The paper discusses on-line N2O measurements from six full-scale, coal-fired utility boilers that indicate direct N2O emissions of < 5 ppm. Laboratory and pilot-scale experiments conducted to further characterize direct N2O emissions are consistent with the field data indicating on-line N2O concentrations < 5 ppm. Further sub-scale coal experiments using air staging and natural gas reburning for NOx control show only slight increases in N2O emissions. These results question the reliability of the existing N2O data base, much of which is likely to be affected by a sampling artifact by which N2O can be produced in sample containers, awaiting analysis, through an as-yet-unknown mechanism possibly involving No, SO2, and H2O. Time resolved measurements of N2O, NO, and SO2 from combustion emissions, collected in stainless steel sample containers, show that N2O concentrations in wet samples can increase to levels greater than 100 ppm in < 24 hours. These increases are reduced (but not eliminated) in dried samples. All samples show that NO reacts (possibly forming N2O) within 4 hours. SO2 concentrations decrease with time at rates related to the sample dryness. These results suggest the need for further research to identify other direct and indirect sources of N2O.