Nitrogen Isotopic Composition of Coal-Fired Power Plant NOx: Influence of Emission Controls and Implications for Global Emission Inventories

Despite the potential use of delta N-15 as a tracer of NOx source contributions, prior documentation of delta N-15 of various NOx emission sources is exceedingly limited. This manuscript presents the first measurements of the nitrogen isotopic composition of NO (delta N-15-NOx) emitted from coal-fired power plants in the U.S. at typical operating conditions with and without the presence of selective catalytic reduction (SCR) and selective noncatalytic reduction (SNCR) technology. To accomplish this, a novel method for collection and isotopic analysis of coal-fired stack NOx emission samples was developed based on modifications of a historic U.S. EPA stack sampling method. At the power plants included in this study, large differences exist in the isotopic composition of NOx emitted with and without SCRs and SNCRs; further the isotopic composition of power plant NOx is higher than that of other measured NOx emission sources confirming its use as an environmental tracer. These findings indicate that gradual implementation of SCRs at power plants will result in an industry-wide increase in delta N-15 values of NOx and NOy oxidation products from this emission source.