Laboratory and field methods for measurement of
gaseous emission from buildings and building materials
It is a well known fact that toxic gas emissions occur inside many buildings. It is not in the scope of this text to try to describe the mechanisms of such emissions but rather to describe analytical tools, which can be used to approve or disapprove emission of certain gas compounds from building materials or in-situ inside a building.
The basic principle of the methods is to trap emerging gas molecules inside a fixed volume. A constant flow of molecules into this volume will increase the concentration linearly with time.
Analysis of surface active and water soluble compounds like acetaldehyde, ammonia and the low fatty acids at very low concentrations is not easy, especially for samples in a fixed volume. We have however many years of experience in dealing with such problems and we are confident that the particular methods will allow determination of very low emissions. Also, simulation of very low emissions (as well as method calibration) can be made using gas permeation devices. Such devices also provide traceability to mass standards.
A laboratory method for measurement of emission from building materials
A system for measurement of emissions of known gas compounds from sample slabs of building materials comprises an FTIR spectrometer and a specialized long path sample cell with room for the sample slabs. Observation of the enclosed gas is continous and spectra can be produced at time intervals as desired. One hour integration time would the produce 24 spectra per day. GC analysis usually requires sample accumulation in adsorption tubes, transport of the tubes and a desorption method for injection into a gas chromatograph. Some crucial compounds, like formaldehyde, do not lend themselves very well for GC determination. The FTIR method advised has the advantage that no sampling is required. The gas compounds are constantly being observed as they are emitted into the enclosed air volume. And the concentration rises with time.
A field method for direct measurement of gaseous emissions inside buildings
The analytical tool in this case comprises a transportable FTIR spectrometer with a long path open beam gas cell, i.e. a probe beam of infrared radiation penetrates part of the air in a room. No sampling and no transport assures very high "sample fidelity". Air exchange rates in homes are typically 0.5 exchanges per hour. By bringing down the air exchange rate to the lowest possible value one also gains method sensitivity with time. Measurements at standard and decreased air exchange rates also provides a possibility to distinguish between background concentrations in the ventilation air from the outside and concentrations from within the sample area. The former stay constant while the latter increase in concentration. I anticipate that normal concentrations in the low ppb range will be discoverable with a rolling FTIR / 100m open gas cell combination. Finally, with the decreased air exchange rate, a number of apartments may be scrutinized during a working day with a rolling FTIR analyzer.
A tool for air quality certification in buildings
A standardized method for air quality certification can probably be developed and applied as a valuable tool for the building market.