LETTERS Methyl chloride as a gaseous tracer for wood burning? Dear Sir: In recent years a connection has been drawn between levels of methyl chloride (CH3C1) in the atmosphere and levels of wood burning (13). Methyl chloride has been proposed and applied as a gaseous tracer for monitoring levels of residential wood burning, with seemingly good correlation (3, 4). This proposed link between wood combustion and methyl chloride levels is inconsistent with the very low chlorine content of wood and especially of cellulose. The premise for CH3C1 as a product of wood combustion apparently lies in papers by Palmer (5)and Lovelock (9, who suggest that combustion contributes to levels of CH3C1 in the atmosphere. Lovelock states without literature citation that “Approximately l % of the chlorine content of vegetable matter is converted to methyl chloride during smouldering combustion.” Palmer in turn cites a personal communication from Lovelock stating that “1 cm3 of methyl chloride gas [is] produced for each gram of cellulose burned in glowing combustion.” However, chlorine exists in cellulose only as an impurity imparted through isolation or processing, and Lovelock’s suggested yield of 1 cm3 CH3Cl (approximately 2.1 mg) per gram of cellulose implies that the cellulose substrate contained at least 1.5 mg C1 per gram (1500 ppm) even if C1 were converted quantitatively to CH3C1. This is more than 10 times the level of chlorine found in qualitative filter papers (Whatman No. 1 typically contains 130 ppm C1 by the manufacturer’s analysis), which suggests that Lovelock used a very impure cellulose, possibly one isolated from wood by delignification using chlorine or chlorite. Palmer’s analysis cites the work of Bethge and Troeng (7) in stating that “natural chlorine content of wood pulp and other cellulosic materials ranged from 0.07-2.68 mg g-l.” However, most of these samples were processed materials, many of which were no doubt treated with chorine or chlorinated compounds. The only wood sample in the literature cited contained 230 ppm of C1, and this concentration must be considered high in view of more recent results in which wood and bark from six species were found to contain 252 Environ. Sci. Technol., Voi. 23, No. 3, 1989
