In　this　study,　the　mass　concentrations　of　PM2.5,　water-soluble　inorganic　ions　(Na+,　NH4+,　K+,　Mg2+,　Ca2+,　F-,　Cl-,　NO2-,　NO3-,　SO42-,　PO43-),　carbonaceous　components　(organic　carbon　OC,　element　carbon　EC)　and　gaseous　pollutants,　and　meteorological　elements　were　monitored　in　real　time　in　Beijing　urban　area　from　November　27,　2018　to　January　15,　2019.　At　the　same　time,　the　concentrations　of　PM2.5,　its　major　water-soluble　ion　components　and　carbonaceous　components　in　winters　from　1999　to　2018　in　Beijing,　were　collected　to　analyze　their　variation　characteristics.　The　evolutions　of　PM2.5　and　its　components　in　the　clean　days　and　two　typical　heavy　pollution　processes　during　the　monitoring　period　were　mainly　discussed.　The　results　showed　that　the　average　mass　concentration　of　PM2.5　during　the　study　period　was　53.5μg/m3,　almost　lower　than　those　in　winters　in　Beijing　since　1999,　and　the　main　atmospheric　pollution　sources　displayed　a　significant　change　from　traditional　soot-type　pollution　source　to　both　coal-fired　and　motor　vehicle　exhaust-type　pollution　sources.　High　relative　humidity,　and　weak　southwest　wind　were　favorable　for　the　formation　of　heavy　pollution.　The　average　concentrations　of　PM2.5　during　the　clean　days,　pollution　episode　I　and　II　were　32.5,　138.9,　and　146.8μg/m3,　respectively.　The　diurnal　profiles　of　PM2.5　were　different　in　the　different　periods.　The　ion　concentrations　presented　the　order　of　NO3-＞NH4+＞SO42-＞Cl-＞K+＞Ca2+＞Na+＞PO43-＞F-＞NO2-~Mg2+,　and　their　mean　total　concentration　was　24.6μg/m3,　accounting　for　46.0%　of　PM2.5,　of　which　SNA　was　the　most　important　component,　accounting　for　83.7%　of　the　total　water-soluble　ions.　The　concentrations　of　carbonaceous　composition　reached　the　lowest　value　in　winters　in　Beijing　since　1999,　and　followed　the　order　of　primary　organic　carbon　POC＞EC＞secondary　organic　carbon　SOC,　and　the　correlation　coefficient　between　OC　and　EC　was　0.99,　indicating　that　the　primary　combustion　source　had　a　greater　contribution　to　atmospheric　pollution.　NH4+　was　enriched　in　PM2.5　during　the　clean　days　and　pollution　II,　and　existed　mainly　in　the　form　of　(NH4)2SO4,　NH4NO3　and　NH4Cl,　but　lower　in　pollution　I,　and　existed　only　as　(NH4)2SO4　and　NH4NO3.　During　the　periods　of　pollution　I　and　II,　the　formation　of　SO42-　was　mainly　affected　by　relative　humidity　and　NH3during　the　daytime　and　nighttime,　however,　the　formation　of　NO3-　was　mainly　affected　by　O3　and　NH3　during　the　daytimee,　and　by　relative　humidity　and　NH3　during　the　nighttime.　©　2020,　Editorial　Board　of　China　Environmental　Science.　All　right　reserved.