• Journal of Korean Society for Atmospheric Environment
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• v.21 no.5
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• pp.547-555
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• 2005

In this study, an analytical expression for aerosol mass transfer at spherical collector in the low Knudsen number region was obtained. Happel's zero shear stress cell model was extended in the low Knudsen number region and the result was compared with numerical solution results. The zero vorticity model based on the Kuwabara's cell model was also extended in the low Knudsen number region and compared with Happel's results. The results showed that both analytic and numerical solution agree very well with each other in low Knudsen number region. Happel's zero shear stress model also agrees with Kuwabara's zero vorticity model without significant loss of accuracy. The obtained solution converges to the original solution of Lee et al. (1999) when Knudsen number approaches to zero. Subsequently, this study derived most general type of analytic solution for aerosol mass transfer of spherical collector including the finite Knudsen number region.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.23 no.2
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• pp.262-271
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• 1999

A study of aerosol dynamics has been done to obtain axially and radially varying size distributions of particles generated in the Modified Chemical Vapor Deposition process. Heat and mass transfer have also been studied since particle generation and deposition strongly depend on the temperature field in a tube. Bimodal size distributions of particles have been obtained both in the particulate flow and in the deposited particle layer for the first time using the sectional method to solve aerosol dynamics. Variations of geometric mean diameter, geometric standard deviation have been studied for various parameters; flow rates and maximum wall temperature. The comparison between one-dimensional and two-dimensional approaches has also been made.

• Journal of Korean Society for Atmospheric Environment
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• v.26 no.2
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• pp.202-218
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• 2010

It is well known that the atmospheric inorganic aerosol has the hysteresis phenomena depending on the history of relative humidity. However, the current computational researches have assumed that the physical/chemical state of atmospheric aerosol is only determined by a branch of hysteresis, efflorescence or deliquescence. In this work, we applied the MATLAB-based UHAEROm thermodynamics module to simulate the dynamic interaction between gaseous species $NH_3$ and $HNO_3$, and the two mono-disperse particulate populations in the course of efflorescence and deliquescence, respectively. We conducted the 10 case studies considering the particulate phase with the atmospherically prevailing chemical composition and found that the final states of the particles are determined through the qualitatively five different trajectories by the dynamic interaction between gaseous and two different kinds of particulates. As a result, we show that the coexistence of meta-stable and stable particles drives the different physical/chemical destination comparing with the ones generated from the solitary efflorescence or deliquescence branch.

• Korean Journal of Remote Sensing
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• v.29 no.3
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• pp.325-329
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• 2013

This present study describes an application of UV scanning spectrometer $O_4$ data for retrieval of aerosol vertical profiles in Seoul during the measurement period that includes two Asian dust event days. The results show large variations of aerosol load in vertical and temporal scales. Large variations in aerosol were observed at 1 km in height during the daytime in the measurement period when the Asian dust events took place. The aerosol load, however, was found to be largest at the surface compared to those retrieved at the higher atmospheric layers. The results also clearly identified the diurnal patterns of aerosol vertical distributions. The aerosol load was high in the morning and noon whereas it was low in the afternoon. This study demonstrates that UV scanning spectrometer observations of the oxygen dimer can serve as a potential method for determination of atmospheric aerosol vertical distributions and optical properties.

• Proceedings of the KSRS Conference
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• 2003.11a
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• pp.1203-1205
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• 2003

To detect dust-loaded air-mass over land and ocean, we propose an index, which is essentially the difference in Rayleigh-corrected reflectance between 412 and 443 nm bands of SeaWiFS. Radiative transfer simulations are conducted to show that the index is linearly related to the optical thickness of modeled dust-contaminated aerosol while showing insensitivity against non-absorbing model aerosols. Asian SeaWiFS data set of 2001 spring is used to produce daily composite imagery of the index, which compares well with TOMS Aerosol Index and with predicted aerosol optical thickness predicted by CFORS chemical weather forecast.

• Journal of ILASS-Korea
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• v.3 no.3
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• pp.14-22
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• 1998

The growth by steam condensation of an hygroscopic aerosol is investigated using the condensation rate model which has been derived from the mass and heat transfer equations. The present model accounts for both the solute and Kelvin effects. When the hygroscopicity is considered, condensation can occur on hygroscopic seed particles even under subsaturated steam conditions. This study focuses on the effect of hygroscopicity on the evolution of the particle size distribution and decay of the total aerosol concentration. It is found that hygroscopicity causes the particle size distribution to rapidly move upward even in a very short time, resulting in substantially higher decay of the total aerosol concentration than the case without considering hygroscopicity.

• Nuclear Engineering and Technology
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• v.50 no.6
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• pp.849-853
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• 2018

Mechanistic calculations for wet scrubbing of aerosol/vapor from gas bubble rising in liquid pool are essential to safety of sodium-cooled fast reactor. Hence, scrubbing of volatile fission product from mixed gas bubble rising in sodium pool is presented in this study. To understand this phenomenon, a theoretical model has been setup based on classical theories of aerosol/vapor removal from bubble rising through liquid pools. The model simulates pool scrubbing of sodium iodide aerosol and cesium vapor from a rising mixed gas bubble containing xenon as the inert species. The scrubbing of aerosol and vapor are modeled based on deposition mechanisms and Fick's law of diffusion, respectively. Studies were performed to determine the effect of various key parameters on wet scrubbing. It is observed that for higher vapor diffusion coefficient in gas bubble, the scrubbing efficiency is higher. For aerosols, the cut-off size above which the scrubbing efficiency becomes significant was also determined. The study evaluates the retention capability of liquid sodium used in sodium-cooled fast reactor for its safe operation.

• Particle and aerosol research
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• v.9 no.3
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• pp.163-171
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• 2013

Soot particles emitted from combustion processes are often coated by non-absorbing organic materials, which enhance the global warming effect of soot particles. It is of importance to study the condensation characteristics of soot particles experimentally and theoretically to reduce the uncertainty of the climate impact of soot particles. In this study, the condensational growth of soot particles in a tubular coater was modeled by a one-dimensional (1D) plug flow model and a two-dimensional (2D) laminar flow model. The effects of 2D heat and mass transports on the predicted particle growth were investigated. The temperature and coating material vapor concentration distributions in radial direction, which the 1D model could not accounted for, affected substantially the particle growth in the coater. Under the simulated conditions, the differences between the temperatures and vapor concentrations near the wall and at the tube center were large. The neglect of these variations by the 1D model resulted in a large error in modeling the mass transfer and aerosol dynamics occurring in the coater. The 1D model predicted the average temperature and vapor concentration quite accurately but overestimated the average diameter of the growing particles considerably. At the outermost grid, at which condensation begins earliest due to the lowest temperature and saturation vapor concentration, condensing vapor was exhausted rapidly because of the competition between condensations on the wall and on the particle surface, decreasing the growth rate. At the center of the tube, on the other hand, the growth rate was low due to high temperature and saturation vapor concentration. The effects of Brownian diffusion and thermophoresis were not high enough to transport the coating material vapor quickly from the tube center to the wall. The 1D model based on perfect radial mixing could not take into account this phenomenon, resulting in a much higher growth rate than what the 2D model predicted. The result of this study indicates that contrary to a previous report for a thermodenuder, 2D heat and mass transports must be taken into account to model accurately the condensational particle growth in a coater.

• Korean Journal of Remote Sensing
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• v.36 no.2_1
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• pp.155-165
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• 2020

In this present study, the sensitivity of O₄ Air Mass Factor (AMF) to Aerosol Peak Height (APH) has been investigated using radiative transfer model according to various parameters(wavelength (340 nm and 477 nm), aerosol type (smoke, dust, sulfate), aerosol optical depth (AOD), surface reflectance, solar zenith angle, and viewing zenith angle). In general, it was found that O₄ AMF at 477 nm is more sensitive to APH than that at 340 nm and is stably retrieved with low spectral fitting error in Differential Optical Absorption Spectroscopy (DOAS) analysis. In high AOD condition, sensitivity of O₄ AMF on APH tends to increase. O₄ AMF at 340 nm decreased with increasing solar zenith angle. This dependency isthought to be induced by the decrease in length of the light path where O₄ absorption occurs due to the shielding effect caused by Rayleigh and Mie scattering at high solar zenith angles above 40°. At 477 nm, as the solar zenith angle increased, multiple scattering caused by Rayleigh and Mie scattering partly leads to the increase of O₄ AMF in nonlinear function. Based on synthetic radiance, APHs have been retrieved using O₄ AMF. Additionally, the effect of AOD uncertainty on APH retrieval error has been investigated. Among three aerosol types, APH retrieval for sulfate type is found to have the largest APH retrieval error due to uncertainty of AOD. In the case of dust aerosol, it was found that the influence of AOD uncertainty is negligible. It indicates that aerosol types affect APH retrieval error since absorption scattering characteristics of each aerosol type are various.

• Asian Journal of Atmospheric Environment
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• v.11 no.4
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• pp.300-312
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• 2017

To improve the understanding of secondary organic aerosol (SOA) formation from the photo-oxidation of anthropogenic and biogenic precursors at the regional background station on Baengnyeong Island, Korea, gas phase and aerosol chemistries were investigated using the Proton Transfer Reaction Time of Flight Mass Spectrometer (PTR-ToF-MS) and the Aerodyne High Resolution Time of Flight Aerosol Mass Spectrometer (HR-ToF-AMS), respectively. HR-ToF-AMS measured fine particles ($PM_1$; diameter of particle matter less than $1{\mu}m$) at a 6-minute time resolution from February to November 2012, while PTR-ToF-MS was deployed during an intensive period from September 21 to 29, 2012. The one-minute time-resolution and high mass resolution (up to $4000m{\Delta}m^{-1}$) data from the PTR-ToF-MS provided the basis for calculations of the concentrations of anthropogenic and biogenic volatile organic compounds (BVOCs) including oxygenated VOCs (OVOCs). The dominant BVOCs from the site are isoprene (0.23 ppb), dimethyl sulphide (DMS, 0.20 ppb), and monoterpenes (0.38 ppb). Toluene (0.45 ppb) and benzene (0.32 ppb) accounted for the majority of anthropogenic VOCs (AVOCs). OVOCs including acetone (3.98 ppb), acetaldehyde (2.67 ppb), acetic acid (1.68 ppb), and formic acid (2.24 ppb) were measured. The OVOCs comprise approximately 75% of total measured VOCs, suggesting the occurrence of strong oxidation processes and/or long-range transported at the site. A strong photochemical aging and oxidation of the atmospheric pollutants were also observed in aerosol measured by HR-ToF-AMS, whereby a high $f_{44}:f_{43}$ value is shown for organic aerosols (OAs); however, relatively low $f_{44}:f_{43}$ values were observed when high concentrations of BVOCs and AVOCs were available, providing evidence of the formation of SOA from VOC precursors at the site. Overall, the results of this study revealed several different SOA formation mechanisms, and new particle formation and particle growth events were identified using the powerful tools scanning mobility particle sizer (SMPS), PTR-ToF-MS, and HR-ToF-AMS.