Dissertation

A novel mass spectrometer for atmospheric measurements & halocarbons during the caribic and sambba aircraft campaigns

Wisher, Adam

2015

Overview

Identification and monitoring of halocarbons in the atmosphere remains important for the purposes of regulation and prediction of stratospheric ozone depletion. Measurements of these and other compounds have created a demand for techniques that improve the number of atmospheric compounds analysable. A prototype time-of-flight gas chromatography-mass spectrometer (GCMS) was characterised for atmospheric measurements. Instrument performance was found to be at the lower end of expectations. A comparison to a quadrupole GC-MS indicated that the TOF GC-MS would be suitable for measurements in polluted environments. As part of this comparison, a number of halocarbons were analysed in London, U.K. as part of the ClearfLo campaign. HCFCs were found at higher concentration than their Northern Hemispheric (NH) baseline values. Furthermore, HFC-134a and HFC-227ea were almost double their NH baseline. CH2Cl2, C2Cl4 and C2HCl3 were encountered at high concentrations and sources of very short-lived bromomethanes (VSLB) were identified close to London. As part of the CARIBIC project, five VSLB were measured in the mid-latitude upper troposphere/ lower stratosphere and tropical troposphere. Higher mixing ratios were encountered over Southeast Asia, likely due to a locally longer CH2Br2 lifetime. Total bromine derived from these five VSLB is at the lower end of the quantity required to balance the stratospheric bromine budget. During the SAMBBA project, biomass burning and natural sources of COS, methyl halides and other halocarbons were assessed over Brazil. Methyl halide emissions from rainforest and savannah fires were quantified. The Cerrado savannah was found to be a strong source of COS. Regional biomass burning emission estimates indicate that this is an important region for emissions of these compounds. Terrestrial, natural sources of CH3Cl, CH3Br and CHCl3 were confirmed over the Amazon rainforest. Emissions from a localised source of CHCl3 were identified and wetlands or agricultural soil disturbance were hypothesised as a likely cause.

• Publisher: ProQuest Dissertations & Theses