  An atmospheric transparency was measured using a LIDAR with a pulsed UV laser
(355nm) at the observation site of Telescope Array in Utah, USA. The
measurement at night for two years in $2007\sim 2009$ revealed that the
extinction coefficient by aerosol at the ground level is
$0.033^{+0.016}_{-0.012} \rm km^{-1}$ and the vertical aerosol optical depth at
5km above the ground is $0.035^{+0.019}_{-0.013}$. A model of the altitudinal
aerosol distribution was built based on these measurements for the analysis of
atmospheric attenuation of the fluorescence light generated by ultra high
energy cosmic rays.
