Statistical atmospheric inversion of small-scale gas emissions by coupling the tracer release technique and Gaussian plume modeling: a test case with controlled methane emissions

This study presents a new method for estimating the pollutant emission rates of a site and its main facilities using a series of atmospheric measurements across the pollutant plumes. This approach is based on a combination of the tracer release method, a Gaussian atmospheric transport model and a statistical atmospheric inversion approach. The conversion between the tracer controlled emission and the measured atmospheric concentrations across the plume provides knowledge on the atmospheric transport. The concept of the method consists of using this knowledge to optimize the configuration of the Gaussian model parameters and the model uncertainty statistics in the inversion system. The pollutant rates of each source are inverted to optimize the match between the concentrations simulated with the Gaussian model and the pollutants' measured atmospheric concentrations, accounting for the Gaussian model uncertainty. This new approach is evaluated with a series of inversions of controlled methane point sources using acetylene as a tracer gas. In these experiments, different configurations of methane and acetylene point source locations are tested to assess the efficiency of this method in comparison with the classic tracer release technique to cope with the distances between the different methane and acetylene sources. The results from these controlled experiments demonstrate that when the targeted and tracer gases are not well collocated, this new approach provides a better estimate of the emission rates than the tracer release technique. As an example, the relative error between the estimated and actual emission rates is reduced from 29 % with the tracer release technique to 8 % with the combined approach in the case of a tracer located 60 metres upwind of a methane source. This method also enables an estimate of different sources within the same site to be provided.