The report documents the technical approach and results achieved while developing a grab sampling method and an automated, on-line gas chromatography method suitable to characterize nitrous oxide (N2O) emissions from fossil fuel combustion sources. The two methods developed have been documented in the form of U.S. EPA/AEERL Recommended Operating Procedures. The combustion of fossil fuels is suspected to contribute to measured increases in ambient concentrations of N2O. Accurate and reliable measurement techniques would help to assess the relative contribution of fossil fuel combustion N2O emissions to the increase in ambient concentrations. The characterization of N2O emissions from fossil fuel combustion sources has been hindered by the lack of suitable and acceptable grab sampling and on-line monitoring methodologies. On-line monitoring techniques are limited and, of those available, instrument costs are often prohibitive, detection levels are often insufficient, and the techniques are often susceptible to interferences present in combustion process effluents.