Modeling of the atmospheric dispersion of odors

French legislation, with the law on air and the rational use of energy (Loi LAURE) of December 30, 1996, gives "everyone the right to breathe air that does not harm their health" and stipulates that a facility must not "generate excessive olfactory nuisances". Since 1996, legislation governing facilities classified for environmental protection (ICPE) has been expanded to cover the control of odor emissions and their impact. These include

• the decree of February 2, 1998 (and its application circular DPPR/SEI of February 17, 1998), which for the first time defines odor concentration and flow;

• the sectoral decree of February 12, 2003 applicable to ICPEs subject to authorization under heading 2730 (treatment of cadavers, waste or by-products of animal origin...).), which stipulates that odor concentration within a 3 km radius of the site must not exceed 5 or _E · m ^–3 (European odor unit per cubic meter of air) for more than 175 hours per year for existing facilities, or more than 44 hours per year for new facilities, and that in the absence of an atmospheric dispersion study, odor concentration must not exceed 1,000 or _E · m ^–3 ;

• the sectoral decree of January 7, 2002, applicable to composting centers subject to declaration, which stipulates that the inspector of classified installations may request, at the operator's expense, that a campaign be carried out to assess the olfactory impact of the facility, in order to qualify the impact and any annoyance, and to enable better prevention of nuisances. This assessment can be carried out using atmospheric dispersion simulation tools based on mathematical models.

In addition to meeting regulatory requirements, atmospheric dispersion simulation enables :

• assess the olfactory impact of an existing or future facility even before it is set up, for operating permit applications;

• calculate limit values at the deodorization plant outlet in order to draw up specifications for implementation;

• provide food for thought when making strategic choices.

The aim of this dossier is to present the overall methodological approach for simulating the atmospheric dispersion of odors using models. After outlining the main physical mechanisms involved in atmospheric dispersion and the different types of mathematical models adapted to the odor problem and their implementation, we explain the methodology to be followed...