Dust Deposition - Mineral Dust: A Key Player in the Earth System - page 193

micrometer aerosol size distribution. Based on the bias of the models, Huneeus
et al. ( 2011 ) suggest that the range of possible emissions for North Africa is 400-
2,200 Mt year 1 and 26-526 Mt year 1 for the Middle East, i.e., a factor of 5 and

20, respectively.
In conclusion, the relatively “good agreement” between simulated and observed
atmospheric dust load appears to be the result of the compensation of the uncertain-
ties associated with the different terms of the atmospheric dust cycle (as illustrated
by the huge differences in the simulated life times). This results mainly from the fact
that the dust load remains the only term of the mass budget reasonably constrained
by observations. Thus, one of the main conclusions of this intercomparison exercise
is the critical need for additional measurements to better constrain the mass budget
in dust models. Since at this time no quantitative techniques allow measurements
of dust emissions on a large scale, improving dust deposition modelling and
measurements should be a good way to better constrain the dust mass budget (see,
e.g., Han et al. 2008 ; Mahowald et al. 2005 ).

8.5 Conclusion

The dust mass budget is underconstrained in atmospheric dust models, leading
to large uncertainties in both dust emission and deposition. These uncertainties
strongly limit our capabilities to fully assess the radiative or biogeochemical impacts
of dust. A promising way to improve simulations of the dust cycle is to reinforce
research on deposition, both in terms of theoretical and numerical representation
of dry and wet processes in models and by developing a dense and standardized
dust deposition network in the vicinity of and far from source regions. This network
should operate continuously throughout the year since annual dust deposition can
be dominated by the sporadicity of dust events and the discontinuity of precipitation
involved in wet removal.

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