Saturday, 16 July 2016

Dust Transport Model

The emission of dust or mineral dust has impact on the environment, climate, health, flora & fauna, wild life, vehicle transport visibility, and ocean biodiversity. The dust dispersion and transport is determined by atmospheric conditions. The dust transport scheme includes dust uplifting into the atmosphere, dust entrainment, atmospheric advection and mixing, and gravitational sedimentation.

A model can be designed that can include the dust dispersion, the dust plume transport mechanism, the adsorption of various gaseous and chemical materials on the dust particles and the fall out of the dust particles. Dust aerosol or dust particle modeling is essential for the knowledge of nutrient transport mechanism, land-use change, and ecosystem health. An efficient model can tell the amount and distribution of these dust particles where they are finally deposited and thus their harmful effects can be predicted. There are many pre-existing related models like, Dust Entrainment and Deposition (DEAD) model, Model of Atmospheric Chemistry and Transport (MATCH) and Chemical Transport Model (CTM). These models can be further explored and combined to form a new model that should be efficient in modeling the processes of dust uplifting, transportation and deposition. Long term data collection is a must for such model.


Many factors like wind friction speed, soil moisture content and vegetation cover are important for dust uplifting and dispersion model. The total vertical mass flux of dust is also required for calculating dust entrainment. The vegetation acts as a constraint and a sink to atmospheric momentum for significant dust plumes. The vegetation area index and stem/leaves index are essential to model this phenomenon. After being dispersed into the air and after their transport and adsorption processes, dust particles finally fall out due to condensation of water and other gases. These dust particles act as carriers of reactants while in the atmosphere. Dust particles mainly contain Al, Ca, Fe, K, Mg, Mn, Si, and Ti. The impacts of dust on the geochemical cycle can be found out by modeling the phenomenon of adsorption of the reactants into the dust particles. The physical-chemical properties of individual dust particles are essential for the model. The particles at last settle gravitationally at their terminal velocities. The drag coefficient and the slip correction factor are required for determination of this velocity. The effect of all these factors can be studied and included in the design of dust transport model.

When the source of dust is not properly characterized the dust transport modeling becomes tricky. The dust model can be improved when factors like land use, vegetation cover, soil composition, presence of micronutrients in mineral dust, presence of aerosols, sedimentation, and deposition (wet & dry) are properly incorporated into the model. If the data is collected fairly continuously with predetermined and close intervals, it can be comfortable extrapolated to large scale. The data should be collected from near source till to the deposition point at proper points and distances.  
Geographic information systems (GIS) and remote sensing (RS) can also be integrated into the model to further enhance the results. Using GIS and RS, the vastness of dust emission and the accurate hotspots and be identified and mapped accordingly.         

References:

1.      E. Khodabandehloo et al., “Spatiotemporal Modeling of Dust Storm Sources Emission in West Asia”, International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences (2013) Vol. XL-1/W3: 235-239. (WWW)

2.      Prof. Robert A. Duce and Prof. Peter Liss, “Workshop on Modelling and Observing the Impacts of Dust Transport/Deposition on Marine Productivity”, Sliema, Malta, 7-9 March 2011. (WWW)


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