• 대기
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• 제30권4호
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• pp.391-404
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• 2020

To understand the characteristics of the relationship between visibility and particulate matter (PM) in different meteorological conditions, we investigated the contributions of PM and relative humidity (RH) to visibility in Seoul, South Korea. For the period from 2001 to 2018, both PM and RH show descending trends, resulting in a visibility increase. PM has little impact on the hourly variation of visibility, which could be explained more by the RH variability. Meanwhile, the daily change of PM accounts for daily visibility variation. For the monthly variation of visibility, both PM and RH showed similar influence. The correlation coefficients of PM10, PM2.5, and RH with visibility was -0.486, -0.644, and -0.556, respectively, which became higher during the high PM seasons of spring and winter. The correlation coefficient between PM2.5 and visibility was -0.454 for RH higher than 80%, and -0.780 for RH between 40% and 60%. From 2017 to 2018, there were 10 cases of extreme visibility impairment, among which five cases were incurred by high PM pollution, and two cases were by high humidity. Further analysis with PM chemical composition measurements is required to better understand the characteristics of visibility in Seoul.

• Journal of Korean Society for Atmospheric Environment
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• 제19권E3호
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• pp.99-120
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• 2003

Visibility impairment in an urban area is mainly caused by airborne fine particulate matters. Visibility in a clean air environment is more sensitive to the change of PM$_{2.5}$ particle concentrations. However, a proportionally larger reduction in fine particle concentration is needed to achieve a small increment of visibility improvement in polluted areas. Continuous optical monitoring of atmospheric visibility and extensive aerosol measurements have been made in the urban atmosphere of Kwangju, Korea. The mean for fine particulate mass from 1999 to 2002 at Kwangju was measured to be 23.6$\pm$20.3 $\mu\textrm{g}$/㎥. The daily average seasonal visual range was measured to be 13.1, 9.2, 11.0, and 13.9 km in spring, summer, fall, and winter, respectively. The mean light extinction budgets by sulfate, nitrate, organic carbon, and elemental carbon aerosol were observed to be 27, 14, 22, and 12%, respectively. It is highly recommended that a new visibility standard and/or a fine particle standard be established in order to protect the health and welfare of general public. Much more work needs to be done in visibility studies, including long-term monitoring of visibility, improvement of visibility models, and formulating integrated strategies for managing fine particles to mitigate the visibility impairment and climate change.e.

• Journal of Korean Society for Atmospheric Environment
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• 제24권E2호
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• pp.92-101
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• 2008

The objective of this study is to evaluate and improve the capability of the Weather Research and Forecasting (WRF) model in simulating fog and visibility in local airports over Korea. The WRF model system is statistically evaluated for the 48-fog cases over Korea from 2003 to 2006. Based on the 4-yr evaluations, attempts are made to improve the simulation skill of fog and visibility over Korea by revising the statistical coefficients in the visibility algorithms of the WRF model. A comparison of four existing visibility algorithms in the WRF model shows that uncertainties in the visibility algorithms include additional degree of freedom in accuracy of numerical fog forecasts over Korea. A revised statistical algorithm using a linear-regression between the observed visibility and simulated hydrometeors and humidity near the surface exhibits overall improvement in the visibility forecasts.

• 한국대기환경학회지
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• 제29권5호
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• pp.682-691
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• 2013

The aerosol extinction vertical profile and surface visibility have been derived from the Microtops-II sunphotometer observation during the winter 2011 intensive observation period (IOP) at Seoul, Korea. Using models of degradation of aerosol optical thickness (AOT) and aerosol scale height, we have performed extinction-visibility modulation to determine the height dependent aerosol extinction and visibility. It is shown that the aerosol loading is relatively low during IOP (mean $AOT_{550}=0.22{\pm}0.08$, ${\AA}$ngstr$\ddot{o}$m exponent=$1.14{\pm}0.26$). Modeled extinction by use of Microtops II sunphotometer data shows good agreement with measurements by the Multi-wavelenth Polarization Lidar (MPoLAR), and the derived surface visibility are consistent with data from the transmissometer. These results emphasize the use of a vertically resolved extinction from AOT to predict visibility conditions at ground level.

• 한국대기환경학회지
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• 제10권1호
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• pp.1-23
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• 1994

Visibility impairment phenomenon due to various air pollutants is a highly complex problem To understand this problem in Seoul, (1) theoretical background of visibility impairment; (2) methods to quantify visual range and to assess contribution of each air pollutant to the visibility impairment problem; and (3) previous field measurements and modeling studies, both in Korea and abroad, are critically reviewed.

• 환경영향평가
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• 제13권4호
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• pp.197-211
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• 2004

Visibility impairment was known as an indicator of the increased air pollution. In many previous studies, it is known that both directly emitted fine particles mainly from vehicles and secondary aerosols from photochemical reactions could contribute to this visibility impairment in addition to the meteorological condition. Furthermore, the visibility showed different change patterns according to the geographical condition. In order to research into the influence of these factors on visibility, this study analyzed the visibility at 15:00, observed from 1990 to 2001 in Seoul, Ganghwa, Susan, Gwangju, Jeju. As a result, the visibility was increased in Seoul except the rainfall period, but in Susan, Gwangju, Jeju, it decreased with the relative humidity (RH). Especially, in Seoul, the number of low visibility days was larger than other sites and variations of the visibility were sensitive to the concentration of air pollutants, such as TSP, $NO_2$, $O_3$. The visibility impairment was mainly observed in meteorological condition of RH<50% and relatively stationary front. Therefore it is inferred that photochemical smog could lead to the low visibility in Seoul. On the other hands, in Ganghwa and Susan, when RH was 60~70%, the low visibility observed under the influence of the transports of air pollutants from nearby cities as well as humid air mass from coastal region. And in Jeju, sea fog and humid air mass caused the visibility impairment when the RH was larger than 80%. Finally, during the observational period, some cases of low visibility phenomena were simultaneously observed in the vast region including Seoul, Susan, Ganghwa. It not only includes the visibility aggravation by Asian Dust, but also could be caused by the movement and diffusion of flying dust or secondary aerosols. Moreover, the result shows that these phenomena could be mainly influenced by meteorological factors covering the wide regions.

• 한국환경과학회지
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• 제8권6호
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• pp.639-643
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• 1999

After analyzing the correlation between air pollution and visibility, TSP and $NO_2$ is responsible for poor visibility in Pusan. After analyzing the correlation between meteorological factors and visibility, general pattern of humidity has clear negative correlation. The variation of wind speed has a positive correlation. In order to investigate the cause of poor visibility in Pusan area, the Andersen sampler and PM-2.5 are used to collect and analyze aerosol. This study was carried out to monitor the visibility using Forward scattering meter and to find out the characteristics and the cause of good visibility case and poor visibility case by measuring and analyzing a variety of parameters, such as particle size distributions, chemical compositions, and meteorological conditions in Pusan. According to the analysis of intensive sampling, $NO_3^-,NH_4^+$ ion concentration increased together with the mass concentration around $0.5\~2.5{\mu}m$ approximately during the case of poor visibility. $NH_4NO_3,\;NH_4Cl,\;and\;NaCl$ were thought to be the major components of fine particles.

• 한국대기환경학회지
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• 제9권1호
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• pp.51-60
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• 1993

In order to study on the cause of visibility aggravation, we have selected the days of low-visibility observed in Seoul with haziness that was below 6km from 12 to 15 LST. According to the examinations, the number of low-visibility days satisfying the criteria is 30 days in 1989, 39 days in 1990, and 35 days in 1991, respectively. The annual number of low visibility days appears to increase mainly due to an increase in emission of air pollutants and in anthropogenic water vapor in the biosphere. The relationship between visibility and air pollutants(TSP, $NO_2, SO_2, O_3$) of selected days is also studied. Air pollution concentrations of selected days are much higher than those of other days. It is observed that the cause of visibility aggravation in Seoul is mainly smog and air pollutants. In particular, the visibility reduction and high $SO_2$ concentrations at Seoul in winter are similar phenomena that occurring with London smog, while the visibility reduction and high $O_3$ concentrations at Seoul in summer are also similar to the type of Los Angeles smog.

• 한국대기환경학회지
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• 제12권4호
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• pp.473-478
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• 1996

Using data observed from 1966 to 1994, long-term trends of visibility at 15:00 in Seoul and Chunchon were analyzed. Annual average visibility in Seoul has been decreased continuously. In particular, annual number of days for visibility more than 15km was remarkably reduced since 1980. Also, the trend of the visibility in Chunchon was similar to that of Seoul. But the variations were small to compare with Seoul. Long-term trends of relative humidity (RH) and specific humidity (q) at 15:00 in Seoul have been slightly decreased. Cumulative frequency distributions of visibility for ranges of RH (0 $\sim 50%, 50 \sim 60%, 60 \sim 70%, 70 \sim 80%, 80 \sim 90%, 90 \sim 100%$) at 15:00 in Seoul and Chunchon were generally decreased during the second period (1984 $\sim$ 1994) as compared with the first period (1973 $\sim$ 1983), except for the range of 90 to 100% RH. Despite of decreasing phenomena of RH, characteristics of urban climates in Seoul, visibility degraded due to an increase of air pollution.

• 한국대기환경학회지
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• 제10권3호
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• pp.203-208
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• 1994

The trend of visibility variation of Seoul during 1980-1993 is analyzed. Annual average visibility has been decreased during the 1980s except 1988 and 1989 but not decreasing during the early 1990s. Also, the number of days with haze during 1983-1993 did not increase. Mixing height is deemed to be a dominant factor determining visibility. During the period, the difference between the average visibility at 6 p.m and 9 a.m decreased with the average visual range at 9 a.m slightly increased. Thus there is possibility that the effect of Photochemcial reactions becomes noticeable. The number of vehicles and the concentration of criteria air pollutants on the trend of visibility variation of Seoul would not be directly related to the variation of visibility.