Studies of trace gases in the troposphere using broadband cavity enhanced absorption spectroscopy

The aim of this Ph.D. was to develop and deploy a broadband cavity enhanced absorption spectrometer for use in the field, to test the instrument in a variety of locations, and to contribute to the body of knowledge both on spectroscopic measurement techniques and on the chemical composition of the troposphere through analysis of datasets from both this instrument and others. The first ship-deployment of the cavity instrument provided challenging conditions but retrieved a detection limit for IO of 20 pptv over 10 min and measurements of NO2 with a detection limit of 0.9 ppbv over 10 min. Additional IO measurements were attempted at a coastal site thought to be a greater IO source but IO was not observed above the detection limit. The final deployment detailed here was for the measurement of the sum of NO3 and N2O3 concentrations on the BT tower at 160m above London. A highly variable, month-long dataset was obtained showing a strong diurnal cycle with very low daytime concentrations measured. The maximum night-time mixing ratio was approximately 800 pptv, with a limit of detection of 2 pptv over 15 s. The results from this campaign were compared with models to aid our understanding of nocturnal processes occurring in this region. It was found that night-time enhancements in NO3 and N2O5 often coincided with air masses containing little NO and moderate O3. Those of low turbulence also favoured the night-time enhancement. N2O3 was found to be very reactive and calculated lifetimes were short. Estimates of the heterogeneous uptake of N2O5 onto water suggest a small contribution of around 8 ppbv per night of HNO3 via this route.EThOS - Electronic Theses Online ServiceGBUnited Kingdo