Air Sampling Instructions

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Depending on the contaminants of concern, air samples may be collected using several techniques, including: whole air sampling, solid sorbent sampling (active or passive), impinger sampling, and filter sampling.

 

Whole Air Sampling

Perhaps the simplest means of collecting an air sample is by collecting a whole air sample in a sample bag (e.g. Tedlar bag) or sample canister (e.g. Summa canister). This sampling technique is appropriate for collection of permanent gases (e.g. oxygen, nitrogen, methane, etc.), reduced sulfur compounds (e.g. hydrogen sulfide, methyl mercaptan, etc.), and volatile organic compounds (VOCs).

Tedlar bags are strongly recommended for sampling of reduced sulfur compounds (especially hydrogen sulfide and mercaptans). They may also be used for sampling of permanent gases and/or VOCs, depending on your data quality objectives. Since the holding time for bag samples is very short (24-72 hours), we ask that you please coordinate in advance with the laboratory when you are planning on collecting samples in this manner. Tedlar bags are often collected using a lung sampler (a.k.a. “lung box” or “vacuum box”), which fills the bag with sample directly using the pressure difference in the box. Using a lung sampler, the sample path does not come into contact with the pump, which makes this technique appropriate for sampling of reduced sulfur compounds.  Other tedlar bag sampling techniques may be possible or appropriate depending on your situation and data quality objectives. Please call the lab with questions.

Canisters are recommended for sampling of VOCs (up to approximately C12) and permanent gases. One advantage of using canisters as opposed to bags is a longer holding time; a wide range of VOCs have been shown to be stable in canisters at low concentrations for at least 30 days. Canisters are cleaned, certified to project specifications (either batch or individually certified), and evacuated by the laboratory prior to sampling. Since the vacuum inside the canister drives sampling, no additional equipment is necessary. Canisters may be collected as “grab” samples (instantaneous fill) or “time-integrated” samples (where the laboratory also provides a flow controller/critical orifice assembly). For time-integrated canister sampling, the client must inform the lab of the desired sampling duration and/or flow rate.

Analytical testing dotsSolid Sorbent Sampling (Active)

Another air sampling technique draws air through a tube filled with a solid sorbent material (or combination of sorbents); contaminants in the air are chemically adsorbed onto the material in the tube. This sampling technique is appropriate for collection of many VOCs and semi-volatile organic compounds (SVOCs), including polycyclic aromatic hydrocarbons (PAHs), PCBs/Pesticides, aldehydes, ammonia, amines, and carboxylic (volatile fatty) acids. It is important to note that there are numerous types of sorbent materials available — each customized to best capture a particular chemical or class of chemicals. No one sorbent material will collect all types of air contaminants.

To perform active solid sorbent sampling, a personal sampling pump is needed. The pump should be calibrated with an air flow calibrator to pull sample air through the sorbent tube at a known flow rate for a known amount of time, yielding the sample volume. In order for the laboratory to report your results in concentration units (i.e. “ppmV/mg/m3” or “ppbV/µg/m3”), the client must provide the sample volume on the chain of custody form. For the most accurate results, pump calibration should be performed with an example of the sample media in-line, to account for any backpressure. The client may ask the lab to provide an extra “calibration tube” along with their sample tubes.

Learn about Passive Air Sampling...

Analytical testing dotsSolid Sorbent Sampling (Passive)

Selected solid sorbent media may be used in “passive” mode — meaning that adsorption of contaminants onto the sorbent media takes place via diffusion rather than actively pulling the air through the media with a pump. Passive sampling has several advantages: it is discreet, the sampling media is easy to deploy, and the technique can be used for long-term sampling. Applications such as odor investigations and ambient air perimeter (“fenceline”) monitoring are good candidates for passive solid sorbent sampling. To provide quantitative results, an experimentally determined “sampling rate” or “uptake rate” must exist for each compound of concern with the sorbent sampling media. Contact the laboratory to discuss if passive sampling may be an appropriate option for your upcoming sampling project.

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Impinger Sampling

Some airborne contaminants may be sampled using liquid impingers. Similar to solid sorbent sampling, contaminants of concern in the air chemically react with (and/or are physically dissolved into) an aqueous solution as sample air is bubbled through the liquid.  Impinger sampling is commonly used for measurement of various contaminants in stationary sources (e.g. Hydrogen Halide/Halogens via EPA Method 26, Metals via EPA Method 29) and was historically used for workplace monitoring of selected contaminants (e.g. aldehydes, ammonia). In addition, a few ambient air methods involving impinger sampling exist (e.g. EPA TO-8 for phenol/cresols and EPA TO-5 for aldehydes).  For workplace monitoring and ambient/indoor air monitoring, many alternative methods now exist which use treated sorbent tubes instead of impingers. Impinger sampling is still used for stationary source measurements and other selected applications where sorbent tubes are not a suitable choice (e.g. high temperature/moisture levels).

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Filter Sampling

Collection of contaminants in the aerosol (particulate) and/or vapor phase may be conducted using filter cassettes. To collect vapor phase contaminants, the filter media must be chemically treated such that the contaminant of concern chemically reacts with the media to form a stable derivative. Filter sampling is most often used for particulate matter and inorganic species such as metals. Similar to solid sorbent sampling, filter sampling uses a calibrated personal sampling pump to pull a known volume of air through a filter cassette.

Whatever your air sampling application, please make sure to coordinate with your laboratory in advance to ensure that you meet your data quality objectives.

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