The use of airconditioning in offices located in hot-humid regions creates differences between indoor and outdoor air temperatures. Previous studies, which focused on artificial environments, found that air temperature step changes affect human thermal sensations and comfort. However, their effect on workers' perceived arousal has been rarely discussed. The purpose of the present study is to evaluate the effects of air temperature step changes (both up-step and down-step) on thermal perception and perceived arousal. Thirty-seven workers from two offices in Jakarta responded to a rating scale questionnaire about thermal perception that covered the following sub-topics: overall and local thermal sensations, thermal comfort, satisfaction, adjustment, and perceived arousal (i.e., alertness, freshness, and concentration) during working time. Air temperature and relative humidity around the subjects were recorded every 5 minutes by a data logger, from 10:00 to 17:00. During lunch time, the subjects walked to a nearby restaurant, exposing themselves to non-shaded outdoor temperature before returning to the office. Office A workers experienced larger temperature changes than Office B workers. Indoor and outdoor temperatures of Office A were 22.9 °C and 32.1 °C, respectively, whereas, for Office B they were 24.2 °C and 29.5 °C, respectively. Perceived arousal decreased significantly in Office A after the workers experienced the change in air temperature. However, no significant difference in perceived arousal was registered in Office B, likely due to a larger gap between indoor and outdoor air temperatures in the case of Office A. The data of just before and after the temperature step changes were analyzed: no negative correlations were found between changes in the overall thermal sensation and alertness (p < 0.05), freshness (p < 0.05), or concentration (p < 0.01). Therefore, warm sensations after the air temperature changes, associated with a hysteresis effect, should have lowered the perceived arousal. Our findings suggest that thermal perception and perceived arousal are altered by relatively large changes in air temperature. These changes are determined not only by the range of air temperature steps, but also by the air temperature experienced previously. In addition, mild air temperature changes in the actual environment, combined with exercise, food intake, and direct radiation exposure, induced warmer thermal sensations than those simulated through laboratory experiments.
