Soonchang Yoon - Academia.edu (original) (raw)

Papers by Soonchang Yoon

Research paper thumbnail of 준실시간 연속관측을 통한 제주 고산 PM 2.5 Oc와 Ec의 계절별 사례별 특성

Journal of Korean Society for Atmospheric Environment, 2013

At Gosan ABC superstation in Jeju Island, we measured organic carbon (OC) and elemental carbon (E... more At Gosan ABC superstation in Jeju Island, we measured organic carbon (OC) and elemental carbon (EC) in PM 2.5 from October 2009 to June 2010 using a Sunset Laboratory Model-4 Semi-Continuous OC/EC Field Analyzer. It employs TOT (Thermal-Optical-Transmittance) method with NIOSH 5040 protocol and enables to continuously monitor OC and EC concentrations with 1-hour time resolution. The mean values of OC and EC for the entire period of measurements were 2.1±1.4 μg/m³ and 0.7±0.6 μg/m³, respectively. The OC/EC ratio was 3 and EC accounted 25±2.1% of total carbon (TC, TC=OC+EC). Although OC and EC showed similar trend in seasonal variation, the ratio of OC to EC was the highest in early summer when temperature was the highest and the air was affected by biomass burning in the southern part of China. In winter, the high OC and EC concentrations were likely influenced by increased coal combustion from residential heating. The high OC and EC concentrations were observed during events such as haze, dust, and the combination of the two. During the haze events, OC and EC were enhanced with increase in PM 10 , PM 2.5 , SO₂, and NO₂ with broad maxima. When dust occurred, both OC and EC started decreasing after reaching their maxima a couple of hours before PM 10 maximum. The peak separation of carbonaceous species and aerosol masses with time was more noticeable when haze event was followed by dust plume. These results confirm that OC and EC are key components of haze occurring in the study region.

Research paper thumbnail of PACDEX 캠페인 자료로 분석한 블랙카본을 포함한 축적모드 에어로솔의 구름응결핵 가능성

Journal of Korean Society for Atmospheric Environment, 2010

Research paper thumbnail of Dependence of cloud microphysical and macrophysical properties on aerosol in Northeast Asia

The effects of aerosol on the microphysical and macrophysical properties of shallow stratocumulus... more The effects of aerosol on the microphysical and macrophysical properties of shallow stratocumulus over Northeast Asia are investigated a bin-based meso-scale cloud model with inhomogeneous aerosol fields, in terms of aerosol composition and number concentration. We selected two shallow stratocumulus cases with maritime and polluted conditions during March 2005. To attempt to interpret aerosol-cloud link, numerical simulations are designed with switching aerosol condition as well as employing a wide variation in aerosol concentrations, while keeping the synoptic forcing the same. The reduction of cloud effective radius and the enhancement of optical depth with increasing column aerosol number concentration are obvious regardless of aerosol composition and meteorological settings. Enhanced aerosol number concentration results in increased liquid water path in humid case, but invariant liquid water path in dry case primarily due to the difference in microphysical cloud droplet growth b...

Research paper thumbnail of Comparison of light-absorption properties of aerosols observed in East and South Asia

In this study, we compared light-absorption properties of aerosols observed in East and South Asi... more In this study, we compared light-absorption properties of aerosols observed in East and South Asia from black carbon (BC) mass concentration, aerosol scattering () and absorption () coefficients measurements at four sites: Korea Climate Observatory-Gosan (KCO-G), Korea Climate Observatory-Anmyeon (KCO-A), Maldives Climate Observatory-Hanimaadhoo (MCO-H) and Nepal Climate Observatory-Pyramid (NCO-P). No significant seasonal variations of BC mass concentration, and , despite of wet removal of aerosols by precipitation in summer, were observed in East Asia, whereas dramatic changes of light-absorbing aerosol properties were observed in South Asia between dry and wet monsoon periods. Although BC mass concentration in East Asia is generally higher than that observed in South Asia, BC mass concentration at MCO-H during winter dry monsoon is similar to that of East Asia. The observed solar absorption efficiency () at 550 nm, where , at KCO-G and KCO-A is higher than that in MCO-H due to la...

Research paper thumbnail of Lidar network observations of tropospheric aerosols

SPIE Proceedings, 2008

Observations of tropospheric aerosols (mineral dust, air-pollution aerosols, etc.) and clouds are... more Observations of tropospheric aerosols (mineral dust, air-pollution aerosols, etc.) and clouds are being conducted using a network of two-wavelength (1064nm, 532nm) polarization (532nm) lidars in the East Asian region. Currently, the lidars are operated continuously at 23 locations in Japan, Korea, China, Mongolia and Thailand. A real-time data processing system was developed for the network, and the data products such as the attenuated backscatter coefficients and the estimated extinction coefficients for non-spherical and spherical aerosols are generated automatically for online network stations. The data are used in the real-time monitoring of Asian dust as well as in the studies of regional air pollution and climate change.

Research paper thumbnail of Aerosol and yellow-sand monitoring with a micro pulse lidar in Seoul

Technical Digest. CLEO/Pacific Rim '99. Pacific Rim Conference on Lasers and Electro-Optics (Cat. No.99TH8464)

Yellow-sand events are the strongest natural signal of the long-range transport of air pollution.... more Yellow-sand events are the strongest natural signal of the long-range transport of air pollution. However, the state-of-art technology such as isentrophic trajectory models and satellite imaging techniques has limitations on the exact path or height of yellow-sand movement in the atmosphere. In this paper we are presenting the vertical profiles of the light extinction coefficient by the tropospheric aerosols measured

Research paper thumbnail of Comparison of aerosol optical depth between CALIOP and MODIS-Aqua for CALIOP aerosol subtypes over the ocean

Journal of Geophysical Research: Atmospheres, 2013

The Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) aerosol optical depth (AOD) has bee... more The Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) aerosol optical depth (AOD) has been compared with the Moderate Resolution Imaging Spectroradiometer (MODIS)-Aqua AOD using Level 2 products of both instruments. Such comparisons have been performed for five different aerosol subtypes classified by CALIOP algorithm, namely clean marine, dust, polluted dust, polluted continental, and biomass burning, over the ocean from June 2006 to December 2010. MODIS AOD at 550 nm (0.111 ± 0.079) for the collocated data pairs is about 63% higher than CALIOP AOD at 532 nm (0.068 ± 0.073). For clean marine, MODIS AOD (0.110 ± 0.064) is almost twice the CALIOP AOD (0.056 ± 0.038), and the difference between the AOD values has a strong latitude dependence likely related to the surface wind speed over the ocean. The difference in AOD for dust (13%) is observed to be the lowest among the five aerosol types under consideration, but it shows a slight regional variation. The discrepancy of AOD for dust also shows strong dependency on the layer mean of the particulate depolarization ratio. CALIOP AOD is higher than MODIS AOD for both polluted dust and polluted continental by 15% and 29%, respectively, for most of the ocean. One of the possible reasons for the difference is the misclassification of clean marine (or marine + dust) as polluted dust and polluted continental in the CALIOP algorithm. For biomass burning, uncertainty in the layer base altitude is thought to be one of the main reasons for the lower value of CALIOP AOD.

Research paper thumbnail of 에어로졸 광학변수가 대기복사가열률 산정에 미치는 민감도 분석

Research paper thumbnail of Large-scale connection between aerosol optical depth and summer monsoon circulation, and precipitation over northeast Asia

We investigated the large-scale connection between columnar aerosol loads and summer monsoon circ... more We investigated the large-scale connection between columnar aerosol loads and summer monsoon circulation, and also the precipitation over northeast Asia using aerosol optical depth (AOD) data obtained from the 8-year MODIS, AERONET Sun/sky radiometer, and precipitation data acquired under the Global Precipitation Climatology Project (GPCP). These high-quality data revealed the large-scale link between AOD and summer monsoon circulation, precipitation in July over northeast Asian countries, and their distinct spatial and annual variabilities. Compared to the mean AOD for the entire period of 2001-2008, the increase of almost 40-50% in the AOD value in July 2005 and July 2007 was found over the downwind regions of China (Yellow Sea, Korean peninsula, and East Sea), with negative precipitation anomalies. This can be attributable to the strong westerly confluent flows, between cyclone flows by continental thermal low centered over the northern China and anti-cyclonic flows by the wester...

Research paper thumbnail of Asian dust event observed in Seoul, Korea, during 29–31 May 2008: Analysis of transport and vertical distribution of dust particles from lidar and surface measurements

Science of The Total Environment, 2010

In this study, we investigate the transport of dust particles, its vertical distribution, and the... more In this study, we investigate the transport of dust particles, its vertical distribution, and the associated meteorological conditions during an Asian dust event that was observed in Seoul, Korea on May 29-31, 2008. This study analyzes data from ground-based and space-borne 2-wavelength polarization lidars, particulate mass concentrations, and synoptic weather data. Surface meteorological station observations of dust phenomena, dust transport model, and weather maps consistently show that the dust particles were transported from the source regions (Inner Mongolia, Man-Ju, and Ordos areas) to Korea via the northeastern part of China. Network observations of the PM(10) concentrations in Korea revealed that a majority of the heavy dust particles traveled across South Korea from the northwest to the southeast direction with a horizontal scale of 250-300km and a traveling speed of approximately 40kmh(-1). This extraordinary dust event, in terms of its intensity and timing during the year, occurred due to the blockage of an unusually intensified low-pressure system in the northeastern part of China as well as high-pressure system centered over the Sea of Okhotsk and the Kuril Islands. The low values of the particle depolarization ratio (delta(532)) (<or=0.05) and color ratio (CR) during the pre-dust period indicate the presence of spherical, non-dust, and relatively small particles. The mean delta(532) value was approximately 0.123+/-0.069 between altitudes of ground approximately 2.8km, and 0.161+/-0.049 for near-surface dust layer (ground approximately 1.2km). This value is quite similar to that obtained during the 3-year SNU-Lidar measurements in Seoul (delta(532) approximately 0.136+/-0.027). The value of delta(532) during the 2nd multilayered dust episode ranged between 0.081 and 0.120 for near-surface dust layers, and between 0.076 and 0.114 for elevated dust layers. The CALIPSO measurements of beta(532), delta(532), and CR also revealed the presence of dense dust aerosols along the transport route.

Research paper thumbnail of The effect of aerosol representation on cloud microphysical properties in Northeast Asia

Meteorology and Atmospheric Physics, 2013

Research paper thumbnail of Estimation of Direct Radiative Forcing of Asian Dust Aerosols with Sun/Sky Radiometer and Lidar Measurements at Gosan, Korea

Journal of the Meteorological Society of Japan, 2004

In this study the aerosol direct radiative forcing (ADRF) of Asian dust is evaluated by model sim... more In this study the aerosol direct radiative forcing (ADRF) of Asian dust is evaluated by model simulation at Gosan, Jeju using the data from a sun/sky radiometer, a Micro-Pulse Lidar (MPL), and column radiometer measurements of solar downwelling irradiance in April, 2001. We suggest a method of determining aerosol parameters for the radiative transfer model from the Aerosol Robotic Network (AERONET) data set. Since the AERONET measurements provide the refractive indices at only four wavelengths, and the aerosol parameters can be calculated at these wavelengths with a Mie code, we use a linear regression method for extending these measurements to the full wavelength spectrum of the radiative transfer model. The aerosol forcing by the Asian dust aerosols is estimated and compared to the aerosol forcing of non-dust aerosols. On the Asian dust event day, April 13, the daily average ADRF was estimated as À58.1 W/m 2 at the surface and À25.7 W/m 2 at the top of the atmosphere (TOA). On April 15, a nondust day slightly influenced by anthropogenic aerosols, the ADRF was À29.0 W/m 2 at the surface and À11.6 W/m 2 at the TOA. Although the Asian dust aerosols show larger forcing, its forcing efficiency (forcing per unit optical thickness) is smaller than that of non-dust aerosols; À41.0 W/m 2 /t 670 at the TOA and À94.9 W/m 2 /t 670 at the surface on the dust day for dust aerosols, as opposed to À50.0 W/m 2 /t 670 at the TOA and À129.3 W/m 2 /t 670 at the surface on the non-dust day for non-dust aerosols. We believe that this is due to the larger single scattering albedo of dust aerosols, which causes smaller absorption, and the larger asymmetry factor which causes more forward scattering or less reflection, compared to anthropogenic aerosols. The model results were validated with the surface irradiance measurement data and the comparison showed a good agreement. The radiative transfer calculation underestimates the solar irradiance of 2@3% on average. The aerosol profiles measured by lidar are used to estimate the influence of the vertical distribution of Asian dust aerosols on the ADRF. Using the vertical aerosol profiles, we found an

Research paper thumbnail of Overview of the Atmospheric Brown Cloud East Asian Regional Experiment 2005 and a study of the aerosol direct radiative forcing in east Asia

Journal of Geophysical Research, 2007

Research paper thumbnail of Comparison of vertical dust flux by implementing three dust emission schemes in WRF/Chem

Journal of Geophysical Research, 2011

Vertical dust flux parameterizations were assessed by implementing three different dust emission ... more Vertical dust flux parameterizations were assessed by implementing three different dust emission schemes, namely, those of Marticorena and Bergametti (1995), Lu and Shao (1999), and Shao (2004) (hereinafter referred to as MB, LS, and S04 schemes, respectively) in Weather Research and Forecasting with Chemistry (WRF/Chem). Through sensitivity tests, the scattering of vertical dust fluxes resulting from different parameterizations was shown even under the condition of same horizontal sand flux. The difference between the estimated vertical dust fluxes of three emission schemes ranges from the order of 10 1 for sand to the order of 10 2 for clay. The MB scheme generally produces higher dust emissions than the LS and S04 schemes, and the difference is the greatest for clay because the MB scheme considers vertical dust flux to be related to clay content, while the LS and S04 schemes consider it to be inversely proportional to surface hardness. To investigate the performance of each dust emission scheme in the simulation of Asian dust events, a case study was carried out for a severe Asian dust event that took place between 30 March and 1 April 2007. Simulation results reproduced the outbreak and transport pattern of dust plumes satisfactorily. However, the estimated dust emission amounts in each scheme differed greatly, particularly in loamy soil. The total dust emission amounts averaged for the main dust source region in this Asian dust event for five consecutive days are 84 Tg, 149 Tg, and 532 Tg for the LS, S04, and MB schemes, respectively.

Research paper thumbnail of Seasonal characteristics of air masses arriving at Gosan, Korea, using fine particle measurements between November 2001 and August 2003

Journal of Geophysical Research, 2007

Radio frequency (RF) magnetron sputtering is a versatile deposition technique that can produce th... more Radio frequency (RF) magnetron sputtering is a versatile deposition technique that can produce thin, uniform, dense calcium phosphate coatings. In this paper, principle and character of magnetron sputtering is introduced, and development of the hydroxyapatite and its composite coatings application is reviewed. In addition, influence of heat treatment on magnetron sputtered coatings is discussed. The heat treated coatings have been shown to exhibit bioactive behaviour both in vivo and in vitro. At last, the future application of the bioactive ceramic coating deposited by magnetron sputtering is mentioned.

Research paper thumbnail of Intercomparisons of cloud-top and cloud-base heights from ground-based Lidar, CloudSat and CALIPSO measurements

International Journal of Remote Sensing, 2011

ABSTRACT This study presents results of the intercomparison of cloud-top height (CTH) and cloud-b... more ABSTRACT This study presents results of the intercomparison of cloud-top height (CTH) and cloud-bottom height (CBH) obtained from a space-borne active sensor Cloud Profiling Radar (CPR), the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP), the space-borne passive sensor Moderate Resolution Imaging Spectroradiometer (MODIS) and ground-based Lidar measurements. Three selected cases (one daytime and two night-time cases) involving various cloud conditions such as semi-transparent thin cirrus, opaque thick tropospheric clouds and multi-layered clouds are studied, with special attention to CBH. The space-based CALIOP provides reliable heights of thin high-altitude cirrus clouds containing small ice particles, but the 94 GHz CPR has low sensitivity to these clouds. The CTHs retrieved from the CPR and CALIOP for thick tropospheric clouds are in good agreement with each other. Discrepancies between the CPR and the CALIOP values of the CBH for thick opaque clouds arise from strong Lidar signal attenuations. In cloud-overlap conditions (i.e. multi-layered clouds are present), the CALIOP has difficulties in determining the cloud vertical structure (CVS) for thick clouds underlying thin cirrus clouds due to signal attenuations, whereas the CPR detects the CTH and CBH of both the cloud layers. This fact is also confirmed by the comparison of seasonal variations of occurrences of CBH and CTH retrieved from 1 year measurements. The CBHs derived from the CPR and ground-based Lidar are generally in good agreement with each other. Especially, comparison of CBH between the ground-based Lidar and CPR retrieved from June 2006 to October 2008 shows an excellent linear relationship (coefficient of determination, R ∼ 0.996).

Research paper thumbnail of Observation of enhanced water vapor in Asian dust layer and its effect on atmospheric radiative heating rates

Geophysical Research Letters, 2004

Research paper thumbnail of Characteristics of the transport and vertical structure of aerosols during ABC-EAREX2005

Atmospheric Environment, 2008

In this study, we investigate the physio-chemical and optical properties of Asian spring continen... more In this study, we investigate the physio-chemical and optical properties of Asian spring continental outflow and its relation to synoptic transport patterns. Ground-based highly time-resolved measurements of aerosol chemical and physical properties, and lidar measurements of aerosol vertical distributions at Gosan, Korea during ABC-EAREX2005 have been analyzed. Two selected cases, based on PM 10 and PM 2.5 mass concentrations, indicate that pollution-dominant airmass preceded by the appearance of a major mineral dust plume with about 12 h time-lag. At the ground level, pollution aerosol components (NO 3 À , SO 4 2À , and NH 4 þ) showed distinct peaks first and the enhancement of soil components (Ca 2þ) appeared approximately 12 h later. Although lidar measurements reveal that spherical pollution particles were observed near the surface prior to a major plume of non-spherical mineral dust, elevated dust layers were simultaneously observed in the free troposphere overlying the ground-level pollution plume. Chemical transport model simulations of the horizontal distributions of dust and sulfate aerosols illustrate well the pollution plume preceding the dust-laden airmass. Backward trajectory and NCAR/PSU MM5 analysis show that the preceding pollution plume and following dust plume were consecutively transported under fast northwesterly/northerly winds formed between anticyclonic and cyclonic flows at the ground level.

Research paper thumbnail of Influences of relative humidity on aerosol optical properties and aerosol radiative forcing during ACE-Asia

Atmospheric Environment, 2006

In situ measurements at Gosan, South Korea, and onboard C-130 aircraft during ACE-Asia were analy... more In situ measurements at Gosan, South Korea, and onboard C-130 aircraft during ACE-Asia were analyzed to investigate the influence of relative humidity (RH) on aerosol optical properties and radiative forcing. The temporal variation of aerosol chemical composition at the Gosan super-site was highly dependent on the air mass transport pathways and source region. RH in the springtime over East Asia were distributed with very high spatial and temporal variation. The RH profile onboard C-130 aircraft measurements exhibits a mixed layer height of about 2 km. Aerosol scattering coefficient (s sp) under ambient RH was greatly enhanced as compared with that at dry RH (RHo40%). From the aerosol optical and radiative transfer modeling studies, we found that the extinction and scattering coefficients are greatly enhanced with RH. Single scattering albedo with RH is also sensitively changed in the longer wavelength. Asymmetry parameter (g) is gradually increased with RH although g decreases with wavelength at a given RH. Aerosol optical depth (AOD) at 550 nm and RH of 50% increased to factors 1.24, 1.51, 2.16, and 3.20 at different RH levels 70, 80, 90, and 95%, respectively. Diurnal-averaged aerosol radiative forcings for surface, TOA, and atmosphere were increased with RH because AOD was increased with RH due to hygroscopic growth of aerosol particles. This result implies that the hygroscopic growth due to water-soluble or hydrophilic particles in the lower troposphere may significantly modify the magnitude of aerosol radiative forcing both at the surface and TOA. However, the diurnal-averaged radiative forcing efficiencies at the surface, TOA, and atmosphere were decreased with increasing RH. The decrease of the forcing efficiency with RH results from the fact that increasing rate of aerosol optical depth with RH is greater than the increasing rate of aerosol radiative forcing with RH.

Research paper thumbnail of Air mass characterization and source region analysis for the Gosan super-site, Korea, during the ACE-Asia 2001 field campaign

Atmospheric Environment, 2005

This paper presents results of air mass characterization and the associated microphysical and opt... more This paper presents results of air mass characterization and the associated microphysical and optical properties of Asian aerosols, using the cluster analysis technique for classifying air mass back-trajectories arrived at Gosan on the Jeju Island, Korea during the ACE-Asia campaign. Five distinct clusters of trajectories were taken to explain each transport regime. The temporal variation of the transported air masses could be well explained by the consecutive and stepwise change of air masses between statistically classified clusters. The cluster-mean trajectory exhibited its close relationship with the synoptic-scale circulation pattern. In addition, it was shown that the composite of mean sea-level pressure field is useful for explaining favorable meteorological conditions for long-range transport of dust and anthropogenic pollution in East Asia. The highest light scattering and absorption coefficients for sub-10-and submicron aerosols as well as highest concentrations of 222 Rn and condensation nuclei are associated with the air mass types accompanying dusts and pollutants. The cluster-mean single scattering albedo (SSA) for sub-10-and submicron aerosols ranged 0.88-0.90 and 0.81-0.86, respectively. This value of SSA indicates the large contribution of submicron aerosol for the light absorption in East Asia. The concentration of 222 Rn and aerosol microphysical and optical properties for marine air mass suggests that the marine air masses are somewhat influenced by continental outflows. The minor differences in aerosol microphysical and optical properties among continental clusters with similar routes and different transport speed implies that the effect of transport speed may not be significant if the transport routes are similar.

Research paper thumbnail of 준실시간 연속관측을 통한 제주 고산 PM 2.5 Oc와 Ec의 계절별 사례별 특성

Journal of Korean Society for Atmospheric Environment, 2013

At Gosan ABC superstation in Jeju Island, we measured organic carbon (OC) and elemental carbon (E... more At Gosan ABC superstation in Jeju Island, we measured organic carbon (OC) and elemental carbon (EC) in PM 2.5 from October 2009 to June 2010 using a Sunset Laboratory Model-4 Semi-Continuous OC/EC Field Analyzer. It employs TOT (Thermal-Optical-Transmittance) method with NIOSH 5040 protocol and enables to continuously monitor OC and EC concentrations with 1-hour time resolution. The mean values of OC and EC for the entire period of measurements were 2.1±1.4 μg/m³ and 0.7±0.6 μg/m³, respectively. The OC/EC ratio was 3 and EC accounted 25±2.1% of total carbon (TC, TC=OC+EC). Although OC and EC showed similar trend in seasonal variation, the ratio of OC to EC was the highest in early summer when temperature was the highest and the air was affected by biomass burning in the southern part of China. In winter, the high OC and EC concentrations were likely influenced by increased coal combustion from residential heating. The high OC and EC concentrations were observed during events such as haze, dust, and the combination of the two. During the haze events, OC and EC were enhanced with increase in PM 10 , PM 2.5 , SO₂, and NO₂ with broad maxima. When dust occurred, both OC and EC started decreasing after reaching their maxima a couple of hours before PM 10 maximum. The peak separation of carbonaceous species and aerosol masses with time was more noticeable when haze event was followed by dust plume. These results confirm that OC and EC are key components of haze occurring in the study region.

Research paper thumbnail of PACDEX 캠페인 자료로 분석한 블랙카본을 포함한 축적모드 에어로솔의 구름응결핵 가능성

Journal of Korean Society for Atmospheric Environment, 2010

Research paper thumbnail of Dependence of cloud microphysical and macrophysical properties on aerosol in Northeast Asia

The effects of aerosol on the microphysical and macrophysical properties of shallow stratocumulus... more The effects of aerosol on the microphysical and macrophysical properties of shallow stratocumulus over Northeast Asia are investigated a bin-based meso-scale cloud model with inhomogeneous aerosol fields, in terms of aerosol composition and number concentration. We selected two shallow stratocumulus cases with maritime and polluted conditions during March 2005. To attempt to interpret aerosol-cloud link, numerical simulations are designed with switching aerosol condition as well as employing a wide variation in aerosol concentrations, while keeping the synoptic forcing the same. The reduction of cloud effective radius and the enhancement of optical depth with increasing column aerosol number concentration are obvious regardless of aerosol composition and meteorological settings. Enhanced aerosol number concentration results in increased liquid water path in humid case, but invariant liquid water path in dry case primarily due to the difference in microphysical cloud droplet growth b...

Research paper thumbnail of Comparison of light-absorption properties of aerosols observed in East and South Asia

In this study, we compared light-absorption properties of aerosols observed in East and South Asi... more In this study, we compared light-absorption properties of aerosols observed in East and South Asia from black carbon (BC) mass concentration, aerosol scattering () and absorption () coefficients measurements at four sites: Korea Climate Observatory-Gosan (KCO-G), Korea Climate Observatory-Anmyeon (KCO-A), Maldives Climate Observatory-Hanimaadhoo (MCO-H) and Nepal Climate Observatory-Pyramid (NCO-P). No significant seasonal variations of BC mass concentration, and , despite of wet removal of aerosols by precipitation in summer, were observed in East Asia, whereas dramatic changes of light-absorbing aerosol properties were observed in South Asia between dry and wet monsoon periods. Although BC mass concentration in East Asia is generally higher than that observed in South Asia, BC mass concentration at MCO-H during winter dry monsoon is similar to that of East Asia. The observed solar absorption efficiency () at 550 nm, where , at KCO-G and KCO-A is higher than that in MCO-H due to la...

Research paper thumbnail of Lidar network observations of tropospheric aerosols

SPIE Proceedings, 2008

Observations of tropospheric aerosols (mineral dust, air-pollution aerosols, etc.) and clouds are... more Observations of tropospheric aerosols (mineral dust, air-pollution aerosols, etc.) and clouds are being conducted using a network of two-wavelength (1064nm, 532nm) polarization (532nm) lidars in the East Asian region. Currently, the lidars are operated continuously at 23 locations in Japan, Korea, China, Mongolia and Thailand. A real-time data processing system was developed for the network, and the data products such as the attenuated backscatter coefficients and the estimated extinction coefficients for non-spherical and spherical aerosols are generated automatically for online network stations. The data are used in the real-time monitoring of Asian dust as well as in the studies of regional air pollution and climate change.

Research paper thumbnail of Aerosol and yellow-sand monitoring with a micro pulse lidar in Seoul

Technical Digest. CLEO/Pacific Rim '99. Pacific Rim Conference on Lasers and Electro-Optics (Cat. No.99TH8464)

Yellow-sand events are the strongest natural signal of the long-range transport of air pollution.... more Yellow-sand events are the strongest natural signal of the long-range transport of air pollution. However, the state-of-art technology such as isentrophic trajectory models and satellite imaging techniques has limitations on the exact path or height of yellow-sand movement in the atmosphere. In this paper we are presenting the vertical profiles of the light extinction coefficient by the tropospheric aerosols measured

Research paper thumbnail of Comparison of aerosol optical depth between CALIOP and MODIS-Aqua for CALIOP aerosol subtypes over the ocean

Journal of Geophysical Research: Atmospheres, 2013

The Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) aerosol optical depth (AOD) has bee... more The Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) aerosol optical depth (AOD) has been compared with the Moderate Resolution Imaging Spectroradiometer (MODIS)-Aqua AOD using Level 2 products of both instruments. Such comparisons have been performed for five different aerosol subtypes classified by CALIOP algorithm, namely clean marine, dust, polluted dust, polluted continental, and biomass burning, over the ocean from June 2006 to December 2010. MODIS AOD at 550 nm (0.111 ± 0.079) for the collocated data pairs is about 63% higher than CALIOP AOD at 532 nm (0.068 ± 0.073). For clean marine, MODIS AOD (0.110 ± 0.064) is almost twice the CALIOP AOD (0.056 ± 0.038), and the difference between the AOD values has a strong latitude dependence likely related to the surface wind speed over the ocean. The difference in AOD for dust (13%) is observed to be the lowest among the five aerosol types under consideration, but it shows a slight regional variation. The discrepancy of AOD for dust also shows strong dependency on the layer mean of the particulate depolarization ratio. CALIOP AOD is higher than MODIS AOD for both polluted dust and polluted continental by 15% and 29%, respectively, for most of the ocean. One of the possible reasons for the difference is the misclassification of clean marine (or marine + dust) as polluted dust and polluted continental in the CALIOP algorithm. For biomass burning, uncertainty in the layer base altitude is thought to be one of the main reasons for the lower value of CALIOP AOD.

Research paper thumbnail of 에어로졸 광학변수가 대기복사가열률 산정에 미치는 민감도 분석

Research paper thumbnail of Large-scale connection between aerosol optical depth and summer monsoon circulation, and precipitation over northeast Asia

We investigated the large-scale connection between columnar aerosol loads and summer monsoon circ... more We investigated the large-scale connection between columnar aerosol loads and summer monsoon circulation, and also the precipitation over northeast Asia using aerosol optical depth (AOD) data obtained from the 8-year MODIS, AERONET Sun/sky radiometer, and precipitation data acquired under the Global Precipitation Climatology Project (GPCP). These high-quality data revealed the large-scale link between AOD and summer monsoon circulation, precipitation in July over northeast Asian countries, and their distinct spatial and annual variabilities. Compared to the mean AOD for the entire period of 2001-2008, the increase of almost 40-50% in the AOD value in July 2005 and July 2007 was found over the downwind regions of China (Yellow Sea, Korean peninsula, and East Sea), with negative precipitation anomalies. This can be attributable to the strong westerly confluent flows, between cyclone flows by continental thermal low centered over the northern China and anti-cyclonic flows by the wester...

Research paper thumbnail of Asian dust event observed in Seoul, Korea, during 29–31 May 2008: Analysis of transport and vertical distribution of dust particles from lidar and surface measurements

Science of The Total Environment, 2010

In this study, we investigate the transport of dust particles, its vertical distribution, and the... more In this study, we investigate the transport of dust particles, its vertical distribution, and the associated meteorological conditions during an Asian dust event that was observed in Seoul, Korea on May 29-31, 2008. This study analyzes data from ground-based and space-borne 2-wavelength polarization lidars, particulate mass concentrations, and synoptic weather data. Surface meteorological station observations of dust phenomena, dust transport model, and weather maps consistently show that the dust particles were transported from the source regions (Inner Mongolia, Man-Ju, and Ordos areas) to Korea via the northeastern part of China. Network observations of the PM(10) concentrations in Korea revealed that a majority of the heavy dust particles traveled across South Korea from the northwest to the southeast direction with a horizontal scale of 250-300km and a traveling speed of approximately 40kmh(-1). This extraordinary dust event, in terms of its intensity and timing during the year, occurred due to the blockage of an unusually intensified low-pressure system in the northeastern part of China as well as high-pressure system centered over the Sea of Okhotsk and the Kuril Islands. The low values of the particle depolarization ratio (delta(532)) (<or=0.05) and color ratio (CR) during the pre-dust period indicate the presence of spherical, non-dust, and relatively small particles. The mean delta(532) value was approximately 0.123+/-0.069 between altitudes of ground approximately 2.8km, and 0.161+/-0.049 for near-surface dust layer (ground approximately 1.2km). This value is quite similar to that obtained during the 3-year SNU-Lidar measurements in Seoul (delta(532) approximately 0.136+/-0.027). The value of delta(532) during the 2nd multilayered dust episode ranged between 0.081 and 0.120 for near-surface dust layers, and between 0.076 and 0.114 for elevated dust layers. The CALIPSO measurements of beta(532), delta(532), and CR also revealed the presence of dense dust aerosols along the transport route.

Research paper thumbnail of The effect of aerosol representation on cloud microphysical properties in Northeast Asia

Meteorology and Atmospheric Physics, 2013

Research paper thumbnail of Estimation of Direct Radiative Forcing of Asian Dust Aerosols with Sun/Sky Radiometer and Lidar Measurements at Gosan, Korea

Journal of the Meteorological Society of Japan, 2004

In this study the aerosol direct radiative forcing (ADRF) of Asian dust is evaluated by model sim... more In this study the aerosol direct radiative forcing (ADRF) of Asian dust is evaluated by model simulation at Gosan, Jeju using the data from a sun/sky radiometer, a Micro-Pulse Lidar (MPL), and column radiometer measurements of solar downwelling irradiance in April, 2001. We suggest a method of determining aerosol parameters for the radiative transfer model from the Aerosol Robotic Network (AERONET) data set. Since the AERONET measurements provide the refractive indices at only four wavelengths, and the aerosol parameters can be calculated at these wavelengths with a Mie code, we use a linear regression method for extending these measurements to the full wavelength spectrum of the radiative transfer model. The aerosol forcing by the Asian dust aerosols is estimated and compared to the aerosol forcing of non-dust aerosols. On the Asian dust event day, April 13, the daily average ADRF was estimated as À58.1 W/m 2 at the surface and À25.7 W/m 2 at the top of the atmosphere (TOA). On April 15, a nondust day slightly influenced by anthropogenic aerosols, the ADRF was À29.0 W/m 2 at the surface and À11.6 W/m 2 at the TOA. Although the Asian dust aerosols show larger forcing, its forcing efficiency (forcing per unit optical thickness) is smaller than that of non-dust aerosols; À41.0 W/m 2 /t 670 at the TOA and À94.9 W/m 2 /t 670 at the surface on the dust day for dust aerosols, as opposed to À50.0 W/m 2 /t 670 at the TOA and À129.3 W/m 2 /t 670 at the surface on the non-dust day for non-dust aerosols. We believe that this is due to the larger single scattering albedo of dust aerosols, which causes smaller absorption, and the larger asymmetry factor which causes more forward scattering or less reflection, compared to anthropogenic aerosols. The model results were validated with the surface irradiance measurement data and the comparison showed a good agreement. The radiative transfer calculation underestimates the solar irradiance of 2@3% on average. The aerosol profiles measured by lidar are used to estimate the influence of the vertical distribution of Asian dust aerosols on the ADRF. Using the vertical aerosol profiles, we found an

Research paper thumbnail of Overview of the Atmospheric Brown Cloud East Asian Regional Experiment 2005 and a study of the aerosol direct radiative forcing in east Asia

Journal of Geophysical Research, 2007

Research paper thumbnail of Comparison of vertical dust flux by implementing three dust emission schemes in WRF/Chem

Journal of Geophysical Research, 2011

Vertical dust flux parameterizations were assessed by implementing three different dust emission ... more Vertical dust flux parameterizations were assessed by implementing three different dust emission schemes, namely, those of Marticorena and Bergametti (1995), Lu and Shao (1999), and Shao (2004) (hereinafter referred to as MB, LS, and S04 schemes, respectively) in Weather Research and Forecasting with Chemistry (WRF/Chem). Through sensitivity tests, the scattering of vertical dust fluxes resulting from different parameterizations was shown even under the condition of same horizontal sand flux. The difference between the estimated vertical dust fluxes of three emission schemes ranges from the order of 10 1 for sand to the order of 10 2 for clay. The MB scheme generally produces higher dust emissions than the LS and S04 schemes, and the difference is the greatest for clay because the MB scheme considers vertical dust flux to be related to clay content, while the LS and S04 schemes consider it to be inversely proportional to surface hardness. To investigate the performance of each dust emission scheme in the simulation of Asian dust events, a case study was carried out for a severe Asian dust event that took place between 30 March and 1 April 2007. Simulation results reproduced the outbreak and transport pattern of dust plumes satisfactorily. However, the estimated dust emission amounts in each scheme differed greatly, particularly in loamy soil. The total dust emission amounts averaged for the main dust source region in this Asian dust event for five consecutive days are 84 Tg, 149 Tg, and 532 Tg for the LS, S04, and MB schemes, respectively.

Research paper thumbnail of Seasonal characteristics of air masses arriving at Gosan, Korea, using fine particle measurements between November 2001 and August 2003

Journal of Geophysical Research, 2007

Radio frequency (RF) magnetron sputtering is a versatile deposition technique that can produce th... more Radio frequency (RF) magnetron sputtering is a versatile deposition technique that can produce thin, uniform, dense calcium phosphate coatings. In this paper, principle and character of magnetron sputtering is introduced, and development of the hydroxyapatite and its composite coatings application is reviewed. In addition, influence of heat treatment on magnetron sputtered coatings is discussed. The heat treated coatings have been shown to exhibit bioactive behaviour both in vivo and in vitro. At last, the future application of the bioactive ceramic coating deposited by magnetron sputtering is mentioned.

Research paper thumbnail of Intercomparisons of cloud-top and cloud-base heights from ground-based Lidar, CloudSat and CALIPSO measurements

International Journal of Remote Sensing, 2011

ABSTRACT This study presents results of the intercomparison of cloud-top height (CTH) and cloud-b... more ABSTRACT This study presents results of the intercomparison of cloud-top height (CTH) and cloud-bottom height (CBH) obtained from a space-borne active sensor Cloud Profiling Radar (CPR), the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP), the space-borne passive sensor Moderate Resolution Imaging Spectroradiometer (MODIS) and ground-based Lidar measurements. Three selected cases (one daytime and two night-time cases) involving various cloud conditions such as semi-transparent thin cirrus, opaque thick tropospheric clouds and multi-layered clouds are studied, with special attention to CBH. The space-based CALIOP provides reliable heights of thin high-altitude cirrus clouds containing small ice particles, but the 94 GHz CPR has low sensitivity to these clouds. The CTHs retrieved from the CPR and CALIOP for thick tropospheric clouds are in good agreement with each other. Discrepancies between the CPR and the CALIOP values of the CBH for thick opaque clouds arise from strong Lidar signal attenuations. In cloud-overlap conditions (i.e. multi-layered clouds are present), the CALIOP has difficulties in determining the cloud vertical structure (CVS) for thick clouds underlying thin cirrus clouds due to signal attenuations, whereas the CPR detects the CTH and CBH of both the cloud layers. This fact is also confirmed by the comparison of seasonal variations of occurrences of CBH and CTH retrieved from 1 year measurements. The CBHs derived from the CPR and ground-based Lidar are generally in good agreement with each other. Especially, comparison of CBH between the ground-based Lidar and CPR retrieved from June 2006 to October 2008 shows an excellent linear relationship (coefficient of determination, R ∼ 0.996).

Research paper thumbnail of Observation of enhanced water vapor in Asian dust layer and its effect on atmospheric radiative heating rates

Geophysical Research Letters, 2004

Research paper thumbnail of Characteristics of the transport and vertical structure of aerosols during ABC-EAREX2005

Atmospheric Environment, 2008

In this study, we investigate the physio-chemical and optical properties of Asian spring continen... more In this study, we investigate the physio-chemical and optical properties of Asian spring continental outflow and its relation to synoptic transport patterns. Ground-based highly time-resolved measurements of aerosol chemical and physical properties, and lidar measurements of aerosol vertical distributions at Gosan, Korea during ABC-EAREX2005 have been analyzed. Two selected cases, based on PM 10 and PM 2.5 mass concentrations, indicate that pollution-dominant airmass preceded by the appearance of a major mineral dust plume with about 12 h time-lag. At the ground level, pollution aerosol components (NO 3 À , SO 4 2À , and NH 4 þ) showed distinct peaks first and the enhancement of soil components (Ca 2þ) appeared approximately 12 h later. Although lidar measurements reveal that spherical pollution particles were observed near the surface prior to a major plume of non-spherical mineral dust, elevated dust layers were simultaneously observed in the free troposphere overlying the ground-level pollution plume. Chemical transport model simulations of the horizontal distributions of dust and sulfate aerosols illustrate well the pollution plume preceding the dust-laden airmass. Backward trajectory and NCAR/PSU MM5 analysis show that the preceding pollution plume and following dust plume were consecutively transported under fast northwesterly/northerly winds formed between anticyclonic and cyclonic flows at the ground level.

Research paper thumbnail of Influences of relative humidity on aerosol optical properties and aerosol radiative forcing during ACE-Asia

Atmospheric Environment, 2006

In situ measurements at Gosan, South Korea, and onboard C-130 aircraft during ACE-Asia were analy... more In situ measurements at Gosan, South Korea, and onboard C-130 aircraft during ACE-Asia were analyzed to investigate the influence of relative humidity (RH) on aerosol optical properties and radiative forcing. The temporal variation of aerosol chemical composition at the Gosan super-site was highly dependent on the air mass transport pathways and source region. RH in the springtime over East Asia were distributed with very high spatial and temporal variation. The RH profile onboard C-130 aircraft measurements exhibits a mixed layer height of about 2 km. Aerosol scattering coefficient (s sp) under ambient RH was greatly enhanced as compared with that at dry RH (RHo40%). From the aerosol optical and radiative transfer modeling studies, we found that the extinction and scattering coefficients are greatly enhanced with RH. Single scattering albedo with RH is also sensitively changed in the longer wavelength. Asymmetry parameter (g) is gradually increased with RH although g decreases with wavelength at a given RH. Aerosol optical depth (AOD) at 550 nm and RH of 50% increased to factors 1.24, 1.51, 2.16, and 3.20 at different RH levels 70, 80, 90, and 95%, respectively. Diurnal-averaged aerosol radiative forcings for surface, TOA, and atmosphere were increased with RH because AOD was increased with RH due to hygroscopic growth of aerosol particles. This result implies that the hygroscopic growth due to water-soluble or hydrophilic particles in the lower troposphere may significantly modify the magnitude of aerosol radiative forcing both at the surface and TOA. However, the diurnal-averaged radiative forcing efficiencies at the surface, TOA, and atmosphere were decreased with increasing RH. The decrease of the forcing efficiency with RH results from the fact that increasing rate of aerosol optical depth with RH is greater than the increasing rate of aerosol radiative forcing with RH.

Research paper thumbnail of Air mass characterization and source region analysis for the Gosan super-site, Korea, during the ACE-Asia 2001 field campaign

Atmospheric Environment, 2005

This paper presents results of air mass characterization and the associated microphysical and opt... more This paper presents results of air mass characterization and the associated microphysical and optical properties of Asian aerosols, using the cluster analysis technique for classifying air mass back-trajectories arrived at Gosan on the Jeju Island, Korea during the ACE-Asia campaign. Five distinct clusters of trajectories were taken to explain each transport regime. The temporal variation of the transported air masses could be well explained by the consecutive and stepwise change of air masses between statistically classified clusters. The cluster-mean trajectory exhibited its close relationship with the synoptic-scale circulation pattern. In addition, it was shown that the composite of mean sea-level pressure field is useful for explaining favorable meteorological conditions for long-range transport of dust and anthropogenic pollution in East Asia. The highest light scattering and absorption coefficients for sub-10-and submicron aerosols as well as highest concentrations of 222 Rn and condensation nuclei are associated with the air mass types accompanying dusts and pollutants. The cluster-mean single scattering albedo (SSA) for sub-10-and submicron aerosols ranged 0.88-0.90 and 0.81-0.86, respectively. This value of SSA indicates the large contribution of submicron aerosol for the light absorption in East Asia. The concentration of 222 Rn and aerosol microphysical and optical properties for marine air mass suggests that the marine air masses are somewhat influenced by continental outflows. The minor differences in aerosol microphysical and optical properties among continental clusters with similar routes and different transport speed implies that the effect of transport speed may not be significant if the transport routes are similar.