A Fourier transform infrared (FTIR) spectrometer interfaced to a 2.5 m base path, open multi- pass cell was used to monitor indoor air in post-fumigation dwellings. The residual chemicals studied were the fumigant, methyl bromide and its odor additive, chloropicrin (Cl3CNO2). Indoor measurements with a time resolution of 15 minutes were performed for two houses of different age. Our results indicate that the newer dwelling, which contained insulation materials, appeared to retain substantial amounts of the fumigant. The highest concentration measured for methyl bromide was 24 ppm, close to five times the allowed TLV (Threshold Limit Value) of 5 ppm. For chloropicrin, we also observed a surprising level of close to 0.4 ppm, four times the TLV of 0.1 ppm. It was noted that the concentrations were very susceptible to any air movement such as that due to door opening. Analyses utilizing the conventional adsorption-desorption/GC technique were performed simultaneously by the Worker Health and Safety Branch of the California EPA. Although the vast difference in time resolution of the two methods precludes direct comparison of the data, averaging our measurements over the same integration time indicated that the FTIR methods gives significantly higher values than those obtained by the conventional method, especially when the pollutant concentrations are low.
A new Fourier transform infrared (FTIR) spectrometer has been set up at the California Department of Flood and Agriculture for monitoring gas phase pesticides and inert ingredients used in the formulation of pesticides. To allow detection of trace quantities down to the ppm range, the FTIR instrument has been interfaced to a custom, external open multiple reflection system with a base pathlength of 2.5 m. The mirror system is of the double corner cube White type design capable of achieving a total absorption pathlength of 140 m. Our initial application was to monitor the concentration of methyl bromide after controlled releases of this fumigant into an indoor environment.
A compact differential optical absorption spectrometer with a 2.5 m base path has been constructed for indoor air
measurements. The mirror system can achieve a total pathlength of up to 220 m. A cooled photodiode array is used
as a detector with a detection limit equivalent to an absorbance of less than 0.0001 (3 α level with 2 mm averaging).
This paper describes the setup of the instrument and explains the data acquisition and analysis procedures used.
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