Remote sensing of trace gases in the urban and marine boundary layers

The thesis investigates the application of Concurrent Multi-Axis Differential Optical Absorption Spectroscopy (CMAX-DOAS) for the retrieval of trace gases and aerosols with a particular focus on their spatial and temporal distributions within the urban and marine boundary layers. The CMAX-DOAS technique is a scattered light DOAS instrument with several concurrent viewing directions that is capable of measuring trace gas species and aerosol with fast temporal resolution but also large spatial scale information unlike current in situ techniques.;In the urban boundary layer, the capability of the CMAX-DOAS for the retrieval of aerosol optical depth (AOD) measurements has been quantified. Modelled O4 slant columns calculated using AODs retrieved by a lidar instrument deployed alongside the CMAX-DOAS, showed very good agreement (r=0.98) for cloud free measurements. However, retrieval for AOD from the current CMAX-DOAS was more limited.;CMAX-DOAS NO2 measurements in the urban boundary layer (UBL) have been used to provide a link between tropospheric NO2 columns measured by the satellite-based Ozone Monitoring Instrument (OMI) and measurements obtained near-surface. A FOV weighted algorithm has been developed and the agreement is very good between the satellite columns and near-surface NO2 for spring (r = 0.83) and summer (r = 0.64) months.;Finally, the thesis presents the first measurements of iodine monoxide (IO) in the mid-latitude marine boundary layer (MBL) by a MAX-DOAS instrument, the retrieval of bromine monoxide (BrO) has also been performed. The range of viewing geometries of the CMAX-DOAS instrument provides additional information about the spatial distribution of halogen oxides in a coastal MBL, which has previously not been documented.