Several relationships between the atmospheric optical depth tau and common near-surface meteorological parameters (such as pressure and temperature) are derived. Also, relations between tau and some indicators of atmospheric pressure daily variation are proposed and tested. The accuracy of all types of regressions is lower during dust storm seasons, while during "clear" sky periods the accuracy is usually good, Atmospheric pressure is recommended more than ambient temperature as a regression parameter. The influence of the season and local solar time on the regression's accuracy is important mainly during the dust storm period. The regression accuracy is higher at VL? site (47.57 degreesN, 225.74 degreesW in Utopia Planitia) than at VL1 site (22.27 degreesN, 49.97 degreesW in Chryse Planitia). Optical depth is well correlated to the daily variation of surface pressure and to the standard deviation of daily surface pressure.