Quantifying the impact of biomass burning and stratosphere-trposphere exchange on tropospheric ozone using Aura data and 3-D modelling.

This project used a chemical transport model, or CTM (GEOS-CHEM) to interpret data from the MLS instrument on the Aura satellite. The instrument measures a variety of chemical species in the stratosphere and upper troposphere; these include some (HCN, CO, CH3CN) which are produced by biomass burning.

Lots of plant material gets burned in many parts of the world, either by people or due to natural causes such as fires started by lightning. The resulting pollution contains a variety of chemicals and affects air quality in a variety of ways. Some of the chemicals produced can be detected from space by instruments on satellites. We used a computer program to understand some of the data from one such instrument.

It was known at the start of the project that HCN measurements in the tropical lower stratosphere form a globally averaged record of the surface emissions of HCN, which in turn are linked to biomass burning. This process was modelled using the CTM and it was demonstrated that the inter-annual variability in HCN was caused by variability in the biomass-burning source and not by variability in transport processes.
The "Black Saturday" fires in Australia occurred during the course of the project. The pollution from this event behaved in a very unusual way, reaching the stratosphere where MLS could observe it and track its transport for several weeks. The plume was observed to contain large amounts of CO and HCN, as expected. It was also demonstrated that the plume contained large enough amounts of methanol (CH3OH) to be detected by MLS.