Kanokkanjana, K; Cheewaphongphan, P; Garivait, S
Black carbon (BC) contributes directly and indirectly to the Earth's radiative balance change, and consequently, has impact on global warming as the second largest contributor after carbon dioxide. One of the major sources of aerosol emission from biomass burning is open burning of agricultural residues. In many countries, open burning in the paddy field is a common way to eliminate rice residues after harvesting, including Thailand, one of the world's largest rice exporters. During rice harvesting seasons, open burning of rice residues in the field releases a large amount of aerosols. However, limited studies have been conducted to quantify BC emissions from open burning of rice residues in Thailand.
This study aims to assess amount of BC emission from open burning of rice residues in Thailand. Open burning experiments were conducted both in the field and in the chamber to simulate open burning in order to determine emission factor of BC emissions, including PM2.5, CO, and CO2 through continuous real time equipment measurement. Field experiments were carried out in paddy field in central region of Thailand to obtain biomass load (g/m(2)), residue to product ratio (RPR), fraction of biomass subject to burning in the field after utilization (%), and combustion efficiency (%), respectively. Rice residues and ash were also collected to determine moisture content in the laboratory to obtain biomass load in dry matter.
Field experiments were conducted in Samutsakhon province to represent for irrigated paddy field; and in Nakhonsawan province to represent for rain-fed paddy field. Biomass load of rice straw in irrigated and rain-fed paddy field are 360 +/- 140 and 507 +/- 305 g/m(2), respectively. Result of RPR in irrigated area is 0.85 +/- 0.48 and rain-fed area is 0.55 +/- 10.11.
Emission factor results of BC from open burning experiment in the chamber are 0.79 +/- 0.36 gBC/kg(dm) from rain-fed rice residues burning and 0.72 +/- 0.03 gBC/kgdm from irrigated rice residues burning.
Burned area of irrigated and rain-fed paddy field was obtained from agricultural statistical data and questionnaire results. Total burned area of irrigated paddy field is 2.69 million ha, and rain-fed paddy field is 1.21 million ha. Black carbon emission from irrigated paddy field is 6,973 +/- 113 ton/y and from rain-fed paddy field is 4,846 +/- 1,329 ton/y. Total amount of BC released from in-field open burning in Thailand is 11,819 ton annually.