Nitrous oxide emissions from fossil fuel combustion

Abstract

The role of coal combustion as a significant global source of nitrous oxide (N 2 O) emissions was reexamined through on‐line emission measurements from six pulverized‐coal‐fired utility boilers and from laboratory and pilot‐scale combustors. The full‐scale utility boilers yielded direct N 2 O emission levels of less than 5 ppm. The sub‐scale combustor test data were consistent with full‐scale data, and also showed N 2 O emission levels not exceeding 5 ppm, although these levels increased slightly when various combustion modifications to lower NO emissions were employed. These on‐line emission measurements are very different from previously published data. The discrepancy is shown to be due to a sampling artifact by which significant quantities of N 2 O can be produced in sample containers which have been used in establishing the previously employed N 2 O data base. Consequently, we conclude that N 2 O emissions bear no direct relationship to NO emissions from these combustion sources, and that this direct source of N 2 O is negligible. Other indirect routes for the conversion of NO into N 2 O outside the combustor and other combustion sources not examined by this study, however, cannot be ruled out.