Supplementary material to "A Human-Portable Mass Flux Method for Methane Emissions Quantification: Controlled Release Testing Performance Evaluation"

SM1. Description of pneumatic "trough" or "trap" method to determine the CH4 content of the gas released from each CNG tank during the experiments.A pneumatic trough, or water trap, is a simple and effective method for collecting small gas samples that do not readily dissolve in water.Water is used to isolate the sample from atmospheric contaminants.To begin, a sample syringe was submerged upright in a bucket filled with water, displacing any existing gas inside.Once the syringe was void of atmospheric gas, it was inverted, and gas was introduced into the bucket at the bottom of the syringe using a hose.As gas flowed in, it displaced the water in the syringe.When the syringe was sufficiently filled with gas, we inserted a plunger into the syringe while keeping it inverted and underwater, sealing the gas inside.The syringe was then removed from the water, and a needle was attached to