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Lanzhou is located in a steep Alpine valley characterized by strong and persistent temperature inversions during winter.The city has been one of the most polluted cities in China,and is ideally located for the study of the sources,concentrations,transport,and transformation processed of the fine particle,especially for inland of China.In this study,An Aerodyne high resolution time-of-flight aerosol mass spectrometer(HR-ToF-AMS)was deployed along with a Scanning Mobility Particle Sizer(SMPS)and an Aethalometer during Jan.10 to Feb.4,2014 to monitor the chemical variation of sub-micrometer aerosol(PM1)in real time.The average PM1 mass concentration during this study was 57.3(± 9.5)μg m-3,with mean composition consisting of organics(51%),nitrate(17%),sulfate(13%),ammonium(10%),BC(6%),and chloride(3%).Positive matrix factorization(PMF)with the multilinear engine(ME-2)algorithm was applied to analyzing the organic mass spectra and identified six organic aerosol(OA)factors,representing,respectively,four primary OA(POA)emission sources(traffic,food cooking,biomass burning,and coal combustion)and two secondary oxygenated OA(OOA)types – a semi-volatile(SV-OOA)and a low-volatility(LV-OOA)OOA.Comparison with the results explored during 2012 summer,two more POA factors(biomass burning and coal combustion)were observed which were mainly used for heating and accounted for more than 30%of OA.The diurnal profiles of sulfate and SV-OOA displayed a broadly peak between~10:00-15:00,while those of nitrate,ammonium and LV-OOA showed a narrower peak at~12:00-18:00.These patterns were evidently different from the results of 2012 summer.The chemical evolution of SOA(SV-OOA and LV-OOA)and their correlations with meteorological parameters have been evaluated.