Introduction

Gaussian dispersion models are used since many years to evaluate the average concentrations supposed in industrial site environments. The emitted fluxes either known (because measured) or are thus arbitrarily fixed (in the case of nonexisting sites). The landscape roughness should not be too important to not disturb the wind flow around the emission source.

We seek to determine, based on concentration measurements in the environment, the emission flow through an evaluation of dispersion ratio (ßi) connecting the concentrations measured in the environment (Ci) to the emitted flux (E) :

Ci = ßi * E

Gaussien model is used here to determine the dispersion ratio ßi of each measuring point retained, as presented in folowing figure.

If the emitted flux E is arbitrarily set to 1, then the dispersion pattern results in the procurement of each dispersion ratio
ßi.

From the gas concentration measurements that we attempt to quantify Ci, one can then determine the emitted flux (E):

E = Ci / ßi

By multiplying the measuring points and by leading this method to the level of the latters, one can evaluate the results dispersion and thus determine uncertainties related to the method.

Equipment

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.

Guidelines

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