Exposure to Air Pollution - A Novel Staircase-Function Response Mechanism of Stress Restoration

Abstract

Introduction: Given the epidemiological facts that exposure to air pollution induce the stress, reasonable hypothesis is made that it also hampers the stress restoration and further cause the mental health concerns. However, no studies examined the specific mechanisms so far.Methods: We adopted an environmental physio-psychological experiment paradigm of stress recovery to investigate the question. The experiment had three steps:(1) After entering the lab and sit in front of a computer monitor, participants were asked to relax for 1 minute.(2) Participants then took 10-minutes oral English tasks in the form of TOEFL test for evoking the stress.(3) Immediately after the stress evocation, 110 participants were randomly divided into seven groups. Then they were asked to relax for 3 minutes in the front of the monitor that displayed one group of blank pictures and six target groups of air pollution pictures with PM2.5 concentrations ranging from 11, 32, 51, 108, 165, to 231 μg/m3, respectively.During the experiment, Galvanic Skin Reaction (GSR) were selected as stress indicators and acquired using a BIOPAC MP 150 System and aggregated for obtaining the mean and maximum of GSR for each 10-seconds interval using Acqknowledge 4.0.Results and Discussion: According to the stress recovery patterns, six target groups were regrouped into three categories that matched the Air Quality Grading system in China well. For the first one with PM2.5 of 11-32 μg/m3 (Grade: Good), participants presented the most obvious stress reductions of around 20% by the end of the third minutes. For the second one with PM2.5 of 51-108 μg/m3 (Grade: Fine and Mild Pollution), moderate stress reductions of less than 10% were observed. For the third one (Grade: Moderate and Severe Pollution), participants’ stress levels have not been reduced, but increased since the second minute. It revealed that there was a novel staircase-function response mechanism of stress restoration to air pollution exposure.