• Korean Journal of Remote Sensing
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• v.34 no.3
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• pp.507-517
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• 2018

Aerosol optical depth (AOD) data retrieved by the Communication, Ocean and Meteorological Satellite (COMS) during 2011-2014 were compared with AOD measurements from 134 Aerosol Robotic Network (AERONET) sites over the East Asia. Overall, COMS and AERONET AODs were weakly correlated (R = 0.297). The agreement between COMS and AERONET AODs was improved when data from near Korean peninsula sites were selected (R = 0.475). Regression analysis results for each AERONET site are vary from R=0.026 at AOE_Baotou to 0.905 at DRAGON_Anmyeon. It was also shown that the bias in COMS AOD was not systematic with respect to effective radius, precipitable water, surface reflectance, and sun zenith angle. Together, these results suggest that COMS AOD measurements may be suitable for near Korea. Finally, the current results will help to improve the retrieval algorithm and vary when using alternative COMS AOD version in the future.

• Journal of Korean Society for Atmospheric Environment
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• v.29 no.3
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• pp.264-274
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• 2013

This study investigates long-term trends and characteristics of aerosol light scattering coefficient at Seoul and Baengnyeongdo in order to understand aerosol optical and radiative properties around Korea. The analysis period is limited to one year of 2011. First, the aerosol scattering coefficients (${\sigma}_{sp}$) of both sites show strong linear dependence on the $PM_{2.5}$ mass concentrations with significant correlations between both. Further, correlations and sensitivity between ${\sigma}_{sp}$ and $PM_{2.5}$ increase with relative humidity, implying both relationships are strongly dependent upon moisture amounts in the atmosphere. This study applied 3-step careful quality control procedures to the analysis of ${\sigma}_{sp}$ for the insurance of data confidence. For the relationship analysis of extinction coefficients (${\sigma}_{ext}$) to visibility and aerosol optical depth, ${\sigma}_{sp}$ observed at 3 p.m. have been used with help of aerosol absorption coefficients (${\sigma}_{ap}$) in order to remove its dependence upon relative humidity, and also those of rainy period have been excluded. As expected, ${\sigma}_{ext}$ estimated are inversely proportional to visibility observation by eye. Finally, aerosol extinction coefficients have been vertically integrated with an assumption of nearly well-mixed within an e-folding height to determine aerosol optical depth, and compared with those retrieved from sunphotometer. The results show a reasonable agreement in spite of an inherent difference of each definition. We expect these findings would help to eventually understand aerosol radiative forcing and its effect on the regional climate change around Korea.

• Korean Journal of Remote Sensing
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• v.32 no.6
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• pp.681-691
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• 2016

Using various satellite measurements in UV, visible and IR, diverse algorithms to retrieve aerosol information have been developed and operated to date. Advanced Himawari Imager (AHI) onboard the Himawari 8 weather satellite was launched in 2014 and has 16 channels from visible to Thermal InfRared (TIR) in high temporal and spatial resolution. Using AHI, it is very valuable to retrieve aerosol optical properties over dark surface to demonstrate its capability. To retrieve aerosol optical properties using visible and Near InfRared (NIR) region, surface signal is very important to be removed which can be estimated using minimum reflectivity method. The estimated surface reflectance is then used to retrieve the aerosol optical properties through the inversion process. In this study, we retrieve the aerosol optical properties over dark surface, but not over bright surface such as clouds, desert and so on. Therefore, the bright surface was detected and masked using various infrared channels of AHI and spatial heterogeneity, Brightness Temperature Difference (BTD), etc. The retrieval result shows the correlation coefficient of 0.7 against AERONET, and the within the Expected Error (EE) of 49%. It is accurately retrieved even for low Aerosol Optical Depth (AOD). However, AOD tends to be underestimated over the Beijing Hefei area, where the surface reflectance using the minimum reflectance method is overestimated than the actual surface reflectance.

• Journal of Korean Society for Atmospheric Environment
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• v.24 no.6
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• pp.629-640
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• 2008

This study investigates long-term trends and characteristics of aerosol optical depth ($\tau_a$) and Angstrom exponent (${\AA}$) around Korea in order to understand aerosol effects on the regional climate change. The analysis period is mainly from 1999 to 2006, and the analysis sites are Anmyun and Gosan, the background monitoring sites in Korea, and two other sites of Xianghe in China and Shirahama in Japan. The annual variations of $\tau_a$ at Anmyun and Gosan have slightly systematic increasing and decreasing trends, respectively. $\tau_a$ at Anmyun shows more substantial variation, probably because of it's being closer and vulnerable to anthropogenic influence from China and/or domestic sources than Gosan. Both values at Gosan and Anmyun are approximately 1.5 times greater than those at Shirahama. The monthly variation of $\tau_a$ exhibits the highest values at late Spring and the lowest at late-Summer, which are thought to be associated with the accumulation of fine aerosol formed through the photochemical reaction before the Jangma period and the scavenging effect after the Jangma period, respectively. Meanwhile, the episode-average $\tau_a$ for the Yellow dust period increases 2 times greater than that for the non-Yellow dust period. A significant decrease in ${\AA}$ for the Yellow dust period is attributable to an increase in the loading of especially the coarse particles. Also we found no weekly periodicity of $\tau_a$'s, but distinct weekly cycle of $PM_{10}$ concentrations, such as an increase on weekdays and a decrease on weekends at Anmyun and Gosan. We expect these findings would help to initiate a study on aerosol-cloud interactions through the combination of surface aerosol and satellite remote sensing (MODIS, Calipso and CloudSat) in East Asia.

• Journal of Korean Society for Atmospheric Environment
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• v.24 no.4
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• pp.470-482
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• 2008

Seasonal variations of chemical composition and optical properties of aerosols at Seoul and Gosan were investigated using the ground-based aerosol measurements and an optical model calculation. The mass fraction of elemental carbon was $8{\sim}17%$, but its contribution on light absorption was high up to $29{\sim}48%$ in Seoul. In Gosan, the contribution of water soluble aerosols on aerosol extinction was $83{\sim}94%$ due to the high mass fraction of these particles in the range of $56{\sim}88%$. Model calculation showed that the water holding capacity of aerosols was larger in Gosan than in Seoul because of higher relative humidity and temperature along with abundant water soluble aerosols. Difference between measured and calculated aerosol optical depths was the highest in summer. This was because aerosol optical depth calculated from ground-based measurements could not consider aerosol loadings at high altitude in spite of high column-integrated aerosol loadings observed by Sun photometer. Although hygroscopic growth was expected to be dominant in summer, the mass concentration of water soluble aerosols was too low to permit this growth.

• Journal of Korean Society for Atmospheric Environment
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• v.30 no.1
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• pp.1-17
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• 2014

Temporal variations of optical properties of urban aerosol in Seoul were estimated by the Optical Properties of Aerosols and Clouds (OPAC) model, based on hourly aerosol sampling data in Seoul during the year of 2010. These optical properties were then used to calculate direct radiative forcing during the study period. The optical properties and direct radiative forcing of aerosol were calculated separately for four chemical components such as water-soluble, insoluble, black carbon (BC), and sea-salt aerosols. Overall, the coefficients of absorption, scattering, and extinction, as well as aerosol optical depth (AOD) for water-soluble component predominated over three other aerosol components, except for the absorption coefficient of BC. In the urban environment (Seoul), the contribution of AOD (0.10~0.12) for the sum of OC and BC to total AODs ranged from 23% (spring) to 31% (winter). The diurnal variation of AOD for each component was high in the morning and low in the late afternoon during the most of seasons, but the high AODs at 14:00 and 15:00 LST in summer and fall, respectively. The direct negative radiative forcing of most chemical components (especially, $NO_3{^-}$ of water-soluble) was highest in January and lowest in September. Conversely, the positive radiative forcing of BC was highest in November and lowest in August due to the distribution pattern of BC concentration.

• Atmosphere
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• v.21 no.3
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• pp.311-317
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• 2011

Aerosol optical properties from the radiation measurements by SKYNET PREDE skyradiometers, POM-01 and POM-02 were compared during the inter-calibration campaign at Seoul in February 2009. The monochromatic solar flux at the top of the atmosphere ($F_0$) gave a relative standard deviation (RSD) of 9-10% for both instruments. This comparatively high value of RSD was probably because $F_0$ was determined at short time intervals, in the morning and afternoon, using the measurements made in the polluted environment of Seoul. Although POM-02 was more effective in tracking the solar radiation, aerosol optical depths (AODs) from the two instruments were very similar after the cloud screening procedure. The squared correlation coefficients ($R^2$) of single scattering albedo (SSA) and real and imaginary refractive indices between the two instruments was around 0.5 but increased to 0.7-0.8 when only using AOD greater than 0.4. Nevertheless, mean values of the Angstrom exponent, SSA, and the imaginary refractive index of POM-02 were higher than those of POM-01.

• Korean Journal of Remote Sensing
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• v.34 no.6_1
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• pp.857-868
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• 2018

The microphysics and spatio-temporal distribution of atmospheric aerosols are responsible for estimating the optical properties at a given location. Its accurate estimation is essential to plan efficient simulation for radiative transfer. For this sake, synergetic use of reanalysis data with optics database was used as a potential tool to precisely derive the aerosol model on the basis of the major representative particulates exist within a model grid. In detail, mixing of aerosol types weighted by aerosol optical depth (AOD) components has been developed. This synergetic aerosol model (SAM) is spectrally extended up to $40{\mu}m$. For the major aerosol event cases, SAM showed that the mixed aerosol particles were totally different from the typical standard aerosol models provided by the radiative transfer model. The correlation among the derived aerosol optical properties along with ground-based observation data has also been compared. The current results will help to improve the radiative transfer model simulation under the real atmospheric environment.

• Particle and aerosol research
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• v.13 no.4
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• pp.141-150
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• 2017

Using the NASA's Modern-Era Retrospective Analysis for Research and Applications, version 2 (MERRA-2) reanalysis for aerosol optical depth (AOD) and satellite-observed carbon monoxide (CO) data, we examined the basic pattern of AOD variations over the three polar stations of Korea: Jangbogo and King Sejong stations in the Antarctica, and Dasan station in the Arctic area. AOD values at King Sejong and Dasan station show the maximum peaks in spring, which looks associated with the high amount of atmospheric CO emitted from the natural burning and the biomass burning. Jangbogo station shows the much less AOD compared to other two stations, and seems not strongly affected by the transport of airborne particles generated from mid-latitude regions. All three polar stations show the AOD increasing trend in general, indicating that the polar background air quality becomes polluted.

• Korean Journal of Remote Sensing
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• v.29 no.2
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• pp.243-251
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• 2013

The optical properties of long-range transported Asian dust were studied by the satellite observations and Sun/sky radiometer measurements from the Aerosol Robotic Network(AERONET) in Northeast Asia. The movement of Asian dust from source regions to downwind areas was tracked by the Ozone Monitoring Instrument(OMI) derived aerosol product imagery. The optical properties of Asian dust were classified for geographical locations, which are source regions such as deserts area in Dunhuang and Inner Mongolia, downwind areas such as Yulin and Beijing, and long-range transported regions such as Korea(Anmyon and Gosan) and Japan(Noto). In general, relatively higher aerosol mass loadings with larger aerosol particles at desert regions were found. Aerosol Optical Depth(AOD) decreased significantly in downwind areas and long-range transported areas, which was accompanied by increased Angstrom exponents. This indicates the effects of aerosol mixing with various pollutants during transport of Asian dust plume on aerosol optical properties. Moreover, relatively high Single-Scattering Albedo(SSA) at 440 nm values ranging from 0.90 - 0.96 and increasing tendency of SSA with wavelength were observed at source region. The spectral dependence of SSA decreased during long-range transport.