Sampling and Stability of Methyl Bromide on Activated Charcoal

Monitoring methyl bromide (CH3Br) emission into the atmosphere following soil fumigations requires sensitive and reproducible sampling methods. The factors affecting the sampling efficiency and stability of CH3Br on activated charcoal sampling tubes were identified and evaluated in this study. The number of tubes required for accurate sampling using activated coconut and petroleum charcoal tubes was determined for various sampling flow rates and sampling intervals. Breakthrough of CHoBr on both types of tubes increased with increasing flow rates and sampling intervals. CHsBr hydrolyzed rapidly on moist charcoal, and the reaction was enhanced by temperature. At 40 “C and 21% moisture content, the half-lives of degradation were only 11 h on coconut charcoal and 17 h on petroleum charcoal. The rapid hydrolysis of CH3Br on charcoal was caused by the high pH of the charcoal. To prevent degradation of CHsBr bromide, charcoal samples should be always kept at low temperature and under dry conditions during transport and storage. Correction for loss due to degradation during sampling may be necessary if samples are taken from atmospheres with high temperature and humidity.