Sains Malaysiana 41(6)(2012): 747–754

Evaluation of Dry Deposition Velocity of SO₂ by Bowen Ratio and Resistance

Model Over Rice Paddy in Tropical Climate

(Pengukuran Halaju Pemendapan Kering SO₂ Menggunakan Model Nisbah Bowendan

Rintangan di Kawasan Penanaman Padi Beriklim Tropika)

Orachorn Chimjan* & Pojanee Khummongkol

Environmental Technology Division, School of Energy, Environment and Materials

King Mongkut’s University of Technology Thonburi, 126 Pracha-U-Thit Rd., Bangmod, Thungkru

Bangkok 10140, Thailand

Received: 13 October 2011 / Accepted: 4 January 2012

ABSTRACT

The Bowen ratio method was applied to determine dry deposition velocity of SO₂ over rice paddy in the tropical climate condition (hot and humid). The meteorological parameters and SO₂ concentration required by the method were monitored online during July – December 2007. The deposition velocity was evaluated under the wet and dry climatic conditions. The median values of the velocity in daytime in the wet season were in ranges of 0.24 - 0.41 cm s-1, and 0.42 - 0.77 cm s-1 in the dry season. The SO₂ dry deposition velocity was found to be very low for all the nighttime measurements and independent of seasonal variation. A relationship between the deposition velocity and the humidity was seen in which the SO₂ velocity inversely increased with the relative humidity. The velocity determined by the Bowen ratio study was compared to Wesely resistance model. The comparative study showed that the SO₂ deposition velocity obtained by the resistance model was higher than the Bowen ratio in the wet season (high humidity) but lower in the dry season (low humidity). This indicated the effect of humidity on the deposition velocity under the tropical climatology. The parameterization terms to calculate the SO₂ deposition in the resistance model need to be modified for the tropical region.

Keywords: Bower Ratio method; dry deposition of SO₂; resistance model; tropical region

ABSTRAK

Kaedah Nisbah Bowen telah digunakan untuk menentukan halaju pemendapan kering SO₂ di kawasan penanaman padi beriklim tropika (panas dan lembab). Parameter meteorologi dan SO₂ yang diperlukan bagi kaedah ini telah diukur secara berterusan dari bulan Julai hingga Disember 2007. Penentuan halaju pemendapan telah ditentukan dalam keadaan iklim basah dan kering. Nilai median halaju di siang hari pada musim hujan adalah dalam julat 0.24 - 0.41 cm s-1, dan 0.42 - 0.77 cm s-1 pada musim kering. Halju pemendapan kering SO₂ didapati sangat rendah untuk semua ukuran pada waktu malam dan ianya tidak bergantung kepada variasi musim. Hubungan antara halaju pemendapan dan dan kelembapan dapat diperhatikan di mana halaju pemendapan SO₂ adalah berkadar songsang dengan kelembapan relatif. Halaju pemendapan Bowen juga telah dibandingkan dengan Model Rintangan Wesely. Kajian perbandingan menunjukkan halaju pemendapan SO₂yang diperoleh daripada model rintangan adalah lebih tinggi berbanding nisbah Bowen pada musim hujan (kelembapan tinggi) tetapi lebih rendah pada musim kering (kelembapan rendah). Ini menunjukkan kesan kelembapan kepada halaju di kawasan beriklim tropika. Terma penggunaan parameter bagi pengiraan pemendapan SO₂ dalam model rintangan harus di ubahsuai bagi penggunaan di rantau tropika.

Kata kunci: Pemendapan kering SO₂; kaedah nisbah Bowen; model rintangan; rantau tropika

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*Corresponding author; email: aorsung@hotmail.com