The emission rates of diffuse and heterogeneous distributed sources are difficult to determine because point measurements are not representative. Therefore a method was further developed to determine gaseous emission rates by measurements of path-integrated mixing ratios with open-path spectroscopic systems in the exhaust plume (VOC, NH$-3$/, CH$-4$/, N$-2$/O, CO, CO$-2$/) and of meteorological parameters. Inverse dispersion modeling is used to quantify the emission rates afterwards with these data. The measurements are performed by Fourier Transform Infrared (FTIR) spectroscopy and Differential Optical Absorption Spectroscopy (DOAS) at 50 to 500 m optical path lengths about 1 to 20 m above ground level. The measurement accuracy for greenhouse gases and ammonia is about plus or minus 10% and for BTX about plus or minus 30%. The whole method was validated at a livestock building with a single exhaust chimney. The Gaussian model PAL was applied for inverse modeling to investigate limited pieces of land and isolated facilities in flat terrain. Including the accuracy of the dispersion simulations the determined emission rates have an error margin of about plus or minus 30%. Results of measurement campaigns are discussed as emission rates of ammonia from slurry spreading as well as of benzene from gas stations and a tank farm.
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