Modelling mineral dust lifting and transport in GEM-AQ: Sensitivity studies and comparison with measurements.

摘要

As one of the major contributors to the global yearly aerosol production, mineral dust has a significant impact on the regional and global climate as well as air quality. A dust emission and deposition module, based on the work of Zender (2003) (Dust Entrainment and Deposition (DEAD) Model), is developed and implemented in the Canadian Global Environmental Multiscale Air Quality (GEM-AQ) (Kaminski et al., 2008) model.Dust removal processes including the dry and wet depositions are also integrated in our dust module in GEM-AQ. Dry deposition dominates in the dust source regions and can account for up to 50% of dust removal. Wet deposition is dominant in the regions located downwind of dust source areas, particularly over the ocean surface, and could be responsible for up to 80% of dust removal from the atmosphere. Global pictures for different seasons of 2001 illustrating the relative contributions of both deposition processes to the removal of dust particles are generated by GEM-AQ. Several regions of strong dry and wet deposition are identified and North America appears to be the region where dry and wet depositions play an equally important role in dust removal.Several ground-based measurements such as the AERONET and IMPROVE are also used in this study to evaluate the GEM-AQ performance in modeling dust activity. The historic dust storms that occurred in Eastern Asia and North America are simulated with the configurations of global variable resolution (GV) in GEM-AQ and the model yields promising results compared to measurements, being able to properly reproduce the magnitude of dust aerosol in the background as well as to capture the dates of peaks for those dust episodes at various observational sites. In addition, examination of dust vertical distribution in GEM-AQ reveals that dust particles can be vertically transported up to the tropopause in sub-tropical region between 30°5 and 30° N.1Tg =1012 gSensitivity tests for dust lifting mechanism are carried out in both a box model and the GEM-AQ model. It has been found that the particle size distribution in the parent soil plays also an important role in determining the dust emission. Dust source regions such as Northern Africa and Northern China respond to the parameterizations of dust emission scheme with different sensitivities in GEM-AQ. For the fist time, the input data for surface roughness length and particle size distribution, which are obtained by either field measurements or remote sensing techniques in the soils of the arid and semi-arid areas worldwide, are implemented and the different parameterizations of a dust emission scheme are suggested and applied into different dust source regions in a global scale for the GEM-AQ model. While compared to satellite measurements TOMS, the GEM-AQ model yields promising results in correctly detecting both the 'hot spots' and the relative strength of dust emissions for dust source areas. The total dust emission in 2001 is predicted by the GEM-AQ as 3.6x103 Tg1.