Gray cityscape caused by particulate matter pollution hampers human stress recovery

Air pollution has caused degraded visibility and gray cityscape in many developing countries. Though this visual change affects daily life from various aspects, there still lacks evidence on how it influences human psychological and physiological wellbeing. Based on a psychophysiological experiment, this study found that degraded cityscape caused by particulate matter (PM) pollution impeded human stress recovery and caused mental discomfort. We exposed 96 college student participants to fixed-scene images with six varied PM pollution levels during a 3-min post-stress recovery. We measured participants’ self-reported and physiological stress before the stressor, after the stressor and after the recovery. Stress recovery percentages among groups were compared. Both self-reported and physiological stress measurements showed that participants viewing clean cityscape photos recovered faster and 30–60% better than those viewing low-visibility cityscape photos. The final stress recovery percentages after 3-min recovery varied among indicators but generally followed a decreasing trend as the visibility impaired. The results convince a potentially indirect pathway through which the gray cityscape reduces well-being by hampering stress recovery. We discuss underlying mechanisms of the recovery-hampering effect of gray cityscape and call for more attention to this mild psychophysiological outcome.