Integrative Air Sampling
Integrative sampling requires collection of airborne substances over an extended period of time. Samples are typically returned to an analysis facility for processing and results are typically available some time after the sampling event. This is required when it is too expensive or inconvenient to undertake continuous real-time measurements, or when sensitivity requirements are such that continuous methods are unable to provide the necessary detection limits. Integrative sampling can include passive or active methods requiring use of a pump to draw air through a sorbent material or filter media.
Integrative samples are required for some substances where the air quality standard requires it. For example, the Ontario point-of-impingement limit for dust is 120 µg/m3 averaged over 24 hours, thus requiring results integrated over 24 hours.
Often, but not always, sampling protocols are required that necessitate integrative sampling, sometimes due to the analysis techniques used in the laboratory. For example, speciated VOC sampling requires collection in the field on a sorbent medium (e.g., charcoal). Sorbed VOCs are then extracted in the lab and analyzed by GC-MS; see webpage on VOC analysis for further details.
Many jurisdictions require that air quality sampling techniques follow certain standard protocols. For example, many jurisdictions in North America require use of the US EPA Compendium of Methods to determine levels of toxic organic compounds in ambient air. For example, one of these methods describes the use of a filter and polyurethane foam sorbent set in a high-volume air sampler to collect the sample. This is an integrative sampling technique; analysis follows by GC-MS.
It is not always necessary to use sorbent media for integrative sampling where whole-air samples can be collected over an extended period of time in Tedlar bags or in a SUMMA canister using controlled flow orifices. Also, these whole-air collection techniques can be used to collect instantaneous, or grab, samples where necessary; grab samples are not considered integrative.
It is not always necessary to use active sampling methods to collect integrated samples; see passive sampling webpage for more details.