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As part of the Megacity Air Pollution Studies (MAPS)-Seoul campaign, three types of research flights were conducted over the Seoul Metropolitan Area (SMA) from May till June 2015 to measure the spatial distribution of a pollution plume near a power plant and petrochemical complex, the vertical profiles of pollutants on the western coast of Korea, and the pollutant distribution in the SMA. The pollution plume (~0–700 m) was highly concentrated and dominated by organic aerosol (OA), which very likely oxidized in the plume, as it showed slightly less oxidation near the source and significantly less oxidation at altitudes above the plume. One vertical profile displayed transitions in concentration and changes in the dominant components, suggesting that the particle sources and/or processing differed above ~1000 m; below 1000 m, where the total mass and OA concentrations were high, sulfate and likely transport sources predominated. The other profile, which was assessed during a separate flight, exhibited sharp increases in the OA number concentration and mean diameter, less oxidized organic content, and higher organic and nitrate concentrations above 1400 m, indicating high-altitude transport and a cleaner boundary layer. Finally, flights investigating the distributions of pollutants in the central, upwind, and downwind SMA regions generally detected high levels of oxidation downwind as well as different aerosol masses between the low and high altitudes. This study highlights the necessity of understanding the complex vertical structures of particle layers, such as those identified in and around the SMA, in order to facilitate the adoption of efficient air quality control strategies and enhance air quality forecasting.

Clouds, fogs, and rain can serve as useful integrators of both atmospheric aerosols and soluble trace gases. To better understand the chemical characteristics of sea fog and rain in the North and South Pacific Ocean, fog and rain were measured aboard the R/V ARAON in 2012 and 2014, respectively, as part of the Ship-borne Pole-to-Pole Observations (SHIPPO) project. The mean sea fog pH (3.59) was lower than the mean rain pH (4.54), reflecting greater inputs of non-sea-salt (nss)-SO42−. For the collected rain, nss-Ca2+ and nss-Mg2+ from mineral dust particles were the major contributors to acidity neutralization. NO3− concentrations, which are derived from scavenging of gaseous nitric acid and aerosol nitrate, were higher than NH4+ concentrations, indicating that terrestrial and/or local anthropogenic NO3− sources outweighed contributions from anthropogenic or biological oceanic NH3/NH4+ sources. The ratio of Cl−/Na+ in the sea fog was slightly lower than that in the sea water due to HCl volatilization from scavenged sea-salt particles. The ratio of NH4+/ nss-Ca2+ was lower in the rain than in the sea fog, revealing the influence of mineral dust particles at altitudes above the sea fog layer. The average sea fog water TOC concentration, 13.2 ppmC, was much higher than the measured TOC concentrations in marine fogs and clouds in other remote environments, likely due to continental influence; the TN and TOC concentrations in the fog water were much higher than those in the rain. The sea fog and rain chemical properties measured during research cruises like these enhance our understanding of wet deposition and cloud condensation nuclei sources and processes in the Pacific Ocean.

Brown carbon (BrC) aerosols have important warming effects on Earth's radiative forcing. However, information on the evolution of the light-absorption properties of BrC aerosols in the Asian outflow region is limited. In this study, we evaluated the light-absorption properties of BrC using in-situ filter measurements and sky radiometer observations of the ground-based remote sensing network SKYradiometer NETwork (SKYNET) made on Fukue Island, western Japan in 2018. The light-absorption coefficient of BrC obtained from filter measurements had a temporal trend similar to that of the ambient concentration of black carbon (BC), indicating that BrC and BC have common combustion sources. The absorption Angstrom exponent in the wavelength range of 340-870 nm derived from the SKYNET observations was 15% higher in spring (1.81 ± 0.30) than through the whole year (1.53 ± 0.50), suggesting that the Asian outflow carries light-absorbing aerosols to Fukue Island and the western North Pacific. After eliminating the contributions of BC, the absorption Angstrom exponent of BrC alone obtained from filter observations had a positive Spearman correlation (rs = 0.77, p < 0.1) with that derived from SKYNET observations but 33% higher values, indicating that the light-absorption properties of BrC were successfully captured using the two methods. Using the atmospheric transport model FLEXPART and fire hotspots obtained from the Visible Infrared Imaging Radiometer Suite product, we identified a high-BrC event related to an air mass originating from regions with consistent fossil fuel combustion and sporadic open biomass burning in central East China. The results of the study may help to clarify the dynamics and climatic effects of BrC aerosols in East Asia.

A bias in clear-sky conditions that will be involved in estimating particulate matter (PM) concentration from aerosol optical depth (AOD) was examined using PM10 from two Aerosol Robotic Network sites in Korea. The study periods were between 2004 and 2007 at Anmyon and between 2003 and 2011 at Gosan, when both PM10 and AOD were available. Mean PM10 when AOD was available (PMAOD) was higher than that from all PM10 data (PMall) by 5.1 and 9.9μg/m3 at Anmyon and Gosan, which accounted for 11% and 26% of PMall, respectively. Because of a difference between mean PM10 under daytime clear-sky conditions (PMclear) and PMAOD, the variations in ΔPM10, the difference of PMall from PMclear rather than from PMAOD, were investigated. Although monthly variations in ΔPM10 at the two sites were different, they were positively correlated to those in ΔT, similarly defined as ΔPM10 except for temperature, at both sites. ΔPM10 at Anmyon decreased to a negative value in January due to an influence of the Siberian continental high-pressure system while ΔPM10 at Gosan was high in winter due to an effect of photochemical production at higher temperatures than at Anmyon.

The performance of a modeling system consisting of WRF model v3.4.1 and CMAQ model v4.7.1 for forecasting fine particle concentrations were evaluated using measurement data at the surface. Twenty-four hour averages of PM2.5 and its major components at Bulgwang (located in the northwest of Seoul) during the period February 2012 through January 2013 were compared with predicted concentrations as well as hourly averages of inorganic ions measured at Yongin (located to the southeast of Seoul) in spring 2012. The mean fractional bias (MFB) of –0.37 for PM2.5 at Bulgwang fell just outside the goal of –0.3, the level of accuracy that the best model can be achieved. Negative values of MFB, especially in winter, along with the correlation coefficient of 0.61 between measured and predicted concentrations showed that the model performance at Bulgwang was closer to that for Europe than that for North America. However, underestimation of SO42– and overestimation of NO3– were similarly observed at Bulgwang as in the United States. Although diurnal variations in the measured values showed distinctive features at Yongin according to the classified patterns, most variations in the predicted values typically showed a peak early in the morning followed by an increase at night.

Particulate matter (PM) in the atmosphere has wideranging health, environmental, and climate effects, many of which are attributed to fine-mode secondary organic aerosols. PM concentrations are significantly enhanced by primary particle emissions from traffic sources. Recently, in order to reduce CO2 and increase fuel economy, gasoline direct injected (GDI) engine technology is increasingly used in vehicle manufactures. The popularization of GDI technique has resulted in increasing of concerns on environmental protection. In order to better understand variations in chemical composition of particulate matter from emissions of GDI vehicle versus a port fuel injected (PFI) vehicle, a high time resolution chemical composition of PM emissions from GDI and PFI vehicles was measured at facility of Transport Pollution Research Center (TPRC), National Institute of Environmental Research (NIER), Korea. Continuous measurements of inorganic and organic species in PM were conducted using an Aerodyne high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS). The HR-ToF-AMS provides insight into nonrefractory PM composition, including concentrations of nitrate, sulfate, hydrocarbon-like and oxygenated organic aerosol, and organic mass with 20 sec time resolution. Many cases of PM emissions during the study were dominated by organic and nitrate aerosol. An overview of observed PM characteristics will be provided along with an analysis of comparison of GDI vehicle versus PFI vehicle in PM emission rates and oxidation states.

Particle-phase concentrations were measured at 10, 80, and 200 m from the roadside of a national highway near Seoul in January and May 2008. The highway has two lanes each way, with an average hourly traffic volume of 1,070 vehicles. In January 2008, PM 10 concentrations decreased from 10 to 80 m but increased at 200 m. Black carbon (BC) decreased only slightly with distance due to the influence of biomass burning and open burning from the surrounding areas. In May 2008, the effect of secondary formation on both PM 10 and PM 2.5 was significant due to high temperatures compared with January. Because on-road emissions had little effect on secondary formation for a short time, variations in PM 10 concentrations became smaller, and PM 2.5 concentrations increased with distance. The effects of fugitive dust on PM concentrations were greater in May than in January when the mean temperature was below freezing. In the composition variations, the amounts of primary ions, organic carbon (OC), and BC were larger in January, while those of secondary ions and others were larger in PM 10 , as well as PM 2.5 in May.

The inorganic ions in PM2.5 were measured downwind of metropolitan Seoul using a particle-into-liquid sampler over three periods. Five diurnal patterns, including a low-concentration pattern (L) and a high-concentration pattern with a decreasing trend during the day (H-), were distinguished for the first period from February to June 2012. The sum of ion concentrations increased primarily due to NO3 (-) with decreasing temperature and increasing relative humidity, which caused preferential partitioning of NO3 (-) into the particulate phase. The peak concentration occurred during the morning rush hour for L but was delayed until the next morning for H- due to the time required to form secondary inorganic ions from accumulated pollutants under lower wind speeds. The characteristic features of the patterns observed during the first period were generally similar with those obtained for the other two periods. However, for the second period, comprised of colder months, changes in the diurnal patterns from L to H- were accompanied by increasing temperature, as the effect of photochemical formation of NO3 (-) was larger than that of volatilization. Although the role of long-range transport was not distinct on the whole, the inflow of air masses from cleaner sectors was observed to lower the concentrations.

To improve understanding of the sources and chemical properties of particulate pollutants on the western side of the Korean Peninsula, an Aerodyne High Resolution Time of Flight Aerosol Mass Spectrometer (HR-ToF-AMS) measured non-refractory fine (PM 1 ) particles from May to November, 2011 at Baengnyeong Island, South Korea. Organic matter and sulfate were generally the most abundant species and exhibited maximum concentrations of 36 μg/m 3 and 39 μg/m 3 , respectively. Nitrate concentrations peaked at 32 μg/m 3 but were typically much lower than sulfate and organic matter concentrations. May, September, October, and November featured the highest monthly average concentrations, with lower concentrations typically observed from June through August. Potential source contribution function (PSCF) analysis and individual case studies revealed that transport from eastern China, an area with high SO 2 emissions, was associated with high particulate sulfate concentrations at the measurement site. Observed sulfate aerosol sometimes was fully neutralized by ammonium but often was acidic; the average ammonium to sulfate molar ratio was 1.49. Measured species size distributions revealed a range of sulfate particle size distributions with modes between 100 and 600 nm. Organic aerosol source regions were widespread, including contributions from eastern China and South Korea. Positive matrix factorization (PMF) analysis indicated three “factors,” or types of organic aerosol, comprising one primary, hydrocarbon-like organic aerosol (HOA) and two oxidized organic aerosol (OOA) components, including a more oxidized (MO-OOA) and a less oxidized (LO-OOA) oxidized organic aerosol. On average, HOA and OOA contributed 21% and 79% of the organic mass (OM), respectively, with the MO-OOA fraction nearly three times as abundant as the LO-OOA fraction. Biomass burning contributions to observed OM were low during the late spring/early summer agricultural burning season in eastern China, since airflow into eastern China during the Asian Monsoon generally prevents transport of emissions eastward to the Korean Peninsula. Concentrations of the m/z 60 AMS biomass burning marker were more abundant in autumn, when transport patterns appeared to bring some smoke from fires in northern Asia to the island.

In the past several decades, biofuels have emerged as candidates to help mitigate the issues of global warming, fossil fuel depletion and, in some cases, atmospheric pollution. To date, the only biofuels that have achieved any significant penetration in the global transportation sector are ethanol and biodiesel. The global consumption of biodiesel was rapidly increased from 2005. The goal of this study was to examine the chemical composition on particulate pollutant emissions from a diesel engine operating on several different biodiesels. Tests were performed on non-road diesel engine. Experiments were performed on 5 different fuel blends at 2 different engine loading conditions (50% and 75%). 5 different fuel blends were ultra-low sulfur diesel (ULSD, 100%), soy biodiesel (Blend 20% and Blend 100%) and canola biodiesel (Blend 20% and Blend 100%). The chemical properties of particulate pollutants were characterized using an Aerodyne High Resolution Time of Flight Aerosol Mass Spectrometer (HR-ToF-AMS). Organic matter and nitrate were generally the most abundant aerosol components and exhibited maximum concentration of 1207 μg/m³ and 30 μg/m³, respectively. On average, the oxidized fragment families (C x H y O₁+, and C x H y O z +) account for ~13% of the three family sum, while ~87% comes from the C x H y + family. The two peaks of C₂H₃O₂ (m/z 59.01) and C₃H 7 O (m/z 59.04) located at approximately m/z 59 could be used to identify atmospheric particulate matter directly to biodiesel exhaust, as distinguished from that created by petroleum diesel in the AMS data.

The characteristics of the volatilization of semi-volatile inorganic ions sampled on a Teflon filter were investigated using a backup nylon filter and annular denuders. The volatilization ratio (VR) was defined as the fraction of the concentration at the backup filter and denuder to the sum of the concentrations collected at the Teflon filter, backup filter, and denuder. Particles whose aerodynamic diameters are less than or equal to 2.5 μm (PM_(2.5)) were sampled for 24 h each season from summer 2011 to spring 2012 at a site, about 35 km southeast of downtown Seoul. Increase in VR with increasing temperature was evident, but the effects of relative humidity were not clear, because seasonal variation in the two variables was correlated, and the variation in relative humidity was smaller than that in temperature. While VRs generally decreased with the amounts sampled on the Teflon filter, details of the volatilization behaviors varied among ions according to concentrations at the Teflon filter and VR. The removal of gaseous species at the upstream denuders affected VRs of semi-volatile ions by shifting the equilibrium among NH_4^+, NO_3^-, and SO_4^(2-).

Mass and ion concentrations of and were measured in Yongin, downwind of the Seoul metropolitan area. Twenty-four hour average samples were collected daily for a month or so in spring and fall of both 2007 and 2008. Asian dust occurred twice in each period except in the fall of 2007. During the Asian dust period, nitrate in fine particles decreased since large amount of cations in coarse particles of Asian dust absorbed it. In spring 2008, sulfate as well as ammonium also increased in coarse particles. In spite of occasional Asian dust events, the influence of secondary formation was dominant over the period. Excessive ammonium over sulfate was enough to neutralize nitrate as well. High correlation coefficients between and sulfate, nitrate, and ammonium indicate a close relationship between secondary formation and biomass burning. Biomass burning and open burning are considered to be important sources of chloride.

Six monitoring stations were selected to characterize the variations in airborne concentrations of heavy metals in South Korea between 1999 and 2012. Three stations represented higher concentrations, and three represented lower concentrations. The heavy metals monitored at these stations include cadmium, chromium, copper, iron (Fe), lead, manganese (Mn), and nickel. During the study period, concentrations of heavy metals at many stations, including those around the Seoul metropolitan area, showed a decreasing trend. However, concentrations of Mn and Fe that are primarily of crustal origin increased at four of the six stations. Some stations were significantly affected by emissions from the local industrial complex (IC), and heavy metal concentrations at those stations were relatively high even in summer. Many heavy metal concentrations were higher in spring than in winter, but wintertime concentrations of Cr and Pb were higher at the stations representing lower concentrations due to the dominant influence of combustion emissions. At stations less affected by emissions from the IC, concentrations of Fe and Mn that are predominantly crustal in origin were higher in spring, when Asian dust (AD) events are most frequent. Although Mn concentrations were also high at stations within the steelmaking IC during AD periods, they were much higher during non-AD periods due to local emissions. Variations in heavy metal concentrations, which are heavily influenced by emissions from the IC, warrant individual analysis because their emission characteristics differ from those of typical cases.