Sains Malaysiana 43(3)(2014): 369–375


Trends in Sulfate Dry Deposition over Mixed Dipterocarp Forest in Thailand using

Relaxed Eddy Accumulation Method

(Corak Pemendapan Kering Sulfat di atas Hutan Dipterokarpa Campuran di Thailand

menggunakan Kaedah Akumulasi Eddy Santai)




1Division of Environmental Technology, School of Energy, Environment and Materials

King Mongkut's University of Technology Thonburi, 126 PrachaUthit Road, Bang Mod, Thungkhru, Bangkok 10140 Thailand


2Faculty of Agriculture Field Science Center, Tokyo University of Agriculture and

Technology 3-5-8 Saiwai-cho, Fuchu, Tokyo 183-8509 Japan


Received: 9 October 2012/Accepted: 8 June 2013



The relaxed eddy accumulation method (REA) was applied for direct measurement of sulfate fluxes over mixed dipterocarp forest. The sampling system using a four-stage filter pack was designed to take updraft or downdraft air samples in the direction of the vertical wind velocity. The deadband of the velocity profile was set at ±0.5 σw in which an air sample with velocity within the set value is rejected. The forest site was located at a latitude of 13o 35' 13.3''N and longitude of 99o 30' 3.9''E Ratchaburi province in Thailand. The sampling period was set in 4 time intervals: 6-12, 12-18, 18-24 and 24-6 h for 3 consecutive days/month (n=144) throughout one year. All the micrometeorological parameters for flux estimation were measured in real time. The concentration and flux of sulfate were found to reach a peak value of 1.32 μg m-3 and 8.35 μg m-2 h-1, respectively, at noon time which indicated the effect of atmospheric instability caused by a high heat transfer during the day. The one-year average deposition velocity was observed to be 0.24 cm s-1.The coefficient β obtained under high ambient temperature and a humid environment in this tropical climate was 0.49. It has also been observed that βis relatively insensitive to atmospheric stability.


Keywords: Dry deposition; forest; sulfate



Kaedah akumulasi eddy santai (REA) telah digunakan untuk pengukuran langsung fluks sulfat di atas hutan dipterokarpa campuran. Sistem pensampelan dengan menggunakan satu pek penapis empat peringkat telah direka untuk mengambil sampel udara draf atas atau bawah yang bergerak dalam arah halaju angin menegak. Paras akhir bagi profil halaju ditetapkan pada ±0.5 σw dan sampel udara dengan halaju di bawah nilai yang ditetapkan adalah ditolak. Tapak hutan tersebut terletak di kedudukan latitud 13o 35' 13.3''N dan longitud 99o 30' 3.9'' E di wilayah Ratchaburi, Thailand. Tempoh persampelan telah dijalankan dalam 4 selang masa: 6-12, 12-18 , 18-24 dan 24-6 jam dalam 3 hari berturut-turut /bulan (n=144) dalam tempoh masa satu tahun. Semua parameter meteorologi mikro untuk anggaran fluks diukur dalam masa sebenar. Sulfat didapati mencapai paras puncak pada kepekatan dan fluks 1.32 μg m-3 dan 8.35 μg m-2 jam-1 masing-masing pada waktu tengahari yang menunjukkan kesan ketidakstabilan atmosfera disebabkan perpindahan haba yang tinggi pada waktu siang. Purata satu tahun kelajuan pemendapan didapati adalah 0.24 cm s-1. Koefisien β yang diperoleh dalam keadaan suhu ambien yang tinggi dan humiditi dalam iklim tropika adalah 0.49. Hasil kajian juga mendapati βis secara relatif tidak sensitif terhadap kestabilan atmosfera.


Keywords: Hutan; pemendapan kering; sulfat



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