# Large-Scale Modeling of Absorbing Aerosols and Their Semi-Direct Effects
## 3 Results  
### Absorbing Aerosol Distribution  
The focus of this work is on the simulated effects of the absorbing aerosol species BC and mineral dust. In the standard version, dust emissions computed for the average of the eight model years are 1530 Mt/yr, the global average dust burden is 16 Mt. Dust atmospheric lifetime is 3.9 days in the eight-year average. For BC the emissions are 8 Mt/yr in the BASE case, global average BC burden is 0.14 Mt, and BC atmospheric lifetime is 4.4 days. For the GFAS case the BC emission is 12 Mt/yr and the global burden is 0.25 Mt, which is 1.8 times higher than for the BASE case. Global average optical thickness at 550 nm is 0.089 overall, of which 0.026 is due to dust aerosol. BC average optical thickness is 0.0005, and average AAOD is 0.0027. For the 'high BC' GFAS case the global average AOD is 0.13, 0.0014 due to BC; AAOD is 0.0060 for this case. In comparison, [PERSON] et al. [3] specifies AOD 0.028, and BC AOD of 0.0015 for multi-model median values of anthropogenic aerosols. Dust and black carbon aerosols contribute to the absorption optical depth of the global aerosol distribution that is a measure of the absorption part of the aerosol extinction. Aerosol absorption leads to increases in atmospheric heating rates, which in turn causes changes in atmospheric stability and cloud cover. The seasonal distribution of the simulated AAOD at 550 nm (eight-year average) is compared to OMI AAOD retrievals at 500 nm (averaged for the years 2004-2010) in Figure 1. Observations of absorption aerosol optical thickness are obtained from the Ozone Monitoring Instrument (OMI) onboard the EOS-Aura satellite platform, which is part of the NASA A-Train satellite constellation [50]. The daily data product is available since 2004 for 355 nm, 388 nm and 500 nm at \(1^{\circ}\times 1^{\circ}\) resolution (dataset name: OMAERUVd, version 003, doi:10.5067/Aura/OMI/DATA3003). This product has e.g., been used to evaluate MERRA aerosol reanalysis fields [51]. Figure 1: (**Top four panels**) Seasonal average of the absorbing aerosol optical depth (AAOD) distribution at 550 nm from the 8-year average BASE simulation. (**Bottom four panels**) Seasonal average of the absorbing aerosol optical depth distribution from the OMI AAOD satellite product at 500 nm, averaged for 2004 to 2010. Both BC and mineral dust aerosol contribute to AAOD, which is reflected in the regional distributions of model results and observations. The aerosol absorption efficiency is considerably higher for BC than for dust aerosol. However, dust optical thicknesses are overall higher, exceeding the BC AOD by a factor 50 in the global average in the model results. Maximum values above 1.0 in the monthly mean dust AOD are also high compared to BC optical thickness values, for which maximum values always remain below 0.03 in the monthly mean. Maximum monthly mean AAOD values of 0.1 are reached in January in the model. The maximum seasonal AAODs in the northern hemisphere spring and summer seasons reflect the well-known seasonal maximum values in dust optical thickness in North Africa and in NH spring in Asia, in both model results and satellite data. The aerosol distribution in North Africa is characterized in particular by the natural mineral dust, which contributes more than 80% to the aerosol-optical thickness in the Sahara region. Although dust particles in the solar wavelength range absorb much less solar radiation than soot particles due to their optical properties, their high optical thickness, and extensive geographical coverage indicate that the influence of mineral dust on atmospheric heating rates cannot be neglected. There is also an overall agreement in the AAOD originating from biomass smoke the dry seasons in South America in NH summer (with values up to 0.025 in the model and 0.035 in the observations), and Sahel in NH winter, where AAOD values reach 0.05 in the model and 0.06 in the observations. Overall, model absorption underestimates the satellite product for the BASE case. For this case.