空氣污染問題不僅受污染源排放、大氣化學反應影響，氣象條件以及地形效應的影響也是造成高污染事件發生的重要因素。過去模式研究指出，臺灣在高壓迴流或是弱綜觀的天氣型態時，會有利於高PM2.5濃度事件發生，雖然位於雲林縣山麓地帶的斗六地區並非臺灣中部PM2.5濃度排放量最高的地區，但斗六地區空氣品質卻經常性不佳。為解析斗六地區空污事件之演變過程，本研究利用新建構的無人機觀測系統與氣膠光達於2020年11月16日至20日，在斗六地區進行高時間解析度的氣象場與氣膠剖面觀測，以提供過去少有的高時間頻率大氣垂直剖面資訊，並透過一系列的資料處理流程與驗證程序，來確保無人機的觀測品質，同時搭配地面空氣品質測站資料和WRF模式模擬的再分析場，整合分析空污事件之演變過程。
研究結果顯示，弱綜觀天氣條件下，斗六地區污染物的傳輸與擴散特徵與海陸風環流、背風渦旋及逆溫結構有關。個案期間夜晚風速皆小於1 m s-1，整體水平擴散條件類似，但在17、18日晚間高污染事件發生時，伴隨雙層逆溫結構，分別為近地面的厚度約200公尺的輻射逆溫與800-1000公尺左右的沉降逆溫，沉降作用同時導致高空環境乾燥無雲，有利加劇夜間地表的輻射冷卻，使地面逆溫強度增強，相較於較低污染之 16、19日夜晚的2.6 ℃ km-1與4.5 ℃ km-1，17、18日逆溫強度分別高達8.0 ℃ km-1與12.1 ℃ km-1，此惡劣的垂直擴散條件使斗六空品站於17日和18日晚間分別測得最高PM2.5濃度達70 μg m-3和99 μg m-3。海風環流約於上午9時建立，將潮濕氣團與沿岸污染物往內陸傳輸，18日下午1時可觀測到明顯的海風鋒面抵達，造成斗六比濕與PM2.5濃度同時上升，而光達觀測顯示1300公尺內NRB數值明顯增加，表示海風鋒面結構超過1000公尺。夜間隨著陸風環流發展，將內陸污染物帶離，斗六高污染濃度在17、18日分別於18時與21時之後下降。模式結果顯示個案期間臺灣海峽區域共出現三個背風渦旋，其中兩個為氣旋式環流，一個為反氣旋式環流，渦旋發展主要受大環境風場影響，而有不同的移動路徑與結構變化，其中氣旋式的背風渦旋會導致近地面污染物北傳，而反氣旋式環流的北風則伴隨沉降所造成的乾空氣移入斗六地區，呼應前述18日夜間高污染發生的條件。整體而言，本研究透過無人機與光達高時間解析的垂直剖面觀測進行分析，從污染物與氣象場空間分布演變探討高污染事件成因，並確立此觀測技術能應用於將來大氣剖面研究。

Douliu is one of the most air-polluted areas in Taiwan. Factors that caused the deterioration of air quality in this area might attribute to emissions, chemical reactions, meteorology, and geographical distribution, etc. Recent modeling studies point out that high PM2.5 concentration events occurred are usually associated with favorite weather conditions (i.e., high-pressure peripheral circulation and weak synoptic weather). To make a statement on the deterioration of PM2.5 events, we employed a new technology, Unmanned Aerial Vehicle (UAV), and an aerosol lidar to observe the high resolution of meteorological and aerosol profiles at Douliu during November 16th-20th, 2020. A series of data validation procedures had applied to ensure the UAV data quality. As a result, the UAV measurements (i.e., meteorological parameters and PM2.5 concentration) are reliable and show in good agreement with vertical structure obtained from lidar observation. In addition to observations (i.e., UAV, lidar, surface air quality, and meteorology data), we also use a WRF model to run a reanalysis for this case study.
According to our results, the roles of land-sea breeze, temperature inversion layer, and leeside vortex in aerosol transportation and dispersion over Douliu during the weak synoptic weather were discovered. The horizontal dispersion condition did not change much during the night of the observation, which was accompanied by the wind speed smaller than 1 m s-1. On November 17th and 18th when the high pollution event occurred, there were two temperature inversion layers in vertical. One was the surface radiative inversion whose depth was about 200 m, and another was the elevated subsidence inversion which was located at around 800-1000 m. The subsidence of the air also led to the dry condition in the sky and was beneficial for radiative cooling at the surface at night. Therefore, the strength of the temperature inversion near the surface increased, compared with the strength of 2.6 ℃ km-1 on the night of 16th and 4.5 ℃ km-1 on the night of 19th, the inversion strength on 17th and 18th were up to 8.0 ℃ km-1 and 12.1 ℃ km-1, respectively. Therefore, these worse vertical dispersion conditions caused the maximum of hourly PM2.5 concentration to be up to 70 μg m-3 in the evening of 17th and 99 μg m-3 in the evening of 18th. The sea breeze circulation developed at about 9 a.m., and the specific humidity and PM2.5 concentration increased at the same time at noon, because the sea breeze transported the pollutant and water vapor from the coastal area to Douliu. The structure of sea breeze front was distinct on November 18th at 1 p.m., and the leading edge of the sea breeze front reached a height greater than 1000 m which was demonstrated from the lidar NRB data. When the land breeze gradually developed, the air quality improved after 18 p.m. on 17th and 21 p.m. on 18th. The result of the numerical simulation indicated there were three leeside vortexes during this case, two were associated with the cyclonic circulation and one was associated with the anticyclonic circulation. The location, structure, as well as direction of rotation with respect to the leeside vortex showed differently is due to the variation of the synoptic winds and how they interacted with the terrain. The cyclonic vortex led northward of the pollutant near the surface, and the anticyclonic vortex brought the dry air of subsidence with the northerly wind over Douliu. Overall, this study used the high temporal resolution vertical observation data from UAV and aerosol lidar to dissect critical factors of PM2.5 deterioration in Douliu area. This work also highlights that the high temporal resolution of UAV and lidar observations can serve as a powerful tool to improve our understanding of the relationship between atmospheric vertical profile and air quality.

Augustin, P., S. Billet, S. Crumeyrolle, K. Deboudt, E. Dieudonné, P. Flament, M. Fourmentin, S. Guilbaud, B. Hanoune, Y. Landkocz, C. Méausoone, S. Roy, F. G. Schmitt, A. Sentchev and A. Sokolov (2020). Impact of Sea Breeze Dynamics on Atmospheric Pollutants and Their Toxicity in Industrial and Urban Coastal Environments. Remote Sensing, 12(4).

Barrett, E. W. and O. Ben-Dov (1967). Application of the lidar to air pollution measurements. Journal of Applied Meteorology and Climatology, 6(3), 500-515.

Cai, W., X. Xu, X. Cheng, F. Wei, X. Qiu and W. Zhu (2020). Impact of "blocking" structure in the troposphere on the wintertime persistent heavy air pollution in northern China. Science of the total environment, 741, 140325.

Campbell, J. R., D. L. Hlavka, E. J. Welton, C. J. Flynn, D. D. Turner, J. D. Spinhirne, V. S. S. III and I. H. Hwang (2002). Full-Time, Eye-Safe Cloud and Aerosol Lidar Observation at Atmospheric Radiation Measurement Program Sites: Instruments and Data Processing. Journal of Atmospheric and Oceanic Technology, 19, 431-442.

Castro, S., W. Emery, G. Wick and W. Tandy (2017). Submesoscale Sea Surface Temperature Variability from UAV and Satellite Measurements. Remote Sensing, 9(11).

Chang, S.-C. and C.-T. Lee (2007). Secondary aerosol formation through photochemical reactions estimated by using air quality monitoring data in Taipei City from 1994 to 2003. Atmospheric Environment, 41(19), 4002-4017.

Chen, Y.-L., Y. Yang and F. M. Fujioka (2008). Effects of Trade-Wind Strength and Direction on the Leeside Circulations and Rainfall of the Island of Hawaii. Monthly Weather Review, 136(12), 4799-4818.

Cheng, W.-L. (2001). Synoptic weather patterns and their relationship to high ozone concentrations in the TaichungBasin. Atmospheric Environment, 35, 4971-4994.

Cheng, W.-L. (2002). Ozone distribution in coastal central Taiwan under sea-breeze conditions. Atmospheric Environment, 36, 3445-3459.

Chuang, M.-T., P.-C. Chiang, C.-C. Chan, C.-F. Wang, E. E. Chang and C.-T. Lee (2008). The effects of synoptical weather pattern and complex terrain on the formation of aerosol events in the Greater Taipei area. Science of the total environment, 399(1-3), 128-146.

Chuang, M.-T., C. C. K. Chou, N.-H. Lin, A. Takami, T.-C. Hsiao, T.-H. Lin, J. S. Fu, S. K. Pani, Y.-R. Lu and T.-Y. Yang (2017). A Simulation Study on PM2.5 Sources and Meteorological Characteristics at the Northern tip of Taiwan in the Early Stage of the Asian Haze Period. Aerosol and Air Quality Research, 17(12), 3166-3178.

Ciesielski, P. E., P. T. Haertel, R. H. Johnson, J. Wang and S. M. Loehrer (2012). Developing High-Quality Field Program Sounding Datasets. Bulletin of the American Meteorological Society, 93(3), 325-336.

Collis, R. T. H. (1965). Lidar observation of cloud. Science, 149(3687), 978-981.

Crazzolara, C., M. Ebner, A. Platis, T. Miranda, J. Bange and A. Junginger (2019). A new multicopter-based unmanned aerial system for pollen and spores collection in the atmospheric boundary layer. Atmospheric Measurement Techniques, 12(3), 1581-1598.

Derimian, Y., M. Choël, Y. Rudich, K. Deboudt, O. Dubovik, A. Laskin, M. Legrand, B. Damiri, I. Koren, F. Unga, M. Moreau, M. O. Andreae and A. Karnieli (2017). Effect of sea breeze circulation on aerosol mixing state and radiative properties in a desert setting. Atmospheric Chemistry and Physics, 17(18), 11331-11353.

Fernald, F. G. (1984). Analysis of atmospheric lidar observations: some comments. Applied optics, 23(5), 652-653.

Gramsch, E., D. Cáceres, P. Oyola, F. Reyes, Y. Vásquez, M. A. Rubio and G. Sánchez (2014). Influence of surface and subsidence thermal inversion on PM2.5 and black carbon concentration. Atmospheric Environment, 98, 290-298.

Guimarães, Ye, Batista, Barbosa, Ribeiro, Medeiros, Souza and Martin (2019). Vertical Profiles of Ozone Concentration Collected by an Unmanned Aerial Vehicle and the Mixing of the Nighttime Boundary Layer over an Amazonian Urban Area. Atmosphere, 10(10).

Helmis, C. G., K. H. Papadopoulos, J. A. Kalogiros, A. T. Soilemes and D. N. Asimakopoulos (1995). Influence of background flow on evolution of saronic gulf sea breeze. Atmospheric Environment, 29(24), 3689-3701.

Holmes, H. A., J. K. Sriramasamudram, E. R. Pardyjak and C. D. Whiteman (2015). Turbulent fluxes and pollutant mixing during wintertime air pollution episodes in complex terrain. Environmental science & technology, 49(22), 13206-13214.

Holton, J. R. (1973). An introduction to dynamic meteorology. American Journal of Physics, 41(5), 752-754.

Hong, J.-S. (2001). Numerical simulation of leeside vortex: Case study.

Hong, S.-Y. and K.-S. S. Lim (2010). Development of an Effective Double-Moment Cloud Microphysics Scheme with Prognostic Cloud Condensation Nuclei (CCN) for Weather and Climate Models. Monthly Weather Review, 138(5), 1587-1612.

Hsu, C.-H. and F.-Y. Cheng (2016). Classification of weather patterns to study the influence of meteorological characteristics on PM2.5 concentrations in Yunlin County, Taiwan. Atmospheric Environment, 144, 397-408.

Hsu, C.-H. and F.-Y. Cheng (2019). Synoptic Weather Patterns and Associated Air Pollution in Taiwan. Aerosol and Air Quality Research, 19(5), 1139-1151.

Jacobson, M. Z. (2005). Fundamentals of atmospheric modeling, Cambridge university press.

Johnson, W. B. (1969). Lidar applications in air pollution research and control. J Air Pollut Control Assoc, 19(3), 176-180.

Jou, B. J.-D. (1994). Mountain-originated mesoscale precipitation system in northern Taiwan: a case study 21 June 1991 Atmospheric and Oceanic Sciences, 5(2), 169-197.

Karppinen, A., S. M. Joffre, J. Kukkonen and P. Bremer (2001). Evaluation of inversion strengths and mixing heights during extremely stable atmospheric stratification. International Journal of Environment and Pollution, 16(1/2/3/4/5/6).

Kim, M.-S. and B. H. Kwon (2019). Estimation of Sensible Heat Flux and Atmospheric Boundary Layer Height Using an Unmanned Aerial Vehicle. Atmosphere, 10(7).

Kitada, T. (1987). Turbulence structure of sea breeze front and its implication in air pollution transport -Application of k-e turbulence model. Boundary Layer Meteorology, 41, 217-239.

Lai, H.-C. and M.-C. Lin (2020). Characteristics of the upstream flow patterns during PM2.5 pollution events over a complex island topography. Atmospheric Environment, 227.

Largeron, Y. and C. Staquet (2016). Persistent inversion dynamics and wintertime PM10 air pollution in Alpine valleys. Atmospheric Environment, 135, 92-108.

Lesouëf, D., F. Gheusi, R. Delmas and J. Escobar (2011). Numerical simulations of local circulations and pollution transport over Reunion Island. Annales Geophysicae, 29(1), 53-69.

Li, N., J. P. Chen, I. C. Tsai, Q. He, S. Y. Chi, Y. C. Lin and T. M. Fu (2016). Potential impacts of electric vehicles on air quality in Taiwan. Science of the total environment, 566-567, 919-928.

Lin, C.-H., C.-H. Lai, Y.-L. Wu, H.-C. Lai and P.-H. Lin (2007). Vertical ozone distributions observed using tethered ozonesondes in a coastal industrial city, Kaohsiung, in southern Taiwan. Environmental Monitoring and Assessment, 127(1-3), 253-270.

Lin, C.-H., C.-H. Lai, Y.-L. Wu, P.-H. Lin and H.-C. Lai (2007). Impact of sea breeze air masses laden with ozone on inland surface ozone concentrations: A case study of the northern coast of Taiwan. Journal of Geophysical Research, 112(D14).

Lin, C.-H., Y.-L. Wu and C.-H. Lai (2010). Ozone reservoir layers in a coastal environment – a case study in southern Taiwan. Atmospheric Chemistry and Physics, 10(9), 4439-4452.

Lin, C.-H., Y.-L. Wu, C.-H. Lai, P.-H. Lin, H.-C. Lai and P.-L. Lin (2004). Experimental investigation of ozone accumulation overnight during a wintertime ozone episode in south Taiwan. Atmospheric Environment, 38(26), 4267-4278.

Liu, C., J. Huang, Y. Wang, X. Tao, C. Hu, L. Deng, J. Xu, H. W. Xiao, L. Luo, H. Y. Xiao and W. Xiao (2020). Vertical distribution of PM2.5 and interactions with the atmospheric boundary layer during the development stage of a heavy haze pollution event. Science of the total environment, 704, 135329.

Liu, H. P. and J. C. L. Chan (2002). Boundary layer dynamics associated with a severe air-pollution episode in Hong Kong. Atmospheric Environment, 36(12), 2013-2025.

Luan, T., X. Guo, L. Guo and T. Zhang (2018). Quantifying the relationship between PM2.5 concentration, visibility and planetary boundary layer height for long-lasting haze and fog–haze mixed events in Beijing. Atmospheric Chemistry and Physics, 18(1), 203-225.

Miller, S. T. K. (2003). Sea breeze: Structure, forecasting, and impacts. Reviews of Geophysics, 41(3).

Miloshevich, L. M., A. Paukkunen, H. Vömel and S. J. Oltmans (2004). Development and Validation of a Time-Lag Correction for Vaisala Radiosonde Humidity Measurements. Journal of Atmospheric and Oceanic Technology, 21(9), 1305-1327.

Muñoz, R. C. and R. I. Alcafuz (2012). Variability of Urban Aerosols over Santiago, Chile: Comparison of Surface PM10 Concentrations and Remote Sensing with Ceilometer and Lidar. Aerosol and Air Quality Research, 12(1), 8-19.

Murayama, T., M. Furushima, A. Oda, N. Iwasaka and K. Kai (1996). Depolarization Ratio Measurements in the Atmospheric Boundary Layer by Lidar in Tokyo. Journal of the Meteorological Society of Japan. Ser. II, 74(4), 571-578.

Nakane, H. and Y. Sasano (1986). Structure of a Sea-breeze Front Revealed by Scanning Lidar Observation. Journal of the Meteorological Society of Japan. Ser. II, 64(5), 787-792.

Neumann, P. P. and M. Bartholmai (2015). Real-time wind estimation on a micro unmanned aerial vehicle using its inertial measurement unit. Sensors and Actuators A: Physical, 235, 300-310.

Park, M.-S. and J.-H. Chae (2018). Features of sea–land-breeze circulation over the Seoul Metropolitan Area. Geoscience Letters, 5(1), 1-12.

Phan, T. T. and K. Manomaiphiboon (2012). Observed and simulated sea breeze characteristics over Rayong coastal area, Thailand. Meteorology and Atmospheric Physics, 116(3-4), 95-111.

Ramanathan, V., M. V. Ramana, G. Roberts, D. Kim, C. Corrigan, C. Chung and D. Winker (2007). Warming trends in Asia amplified by brown cloud solar absorption. Nature, 448(7153), 575-578.

Raynor, G. S., S. Sethuraman and R. M. Brown (1979). Formation and characteristics of coastal internal boundary layers during onshore flows. Boundary-Layer Meteorology, 16(4), 487-514.

Reddy, T. V. R., S. K. Mehta, A. Ananthavel, S. Ali, V. Annamalai and D. N. Rao (2021). Seasonal characteristics of sea breeze and thermal internal boundary layer over Indian east coast region. Meteorology and Atmospheric Physics, 133, 217-232.

Simpson, J. E. (1994). Sea breeze and local winds, Cambridge Universoty Press.

Stein, A. F., R. R. Draxler, G. D. Rolph, B. J. B. Stunder, M. D. Cohen and F. Ngan (2015). NOAA’s HYSPLIT atmospheric transport and dispersion modeling system. Bulletin of the American Meteorological Society, 96(12), 2059-2077.

Stull, R. B. (1988). An introduction to boundary layer meteorology, Springer Science & Business Media.

Stull, R. B. (2015). Practical Meteorology: An Algebra-based Survey of Atmospheric Science.

Su, S.-H., C.-W. Chang and W.-T. Chen (2020). The Temporal Evolution of PM2.5 Pollution Events in Taiwan: Clustering and the Association with Synoptic Weather. Atmosphere, 11(11).

Sun, Z., X. Zhao, Z. Li, G. Tang and S. Miao (2021). Boundary layer structure characteristics under objective classification of persistent pollution weather types in the Beijing area. Atmospheric Chemistry and Physics, 21(11), 8863-8882.

Valkaniotis, S., G. Papathanassiou and A. Ganas (2018). Mapping an earthquake-induced landslide based on UAV imagery; case study of the 2015 Okeanos landslide, Lefkada, Greece. Engineering Geology, 245, 141-152.

Viezee, W. and J. Oblanas (1969). Lidar-observed haze layers associated with thermal structure in the lower atmosphere. Journal of Applied Meteorology and Climatology, 8(3), 369-375.

Villa, T. F., E. R. Jayaratne, L. F. Gonzalez and M. L. (2017). Determination of the vertical profile of particle number concentration adjacent to a motorway using an unmanned aerial vehicle. Environmental Pollution, 230, 134-142.

Wang, L., J. Liu, Z. Gao, Y. Li, M. Huang, S. Fan, X. Zhang, Y. Yang, S. Miao, H. Zou, Y. Sun, Y. Chen and T. Yang (2019). Vertical observations of the atmospheric boundary layer structure over Beijing urban area during air pollution episodes. Atmospheric Chemistry and Physics, 19(10), 6949-6967.

Wang, S. H., H. W. Lei, S. K. Pani, H. Y. Huang, N. H. Lin, E. J. Welton, S. C. Chang and Y. C. Wang (2020). Determination of Lidar Ratio for Major Aerosol Types over Western North Pacific Based on Long-Term MPLNET Data. Remote Sensing, 12(17).

Wang, S. Y., L. E. Hipps, O.-Y. Chung, R. R. Gillies and R. Martin (2015). Long-Term Winter Inversion Properties in a Mountain Valley of the Western United States and Implications on Air Quality. Journal of Applied Meteorology and Climatology, 54(12), 2339-2352.

Wang, Y.-C., S.-H. Wang, J. R. Lewis, S.-C. Chang and S. M. Griffith (2021). Determining Planetary Boundary Layer Height by Micro-pulse Lidar with Validation by UAV Measurements. Aerosol and Air Quality Research, 21(5).

Wei, J., G. Tang, X. Zhu, L. Wang, Z. Liu, M. Cheng, C. Münkel, X. Li and Y. Wang (2018). Thermal internal boundary layer and its effects on air pollutants during summer in a coastal city in North China. Journal of Environmental Sciences, 70, 37-44.

Wetz, T., N. Wildmann and F. Beyrich (2021). Distributed wind measurements with multiple quadrotor unmanned aerial vehicles in the atmospheric boundary layer. Atmospheric Measurement Techniques, 14(5), 3795-3814.

Wu, Y.-L., C.-H. Lin, C.-H. Lai, H.-C. Lai and C.-Y. Young (2010). Effects of Local Circulations, Turbulent Internal Boundary Layers, and Elevated Industrial Plumes on Coastal Ozone Pollution in the Downwind Kaohsiung Urban-Industrial Complex. Terrestrial, Atmospheric and Oceanic Sciences, 21(2).

Xie, Y., X. Ye, Z. Ma, Y. Tao, R. Wang, C. Zhang, X. Yang, J. Chen and H. Chen (2017). Insight into winter haze formation mechanisms based on aerosol hygroscopicity and effective density measurements. Atmospheric Chemistry and Physics, 17(11), 7277-7290.

Yu, C.-H. and R. A. Pielke (1987). Chang-Han, Y., & Pielke, R. A. (1986). Mesoscale air quality under stagnant synoptic cold season conditions in the Lake Powell area. Atmospheric Environment, 20(9), 1751-1762.

Zhu, Y., Z. Wu, Y. Park, X. Fan, D. Bai, P. Zong, B. Qin, X. Cai and K.-H. Ahn (2019). Measurements of atmospheric aerosol vertical distribution above North China Plain using hexacopter. Science of the Total Environment, 665, 1095-1102.

中央氣象局108年觀測年報，2019。中央氣象局。

王聖翔、林能暉，2020: 109年微脈衝雷射雷達系統操作維護及資料解析專案計畫。行政院環保署。

李怡茹，2017: 雲林地區細懸浮微粒的來源解析，國立中央大學大氣物理研究所碩士論文。

周仲島，2001: 綠島中尺度實驗(GIMEX)簡介。氣象預報與分析，6，53-60。

周仲島、修榮光，2015: 屏東平原海風環流之 SPOL 雷達觀測特徵。大氣科學，43(1)，47-67。

林沛練、張隆男、陳景森，1990: 海風邊界層之發展與污染物濃度的日變化，大氣科學，18(4)，287-308。

林美綺，2018: 應用數值模式探討複雜地形下之空氣品質問題，長榮大學資訊管理學系碩士論文。

林博雄、李清勝、鄭文通、林民生，2000: 南海季風實驗期間無人機探空之資料診斷。大氣科學，28(3)，243-262。

柯立晉，2018: 開發適用於大氣邊界層觀測的無人機系統，國立中央大學大氣科學系碩士論文。

陳柏霖，2017: 雲林斗六PM2.5濃度變化與氣膠光學特性及氣象條件之關聯性研究，國立中央大學大氣科學系碩士論文。

陳森豐，2004: 高高屏地區空氣污染物之三度空間分佈，國立成功大學環境工程研究所碩士論文。

黃明雄，1998: 台灣地區大氣氣膠特性之研究-墾丁氣膠組成及濃度對大氣能見度的影響，國立中央大學環境工程學系碩士論文。

蔡清彥，1987: 台灣北部地區局部環流之研究。大氣科學，15(2)，179-198。

蔡清彥、童雅卿，1987: 台灣南端地區局部環流之研究。大氣科學，15(1)，69-88。