We report the synthesis and gas sensing properties of bare and ZnO decorated TeO2 nanowires (NWs). A catalyst assisted-vapor-liquid-solid (VLS) growth method was used to synthesize TeO2 NWs and ZnO decoration was performed using an Au-catalyst assisted-VLS growth method followed by a subsequent heat treatment. Structural and morphological analyses using X-ray diffraction (XRD) and scanning/transmission electron microscopies, respectively, demonstrated the formation of bare and ZnO decorated TeO2 NWs with desired phase and morphology. NO2 gas sensing studies were performed at different temperatures ranging from 50 to 400 oC towards 50 ppm NO2 gas. The results obtained showed that both sensors had their best optimal sensing temperature at 350 oC, while ZnO decorated TeO2 NWs sensor showed much better sensitivity towards NO2 relative to a bare TeO2 NWs gas sensor. The reason for the enhanced sensing performance of the ZnO decorated TeO2 NWs sensor was attributed to the formation of ZnO (n)/ TeO2 (p) heterojunctions and the high intrinsic gas sensing properties of ZnO.

2020년 중국의 COVID-19 폐쇄는 한국의 풍상측에 위치한 중국의 대기오염 배출량을 감소시켰다. 몽골 북부로 부터 중국 동부를 거쳐 한반도에 이르는 지역에서는 2020년 1~2월에 기온 아노말리가 양(+)으로 온난하였고, 2020년 1월에는 동서류 아노말리가 음(−)으로 정체적인 특징을 보였다. 2019년 12월~2020년 3월에 한국 중부 서쪽의 석모리와 파도리에서 중국 배출량 감소의 영향에 따라 PM10, NO2, O3 농도 변동이 나타났다. 파도리에서 PM10, O3 월평균 농도와 최근 4년의 월평균 농도의 비는 2019년 12월과 비교하여 중국의 COVID-19 폐쇄 이후인 2020년 1~3월에 각각 0.7~4.7%, 9.2~22.8%로 감소하였다. 2020년 1월 중국의 춘절 기간에는 석모리와 파도리에서 PM10, NO2, O3 농도가 최근 4년의 춘절 기간과 마찬가지로 감소하였다. 그러나 2020년 1월 평균 농도가 최근 4년 1월과 비교하여 감소한 것은 중국 춘절 전후의 기간에도 배출량이 감소하였던 것과 관련 있다. 2020년 1~3월 석모리의 PM10, NO2, O3 농도의 비 ( /M)는 각각 70.8~89.7%, 70.5~87.1%, 72.5~97.1%이었고, 파도리에서도 각각 79.6~93.5%, 67.7~84.9%, 83.7~94.6% 로 추정 월평균(M)보다 월평균(Os)이 감소하였다. 2020년 1월에 몽골 북부로부터 중국 동부와 한반도에 이르는 지역의 온난화로 인한 광화학 반응으로 최근 4년과 비교하여 AOD가 높게 나타났으나 2020년 3월에는 풍상측인 중국에서 2차 에어로졸을 생성하는 전구물질 배출 감소로 최근 4년과 비교하여 낮은 AOD 분포를 보였던 것으로 분석되었다.

We measured VOCs and NO2 in the indoor and outdoor air at 125 houses in Jeollanam-do and Gyeongsangnamdo, from March 2007 to January 2008. The concentration of benzene measured in the Gwangyang survey group was higher than in Yeosu and Hadong, and showed a statistically significant difference from Yeosu (p<0.05). The concentration of toluene in outdoor air was highest in the Gwangyang survey group. The concentration of NO2 measured in the Yeosu survey group was higher than in Gwangyang and Hadong, and showed a statistically significant difference from Hadong (p<0.01). According to the results of a correlation analysis, VOCs (benzene, toluene, xylene, ethylbenzene) exposure of individuals showed a significant correlation with the residential indoor air (p<0.01). Also, VOCs of residential indoor and outdoor air showed a significant correlation (p<0.01). The concentration of NO2 exposure of individuals measured in the Yeosu comparison group showed a high correlation with the residential indoor air.

The concentration of VOCs, NO2 was measured both inside and outside residential homes surrounding an industrial complex. Measurements were performed in the area of the industrial complexes and around 10 km away from the industrial complex area. Benzene did not exceed the air quality standard value. Toluene exhibited a high value of concentration in outdoor Yeosu investigated group. The concentration of NO2 is higher than outside concentrations of houses in both inside housing research group compared with the group of Gwangyang and Yeosu. Benzene and toluene showed high correlation (p<0.001) in the housing interior in Gwangyang, It showed a high correlation (p<0.01) in the housing interior in the comparison group. In Yeosu there was a high correlation (p<0.001) between the inside and outside of the housing in the survey group. In the control group there was only high correlation (p<0.05) in the inside of the housing.

NO2 concentration characteristics of Busan metropolitan city was analysed by statistical method using hourly NO2 concentration data(1998～2000) collected from air quality monitoring sites of the metropolitan city. 4 representative regions were selected among air quality monitoring sites of Ministry of environment. Concentration data of NO2, 5 air pollutants, and data collected at AWS was used. Both Stepwise Multiple Regression model and ARIMA model for prediction of NO2 concentrations were adopted, and then their results were compared with observed concentration. While ARIMA model was useful for the prediction of daily variation of the concentration, it was not satisfactory for the prediction of both rapid variation and seasonal variation of the concentration. Multiple Regression model was better estimated than ARIMA model for prediction of NO2 concentration.

By using hourly NO2 concentration data(1998～2000) at the Busan Metropolitan City air quality monitoring sites, characteristics of daily mean value of NO2 concentration was discussed in space and time. The correlation between NO2 concentration and other relating air pollutants was analyzed by using SAS program and meteorological parameters as well. After choosing representative 4 areas, this study used hourly concentration data(1998～2000) from air quality monitoring sites on NO2, NO, O3, CO, SO2 and PM10. Typical metropolitan characteristics of two peaks in a day was shown in the variation of NO2 concentration of Busan city.

For the purpose of predicting air pollutants concentration in Pusan coastal urban, we used an Eulerian model of flow and dispersion/chemistry/deposition process considering SST effects which estimate through POM. The results of air quality model including emission from various sources show that the seasonal variation pattern of respective pollutants was affected by the seasonal SST fields and local circulation. Horizontal deviation of diurnal SST was 2.5∼4K, especially large gradients in coastal region. Through numerical simulation of wind fields we predicted that local circulation prevailed during daytime in summer and nighttime in winter. So high concentration distribution showed toward inland in spring and summer seasons, while high concentration distribution showed at inland near coast in autumn and winter.

The concentration of air pollution in a large city such as Pusan has been increased every years due to the increase on fuel consumption at factories and by vehicles as well as the gravitation of the population. In this study, we have analyzed NO2 concentration data and various data of meteorological factors during 1994-1997 to investigate the characteristics of NO2 concentration and how the high NO2 concentration is generated under the meteorological condition. According to the study, NO2 peak concentration at most sites occurred about 1h later after the rush hour. In the characteristics of emissions in sites, sinpyeong- dong was highly contributed to point source while the other sites were highly contributed to line source. The high NO2 concentration had high generation probability when temperature contained typical seasonal characteristics and wind speed was low. Using the relationship between meteorological factors and the daily average NO2 concentration, correlation analysis was practiced. The seasonal variation of the daily average NO2 concentration was correlated with air temperature, solar radiation and wind speed, but the correlation coefficient between meteorological factors and the daily average NO2 concentration was not so much high. Thus we have known that the daily average NO2 concentration is partially explained by meteorological factors.