This paper provides a long-term perspective for ozone concentrations at 20 national air quality monitoring sites in Seoul from 1989 to 1998, which were managed by the Korean Ministry of Environment. Ozone episodes occurred more frequently in the east areas (Bangi, Guui, Seongsu, and Ssangmun) than in the west area (Guro and Oryu). When an ozone episode happened, hourly ozone concentrations over 80 ppb continued for an average of 4.0 hours at all sites. Annual variations in daily mean and maximum oBone concentrations showed broadly consistent upward trends at Ssangmun and Gwanaksan. Monthly mean ozone concentrations were the highest from May to June and the 99$^{th}$ and 95$^{th}$ percentile levels appeared higher during June, July, and August. The diurnal patterns of hourly mean ozone levels in urban areas showed typical photochemical formation and destruction, while the flat diurnal shape before 1996 at Gwanaksan indicated few significant photochemical reactions due to a lack of precursors of ozone. The occurrence of ozone over 80 ppb was ascribed to meteorological conditions such as high temperature, strong solar radiation, low relative humidity, and low wind speed with winds most frequently in a westerly direction.

Atmospheric concentrations of polychlorinated biphenyl (PCB) congeners were measured every two weeks from July, 1999 to January, 2000 at Hankyong University in Ansung, Kyounggi-do. Atmospheric concentrations of ∑$_{24}$PCB showed a range of 19.8～71.9 pg/m3. The highest concentration of PCB homolog was tri-CBs (sum of PCB 18, 27, 28, 33, 38) which had a comparatively higher vapor pressure than other homologs. The contribution ratio of lighter PCB homologs (tri-CBs) to total PCBs was 44.5%, and these homologs were the main components of PCBs. The ratio PCB homologs/deca-CB (PCB 209) suggested that the contribution of vapor phase PCBs increased greatly in summer relative to other seasons. In addition, the regression lines for PCB homologs/deca-CB (PCB 209) and temperature ($^{\circ}C$) appeared as an exponential function with high correlation (R2>0.67, p< 0.01). This suggests that the concentration of vapor phase PCB homologs increases steeply with increasing temperature.

A laboratory- scale dual-column biofilter system was used to study the biofiltration of dimethyl disulfide (DMDS). The gas flow rate and DMDS concentration to the biofilter were varied to study their effect on the remov-al of dimethyl disulfide. Operating parameters such as pH, temperature, and water content were monitored during the biofilter operation and necessary precautions were taken to keep these parameters within the acceptable limits. It was observed that the removal efficiency of DMDS was optimal at neutral pH values. After five month op-eration, the neutralization of the filter beds with sodium carbonate became necessary for the optimum operation of the biofilters. The microbial population already present in the compost mixtures was found to be adequate in treat-ing DMDS. The compost mixtures were found to be similar in terms of biofiltration efficiency of DMDS. However, pressure drops observed in the first column compost mixture (compost/ peat mulch) was extremely high, making this compost economically not feasible. The second mixture (compost/bark) provided pressure drops within accept-able limits. A minimum residence time of 30 seconds at the optimal operating conditions appeared to be adequate for achieving high removal efficiencies (>90%).

A dual -column biofilter system with two different composts was used to investigate the macro-kinetics of dim-ethyl disulfide (DMDS) degradation. The biofilter columns were filled with compost mixtures up to one meter, The gas How rate and DMDS concentration to the biofilters were varied to study their effect on the removal characteris-tics of DMDS. It was found that the biodegradation of DMDS was governed by zero-order reaction -limited macro-kinetics for inlet DMDS concentrations between 10 and 55 ppmv. The overall average zero-order kinetic coeffi-cient for DMDS removal by compost was 0.50 ($\pm$0.1) ppm/sec for both compost mixtures studied. Variations in individual kinetic coefficients were observed due to varying environmental conditions, such as pH and temperature. The kinetic coefficients determined are specific to the system discussed in this work. During high acidity conditions in the filter beds, methyl mercaptan (MM) was observed in the gas samples collected. Appearance of MM was pro-bably due to decreased microbial activity in the lower portions of the biofilter. Considering the neutral pH range required and the presence of methyl mercaptan, it is likely that the microorganisms present in the biofilters used in this research are similar to the T. thioparus (strain E6) species.

In order to study the distribution characteristics of natural volatile organic compounds (NVOCs), we investigated the seasonal variations of $\alpha$-and $\beta$-pinene levels in a pine forest in Florida for a you. The mean concentrations of $\alpha$- and $\beta$-pinene measured during the whole study period were computed to be 125: 86 (N = 65) and 86$\pm$52 pptv (N = 56), respectively. According to our data grouping scheme, the seasonal means for both pinones were observed to peak during fall with their max and min values in summer and winter, respectively. The overall results of our study suggest that terpenes are subject to highly strong temporal variability because of changes in their major source characteristics across seasons.