Quantifying pyro-convective injection heights via obervation of fire energy emissions, and assessing the impact on forward and inversion modelling

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Biomass burning is a major dynamic of the Earth system, and the wildfires involved emit copious quantities of smoke made up of trace gases such as carbon monoxide and particulates such as black carbon. For some species, the total emissions from biomass burning represent amongst the largest single emissions source, but the spatial location of the individual fires and the exact amounts of species emitted are highly variable in both space and time. Use of satellite Earth Observation (EO) data are generally considered to be critical in providing the temporal coverage and spatial sampling necessary for an understanding of these highly variable emissions sources. Once aloft, air currents transport the smoke emissions, affecting their longevity, chemical conversion and fate. Chemical transport models (CTMs) are used to quantify these processes, but unlike all other emissions (except those from aircraft) fires may inject their smoke plumes into various heights in the troposphere and occasionally even lower stratosphere by virtue of the intense heat and convection produced by the burning fuel. Emissions remnants from certain tropical fires have been observed at 15 km altitude, and smoke plumes of individual Canadian stand-replacing forest fires can approach such heights. CTMs require an estimate of emissions injection height in order to correctly prescribe the interaction between the BB plumes and the global atmosphere, but at present there is very little information on this parameter since the 'standard' satellite-EO data on burned area and active fire 'hotspot' detections provides little relevant information. Because of this, CTM runs often assume a single fixed altitude for all BB emissions, usually presuming that all pollutants are contained solely within the lower troposphere or perhaps even the planetary boundary layer. This is clearly unrealistic since many wildfires can be seen capped by a large convective smoke plume rising to many km altitude, but because of a lack of satellite data and methods with which to better parameterise the actual injection height the topic has received far less attention than has estimation of the magnitude and variability of the emissions sources themselves. However, a number of recent key studies have determined the very serious implications that incorrectly prescribed emissions injection heights have for the ability of CTMs to correctly represent emissions transport and fate. Similar problems, causing a currently unknown degree of error, will affect 'top-down' emission estimates based on the inversion of observed atmospheric concentrations of BB species. Experiments have indicated that it is the energy released by a fire that drives the convective updraft responsible for the elevated injection of the smoke emissions. New satellite observations of the energy released by fires therefore offer an excellent opportunity to develop a testable model for pyrogenic injection heights that can be used to supplement current BB datasets on emissions source strength and location, by allowing information on injection altitude to also be derived and used in CTM runs and inversion studies. The aim of this proposal is therefore to develop and test a methodology for using satellite EO to greatly improve the current prescriptions of plume injection heights that are a mandatory field required to model biomass burning emissions in CTMs, and are necessary when inverting the chemistry and transport associated with BB trace gases to infer the magnitude and variability of emissions sources. A new model relating injection height and the vertical distribution of smoke constituents will be a key output from this research, along with a injection height 'climatology' database describing the frequency of elevated injections heights and their spatio-temporal variation across BB affected regions.