Investigating The Trace Gas Emissions Of Biomass Burning In The Earth System

This thesis focuses on the modelling and measurement of atmospheric carbon monoxide (CO) and hydrogen cyanide (HCN), two pyrogenic species used as tracers for biomass burning, the latter particularly for peat fires.

Uncertainties on the photochemical and ocean removal processes of HCN are investigated using a tracer version of the TOMCAT model. The model was validated using satellite Atmospheric Chemistry Experiment Fourier transform spectrometer (ACE-FTS) and ground-based Network for the Detection of Atmospheric Composition Change (NDACC) HCN measurements.

ACE-FTS observations confirm that the recommended NASA JPL HCN+OH reaction rate overestimates the loss. A better agreement is obtained using the rate coefficient for the OH and the O(1D) sink proposed by Kleinböhl et al. (2006). NDACC measurements are used to test the magnitude of two different ocean sink schemes (Li et al., 2003, 2000) which produce TOMCAT simulations very different to the NDACC observations. The agreement was improved by scaling these schemes.

The University of Leicester IASI Retrieval Scheme (ULIRS) is used to retrieve profiles of CO and, for the first time, HCN from atmospheric spectra recorded by the Infrared Atmospheric Sounding Interferometer (IASI). IASI measurements and TOMCAT simulations of CO and HCN are used to investigate the 2015 Indonesian peat fire emissions. It is found that emissions from the GFED database do not reproduce the measurements. A more reasonable agreement for HCN is obtained by scaling the September 2015 GFED emissions to 25%.

Using the INVICAT variational flux inversion model, optimized fluxes of CO and HCN are obtained by assimilating separately satellite observations from the IASI and MOPITT instruments during 2015. These show a considerable improvement relative to the prior. This inverse modelling approach represents a useful technique to improve emissions estimates and potentially the general understanding of fire processes.