Reference data

Monthly averages for all sixteen AERONET sites are summarized in Figures 3. Also shown is the range of monthly averages, based on year-to-year comparisons, as illustrated for four sites in Figures 2.

In an effort to group the AERONET sites in sets of four by surface and dominant aerosol type, some mismatches could not be avoided. Based on the statistics for the Angstrom parameter, especially Banizoumbou and Bahrain appear misplaced. Banizoumbou is a dust-dominated site, but was added to biomass sites, because there are some carbon contributions from biomass burning between November and January (notice the increase in Angstrom parameters). Bahrain lies within a dust-dominated region, however, large Angstrom parameters indicate large contributions of sub-micrometer particles. This indicates that Bahrain data are strongly affected by local pollution, making statistics from this site less useful for regional comparisons.

Aerosol optical depth averages of Figures 3 will be the reference in comparisons to satellite data and model representations. In order to capture uncertainties from year-to-year variations, the presentations of deviations to satellite data and models in subsequent Figures will include the range of variations for monthly averages.

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Figure 3a-d. Monthly averages (symbols) and range (vertical bars) for aerosol optical depths (upper panel) and Angstrom parameters (lower panel). Statistics of the sixteen AERONET-sites are presented in groups for four
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