Centroid values of aerosol optical properties for 8 sub-types based in AERONET inversion data (1993–2018)

Methodology of Data collection: We started from a complete fresh download of the entire AERONET set of all sites for the V2 Inversion product [now in V3 available at [https://aeronet.gsfc.nasa.gov/new_web/download_all_v3_inversions.html], capturing the Level 2.0 Almucantar product that includes all points for each site -- not averages. The original package was obtained as a zip archive named in this fashion: "INV_PFN_Level2_All_Points_V3.tar.gz". The package was unzipped to make available all records for each AERONET site. Data Cleaning: The complete set of files is operated on by a simple C-Shell script to remove all individual retrievals from each site that contained records of either "NAN" or "- 99999999" for any field other than the "aeronet site" name as a text field. Subsequently, we imposed our minimum number of complete records criteria such that any AERONET station that did not report a minimum of 200 complete retrievals as removed. These generally refer to as qualifying sites. NOTE: This same strategy could be performed manually in an editor on each individual file to arrive at the same end result. An example of a C-shell script that can be modified for BASH or any other environment is included as "cleanup.csh". Data Reduction: Finding the minimum number of AERONET inversion retrieval variables that span the greatest variance in the global data set This optimization problem was done using methods of factor analysis, to result in the final working set of files containing complete records of on which to develop our robust global aerosol typology. The details of the intricacies and history of this part of the project are detailed in Giordano 2019. Data Processing: Determining the number of unique aerosol types globally identifiable through bulk columnar aerosol (BCA) Sun photometry This problem of analyzing the global data to determine the individually identifiable unique aerosol "groups" was done by invoking various mathematical unique strategies generally thought of as "cluster analysis." The main goal of this approach is to achieve separability between the individual "groups" while preserving a maximal "homogeneity" within any individual group. The details of the intricacies and history of this part of the project are detailed Giordano 2019 and Hamill et al. 2016. Regarding Uncertainty measures in the reported values: Regarding the calculated uncertainty values that accompany these data, the author offers the summary of both the centroid values for each of the 5 optical properties, and the tabulated centroid values for each of the 8 reference aerosol types to be used as standards to classify measurements of the global aerosol. These are below as Figure1 and Table1 respectively. Table 1: uncertainty values for the 5 optical properties in the typological basis Optical Property EAE 870-440nm AAE 870-440nm SSA 440nm RRI 675nm IRI 675 nm uncertainty ± 0.3 - 0.6 ± 0.3 - 0.6 ± 0.03 - 0.05 ± 0.02 - 0.05 ± 30 - 50%