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

Abstract

Abstract. Highly time-resolved chemical characterization of nonrefractory submicrometer particulate matter (NR-PM1) was conducted in Seoul, the capital and largest metropolis of Korea, using an Aerodyne high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS). The measurements were performed during winter, when elevated particulate matter (PM) pollution events are often observed. This is the first time that detailed real-time aerosol measurement results have been reported from Seoul, Korea, and they reveal valuable insights into the sources and atmospheric processes that contribute to PM pollution in this region. The average concentration of submicron aerosol (PM1 = NR-PM1+ black carbon (BC)) was 27.5 µg m−3, and the total mass was dominated 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), and nitrogen to carbon (N / C) of organic aerosols (OA) were 0.37, 1.79, and 0.018, respectively, which result in an average organic mass-to-carbon (OM / OC) ratio of 1.67. The concentrations (2.6–90.7 µg m−3) and composition of PM1 varied dynamically during the measurement period due to the influences of different meteorological conditions, emission sources, and air mass origins. Five distinct sources of OA were identified via positive matrix factorization (PMF) analysis of the HR-ToF-AMS data: vehicle emissions represented by a hydrocarbon-like OA factor (HOA, O / C = 0.06), cooking activities represented by a cooking OA factor (COA, O / C = 0.14), wood combustion represented by a biomass burning OA factor (BBOA, O / C = 0.34), and secondary organic aerosol (SOA) represented by a semivolatile oxygenated OA factor (SV-OOA, O / C = 0.56) and a low-volatility oxygenated OA factor (LV-OOA, O / C = 0.68). On average, primary OA (POA = HOA + COA + BBOA) accounted for 59 % 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 influenced strongly by secondary aerosol formation, with sulfate, nitrate, ammonium, SV-OOA, and LV-OOA together accounting for 64 % of the PM1 mass during this study. However, aerosol sources and composition were found to be significantly different between clean and polluted periods. During stagnant periods with low wind speed (WS) and high relative humidity (RH), PM concentration 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 local production of secondary aerosol. Low-PM loading periods (12.6 ± 7.1 µg m−3) tended to occur under higher-WS and lower-RH conditions and appeared to be more strongly influenced by regional air masses, as indicated by higher mass fractions of sulfate (12 %) and LV-OOA (20 %) in PM1. Overall, our results indicate that PM pollutants in urban Korea originate from complex emission sources and atmospheric processes and that their concentrations and composition are controlled by various factors, including meteorological conditions, local anthropogenic emissions, and upwind sources.

Secondary organic aerosol production from local emissions dominates the organic aerosol budget over Seoul, South Korea, during KORUS-AQ

“…The PM 1 composition over Seoul is dominated by pNO 3 and SOA, similar to what was observed on the ground during the same time period (Kim et al, 2018). The composition over Seoul is more similar to what has been observed over Mexico City during MILAGRO (DeCarlo et al, 2008) and in Los Angeles during CalNex (Hayes et al, 2013) than observed over large urban areas in Asia (Hu et al, 2016).…”

“…The slope over Seoul (−0.69) is close to the average slope for numerous studies summarized by Chen et al (2015) (−0.60) and similar to the range of slopes (−0.7 to −1.0) for studies impacted by urban pollution (Aiken et al, 2009;Docherty et al, 2011;Ge et al, 2012), including Los Angeles during Cal-Nex (ranges from −0.64 to −0.68 from Hayes et al, 2013, and or chamber studies investigating the photooxidation of combustion exhausts (Heald et al, 2010;Lambe et al, 2012;Jathar et al, 2013;Presto et al, 2014;Liu et al, 2015). This generally indicates that the photochemistry controlling the production of SOA is similar in urban areas, including photooxidation of diesel and gasoline emissions, evaporative diesel and gasoline, and cooking emissions (Hayes et al, 2015;Woody et al, 2016;Janssen et al, 2017;Ma et al, 2017;Kim et al, 2018).…”

“…LO-OOA has lower O/C compared to MO-OOA (Fig. S10); thus, the faster production of LO-OOA likely represents the LO-OOA produced from the photooxidation of SOA precursors (Hayes et al, 2013;Freney et al, 2014;Hu et al, 2016;Kim et al, 2018), while MO-OOA may represent the more-oxidized species or those formed from later generations of oxidation (Robinson et al, 2007;Miracolo et al, 2010;Tritscher et al, 2011;Sato et al, 2017;Schwantes et al, 2017). The PMF factors have very different dilution-corrected concentrations over the Yellow Sea during the transport/polluted event (Fig.…”

Sources and Secondary Production of Organic Aerosols in the Northeastern United States during WINTER

“…In addition, dry deposition velocities of semivolatile species have been shown to be significantly different for some species in winter (Jaeglé et al, 2017). Although in the last few decades there have been a number of wintertime studies of aerosols in Asia (e.g., Cao et al, 2003;Kim et al, 2017;Rengarajan et al, 2007Rengarajan et al, , 2011Takegawa et al, 2005;Xu et al, 2016;Zhang et al, 2015) and Europe (e.g., Bardouki et al, 2003;Castro et al, 1999;Crippa et al, 2013;Lanz et al, 2008;Louvaris et al, 2017;Viana et al, 2006), very few have been conducted in North America (e.g., Budisulistiorini et al, 2016;Öztürk et al, 2013;Song et al, 2001;Strader et al, 1999;Tan et al, 2002;Weimer et al, 2006;Xu et al, 2015). However, most of the North American studies were conducted at least a decade ago, and none were conducted in the northeastern United States (NE-US).…”

“…The amount of OOA reported in urban environments varies greatly depending on the geographical location, but in general, accounts for approximately 50-80% of the total OA mass during the summer. In the winter, fewer studies have reported on measurements of urban OOA (Crippa et al, 2013;Kim et al, 2017;Öztürk et al, 2013;Pirjola et al, 2017;Zhang et al, 2015), showing fractions of OA mass between 20% and 70%.…”