An auto-positioning open-path Fourier Transform Infrared (FTIR) spectrometer can be used to directly measure vertical concentration profiles in a plume downwind from an emission source. The multi-component analysis capabilities of FTIR spectroscopy allow simultaneous measurement of diverse downwind pollutant species. Using concentration measurements and meteorological data, it is possible to estimate the emission fluxes across the plume and, thus, the emission rates of pollutants from the source. The field assessment goals were to conduct the first in a series of field tests of a new measurements system developed to perform such emission rate determinations, and to evaluate the system's performance and feasibility. For these purposes, a simple volume source simulator was constructed to emulate process equipment leaks encountered at chemical plants, refineries, and other facilities. By metering the release rates from the volume source simulator, "actual" release rates were compared to the "estimated" release rates calculated using the measurements system. Using simple data screening techniques, over 90% of the field tests conducted produced run-average emission rate estimates within 20% of the actual emission rates. Half of the tests were within 10% of the actual emission rates.