The　ratio　of　SO2/NO2　together　with　PM2.5/CO　was　applied　to　explain　the　source　of　particulate　matters　(PM)　pollution　in　Beijing.　Polycyclic　aromatic　hydrocarbons　(PAHs)　bounded　with　ultrafine　particles　were　investigated　as　well.　A　total　of　188　graded　PM　in　four-stage　size　segregated　aerosol　particles　were　collected　and　analyzed　by　GC-MS　in　2016　to　investigate　the　sources　and　distribution　patterns　of　PAHs　in　metropolis-Beijing.　A　significant　seasonal　variation　of　16　PAHs　in　PM2.5　around　in　Beijing　was　observed　with　32.93　+/-　15.19　ng　m(-3),　17.77　+/-　8.08　ng　m(-3),　31.61　+/-　12.67　ng　m(-3)　and　78.06　+/-　40.97　ng　m(-3)　in　spring,　summer,　autumn　and　winter,　respectively.　The　ratio　of　SO2/NO2　demonstrated　that　vehicle　emissions　significantly　contributed　to　air　pollution.　On　the　contrary,　the　lower　ratio　of　PM2.5/CO　showed　high　direct　discharge　from　combustion.　Seasonal　distribution　patterns　of　PM0.2/PM2.5　suggested　that　abundant　secondary　aerosols　were　produced　in　the　autumn　and　winter.　The　spread　of　pollutants　was　not　significant　in　winter.　Both　the　combustion　of　fuel　and　coal　were　the　primary　sources　of　PM2.5-bound　PAHs.　A　health　risk　assessment　was　represented　by　benzo　[a]　pyrene　equivalent　(BaPeq)　indicating　potential　cancer　risk　in　Beijing.　Furthermore,　the　lifetime　excess　cancer　risk　(ECR)　was　3.00　x　10(-4),　which　was　higher　than　the　guidelines　of　USEPA　and　European　Commission,　indicating　high　carcinogenic　risk　of　PM2.5　in　Beijing.　Therefore,　more　strictly　control　measures　should　be　taken　to　reduce　PAHs　emissions　from　coal　and　vehicle.