Apportionment of emission source strengths using optical remote sensing and dispersion modeling

Abstract

At the beginning of an air pollution event, pollutants are emitted into the atmosphere by a variety of sources. The knowledge of the emissions of every source is inevitable to carry out adequate reduction measures. Sometimes, the estimation of source strengths from afar is necessary due to the lack of accessibility to the source (e.g.: aircraft in use) or due to the diffuse character of the source (e.g. area sources). Source strengths and concentration measurements are connected by the transport of the pollutant, which can be estimated using a dispersion model. The underlying idea to determine the source strength is to run the dispersion model varying the input parameters as long as needed to obtain the least possible difference of measured and modelled concentrations. The model input is then assumed to be the best estimation of the emission rates. Assuming a passive pollutant, the transport and dispersion can be condensed into a set of linear equations and hence, linear algebra can be used to solve for the source strength (e.g. Singular Value Decomposition). The advantage of concentration measurements along a horizontal path (e.g. by FTIR, DOAS) is to reduce the degree of uncertainty regarding the horizontal dispersion. So the main interest of the modelling approach is to estimate the amount of vertical dispersion that accounts for the dilution of the pollutants. Applying this method to a real case with highly heterogeneous source characteristics in time and space, measurements at an international airport were performed. Some results of these measurements are presented here.