The effect of combustion parameters on the PAH formation from coconut shell combustion in a FBC was investigated. Among the combustion parameters studied which included temperature, excess air, fuel particle size, and fuel moisture content, only excess air proved to have significant influence on the PAH formation. At 750 degreesC, an increase of excess air from 20 to 80% resulted in a twelfth fold reduction of PAH emission. At high excess air levels, the combustion temperature had small influence on PAH emission level. In addition to above mentioned combustion parameters, the addition of secondary air to the freeboard was investigated. Due to the relatively low temperature, the addition of secondary air resulted in higher PAH emission. A strong correlation between the combustion efficiency and the PAH emission was observed. According to the results, the CO concentration can be employed as an indicator of PAH level in the exhaust gas. (C) 2002 Elsevier Science Ltd. All rights reserved.