Dong Soo Lee

Rapid Time Variations in Chemical Composition of Precipitation in South Korea

Data from a monitoring program on precipitation at four sites in South Korea during the period from 1993 to 1998 were analyzed for determining a time trend relationship in chemical composition of precipitation. The concentrations of nss-sulphate, ammonium and calcium were found to have decreased over time at a statistically significant level in Seoul (p<0.05). The concentration of nss-sulphate had declined by a rate of 12% per year for the period from 1993 to 1998. The concentrations of ammonium and calcium decreased by 11% and 12% per year respectively for the same period. The concurrent reduction of cation offsets the change in strong acid anion, thus the annual mean pH of precipitation has been approximately constant. In contrast to the rapid change of sulphate, the second most abundant anion, nitrate, showed no statistically significant decrease. As a result, the nitrate to nss-sulphate ratio (N/S ratio) has increased rapidly; the N/S ratio in precipitation has increased from less than 0.1 in 1985 to nearly 0.5 in 1998 at Seoul. In spite of the short monitoring period, a significant upward trend in the N/S ratio was also observed at all of the other sites suggesting that the nitrogen species contribute more to precipitation acidity throughout Korea.

Development of an automated monitoring system for various gas-phase organic carbonyls in ambient air

An automated monitoring system for various C1 to C5 gas-phase organic carbonyls in ambient air is described. The system consists of a parallel plate diffusion scrubber (PPDS), which is coupled with a high-performance liquid chromatography–ultraviolet (HPLC–UV) system using an automated injection valve. Compared with an annular diffusion scrubber (DS) employed so far for gas-phase carbonyl monitoring, PPDS shows an improved collection efficiency for formaldehyde, acetaldehyde, propionaldehyde, and acetone with >97% at an airflow rate of 0.5 L/min. High gas–liquid concentration ratios of PPDS and an optimised HPLC–UV system allow limits of detection (LOD) in a range of 80–500 pptv. A low liquid hold-up volume of the PPDS results in a short response time of about 10 min. Additionally, the optimised analysis time for 13 carbonyl compounds containing calibration standard enables brief measurement intervals of 25 min. The developed PPDS–HPLC system shows its reliability from urban site monitoring in Seoul, South Korea.

Estimation of Dry Deposition by Using a Filter Pack Method at Chunchon, Korea

Atmospheric gases and particulates were collected using four-stage filter-pack in Chunchon from January through December in 1999. Particulate SO42− and NO3−, and gaseous HNO3, SO2 and NH3 were analyzed. Annual average concentration of SO42−(S), NO3−(S), HNO3 (g), SO2(g) and NH3(g) were 5.75µg/m3, 4.98µg/m3, 0.33ppb, 1.52ppb and 7.25ppb, respectively. Annual dry deposition fluxes were estimated using the measured concentration and dry deposition velocity published by other research group. Annual dry deposition of S was 287kg · (km)−2·y−1, which accounted for about 30% of total S deposition. For N deposition, dry deposition is predominant; about 70% of total N deposition was through dry process mostly as forms of NH3 and HNO3.

Evaluation of Precipitation Composition at an Urban and a Rural Area for the Central Korean Peninsula

Precipitation samples were collected using wet-only samplers on a daily basis at Chunchon (rural area) and Seoul (urban area) from January to December in 1998. The pH, electrical conductivity, and the concentrations of major ions were analyzed. The volume-weighted annual average values of pH for both sites were identical. However, for volume weighted average pH of precipitations below 20 mm in Chunchon was significantly (p<0.05) lower than that in Seoul. The value of [NO3−]/[nss-SO42−], calculated from average composition of rainfalls below 20mm, were 0.42 and 0.61 in Seoul and Chunchon, respectively. This supports that acidification of precipitation by nitrogen oxides, a part of which might be transported from the Seoul metropolitan area, caused the difference in pH between Chunchon and Seoul.

Assuring precision and calibration linearity in ultrasensitive suppressed ion chromatography by using deliberately contaminated hydroxide eluent

EXPERIMENTAL and theoretical studies were conducted to investigate low and non-linear responses in sub-micro molar-level suppressed ion chromatography with a hydroxide eluent. A calculated response was derived using experimentally determined detector effluent ion composition data and compared with measured experimental responses. The calibration curve was non-linear, and its slope varied considerably with different instrumental setups and operating conditions. The non-linearity of the solution conductivity response was determined by two acid-base equilibria of water and carbonic acid, and fluoride ion. By using eluent contaminated with para-toluene sulfonate at micro molar level, the non-linear response was greatly alleviated.