Assessment of organochlorine pesticides in the atmosphere of South Korea: spatial distribution, seasonal variation, and sources.

Organochlorine pesticides (OCPs) are widely used in certain countries. We determined atmospheric concentrations, distribution patterns, and seasonal variations of OCPs at four sites in South Korea for 1 year. Samples of 22 OCPs were collected using a high-volume air sampler, and measured via the isotope dilution method with HRGC/HRMS. In South Korea, pentachlorobenzene (PeCB), hexachlorocyclohexane (HCB), and endosulfan (EnSF) were dominant, accounting for > 87% of total OCPs. Spatial distributions showed significant differences and the highest levels were observed in Seosan (295.2 pg·m-3), indicating the compounding potential of diverse sources as Seosan has concentrated large-scale industrial complexes and agricultural activity (Seoul: 243.6 pg·m-3 > Jeju: 193.5 pg·m-3 > Baengnyeong: 178.2 pg·m-3). The isomeric ratios of OCPs in the South Korean atmosphere indicated that the dominant sources of HCB and dichlorodiphenyltrichloroethane were primarily used in the past; meanwhile, chlordane (CHL) and EnSFs were derived from recent material inputs. Seasonally, OCP concentrations largely peaked in summer with minimum values in winter. This apparent temperature dependence suggests the re-volatilization of accumulated chemicals into the atmosphere. Additionally, an air mass back trajectory indicated the influence of pollutants released from a reservoir through long-range atmospheric transport in the summer. In particular, restricted OCPs are primarily released into the atmosphere by inadvertent sources, such as industrial activities and volatilization from contaminated areas. Thus, severe OCP pollution in Korea is due to the mobile nature of the particles. These data can be useful for the continuous monitoring of long-range transported air pollutants that are transferred between countries.

Oxidation Behavior of Ti-Al-Si-N-O Nanocomposite Films Deposited by Filtered Arc Ion Plating Technique.

Oxidation behavior of nanocomposite films is very important characteristics for application of machining and cutting tools. In this study, Ti-Al-Si-N-O nanocomposite films were fabricated onto WC-Co and Si wafer substrates. The composition of the Ti-Al-Si-N-O films was analyzed by X-ray photo-electron spectroscope (XPS). Also X-ray diffactometer (XRD) analysis was conducted to investigate the crystallinity and phase transformation of the films. As a result of XRD, Ti-Al(18 at.%)-Si-N-O films showed the great oxidation resistance of 950 °C for 30 min in air. Based on glow discharge optical emission spectroscopy (GDOES) depth profiles, Ti-Al(18 at.%)- Si-N-O film annealed at 950 °C for 30 min shows formation of aluminum oxide layer on the film surface. On the other hand, Ti-Al(7.56 at.%)-Si-N-O film had a titanium oxide layer on the surface after annealing at 950 °C for 30 min.

Microstructure and Mechanical Properties of Functional Graded Ti-Al-Si-N-O Nanocomposite Films Deposited by Filtered Arc Ion Plating Technique.

Functional graded Ti-Al-Si-N-O nanocomposite films were deposited onto WC-Co substrate by a filtered arc ion plating system using TiAl and TiSi composite targets under N2/Ar atmosphere. XRD and XPS analyses revealed that the synthesized Ti-Al-Si-N-O films were nanocomposite consisting of nanosized (Ti, Al, Si)N crystallites embedded in an amorphous Si3N4/SiO2 matrix. The hardness of the Ti-Al-Si-N-O films exhibited the maximum hardness values of ~47 GPa at a Si content of ~5.63 at.% due to the microstructural change to a nanocomposite as well as the solid-solution hardening. Besides, Ti-Al-Si-N-O film with Si content of around 5.63 at.% also showed perfect adhesive strength value of 105.3 N. These excellent mechanical properties of Ti-Al-Si-N-O films could be help to improve the performance of machining tools and cutting tools with application of the film. A comparative study on microstructural characteristics among Ti-Al-Si-N-O films with various Si contents is reported in this paper.