국내 배경지역 미세먼지(PM_10) 중 자연방사핵종(^(40)K, ^(232)Th,^(238)U) 농도분석; 2014

Abstract

In this study, a total of 115 PM_10 samples were collected from the Gosan area in Jeju Island, which is a natural background sites, during the year of 2014. This study analyzed using ICP-DRC-MS (Inductively Coupled Plasma - Dynamic Reaction Cell - Mass Spectrometer) the concentrations of potassium, thorium and uranium, and evaluated the annual effective dose by breathing from the results. For the pretreatment, EPA-IO-3.1 method was used. During the study period, the mean mass concentration of PM_10 was 46.31 mg/kg. And the mean concentrations of ^(40)K, ^(232)Th and ^(238)U were 0.56, 1.03 and 0.53 mg/kg, respectively. As a result, concentrations of dust mass with each nuclide ^(238)U, ^(232)Th and ^(40)K were 0 ~ 62.07 (mean: 6.48 ± 7.43 Bq/kg), 0 ~ 16.86 (mean: 4.16 ± 2.98 Bq/kg) and 1.94 ~ 605.76 Bq/kg (mean: 146.90 ± 101.84 Bq/kg), respectively. The activity concentrations of each nuclide were analyzed by atmospheric phenomenon (Asian Dust, Haze, Fog-Mist and Non-Event). During Asian Dust periods (5 samples), the active concentrations of ^(40)K, ^(232)Th and ^(238)U were 328.05, 11.38 and 10.71 Bq/kg, respectively. The ^(232)Th/^(40)K, ^(238)U/^(40)K and ^(232)Th/^(238)U ratio of Asian Dust was 0.033, 0.036 and 1.06, respectively, which was higher than those of other atmospheric phenomenon (0.50~0.82). Each nuclide ^(238)U, ^(232)Th and ^(40)K concentration for air volume is 0 ~ 2.16 (mean: 0.30 ± 0.35 μBq/m3), 0 ~ 2.26 (mean: 0.25 ± 0.37 μBq/m3) and 0.06 ~ 78.14 μBq/m3 (mean: 7.89 ± 10.89 μBq/m3), respectively. The activity concentrations of each nuclide were analyzed by atmospheric phenomenon. During Asian Dust periods (5 samples), the radioactive concentrations of ^(40)K, ^(232)Th and ^(238)U were 40.89, 1.46 and 1.37 μBq/m3, respectively. The five-day backward trajectories have been performed to investigate the inflow pathway of the air mass into the Gosan site, and it was ascertained using the HYSPLIT4 model of National Oceanic and Atmospheric Administration (NOAA, USA). The air mass inflow pathways have been classified by four sectors; China continent (Sector I), Korean peninsula (Sector II), Japan (Sector III) and North Pacific Ocean (Sector IV). The sectional frequencies of air mass inflow into the Gosan area were 34.84 % in Sector I, 22.58 % in Sector II, 11.61 % in Sector III and 5.16 % in Sector IV zone during the study. During Asian dust periods, the air mass inflow was due to Sector I (China continent). As a result of analyzing the air volume, the concentration ratio of ^(238)U/^(40)K, ^(232)Th/^(40)K were 0.036, 0.032 in Sector I, respectively. The concentration ratio of ^(232)Th/^(238)U was measured 0.886 ^(238)U/^(40)K and ^(232)Th/^(40)K were 0.042, 0.032 in Sector II, respectively. And ^(232)Th/^(238)U was measured 0.762. As a result of analyzing the dust mass, the concentration ratio of ^(238)U/^(40)K, ^(232)Th/^(40)K and ^(232)Th/^(238)U were 0.040, 0.030 and 0.747 in Sector I, respectively. ^(238)U/^(40)K, ^(232)Th/^(40)K and ^(232)Th/^(238)U were 0.046, 0.030 and 0.662 in Sector II, respectively. Sector III confirmed that the overall ratio of ^(238)U/^(40)K, ^(232)Th/^(40)K and ^(232)Th/^(238)U to total dust volume and air volume decreased. In the case of Sector IV, the respectively ratio of ^(232)Th/^(40)K and ^(232)Th/^(238)U is the lowest. However, Sector IV was the highest among the other Sector I, II and III. The Eh,Total (inhalation annual effective radiation dose; default mode F) to the public due to natural isotopes of the airborne PM_10 was in the range 17.56 ~ 83.74 nSv/y, depending on the age group. The Eh,Total (15y, male) of Asian Dust was 498.84 nSv/y, which was 8.6 times higher than those of the Non-Event dust (58.17 nSv/y). In 2014 the Raeq (radium equivalent activity) is 40.85 ~ 84.18 Bq/kg (mean: 52.24 ± 18.00 Bq/kg). According to UNSCEAR 1988, the world average Raeq is 89.0 Bq / kg in soils. So this study was measured to be similar to the world average Raeq. In this study, the ratio of each nuclide was compared according to the inflow route. As a result, it was confirmed that the ratio of each nuclide was slightly different according to the inflow route. It is expected that this will be a preliminary data for analyzing the sources and various weather phenomena of fine dust on the peninsula.