Aerosol fields

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Figure 3.6 Spectral variations for single-scattering properties of total aerosol. Annual global fields for the column-integrated properties of extinction (AOD, left), single-scattering albedo (ffl0 center) and asymmetry factor (g, right) are presented at UV (380 nm), visible (550 nm), near-IR (1050 nm), and far-infrared (9750 nm) wavelengths.

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Figure 3.6 Spectral variations for single-scattering properties of total aerosol. Annual global fields for the column-integrated properties of extinction (AOD, left), single-scattering albedo (ffl0 center) and asymmetry factor (g, right) are presented at UV (380 nm), visible (550 nm), near-IR (1050 nm), and far-infrared (9750 nm) wavelengths.

serves as the basis: one uses current (year 2000) emissions while the other applies preindustrial (year 1750) emissions for primary aerosol and precursor gases (Dentener et al. 2006). As these emission inventories were processed using different global models, it was assumed that anthropogenic aerosols only populated the smaller accumulation sizes as a result of added sulfate and carbonaceous particles. Anthropogenic dust, which may have enhanced the coarse size concentrations because of changes in land use, was neglected. Thus, an anthropogenic fraction was defined that relates to AODa, not to the total AOD. This means that the anthropogenic fraction is independent of interannual variations in coarse mode sizes. From simulated monthly maps for the AODa with current and preindustrial emissions, today's anthropogenic fraction fAANT was determined from the normalized difference:

fa, aoda,2000 aoda,1750

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Monthly fields for fAANT are presented in Figure 3.7.

The anthropogenic AOD is defined by the product of the anthropogenic fraction and the accumulation mode AOD: AODant =fA ANTx AODa. Single-scattering albedo and asymmetry factor are those of the accumulation mode

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Figure 3.7 Monthly maps of the anthropogenic fraction of the AOD of the accumulation size mode (for aerosol particles smaller than 0.5 p,m in radius) based on global model simulations.

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Figure 3.7 Monthly maps of the anthropogenic fraction of the AOD of the accumulation size mode (for aerosol particles smaller than 0.5 p,m in radius) based on global model simulations.

(ro0 A, gA); the solar spectral dependencies follow those of the accumulation mode as well. Annual global maps at selected solar wavelengths are shown in Figure 3.8.

The natural aerosol properties are defined by the difference between total and anthropogenic aerosol. Thus, the AOD for natural aerosols is defined by the sum of the accumulation mode AOD, which is not anthropogenic, and the entire coarse mode AOD: AODnat = (1-/ANT) xAODa+AODC. Values for ro0 and g of natural aerosols apply a similar relationship with the appropriate mixing weights.

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