Structure of the atmospheric surface layer over an industrialized equatorial area Yusri Bin Yusup a, ⁎, Wan Ramli Wan Daud b , Azami Zaharim b , Meor Zainal Meor Talib b a School of Industrial Technology, Universiti Sains Malaysia,11800 Penang, Malaysia b Faculty of Engineering, Universiti Kebangsaan Malaysia, 43600 UKM Bangi, Malaysia article info abstract Article history: Received 1 April 2007 Received in revised form 17 November 2007 Accepted 8 April 2008 This paper is written to report observations of the structure of the atmospheric surface layer over a coastal industrialized equatorial area. The observations were recorded at Prai Industrial Park, Penang (5° 22′ N, 100° 23′ E) a relatively simple terrain area during the south-west monsoon season in the period of three months using slow response systems. The limitations of the instruments used and its effects on the results are discussed. Wind turbulence and temperature were measured on a 10 m tower and analyzed using eddy correlation method and Monin–Obukhov similarity relations to obtain the normalized standard deviation of longitudinal (σ u /u ⁎ ), lateral (σ v /u ⁎ ) and vertical wind velocity fluctuations (σ w /u ⁎ ) with respect to stability parameter z/L. From the results of the analysis, we found that most of turbulence is generated by shear or mechanical force. It was found that the average neutral value of σ u /u ⁎ is 2.35, 1.98 for σ v /u ⁎ and 1.47 for σ w /u ⁎ with a significantly lower than the proportionality to the power of 1/3 during unstable atmospheric conditions, and thus do not obey Monin–Obukhov similarity theory. It was observed that σ u /u ⁎ and σ v /u ⁎ values increase linearly in the range of 0 b z/L b 2 and fairly well correlated while σ w /u ⁎ does not. © 2008 Elsevier B.V. All rights reserved. Keywords: Atmospheric surface layer Turbulence Equatorial area Monin–Obukhov similarity theory 1. Introduction The atmospheric surface layer or ASL continues to be one of the most researched atmospheric layers due to its importance and accessibility. Even so, the endeavor to fully describe its physical processes globally is relevant and significant in developing countries such as in South East Asian countries because of the lack of ASL research in these countries. These studies help to understand the ASL and subsequently aid in managing the increasing air pollution problem common in this layer of the atmosphere. Further- more, bulk transport across the entire planetary boundary layer (PBL) is highly dependent on the ASL. Similar studies have been concentrated in western mid- latitude countries and such studies in the equatorial or tropical regions are limited (Agarwal et al., 1995; Krishnan and Kunhikrishnan, 2002; Venkata Ramana et al., 2003). Proper adjustments of the parameters and equations used in modeling air pollution dispersion need to be made to make it more suitable in these areas. Equatorial regions are known for their long and intense exposure to solar radiation throughout the year with high humidity especially in the South East Asian countries besides having different climates, frequent low wind conditions and the presence of monsoon seasons. Unless observed in situ, there is no evidence whether the parameters and empirical equations developed in other countries of different conditions in the various air pollution models can be used in other countries of different conditions. 2. Methodology The campus of the Institusi Teknologi Tunku Abdul Rahman (ITTAR) situated in the center of the Prai Industrial Zone, Penang, Malaysia (5° 22′ N, 100° 23′ E) was chosen as the sampling site. This area is a coastal equatorial urban location with simple terrain in a heavy industrialized area (9 km 2 ). The average height of the buildings in this area is approximately 15 m. Observations were carried out using tower-based meteorological instruments from April 28 to Atmospheric Research 90 (2008) 70–77 ⁎ Corresponding author. Fax: +60 4 6573678. E-mail address: yusriy@usm.my (Y.B. Yusup). 0169-8095/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.atmosres.2008.04.003 Contents lists available at ScienceDirect Atmospheric Research journal homepage: www.elsevier.com/locate/atmos