Boundary-layer structures simulated from TAQM and TAPM prognostics and verified by tethersonde monitoring in central Taiwan

• Main Authors: Chen Guan-Yu, 陳冠宇
• Other Authors: Cheng Wan-Li
• Format: Others
• Language: zh-TW
• Published: 2006
• Online Access: http://ndltd.ncl.edu.tw/handle/35645696189652523112

碩士 === 東海大學 === 環境科學與工程學系 === 94 === In recent years, central Taiwan has become more urbanized and industrialized. As the population density has increased, so has the level of anthropogenic pollutants, especially from industrial and motor vehicle emissions. The transportation and diffusion of such pollutants, which usually cause the air quality to deteriorate, are determined by meteorological factors, such as wind direction, wind speed and mixing height. In this study, a tethersonde was used to monitor air pressure, temperature, humidity, wind direction and speed. The sample pumps were collected air samples at different heights, which were analyzed for concentrations of O3, NOx and CO in autumn 2003. A Meteorological Temperature Profiler (MTP5-HE), which is a new instrument for monitoring the temperature profile, was used to estimate the mixing height variation in selected seasons. In addition, the synoptic weather systems were simulated with the Pennsylvania State University/NCAR fifth generation Mesoscale Model System (MM5) and The Air Pollution Model (TAPM). The air quality was simulated with the Taiwan Air Quality Model (TAQM). The model simulations were then analyzed, and the data from the Taiwan Environmental Protection Administration (TEPA) were compared with the results of the tethersonde monitoring. On 10 October 2003, a cyclone was moving eastward continuously and located northeast of Taiwan, with a very weak pressure gradient covered the whole of Taiwan. The air monitoring stations in central Taiwan showed the ozone concentration reached over 80 ppb at noon on October 10. The Ox (Ox=O3+NO2)concentration was increased up to a maximum for 120 ppb in Tali at noon; until 1500 LST, the Ox concentration was 140 ppb in Nantou. In this high ozone episode, the range of NO2/NOx value in the inland (e.g. Tali and Nantou) were presented from 0.3 to 1.0 and 0.5 to 1.0 in the urban (e.g. Fengyuan and Chunming), and they also showed that NO2 concentrations were almost titrated and accumulated in the inland. At noon on October 10, the NMHC concentration in Hsitun was decreased to 0.2 ppm and the NMHC/NOx value was 10; in Nantou, the NMHC concentration was a constant as 0.3 ppm, but the NMHC/NOx value was 25 and significant increased with NO2 decreased. The NMHC concentration in the inland was less than in urban, so the ozone concentration in the inland was almost controlled by NOx; in the other hand, the NMHC and NOx in the urban varied more than in the inland. In the vertical profiles, the onshore wind at 400 m height caused pollutants to stop moving and accumulate under 400 m on the morning of October 10, 2003. In night, the galley wind presented at 200 m, maximum wind speed was 5 m/s and CO concentration was mixed well above 200 m. For horizontal meteorological simulations, the wind speed of the MM5 and TAPM in autumn of 2003 in central Taiwan presented good agreement, with IOA values between 0.33~0.89. For the temperature simulated, the correlation values of these models reached 0.82 and IOA values were 0.83~0.95. After the frontal system passed over Taiwan, the regional circulation strongly affected the pollutant diffusing height in the vertical and transportation in the horizontal. Under the boundary layer, the atmosphere stratified and the galley wind near the surface limited the pollutant diffusion. The overall results show that air pollutant recirculation is a common feature of coastal cities as a result of the diurnal variation in the sea /land breeze circulation.