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Last update: May 2021

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Animal Emissions

Guidelines for backwards Lagrangian stochastic dispersion technique (bLS) for measuring ammonia emissions

(C). Ineris


The inversion technique of a sotchastic lagrangian model (bls for backwards Lagrangian Stochastic) allows users without excessive knowledge in micrometeorology, using a commercial software easy to use (for example WindTrax), to consider the NH3 emission of small plots of ground by using the horizontal fluxes at only one height under the wind of the experimental plot of ground, as well as weather informations. To apply this method it is preferable that the roughness of the landscape is not too high (not too many elements disturbing the wind flow around the emission source), and where clear positions of conditions up and under-the-wind can be defined, and for gases which one can clearly observe the concentration differences between these two positions.

This protocol is an opposite method of a dispersion model which allows to calculate the tracers emissions of a surface source (Flesh & Wilson, 2005). The dispersion model bLS simulate the transport of the tracer between a source and a measurement site, and one envisage the relationship between, the average concentration of the tracer and the issue rate, (C/F)sim. The issue rate is deduced from:

Where Xobs is the concentration observed (above the concentration upwind) with the position of the measurement site.


Equipment should allow the measurement of meteorological data and gas concentration at time steps that are homogeneous from the meteorological point of view, i.e. if the climate change at a hourly time step, the observed

values should integrate the temporal variability during one hour.

In this last case, it is recommended to use:

  • Sensors with a response time less than 1 minute: optical or photoacoustic
  • Analyzers, open path remote sensing optical analyzers (DOAS, FTIR, TDLAS, etc)
  • Passive samplers with hourly analysis (if concentration levels are high enough),
  • Electronic sensors where the signal can be recorded giving either hourly averages or a collection of at least 5 values within one hour.

Meteorological sensors should include at least temperature, humidity, wind speed and direction.

Guideline details

File (PDF)

See also

Flesch, T., Wilson, J. D., and Yee, E. 1995. Backward time Lagrangian stochastic dispersion models, and their application to estimate gaseous emissions. J. Appl. Meteorol. 34, 1320-1332.

Flesch, T, Wilson, J.D. 2005. Deducing Ground-to-Air Emissions from Observed Trace Gas Concentrations: A Field Trial with Wind Disturbance. J. Appl. Meteorol. 44, 475-484. (pdf)

This method was implemented by INERIS within the framework of the ADEME metrology project, with average concentrations and continuous recordings.

The files described in the report can be used for further tests of procedures of emission measurement. Their organization and their use are relatively complex. They are available by contacting François Gautier.