A Review of Whole Air Sampling
By Ryan Day
The collection of whole air samples with commercially available collection devices, such as stainless steel canisters and gas sample bags, is a widely used sampling method in fields such as environmental science. With this type of sample collection, an aliquot of whole air is collected that can be analyzed directly by laboratories without the need for any collection media to trap a target chemical of interest. This means a wide variety of many different gases can be directly analyzed from the whole air sample using advanced methods such as gas chromatography-mass spectrometry. Further, any number of unrelated compounds can be analyzed from whole air without the inherent limitations of selective media. However, because they have not been historically used to perform personal monitoring, whole air sampling is not commonly associated with industrial hygiene strategies or sampling activities.
The most common type of industrial hygiene air sampling is personal air monitoring, where small personal sampling pumps or passive monitors are used to collect air contaminants through a pre-selected sorbent, filter, or collection media. After the sampling is completed the media is sent to a laboratory to determine time-weighted average exposure concentrations for pre-selected air contaminants recovered from the media. Some sampling activities involve air sampling devices to be set at stationary locations, which are considered area samples rather than personal samples. Whole air methods can be used to collect area air samples in a stationary location over time through the use of automatic inflating gas sample bags without electric pump, lung box-equipped gas sample bags and electric pumps, or stainless steel canisters. If this type of sample were submitted for GC-MS analysis for VOCs, for example, using the EPA TO-15 method, then the presence and concentration (to ppb levels) of literally hundreds of trace compounds can be reported as a time-weighted average—all from a single integrated air sample (provided the sample was collected and analyzed with properly calibrated equipment).
Grab Samples
A simpler, more convenient way in which a whole air sample might be collected for industrial hygiene purposes is by collecting a grab sample. A grab sample is not a time-weighted average sample, but is representative of a snapshot in time. These types of samples can be useful for hazard recognition, hazard identification, or risk assessment purposes, where the results can provide valuable guidance in the development of comprehensive personal air monitoring strategies. This type of sampling is also ideal for identifying unknown odors associated with air quality complaints because a whole air grab sample can be collected quickly when the unknown odor presents itself.
While grab samples can be taken with canisters, they can also be performed using a gas sample bag and a means to inflate it. The traditional method uses an inert vacuum pump to draw air from the ambient air being sampled. The air then passes through the pump and is loaded into the sample bag. This method is easy to use but allows for potential cross contamination from the inner parts of the pump fittings and any connection tubing.
An alternative type of sampling apparatus is a manual-inflating sample bag that allows a whole air grab sample to be collected without special equipment or expertise. Manual-inflating sample bags are reusable and can be air-shipped for overnight delivery and rush analysis. The bag’s construction allows for stable storage of most gases and includes two side panels with retractable handles. Since no electric components or batteries are required, the sample bag is intrinsically safe. When the valve is opened, the user draws air into the bag by pulling on the handles on the bag side walls.
The bags are available in either Tedlar film or multilayer foil. Users can test whole air samples before the sample is submitted to the laboratory, or the whole air grab sample may be tested to determine whether the sample needs to be sent for offsite analysis.
Whole air sampling does have limitations. It may not be as good a method for evaluating air contaminants other than gases, such as particles or biological agents. Certain chemicals are retained in some bags, and some aluminized bags have metal fittings, which are a problem for sulfur gases. Advanced gas chromatography analysis fees associated with whole air sampling may be higher than traditional industrial hygiene analysis fees. Also, anything reactive in the atmosphere may continue to react in the whole air sample. 
Finally, the stability of the whole air sample should be considered. The hold time for a metal foil bag is reasonably long; however, the hold time for a Tedlar bag is typically 3 days, which may mean rush analysis is required. Care must also be taken when shipping sampling bags, which could explode if shipped in an unpressurized plane.
Determining Specific Compounds
Industrial hygienists looking to augment a hazard assessment to determine a sampling strategy might consider grabbing some whole air samples to help determine which specific compounds might be in the breathing air. If you are being asked to identify an unknown nuisance aroma, a whole air sample can help you determine what is present in the air rather than methods that may only rule out certain gases, such as taking measurements with a series of portable gas monitors or collecting air samples onto chemical-specific media. 
Ryan Day
is National Sales Manager at Nextteq.