  The atmospheric aerosol monitoring system of the Pierre Auger Observatory has
been operating smoothly since 2004. Two laser facilities (Central Laser
Facility, CLF and eXtreme Laser Facility, XLF) fire sets of 50 shots four times
per hour during FD shifts to measure the highly variable hourly aerosol
attenuation to correct the longitudinal UV light profiles of the Extensive Air
Showers detected by the Fluorescence Detector. Hourly aerosol attenuation loads
(Vertical Aerosol Optical Depth) are used to correct the measured profiles. Two
techniques are used to determine the aerosol profiles, which have been proven
to be fully compatible. The uncertainty in the VAOD profiles measured
consequently leads to an uncertainty on the energy and on the estimation of the
depth at the maximum development of a shower (X max ) of the event in analysis.
To prove the validity of the aerosol attenuation measurements used in FD event
analysis, the flatness of the ratio of reconstructed SD to FD energy as a
function of the aerosol transmission to the depth of shower maximum has been
verified.
