• Journal of Korean Society for Atmospheric Environment
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• v.20 no.4
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• pp.503-514
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• 2004

In Seoul metropolitan area, nocturnal variation of surface ozone concentrations observed at 27 monitoring sites from 1998 to 2002 showed that high ozone levels occurred frequently during the spring. Frequency distributions for nighttime ozone indicated that elevated concentrations in spring were influenced by advection of different air mass compared to other seasons. Surface wind analysis during the spring revealed that relatively strong southwesterly winds were associated with nocturnal ozone enhancement, which can be attributed to the regional transport of ozone. In order to identify the origin of nocturnal ozone enhancement in spring, 3-day backward trajectories were calculated by HYSPLIT 4 for the episode days and then classified. The results showed that NW, W, and SW flows, indicating influence of polluted air masses from the China continent, have 51% in a]1 the episode days, which suggest that the nocturnal ozone enhancement can occur under the effect of long-range transport of ozone-laden air mass on a regional scale. Case study of nocturnal ozone maxima associated with long-range transport was discussed in more detail in the light of meteorological conditions. Southwesterly synoptic flow along the outer edge of moving high-pressure system was found to be the important cause of nocturnal ozone maxima in Seoul. This flow could lead to be long-range transport of ozone that had effectively accumulated in the stagnating portion of the system located eastern coast of China. Low atmosphere soundings, backward trajectories, and elevated ozone and CO levels at the back-ground tiles gave evidence for regional effects on nocturnal ozone enhancement In Seoul.

• Environmental Sciences Bulletin of The Korean Environmental Sciences Society
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• v.4 no.3
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• pp.127-137
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• 2000

This study presents an analysis of the characteristics of vertical ozone distribution near the surface using ozonesonde data(l995 to 1998), plus surface ozone and meteorological data from the Pohang region. These features were examined in detail using three case studies. The first related to episodes of high surface ozone concentrations during the Spring season when the frontogenesis between the high and low pressure associated with the upper-level jet stream was found to be located near the surface. The second was a 5-day winter period(l3 -17 December, 1997) in the Pohang province when the hourly concentrations exceeded 90 ppb on several occasions owing to low-level jets(LLJs) induced by a nocturnal stable layer. Accordingly, this explains why the high surface ozone concentrations occurred at night as the ozone was transported across the zone by a strong wind speed( over 12.5 ms .1). The third case study was ozone enhancement due to photochemical reactions. In this case, the maximum concentration of ozone exceeded 60 ppb in the summer(23 -28 August, 1997). When an ozone peak appeared within the boundary layer, the occurrence frequency of a low-level jet due to the nocturnal stable layer was about 77%, similarly the occurrence frequency of a near-surface ozone peak relative to the appearance of an LLJ was about 76%. Accordingly, there is clearly a close correlation between the occurrence of LLJs and near-surface ozone peaks.