Analysis of emission profiles from charcoal produced from different tree species by different pyrolysis methods.

Abstract

Charcoal is a major form of biomass fuel for approximately 80% of the Kenyan population. However, the use of charcoal is associated with indoor air pollution where charcoal users are continually exposed to compounds of incomplete combustion which are known to have detrimental effects to human health. This study analyzed the emission profiles of different types of domestically used charcoal produced by different pyrolysis methods. Charcoal samples from three tree species Acacia polyacantha, Acacia xanthophloea and Eucalyptus grandis, produced by both efficient and traditional pyrolysis methods were collected from charcoal producers in Thika, Machakos and Kitengela. The volatiles were collected using a fabricated chimney placed on clay cook-stove such that smoke was vented to a glass canula where it was condensed. Extracted volatiles were then analyzed by gas chromatography-linked mass spectrometry (GC-MS). A total of 22 PAHs were identified together with other groups of compounds that included ketones, aldehydes, phenols, alkanes, alkenes, carboxylic acids, phthalate, esters, and alcohols. The major compounds found in the smoke extracts with known health effects included naphthalene (3), 1-methylnaphthalene (14), 2-methylnaphthalene (5), fluorene (6), phenanthrene (9), anthracene (11), 1-methyl-phenanthrene (14), fluoroanthene (10), benzo(a)anthracene (12) and chrysene (13).There were significant differences (P˂0.05) in the concentrations of fluorine, naphthalene and pyrene emitted from A. polyacantha and A. xanthophlea prepared by traditional pyrolysis. From A. polyacantha concentrations were naphthalene (110.00μg/g), fluorine (72.00μg/g) and pyrene (60.00μg/g) while from A. xanthophlea, concentrations were naphthalene (140.42μg/g), Fluorene (97.35μg/g) and pyrene (71.82μg/g). The volatile emissions from charcoal prepared by traditional pyrolysis had higher concentration of PAHs relative to the accepted levels of 0.1 - 0.2mg/m3. Charcoal prepared by traditional pyrolysis emitted the highest number of PAHs at 6.25mg/m3 while those prepared by efficient pyrolysis produced the lowest concentration at 0.73mg/m3 both from A. xanthophloea. Therefore, there is need to use efficient pyrolysis methods of charcoal production. This will ensure the production of charcoal with low volatile content that are less harmful to the end users.