Beijing,　the　capital　of　China,　suffers　from　severe　atmospheric　aerosol　pollution;　nevertheless,　a　comprehensive　study　of　the　constituents　and　sources　of　PM1　is　still　lacking,　and　the　differences　between　PM1　and　PM2.5　are　still　unclear.　In　this　study,　an　intensive　observation　was　conducted　to　reveal　the　pollution　characteristics　of　PM1　and　PM2.5　in　Beijing　in　autumn.　Positive　matrix　factorization　(PMF),　backward　trajectories　and　a　potential　source　contribution　function　(PSCF)　model　were　used　to　identify　the　source　categories　and　source　areas　of　PM1　and　PM2.5.　The　results　showed　that　the　average　concentrations　of　PM1　and　PM2.5　reached　78.20　mu　g/m(3)　and　95.47　mu　g/m(3)　during　the　study　period,　respectively.　PM1　contributed　greatly　to　PM2.5.　The　PM1/PM2.5　value　increased　from　73.6%　to　90.1%　with　PM1　concentration　growing　from　＜50　mu　g/m(3)　to　＞150　mu　g/m(3).　Higher　secondary　inorganic　aerosol　(SIA)　proportions　(31.3%-70.8%)　were　found　in　PM1.　The　higher　fraction　of　SIA,　OC,　EC　and　typical　elements　in　PM1　illustrated　that　anthropogenic　components　accumulated　more　in　smaller　size　particles.　Three　typical　weather　patterns　causing　the　heavy　pollution　in　autumn　were　found　as　follows:　(1)　Siberian　high　and　uniform　high　pressure　field,　(2)　cold　front　and　low-voltage　system,　and　(3)　uniform　low　pressure　field.　A　PMF　analysis　indicated　that　secondary　aerosols　and　coal　combustion,　vehicle,　industry,　biomass　burning,　and　dust　were　the　important　sources　of　PM,　accounting　for　53.8%,　8.0%,　13.0%,　13.2%　and　12.0%　of　PM1,　respectively,　and　for　47.5%,　9.9%,　12.4%,　8.4%　and　21.8%　of　PM2.5,　respectively.　The　HYSPLIT　and　chemical　components　analysis　indicated　the　potential　contribution　from　biomass　burning　and　fertilization　ammonia　emissions　to　PM1　in　autumn.　The　source　areas　were　similar　for　PM1　and　PM1-2.5　under　general　polluted　conditions,　but　during　the　heavily　polluted　periods,　the　source　areas　were　distributed　in　farther　regions　from　Beijing　for　PM1　than　for　PM1-2.5.　(C)　2018　Elsevier　B.V.　All　rights　reserved.