Mobile extractive Fourier Transfer Infra-Red (MeFTIR)
The Mobile extractive Fourier Transfer Infra-Red (MeFTIR) method is used to map the gas concentrations (ppb or mg/m3) at ground level from various sources. It is able to efficiently screen large areas for hotspot or leaks. The MeFTIR technique is essentially an internal lamp, a multi-reflection cell and an IR-spectrometer. MeFTIR monitors IR-radiation over a broad spectral IR region for the detection and quantification of a range of VOCs and other gases inside the cell.
| Physical Basis of measurements | Measurement of local gas concentration inside a reflection cell, combined with local wind data and positional data. |
| Main Purpose | Concentration mapping and leak search. Emission quantification if used with the Tracer Correlation method or Indirect Flux. |
| Spatial information -Scale -Resolution | From the scale of industrial conglomerates (50 km by 50 km) down to sections of a site (50 m by 50 m) or isolated single sources. Provides spatial concentration information in one dimension along the measurement path. 5 m to 25 m in the horizontal, dependent on the driving speed. |
| Measured Quantity (unit) | Local concentration in extracted air (mg/m3) and (ppb) above reference/start value. |
| Secondary Quantities (units) | 1) Mass concentration ratio of ground plume combined with SOF gives Indirect Flux [kg/h] and plume height information [m] 2) Mass flux [kg/h] via Tracer Correlation method. |
| Complementary data | Geolocation of the measurement vehicle (latitude, longitude). Local wind direction (deg N) and wind speed (m/s) are needed for leak search. |
| Compounds measured | A wide range of VOC compounds including methane, other alkanes (C2-C20), alcohols (C2OH-C8OH), alkenes (C2-C4), amines, dienes, aldehydes, vinyl chloride and aromatic VOCs. Other, non-VOC species, include NH3, CO, HCl and HF. N2O and acetylene are suitable tracer gas species. |
| Detection limits (conc) | The detection limits are species dependent but typically in the 1-20 ppb range. |
| Typical range | From detection limit to saturation (no defined upper limit) |
| Time resolution/ sampling frequency | Sampling frequency varies between measurement modes/species in the range: 1 s – 10 s |
| Typical uncertainties (ppb) or (mg/m3) | 10 % |
