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MeDOAS

MOBILE EXTRACTIVE DIFFERENTIAL ABSORPTION SPECTROSCOPY (MeDOAS)

The Mobile extractive Differential Optical Absorption Spectroscopy (MeDOAS) 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 MeDOAS technique is essentially an internal lamp, a multi-reflection cell and an UV-spectrometer. MeDOAS monitors UV-radiation over a broad spectral IR region for the detection and quantification of BTEX (Benzene, Toluene, Ethylbenzene, Xylene) and other gases inside the cell.

Fluxsense_meodas_optical_lens

MeDDAS optical 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 and MeFTIR 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 Target species are BTEX (Benzene, Toluene, Ethylbenzene and Xylene) but also other gases including; Phenol, Paracresol, Trimethylbenzene, Furfural, Naphtalene, Styrene and SO2 are detectable at significant concentrations.
Detection limits (conc) The detection limits are species dependent but typically in the 1-20 ppb range.
Typical range (conc) 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 %

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FluxSense AB was founded in 2001 to fill a need for reliable diffuse emissions measurements for the petroleum and petrochemical industry. Since then, FluxSense has conducted well over 100 measurement campaigns of industrial and agricultural emissions in Europe, America and Asia.

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