Important contributions of non-fossil fuel nitrogen oxides emissions
Wei Song, Xueyan Liu, Chao‐Chen Hu, Guanyi Chen, Xuejun Liu, Wendell W. Walters, Greg Michalski, Cong‐Qiang Liu
Abstract
Abstract Since the industrial revolution, it has been assumed that fossil-fuel combustions dominate increasing nitrogen oxide (NO x ) emissions. However, it remains uncertain to the actual contribution of the non-fossil fuel NO x to total NO x emissions. Natural N isotopes of NO 3 − in precipitation (δ 15 N w-NO3− ) have been widely employed for tracing atmospheric NO x sources. Here, we compiled global δ 15 N w-NO3− observations to evaluate the relative importance of fossil and non-fossil fuel NO x emissions. We found that regional differences in human activities directly influenced spatial-temporal patterns of δ 15 N w-NO3− variations. Further, isotope mass-balance and bottom-up calculations suggest that the non-fossil fuel NO x accounts for 55 ± 7% of total NO x emissions, reaching up to 21.6 ± 16.6Mt yr −1 in East Asia, 7.4 ± 5.5Mt yr −1 in Europe, and 21.8 ± 18.5Mt yr −1 in North America, respectively. These results reveal the importance of non-fossil fuel NO x emissions and provide direct evidence for making strategies on mitigating atmospheric NO x pollution.