Multi-year investigations of aerosol layer using lidar measurements at Chung-Li, Taiwan Chih-Wei Chiang a,d,n , Subrata Kumar Das b,d , Chuan-Yao Lin c , Jan B. Nee d , Shu-Huang Sun a , Hung-Wei Chiang a , Ming-Ju Yu a , Shu-Ting Zhang e a Department of Mechanical Engineering, Kun Shan University, Tainan 710, Taiwan b PM&A Division, Indian Institute of Tropical Meteorology, Pune 411008, India c Research Center for Environmental Changes, Academia Sinica, Taipei 115, Taiwan d Department of Physics, National Central University, Chungli 320, Taiwan e Department of Soil and Water Conservation, National Chung Hsing University, Taichung, 402, Taiwan article info Article history: Received 15 November 2011 Received in revised form 23 July 2012 Accepted 25 July 2012 Available online 23 August 2012 Keywords: Lidar Aerosol PM 10 abstract Height, evolution and structure of the nocturnal aerosol layers in the lower troposphere is reported by using a ground-based lidar over Chung-Li (24:58 3 N, 121:10 1 E), Taiwan, during the period from March 2002 to December 2008. Investigation shows that the aerosol layers mainly distributed at an altitude range between 0.2 and 3 km. The mean height and depth of the aerosol layer are 0.57 70.11 km and 0.63 70.14 km, respectively. Seasonality is observed for the depth and height of the aerosol layer. The wind shear and temperature inversion is calculated from the radiosonde data. The statistical interpretation shows a correlation between lidar-derived aerosol layer height and wind shear and also with the temperature inversion. The depth and height of aerosol layer have a positive correlation with Bulk Richardson number. The seasonal features of tropospheric aerosols and their impact on the PM 10 mass concentrations are also examined. & 2012 Elsevier Ltd. All rights reserved. 1. Introduction Investigation on the spatio-temporal distribution of tropo- spheric aerosols are important for the assessment of climate, Earth’s radiation, cloud and precipitation formation process, and environmental problems like poor visibility, physiological effects, etc. The quantitative estimation of aerosol effects in the atmo- spheric boundary layer (ABL) and free troposphere regions is highly uncertain due to their complex structure (Vijayakumar et al., 1998). Earlier studies have reported that the ABL is affected by turbulence, especially in some particular geographical regions, for example, near the mountain valley, coastal zone, or basin region (Anthes, 1978; Nieuwstadt, 1984; Coulter, 1990; Greco et al., 1992; Kolev et al., 2000; Sicard et al., 2006; Hennemuth and Lammert, 2006; Shiyuan and Whiteman, 2008; Cuxart, 2008). The atmospheric turbulence has various forms and involved intricately in many phenomena in meteorology and climate studies even in the night time (Lee et al., 2006; Yao and Zhong, 2009). The aerosol content, especially in the lower troposphere fluctuates under the continuous influence of turbulence and can be monitored with active remote sensing tools such as lidar and ceilometer etc. The prospective and limitations of these remote sensing tools to study aerosol layers is discussed in Wiegner et al. (2006). In the present work, we have used ground-based lidar to study the vertical structure of aerosol layer. The lidar use aerosols as a tracer, which upon scattering contributes to the lidar back- scatter intensity from the range resolved measurement. By using this information, the height, evolution and structure of the aerosol layer is determined from the received lidar signal. We have used seven years of lidar data (from March 2002 to December 2008) to investigate the height and evolution of aerosol layer during the night time (defined as a nocturnal aerosol layer; NAL). The relationships between NAL structure and air quality have also been studied. The paper is organized as follows: brief description of the lidar system and data analysis technique is given in Sections 2 and 3 respectively. In Section 4, the results and discussion are given. Finally, Section 5 provides a brief summary. 2. Lidar system description The lidar system is located at the National Central University (NCU), Chung-Li (24:58 3 N, 121:10 1 E, 167 MSL), a semi-urban place in the northwest part of Taiwan. The lidar site is about 20 km away from the sea coast and surrounded by mountain Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/jastp Journal of Atmospheric and Solar-Terrestrial Physics 1364-6826/$ - see front matter & 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jastp.2012.07.005 n Corresponding author at: Department of Mechanical Engineering, Kun Shan University, Tainan 710, Taiwan. Tel.: þ886 6 2050496; fax: þ886 6 2050509. E-mail address: cwchiang@alumni.ncu.edu.tw (C.-W. Chiang). Journal of Atmospheric and Solar-Terrestrial Physics 89 (2012) 40–47