Atmospheric　fine　particulate　pollution　has　been　a　dramatically　environmental　concern　in　all　seasons　in　the　megacity　Beijing　in　recent　years.　A　long-term　real-time　monitoring　campaign　of　non-refractory　submicron　aerosol　(NR-PM1)　at　a　southeastern　urban　site　in　Beijing　from　July　13,　2017　to　May　26,　2018　using　an　Aerodyne　Aerosol　Chemical　Speciation　Monitor　(ACSM)　was　carried　out　to　investigate　the　characteristics　and　evolution　processes　of　NR-PM1　and　its　potential　source　effects.　The　annual　average　concentration　of　NR-PM1　during　the　entire　study　period　was　40.8　μg/m3,　lower　than　that　of　NR-PM1　from　July　2011　to　June　2012,　and　its　seasonal　variation　presented　the　order　of　autumn　and　spring　＞　winter　＞　summer.　The　average　concentration　of　organic　species　Org　in　the　entire　study　was　15.1　μg/m3　and　accounted　for　37%　of　NR-PM1,　being　consistently　a　significant　component　of　NR-PM1　in　the　four　seasons.　The　average　concentrations　of　SO42−　and　NO3−　were　8.6　and　11.1　μg/m3,　respectively,　accounting　for　21%　and　27%　of　NR-PM1,　and　NO3−　and　its　contribution　to　NR-PM1　exceeded　those　of　SO42−,　suggesting　that　secondary　nitrate　became　a　more　dramatic　pollutant.　Note　that　SO42−　in　summer　accounted　for　27%　of　NR-PM1,　higher　than　those　in　the　other　seasons,　indicating　that　secondary　sulfate　formation　was　greatly　important　in　summer,　however,　NO3−　in　summer　accounted　for　22%　of　NR-PM1,　lower　than　those　in　the　other　seasons,　more　likely　due　to　relatively　high　temperature　in　summer　being　favorable　for　dissociation　of　nitrate.　NH4+　and　Cl−　species　presented　lower　mass　concentrations　and　mass　fractions,　and　the　seasonal　variation　of　NH4+　was　similar　to　NO3−,　yet　Cl−　presented　a　typical　seasonal　change　related　to　intense　fossil　fuel　combustion　during　the　heating　period　in　winter　and　biomass　burning　in　autumn　with　an　order　of　winter　＞　autumn　＞　spring　＞　summer.　All　aerosol　species　exhibited　different　diurnal　cycles,　of　which　Org　presented　a　bimodal　mode,　SO42−　and　Cl−　showed　a　flatter　diurnal　pattern,　however,　NO3−　and　NH4+　displayed　more　similar　single-peak　patterns.　The　conversion　of　SO2　to　SO42−　presented　an　obvious　seasonal　variation　with　summer　＞　autumn　＞　spring　＞　winter　driven　by　different　factors.　The　conversion　of　NO2　to　NO3−　also　showed　a　significant　seasonal　change　characterized　by　autumn　＞　summer　and　spring　＞　winter　controlled　by　different　factors.　Relative　humidity,　temperature　and　wind　speed　during　the　study　period　were　significant　meteorological　elements　influencing　NR-PM1　and　its　species,　and　heavy　haze　pollution　episodes　largely　occurred　under　high　relative　humidity　and　low　wind　speed.　High　potential　source　regions　influencing　NR-PM1　pollution　in　Beijing　in　all　seasons　presented　dramatically　distributions　related　to　wind　directions.　©　2020　Elsevier　Ltd