Ji Yi Lee

Speciation and source identification of organic compounds in PM10 over Seoul, South Korea.

Seventy three individual organic compounds in the atmospheric particulate matter with an aerodynamic diameter of less than or equal to a nominal 10 μm (PM10) over Seoul were identified and quantified from April 2010 to April 2011 using gas chromatography/mass spectrometry (GC/MS). These organic compounds were classified into five groups, n-alkanes, polycyclic aromatic hydrocarbons (PAHs), mono-carboxylic acids, di-carboxylic acids (DCAs), and sugars based on their chemical structures and properties. The organic compounds showed higher seasonal average concentrations from fall to winter than from spring to summer due to source strength, except some organic compounds among mono-carboxylic acids, DCAs, sugars such as undecanoic acid, methylmalonic acid, and fructose. Through qualitative data analysis using seasonal concentration variations and relevant diagnostic parameters, it was found that (1) anthropogenic sources such as combustion of fossil fuel and biomass burning attributed more to the formation of the organic aerosols than biogenic sources, and (2) the ambient level of n-alkanes, PAHs, and some compounds of DCAs and sugars was elevated in winter due to the increased primary emissions and larger transport from outside of the organic compounds in winter.

A multivariate receptor modeling study of air-borne particulate PAHs: Regional contributions in a roadside environment.

Understanding the geographic source contributions by particulate polycyclic aromatic hydrocarbons (PAHs) is important for the Korean peninsula due to its downwind location from source areas. Regional influence of particulate PAHs was previously identified using diagnostic ratios applied to mobile source dominated roadside sampling data (Kim et al., 2012b). However, no study has yet been conducted to quantify the regional source contributions. We applied a multivariate receptor modeling tool to identify and quantify the regional source contributions to particulate PAHs in Seoul. Sampling of roadside particulate PAHs was conducted in Seoul, Korea for four years between May 2005 and April 2009, and data analysis was performed with a new multivariate receptor model, Solver for Mixture Problem (SMP). The SMP model identified two sources, local mobile source and transported regional source, and quantified their source contributions. Analysis of the particulate PAHs data reveals three types of episodic periods: a high regional source contribution period with one case, a high mobile source contribution period with three cases, and a normal contribution period with eight cases. Four-year average particulate PAHs source contributions from the two sources are 4.6 ng m(-3) and 10.7 ng m(-3) for regional and mobile sources, respectively and equivalent to 30% and 70% of the total estimated contribution from each of these sources.

Formation of polyaromatic hydrocarbon (PAH)-quinones during the gas phase reactions of PAHs with the OH radical in the atmosphere

Environmental context Atmospheric quinones present a potential toxic risk to human health because of their involvement in the generation of reactive oxygen species. Gas phase reactions of naphthalene and phenanthrene with the OH radical are investigated in a laboratory reaction chamber to provide a preliminary assessment of the importance of the atmospheric formation of quinones. Abstract In light of the potential toxicity of quinones (QNs) to human health, previous studies carried out measurement of QNs in ambient air samples and from motor vehicle emissions to understand the characteristics and the sources of QNs in the atmosphere. The major compounds observed in the ambient air samples comprised two and three benzene rings and included polyaromatic hydrocarbon (PAH)-quinones (PAH-QNs) such as 1,2-naphthoquinone (1,2-NQ), 1,4-naphthoquinone (1,4-NQ), 9,10-phenanthrenequinone (9,10-PQ) and 9,10-anthraquinone (9,10-AQ). Although these PAH-QNs are found in vehicular emissions, they may also be formed by the photochemical reactions of gas phase PAHs with atmospheric oxidants. In this study, to allow an assessment of the importance of the atmospheric formation of PAH-QNs and to understand more clearly the sources of PAH-QNs in the atmosphere, the formation yields of PAH-QNs from the gas phase reactions of naphthalene and phenanthrene with the OH radical were observed in a laboratory reaction chamber. In addition, the phase distribution of the PAH-QNs was determined. For naphthoquinones (NQs), the formation yields of 1,4-NQ and 1,2-NQ were 1.5±0.4 and 5.1±2.7% respectively. The measured yields of PQs were 3.6±0.8% for 9,10-PQ and 2.7±1.1% for 1,4-PQ. From the measured yield data, the atmospheric formation of PAH-QNs was estimated and the importance of the atmospheric formation of PAH-QNs from the gas phase reaction of PAHs with the OH radical is discussed.

Chemical Composition Based Aerosol Optical Properties According to Size Distribution and Mixture Types during Smog and Asian Dust Events in Seoul, Korea

This study investigated the optical properties of aerosols involved in different meteorological events, including smog and Asian dust days. Carbonaceous components and inorganic species were measured in Seoul, Korea between 25 and 31 March 2012. Based on the measurements, the optical properties of aerosols were calculated by considering composition, size distribution, and mixing state of aerosols. To represent polydisperse size distributions of aerosols, a lognormal size distribution with a wide range of geometric mean diameters and geometric standard deviations was used. For the optical property calculations, the Mie theory was used to compute single-scattering properties of aerosol particles with varying size and composition. Analysis of the sampled data showed that the water-soluble components of organic matter increased on smog days, whereas crustal elements increased on dust days. The water content significantly influenced the optical properties of aerosols during the smog days as a result of high relative humidity and an increase in the water-soluble component. The absorption coefficients depended on the aerosol mixture type and the aerosol size distributions. Therefore, to improve our knowledge on radiative impacts of aerosols, especially the regional impacts of aerosols in East Asia, accurate measurements of aerosols, such as size distribution, composition, and mixture type, under different meteorological conditions are required.

Characteristics of Gas- and Particle-phase Polycyclic Aromatic Hydrocarbon (PAH) Distribution in Tunnels

Twenty four individual polycyclic aromatic hydrocarbon (PAH) compounds both in gasand particle-phase were quantified in three tunnels (Namsan Tunnel 3, Jeongneung Tunnel, Bukak Tunnel) to characterize vehiculate emission of PAHs. Gas phase PAHs were dominant in tunnels which consisted of 85% of total PAHs concentrations. Naphthalene and 2-methyl naphthalene were the most abundant gas phase PAH compounds, while the concentrations of fluoranthene and pyrene were highest in the particle phase. Most (96%) of the gas phase PAH compounds consisted of twoand three-aromatic rings whereas most of the particle phase PAHs were in four and five-rings (67%) in tunnels. Average BaP-eq concentrations of PAHs in the particle phase (20.8±11.6 ng m) was about twenty fold higher than that in the gas phase (1.6±0.6 ng m). It means that the particle phase PAHs has more adverse health effect than the gas phase PAHs even though the concentrations of the particle phase PAHs were lower than those of the gas phase PAHs. Compared to previous studies reporting diagnostic ratios for specific PAH compounds, the profile of individual PAH compounds measured in this study reflected well for the vehiculate emissions. We reported, for the first time, on the results of the profile of individual PAH compounds measured in tunnels for both gas and particle phases.

Multicomponent aerosol mass efficiency with various mixture types for polydispersed aerosol

ABSTRACT Based on the filter-sampled chemical composition data the seasonal variation of the optical properties of polydispersed aerosols, extinction, scattering, and absorption coefficient, are estimated for various types of aerosol mixtures. The mixtures considered in this study are the internal mixture, elemental carbon (EC)/non-EC external mixture, and fully external mixture. This study also evaluated the sensitivity of the aerosol optical properties for different size distributions. The results show that the extinction coefficient can be mostly accounted for scattering and generally shows a good agreement with each mixture type in this case study. However, the absorption coefficient shows a different tendency for internal and external mixtures. This study also shows that the aerosol optical properties vary as a function of particle diameter at the same composition and mass concentration. This means that mass extinction, scattering, and absorption efficiencies, which were considered as constants in general, should be reassessed and more specifically described as a function of particle size.

On the multi-day haze in the Asian continental outflow: An importantrole of synoptic condition combined with regional and local sources

The air quality of the megacities in populated and industrialized regions like East Asia is affected by both local and regional emission sources. The combined effect of regional transport and local emissions on multiday haze was investigated through a synthetic analysis of PM2.5 sampled at both an urban site in Seoul, South Korea and an upwind background site on Deokjeok Island over the Yellow Sea during a severe multiday haze episode in late February 2014. Inorganic components and carbonaceous species of daily PM2.5 samples were measured, and gaseous pollutants, local meteorological factors, and synoptic meteorological conditions were also determined. A dominance of fine-mode particles (PM2.5 /PM10 ∼ 0.8), a large secondary inorganic fraction (76 %), high OC /EC (> 7), and highly oxidized aerosols (oxygen-to-carbon ratio of∼ 0.6 and organic-mass-to-carbon ratio of ∼ 1.9) under relatively warm, humid, and stagnant conditions characterize the multiday haze episode in Seoul; however, the early and late stages of the episode show different chemical compositions of PM2.5. High concentrations of sulfate in both Seoul and the upwind background in the early stage suggest a significant regional influence on the onset of the multiday haze. At the same time, high concentrations of nitrate and organic compounds in Seoul, which are local and highly correlated with meteorological factors, suggest the contribution of local emissions and secondary formation under stagnant meteorological conditions to the haze. A slow eastward-moving high-pressure system from southern China to the East China Sea induces the regional transport of aerosols and potential gaseous precursors for secondary aerosols from the North China Plain in the early stage but provides stagnant conditions conducive to the accumulation and the local formation of aerosols in the late stage. A blocking ridge over Alaska that developed during the episode hinders the zonal propagation of synoptic-scale systems and extends the haze period to several days. This study provides chemical insights into haze development sequentially by regional transport and local sources, and shows that the synoptic condition plays an important role in the dynamical evolution of long-lasting haze in the Asian continental outflow region.

Multidimensional Gas Chromatography - Time of Flight Mass Spectrometry of PAH in Smog Chamber Studies and in Smog Samples

Hans Falk (Falk et al., 1956; 1960) published the first papers demonstrating that polycyclic aromatic hydrocarbons underwent a transformation when exposed to ultraviolet light and oxidants. His experiments, in which concentrated spots of individual PAH were irradiated under UV light and exposed to ozone, suggested that PAH were oxidized to unknown products at a very slow rate of about 1 to 5% per hour. However, in 1977, it was shown (Lane & Katz, 1977) that PAH were, indeed, very sensitive to ozone by exposing monolayer distributions of PAH adsorbed on glass plates to ozone and irradiation which closely matched solar irradiation in the 2500A to 5000A region of the spectrum from a quartz lamp. Under lamp irradiation and 0.19 ppm O3, the half lives of Benzo[a]pyrene, Benzo[k]fluoranthene and Benzo[b]fluoranthene were 0.58 h, 3.9 h, and 4.2 h respectively (Lane, 1975). They also were the first to describe how multi-layering of PAH on particles could influence the apparent reaction rate of the PAH in Falk’s experiment, and demonstrated that a rapid surface oxidation reaction formed a “crust” of oxidized products and was then followed by a slower penetration reaction involving the ozone accessing the subsurface material by penetrating the surface oxidized material – much like passing through a crust of bread. In the 1980s the group at the University of California, lead by Roger Atkinson began smog chamber studies to determine the rate of decomposition of a wide variety of PAH and PAH-related compounds when exposed to various oxidants. Their work clearly indicated that the OH radical was the dominant oxidant in the atmosphere (Atkinson et al., 1984; Atkinson, 1988). Most subsequent smog chamber studies to investigate the decomposition of PAH have utilized the OH radical as the oxidant of choice. The first report of a variety of oxidized products of the reaction of Naphthalene with the OH radical in a smog chamber was published in 1994 (Lane & Tang, 1994). Numerous publications have followed, describing the products of the OH radical reactions with naphthalene (Atkinson & Arey, 1994; Bunce et al., 1997; Sasaki et al., 1997; Mihele et al., 2002; Wang et al., 2007; Lee & Lane, 2009; Nishino & Arey, 2009); with acenaphene (SauretSzczepanski & Lane, 2004); with Alkylated naphthalenes (Banceu et al., 2001; Wang et al., 2007) and with phenanthrene (Helmig & Harger, 1994; Esteve et al., 2003; Lee & Lane, 2010).