Because of the mercurial nature of air, collecting air samples differs substantially from collecting water or soil samples. However, the first step remains the same: to identify the sampling method employed and the equipment needed for collecting a representative air sample and effectively sequestering the air sample until it can be analyzed by a laboratory facility. The Tedlar bag collection system collects a representative sample of air in a non-reactive bag for transportation and analysis.
Using this method, the first step is to determine the extent of the sampling effort and to collect and organize the appropriate materials for the project. It is always a best practice to test and clean equipment before use. The Tedlar bag collection system consists of a vacuum box with Teflon tubing, pumps, Tedlar bags with working valves, sample labels, opaque trash bags and chain of custody records and seals. After materials are collected, attach the Teflon tube of the vacuum box to the valve stem of the Tedlar bag, and place the bag in the vacuum box. Seal the vacuum box, and connect the sampling pump to the evacuation tube. The pump should be set to the flow rate of 3 liters per minute. The sampling pump removes air from the vacuum box, which then produces a pressure differential that draws air into the Tedlar bag from the air being sampled. None of the sample ever passes through the pump. When the bag is full, close and lock the valve stem to keep the air sample in place. Upon completion, label the bag with the appropriate identifying information. The label should be marked with a ball point pen rather than a marker because the fumes from the marker may contaminate the air sample. Also, the label should be applied to the edge of the bag beyond the seal as chemicals from the adhesive may enter the bag and affect the composition of the sample. For transportation, the bag must be wrapped in an opaque plastic bag or a cooler to avoid photodegredation. Also, because many compounds degrade very quickly, it is imperative that sample analysis take place within 48 hours of sample collection. As with water and soil samples, chains of custody remain important with air samples. Forms detailing chain of custody should accompany all samples at all times, even on their short journeys to testing facilities.
Images: “Liftoff at Sunrise” by Malcolm Carlaw licensed under CC BY 2.0 ; “Graphic” by Coleman Tharpe