Daeok Youn

Metrics for Ozone and Climate: Three-Dimensional Modeling Studies of Ozone Depletion Potentials and Indirect Global Warming Potentials

es Abstract The concepts of ozone depletion potentials (ODPs) and global warming potentials (GWPs) have been extensively used in policy consideration and scientific studies of ozone and climate issues. Most recent candidate-replacement compounds have atmospheric lifetimes shorter than 1 year in order to limit their environmen- tal effects. Especially for chemicals with extremely short lifetimes, on the order of several to tens of days, the stratospheric halogen loading and ozone loss from such gases strongly depend on the location of emissions. Using a state-of-the-art three- dimensional global chemistry-transport model (CTM) of the troposphere and the stratosphere, we have calculated the potential effects of very short-lived substances (VSLS) such as n-propyl bromide (nPB), iodotrifluoromethane (CF3I), and methyl iodine (CH3I) on atmospheric ozone. The model-derived lifetimes and ODPs of these halogenated compounds for mid-latitude emissions and of CF3I for tropical emissions are presented in this chapter. On the other hand, ozone depletion due to emission of bromochlorofluorocarbons, or Halons, leads to cooling of the climate system in the opposite direction to direct warming contribution of the Halons as greenhouse gases. This cooling is a key indirect effect of Halons on radiative forc- ing or climate. Using atmospheric models, CTMs and a radiative transfer model, we have explicitly calculated the indirect GWPs of Halon-1211 and -1301 for a 100- year time horizon. The calculated indirect effects of Halon-1211 are much smaller than those published in earlier studies. Nevertheless, our new model-based assess- ment of the indirect GWPs of the two major Halons confirms the importance of indirect effects on climate.

Effects of the El Niño on Tropospheric Ozone in a Simulation using a Climate-Chemistry Model

Department of Science Education, Chungbuk National Univerisity, Chungbuk 361-763, KoreaAbstract: We examine the effects of El Nino on tropospheric ozone through the simulation of a Climate-Chemistry modelfor a 40-year period (1971-2010). The Empirical Orthogonal Function (EOF) analysis reveals that the tropospheric ozoneconcentration in the central-eastern Pacific decreases when the El Nino occurs, which is consistent with the observation.However, the increase of ozone over Indian Ocean-Indonesia regions is weak in the simulation compared to theobservations. We analyze details of the 2006 El Nino event to understand the mechanism that caused the change of ozonedue to El Nino. It is found that enhanced convection as well as higher water vapor followed by shortened lifetime hasled to lower the tropospheric ozone. Downward motion induced by the changes of atmospheric circulation due to seasurface temperature forcing, together with the decrease of water vapor, has brought ozone produced in the uppertroposphere over the Indian OceanKeywords: climate model, global atmospheric chemistry model, tropospheric ozone, El Nino요약: 기후-전구대기화학모델을 이용하여 엘니뇨가 대류권 오존에 미치는 영향을 분석하였다. 40년간(1971-2010) 대류권 오존을 EOF 분석한 결과에서 열대 중앙-동태평양에서 오존의 감소가 관측과 유사하게 잘 모의되었다. 그러나 인도양-인도네시아 부근의 오존 증가는 관측에 비해 약하게 모의되었다. 엘니뇨에 의한 오존변동 과정을 이해하기 위하여

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.

Development of a new armor unit against high waves

Coastal hazards such as high waves are expected to increase due to global climate change. Therefore, we investigated new armor unit structures for disaster prevention. Recently, a concrete caisson has been used in many breakwaters against high waves in South Korea, but the demand for concrete armor unit has increased due to the high cost and many installation requirements. Though many new armor units have been developed over the world since Tetrapod in 1950, few have been used due to lack of systematical development. The representative armor units in current use have many advantages, but they cannot be applied to waves higher than 8 m. One of the new armor units developed by the design guide based on recent trend and hydraulic model experiments were conducted. The new armor unit was developed as a single layer due to cost effectiveness. However, the thickness is close to 1.5 times by overlapping the alphabet A and V. It showed higher overtopping compared to a double layer because of the thickness and the high packing density. It has a high interlocking vertically but low horizontally. It shows good stability at 9 m in model testing.