Unexpected response of nitrogen deposition to nitrogen oxide controls and implications for land carbon sink
Mingxu Liu, Fang Shang, Xingjie Lu, Xin Huang, Yu Song, Bing Liu, Qiang Zhang, Xuejun Liu, Junji Cao, Tingting Xu, Tiantian Wang, Zhenying Xu, Wen Xu, Wenling Liao, Ling Kang, Xuhui Cai, Hongsheng Zhang, Yongjiu Dai, Tong Zhu
Abstract
Abstract Terrestrial ecosystems in China receive the world’s largest amount of reactive nitrogen (N) deposition. Recent controls on nitrogen oxides (NO x = NO + NO 2 ) emissions in China to tackle air pollution are expected to decrease N deposition, yet the observed N deposition fluxes remain almost stagnant. Here we show that the effectiveness of NO x emission controls for reducing oxidized N (NO y = NO x + its oxidation products) deposition is unforeseen in Eastern China, with one-unit reduction in NO x emission leading to only 55‒76% reductions in NO y -N deposition, as opposed to the high effectiveness (around 100%) in both Southern China and the United States. Using an atmospheric chemical transport model, we demonstrate that this unexpected weakened response of N deposition is attributable to the enhanced atmospheric oxidizing capacity by NO x emissions reductions. The decline in N deposition could bear a penalty on terrestrial carbon sinks and should be taken into account when developing pathways for China’s carbon neutrality.