Abstract
Abstract. A mineral dust module is developed and implemented into the global aerosol microphysics model, GISS-TOMAS. The model is evaluated against long-term measurements of dust surface mass concentrations and deposition fluxes. Predicted mass concentrations and deposition fluxes are in error on average by a factor of 3 and 5, respectively. The comparison shows that the model performs better near the dust source regions but underestimates surface concentrations and deposition fluxes in more remote regions. Including only sites with measured dust concentrations of at least 0.5 μg m−3, the model prediction agrees with observations to within a factor of 2. It was hypothesized that the lifetime of dust, 2.6 days in our base case, is too short and causes the underestimation in remote areas. However, a sensitivity simulation with smaller dust particles and increased lifetime, 3.7 days, does not significantly improve the comparison. These results suggest that the underestimation of mineral dust in remote areas may result from local factors/sources not well described by the global dust source function used here or the GCM meteorology. The effect of dust aerosols on CCN(0.2%) concentrations is negligible in most regions of the globe; however, CCN(0.2%) concentrations change decrease by 10–20% in dusty regions the impact of dust on CCN(0.2%) concentrations in dusty regions is very sensitive to the assumed size distribution of emissions. If emissions are predominantly in the coarse mode, CCN(0.2%) decreases in dusty regions up to 10–20% because dust competes for condensable H2SO4, reducing the condensational growth of ultrafine mode particles to CCN sizes. With significant fine mode emissions, however, CCN(0.2%) doubles in Saharan source regions because the direct emission of dust particles outweighs any microphysical feedbacks. The impact of dust on CCN concentrations active at various water supersaturations is also investigated. Below 0.1%, CCN concentrations increase significantly in dusty regions due to the presence of coarse dust particles. Above 0.2%, CCN concentrations show a similar behavior as CCN(0.2%).
Highlights
Atmospheric aerosols are important contributors to global climate change
The dust module developed in the TwO-Moment Aerosol Sectional (TOMAS) global microphysics model is evaluated against dust surface mass concentrations, deposition flux data, and mass size distributions
The TOMAS aerosol microphysics model has been incorporated previously into the GISS GCM and uses a moving sectional approach in which the boundaries between size bins are defined in terms of dry aerosol mass (Adams and Seinfeld, 2002)
Summary
Atmospheric aerosols are important contributors to global climate change They perturb the Earth’s energy balance by scattering or absorbing solar and terrestrial radiation, which are known as “direct effects” of aerosols. Mahowald et al, 1999; Mahowald and Luo, 2003) To understand these impacts of mineral dust, its global distribution must be understood and modeled. The purpose of this work is to develop a dust module to be incorporated into a global aerosol microphysics model and to evaluate it against available observations. The dust module developed in the TOMAS global microphysics model is evaluated against dust surface mass concentrations, deposition flux data, and mass size distributions.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
