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Highly time-resolved chemical characterization of nonrefractory submicrometerparticulate matter (NR-PM1) was conducted in Seoul, the capital andlargest metropolis of Korea, using an Aerodyne high-resolution time-of-flightaerosol mass spectrometer (HR-ToF-AMS). The measurements were performedduring winter, when elevated particulate matter (PM) pollution events areoften observed. This is the first time that detailed real-time aerosolmeasurement results have been reported from Seoul, Korea, and they revealvaluable insights into the sources and atmospheric processes that contributeto PM pollution in this region. The average concentration of submicron aerosol (PM1 =  NR-PM1+ blackcarbon (BC)) was 27.5 µg m−3, and the total mass wasdominated by organics (44 %), followed by nitrate (24 %) and sulfate(10 %). The average atomic ratios of oxygen to carbon(O / C), hydrogen to carbon (H / C), andnitrogen to carbon (N / C) of organic aerosols (OA) were0.37, 1.79, and 0.018, respectively, which result in an average organicmass-to-carbon (OM / OC) ratio of 1.67. The concentrations(2.6–90.7 µg m−3) and composition of PM1 varieddynamically during the measurement period due to the influences of differentmeteorological conditions, emission sources, and air mass origins. Fivedistinct sources of OA were identified via positive matrix factorization(PMF) analysis of the HR-ToF-AMS data: vehicle emissions represented by ahydrocarbon-like OA factor (HOA, O / C  =  0.06), cookingactivities represented by a cooking OA factor (COA,O / C  =  0.14), wood combustion represented by a biomassburning OA factor (BBOA, O / C  =  0.34), and secondaryorganic aerosol (SOA) represented by a semivolatile oxygenated OA factor(SV-OOA, O / C  = 0.56) and a low-volatility oxygenatedOA factor (LV-OOA, O / C  =  0.68). On average, primary OA(POA = HOA + COA + BBOA) accounted for59 % the OA mass, whereas SV-OOA and LV-OOA contributed 15 and 26 %,respectively. Our results indicate that air quality in Seoul during winter is influencedstrongly by secondary aerosol formation, with sulfate, nitrate, ammonium,SV-OOA, and LV-OOA together accounting for 64 % of the PM1 massduring this study. However, aerosol sources and composition were found to besignificantly different between clean and polluted periods. During stagnantperiods with low wind speed (WS) and high relative humidity (RH), PMconcentration was generally high (average ±1σ = 43.6 ± 12.4 µg m−3) with enhanced fractions of nitrate (27 %)and SV-OOA (8 %), which suggested a strong influence from localproduction of secondary aerosol. Low-PM loading periods (12.6 ± 7.1 µg m−3) tended to occur under higher-WS and lower-RHconditions and appeared to be more strongly influenced by regional airmasses, as indicated by higher mass fractions of sulfate (12 %) andLV-OOA (20 %) in PM1. Overall, our results indicate that PMpollutants in urban Korea originate from complex emission sources andatmospheric processes and that their concentrations and composition arecontrolled by various factors, including meteorological conditions, localanthropogenic emissions, and upwind sources

atmospheric chemistry and physics

Sources and atmospheric processing of winter aerosols in Seoul, Korea: insights from real-time measurements using a high-resolution aerosol mass spectrometer