Articles | Volume 18, issue 16
Research article
20 Aug 2018
Research article |  | 20 Aug 2018

Wildfires as a source of airborne mineral dust – revisiting a conceptual model using large-eddy simulation (LES)

Robert Wagner, Michael Jähn, and Kerstin Schepanski

Abstract. Airborne mineral dust is a key player in the Earth system and shows manifold impacts on atmospheric properties such as the radiation budget and cloud microphysics. Investigations of smoke plumes originating from wildfires found significant fractions of mineral dust within these plumes – most likely raised by strong, turbulent fire-related winds. This study presents and revisits a conceptual model describing the emission of mineral dust particles during wildfires. This is achieved by means of high-resolution large-eddy simulation (LES), conducted with the All Scale Atmospheric Model (ASAM). The impact of (a) different fire properties representing idealized grassland and shrubland fires, (b) different ambient wind conditions modulated by the fire's energy flux, and (c) the wind's capability to mobilize mineral dust particles was investigated. Results from this study illustrate that the energy release of the fire leads to a significant increase in near-surface wind speed, which consequently enhances the dust uplift potential. This is in particular the case within the fire area where vegetation can be assumed to be widely removed and uncovered soil is prone to wind erosion. The dust uplift potential is very sensitive to fire properties, such as fire size, shape, and intensity, but also depends on the ambient wind velocity. Although measurements already showed the importance of wildfires for dust emissions, pyro-convection is so far neglected as a dust emission process in atmosphere–aerosol models. The results presented in this study can be seen as the first step towards a systematic parameterization representing the connection between typical fire properties and related dust emissions.

Short summary
Wildfires can disturb the lower tropospheric wind conditions and are able to mobilize and inject mineral dust particles into the atmosphere. This study presents a conceptual model of fire-driven dust emissions using large-eddy simulations and evaluates how efficiently wildfires are able to modify the near-surface winds. The results show that typical threshold velocities necessary for dust emission are frequently exceeded and wildfires should be considered a source of airborne mineral dust.
Final-revised paper