An　Aerodyne　Aerosol　Chemical　Speciation　Monitor　(ACSM)　was　deployed　to　in　situ　measure　the　concentrations　of　non-refractory　submicron　particulate　NR-PM1　and　its　species　as　organics　Org,　sulfate　SO42-,　nitrate　NO3-,　ammonium　NH4+　and　chloride　Cl-　at　the　southeast　urban　area　in　Beijing　from　December　2021　to　November　2022,　and　further　investigate　the　change　characteristics　of　NR-PM1　and　its　species　at　different　time　scales,　especially　during　the　different　pollution　periods,　and　the　important　factors　affecting　the　formation　of　secondary　sulfate　and　nitrate.　Meanwhile,　the　positive　matrix　factorization　PMF　and　backward　trajectory　clustering　analysis　were　used　to　study　the　change　characteristics　of　organic　aerosol　OA　components　in　the　different　periods,　and　the　influence　mechanism　of　air　mass　long-distance　transport　on　NR-PM1　and　its　species　in　the　different　periods,　respectively.　The　results　showed　that　the　annual　average　mass　concentration　of　NR-PM1　during　the　study　period　was　(7.60±10.35)　µg/m3,　being　lower　than　the　corresponding　annual　average　since　2016,　and　showed　a　decline　trend　year　by　year.　The　average　concentrations　of　NR-PM1　in　different　seasons　showed　an　obvious　seasonal　variation　characterized　by　autumn　＞　spring　＞　winter　＞　summer,　and　the　diurnal　variations　in　different　seasons　followed　the　order　of　night　＞　day.　The　average　annual　mass　concentration　of　NR-PM1　species　showed　an　order　of　Org＞　NO3-＞　NH4+~　SO42-＞　Cl-,　among　which　Org　contributed　the　largest　fraction　of　NR-PM1　with　about　41.16%,　followed　by　nitrate　33.05%,　ammonium　12.47%,　sulfate　11.99%,　and　chloride　contributing　the　lowest　fraction　with　1.33%.　The　diurnal　variations　of　NR-PM1　concentrations　in　different　seasons　were　all　smaller,　and　the　average　concentrations　of　NR-PM1　and　its　species　in　haze　days　were　higher　than　those　in　ozone　pollution　days　and　clean　days.　The　presence　of　alkaline　NH3　in　the　atmosphere　and　the　meteorological　conditions　during　the　haze　days　were　more　favorable　for　the　secondary　transformation　of　gaseous　precursors.　The　OA　components　were　different　in　different　seasons.　SOA　in　winter,　spring　and　autumn　is　the　main　component　of　OA,　while　POA　in　summer　is　the　main　component　of　OA.　OA　in　haze　and　ozone-polluted　days　was　mainly　affected　by　secondary　organic　matter.　The　transport　pathways　of　air　mass　were　different　in　different　seasons.　It　is　noted　that　the　haze　pollution　days　were　mainly　affected　by　the　short-distance　transports　of　air　mass　from　the　southeast　direction　and　the　south　direction,　and　NO3-　showed　a　greater　contribution　to　NR-PM1.　O3-polluted　days　were　mainly　affected　by　short-distance　transports　of　air　mass　from　the　south　direction,　while　clean　days　were　mainly　affected　by　long-distance　transports　of　air　mass　from　the　northwest　direction.　©　2024　Chinese　Society　for　Environmental　Sciences.　All　rights　reserved.