While the northern extra-tropics are more sensitive to heterogeneous chemistry of N20s, the extended impact of 03 means uptake to aerosol in the tropics is also important. Available laboratory data on the uptake of H02 is used to create a new parameterisation for γH02, with composition, temperature and humidity influencing the value of γH02,, The calculated value is an order of magnitude lower than previously found. Though the global impact of H02 uptake is small, there are regionally significant changes. The model shows sensitivity to the product of this reaction. The impact of heterogeneous chemistry under different emission scenarios (1985 to 2005) is in- vestigated. The impact of heterogeneous uptake (of N20S and H02) on H02 and oxidants is remarkably similar between the years, whereas the impact on components of inorganic aerosol (SO2-4-, N+4, NO-3)) is very different, due to the impact of SO2-4- on aerosol thermodynamics .

In recent years it has been shown that the troposphere is affected by changes in the climate of the stratosphere as well as vice versa. Investigating the downward influence has implications for understanding not only past climate but also for predicting future climate. A simplified, Newtonian-forced general circulation model is used to investigate the impact of changes in the stratosphere on the tropospheric circulation. First the sensitivity of tropospheric climate, tropospheric climate variability and response to stratospheric forcing to the surface temperature relaxation timescale are investigated. Changes to this parameter are shown to have significant impact on the model’s climatology, influencing both the thermal structure of the lower troposphere and the position of the eddy driven mid-latitude jet. The change in mean tropospheric climate influences the annular variability, including its timescale. A strong relationship between this timescale and the magnitude of response to forcing is found, which is consistent with the fluctuation – dissipation theorem. The tropospheric response for both the surface parameter experiments and stratospheric temperature forcings is shown to be remarkably similar. This indicates that the same dynamical feedbacks are triggered, and thus resulting in the same annular mode-like response. Further, the impact of an improved representation of the stratosphere (in a model of greater vertical extent) and its effect on the response to a range of stratospheric heating perturbations is investigated. The extent of the heating perturbations, both in latitude and altitude, are shown to have a significant impact on the tropospheric response. These experiments further reveal an influence of the tropospheric eddy response back onto the stratospheric forcing region which modifies the direct stratospheric response to the heating. This suggests a strong two way coupling between the lower stratosphere and the tropospheric jets and storm track eddies.

L'ozone troposphérique (O3) est un gaz à effet de serre et un polluant atmosphérique majeur. Il est la source principale du radical hydroxyle OH, l'oxydant le plus important dans l'atmosphère, fortement réactif avec les composés organiques et inorganiques. Les concentrations globales d'ozone troposphérique ont augmenté considérablement depuis l'époque pré-industrielle en raison de l'accumulation des émissions anthropiques de précurseurs d'ozone. Mon travail de thèse consiste à étudier la variabilité spatiale et temporelle de l'ozone troposphérique aux échelles globale et régionale telle qu'elle est mesurée par le sondeur IASI (Infrared Atmospheric Sounding Interferometer). Deux instruments IASI ont été lancés à bord des satellites MetOp-A et MetOp-B en 2006 et 2012.La première partie de mon travail consiste en l'étude des mesures O3/IASI: sa sensibilité dans la troposphère, sa variabilité saisonnière et ses modes de transport. Le deuxième volet de mon travail de thèse repose sur des études ciblées. Celles-ci comprennent une première étude sur l'ozone, urbain et rural, et sa relation complexe avec le dioxide d'azote (NO2) mesuré depuis l'espace par GOME-2 (Global Ozone Monitoring Experiment) au-dessus de différentes villes de l'hémisphère nord. Une deuxième étude s'attache à expliquer la source des pics d'ozone observés en région méditerranéenne en été, en utilisant IASI et le modèle de chimie-transport WRF-Chem (Weather Research and Forecasting model coupled with Chemistry). Enfin, en utilisant ces deux jeux de données, je présente en troisième étude l'analyse de la mousson d'été en Asie de l'Est ainsi que son effet sur l'ozone troposphérique. / Tropospheric ozone (O3) is an important greenhouse gas and air pollutant. It is the primary source of the most important oxidant in the atmosphere, the hydroxyl radical OH, that is highly reactive with organic and inorganic compounds. Global tropospheric O3 concentrations have been rising considerably since pre-industrial times as a result of the increase in the anthropogenic emissions of O3 precursors. In this thesis, I will study the temporal and spatial variability of tropospheric O3 on a global and regional scale as measured by IASI (Infrared Atmospheric Sounding Interferometer). The IASI instruments have been launched on-board the MetOp-A and MetOp-B satellites in 2006 and 2012.I first discuss the IASI/O3 measurements, their sensitivity in the troposphere and their seasonal variation and transport processes. I then perform more detailed and focused studies. Those include studying the urban and rural O3 and its relationship with nitrogen dioxyde (NO2) measured from GOME (Global Ozone Monitoring Experiment) over different cities in the Northern Hemisphere; investigating the summertime tropospheric O3 maxima over the Mediterranean region using IASI and the WRF-Chem (Weather Research and Forecasting model coupled with Chemistry) data; and finally, using both satellite and model data, I present my analysis of the East Asian monsoon variability and its effect on the tropospheric O3 column.

Bibliography: leaves 163-172 / x, 173 leaves : ill ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, 1986