The results of preliminary studies showed that the pattern of variation in the concentration of ozone gas is almost always the same day in which the concentration of ozone gas is quite high and stable at 10:00 to 18:00 (see Fig. 1 and Fig. 2). The results of this preliminary study can be used to determine the concentration of ozone gas sampling time for the city of Padang, where the time to be used for sampling is from 10:00 to 18:00.