the models showed that decreased HRV indices were significantly associated with increased PM10, PM2.5 and TVOC levels. Decreased HRV indices were more strongly associated with PM2.5 than with TVOCs and PM10. The greatest effect of PM2.5 on the SDNN was observed among the subjects in the walking mode (Model 5 with PM2.5), whereas small decreases in the SDNN with PM2.5 exposure were observed among the subjects in the subway mode (Model 2 with PM2.5).