Personal　monitoring　for　fine　particulate　matter　(PM2.5)　was　conducted　for　adults　(48　subjects,　18-63　years　of　age)　in　Hong　Kong　during　the　summer　and　winter　of　2014-2015.　All　filters　were　analyzed　for　PM2.5　mass　and　constituents　(including　carbonaceous　aerosols,　water-soluble　ions,　and　elements).　We　found　that　season　(p　=　0.02)　and　occupation　(p　＜　0.001)　were　significant　factors　affecting　the　strength　of　the　personal-ambient　PM2.5　associations.　We　applied　mixed-effects　models　to　investigate　the　determinants　of　personal　exposure　to　PM2.5　mass　and　constituents,　along　with　within-　and　between-individual　variance　components.　Ambient　PM2.5　was　the　dominant　predictor　of　(R-2　=　0.12-0.59,　p　＜　0.01)　and　the　largest　contributor　(＞37.3%)　to　personal　exposures　for　PM2.5　mass　and　most　components.　For　all　subjects,　a　one-unit　(2.72　mu　g/m(3))　increase　in　ambient　PM2.5　was　associated　with　a　0.75　mu　g/m(3)　(95%　CI:　0.59-0.94　mu　g/m(3))　increase　in　personal　PM2.5　exposure.　The　adjusted　mixed-effects　models　included　information　extracted　from　individual＇s　activity　diaries　as　covariates.　The　results　showed　that　season,　occupation,　time　indoors　at　home,　in　transit,　and　cleaning　were　significant　determinants　for　PM2.5　components　in　personal　exposure　(R-beta(2)　=　0.06-0.63,　p　＜　0.05),　contributing　to　3.0-70.4%　of　the　variability.　For　onehour　extra　time　spent　at　home,　in　transit;　and　cleaning　an　average　increase　of　1.7-3.6%　(ammonium,　sulfate,　nitrate,　sulfur),　2.7-12.3%　(elemental　carbon,　ammonium,　titanium,　iron),　and　8.7-19.4%　(ammonium,　magnesium　ions,　vanadium)　in　components　of　personal　PM2.5　were　observed,　respectively.　In　this　research,　the　within-individual　variance　component　dominated　the　total　variability　for　all　investigated　exposure　data　except　PM2.5　and　EC.　Results　from　this　study　indicate　that　performing　long-term　personal　monitoring　is　needed　for　examining　the　associations　of　mass　and　constituents　of　personal　PM2.5　with　health　outcomes　in　epidemiological　studies　by　describing　the　impacts　of　individual-specific　data　on　personal　exposures.　(C)　2018　Elsevier　B.V.　All　rights　reserved.