Comparison of field inspections and dispersion modelling as a tool to estimate odour emission rates from landfill surfaces

This study has the final purpose to estimate the odour impact of a landfill located in Southern Italy, in the region of Puglia, by means of a field inspection that involves the direct assessment of odours in the field by trained assessors, which was carried out following the "plume method" described in the EN 16841:2016, Part 2. The primary aim of this work is to compare different methods for the estimation of Odour Emission Rates from the landfill surface in order to evaluate the method that allows to maximize the correspondence between the simulated odour impact and the outcomes of the direct assessment by field investigations. The motivation of this combined activity relies in the necessity to experimentally verify the hypotheses proposed in recent research work, which highlight the different mechanism determining odour emissions from landfill surfaces compared to the typical volatilization mechanism from passive area source, i.e. natural convection. As a consequence of this different volatilization mechanism, in the case of landfill surfaces, the recalculation of the OER as a function of the wind speed as it is done for other passive area sources may result in significant overestimation of odour impact. This study shows how the correspondence between direct field odour assessments and simulated odour impact is maximized by considering a constant SOER (Specific Odour Emission Rate) in the range of 0.07-0.25 ouE/m2/s. On the other hand, a variable SOER proportional to the square root of the wind speed results in an overestimation of about one order of magnitude of the landfill odour impact. This in turn proves the need to treat landfill surfaces as a particular type of source, requiring specific techniques for the estimation of odour emissions, which must account for the peculiarity of the mechanisms that affect landfill gas emissions into the atmosphere.