Twenty-four　subjects　were　exposed　to　two　levels　of　occupant　pollution　in　a　thermally　neutral　sleeping　environment,　as　indicated　with　average　carbon　dioxide　(CO2)　concentrations　of　800　ppm　and　2000　ppm　during　the　night.　Sleep　quality　was　measured　by　polysomnography　and　a　wrist-type　actigraphy　sensor　simultaneously,　and　also　assessed　by　a　questionnaire.　Physiological　parameters　indicating　responses　of　cardiovascular　and　pulmonary　function　were　measured　repeatedly　prior　to　sleep　and　after　waking　up　in　the　morning.　The　results　show　that　when　exposed　to　the　high　level　of　occupant　pollution　with　the　average　CO2　concentration　being　2000　ppm,　subjects　reported　lower　satisfaction　on　sleep　and　less　easiness　of　awakening,　and　experienced　a　shorter　duration　of　total　sleep　and　deep　sleep　stage,　which　indicates　a　worse　sleep　quality.　Furthermore,　fractional　CO2,　end-tidal　CO2　and　systolic　blood　pressure　measured　in　the　morning　were　significantly　higher.　The　change　of　LF/HF　ratio　of　heart　rate　variability　was　significantly　more　at　the　onset　of　sleep　and　less　during　arousal.　This　suggests　that　when　sleeping　in　an　occupant-polluted　environment,　subjects　experienced　a　slower　automatic　nervous　system　transition　from　a　sympathetically　dominated　state　to　a　parasympathetically　dominated　state　at　night,　and　vice　versa　in　the　morning.　©　2023　Elsevier　Ltd