Long-Term Changes in Summertime Nitrate Chemistry in the Top Boundary Layer of North China
Liang Wen, Jian Gao, Likun Xue, Yang Li, Rui Gao, Wei Tang, Jiaqi Wang, Xiaohui Du, Yujie Zhang, Xinfeng Wang, Yujiao Zhu, Fahe Chai, Jingnan Hu, Guigang Tang, Jianmin Chen, Tao Wang, Aijun Ding, Hartmut Herrmann, Abdelwahid Mellouki, Can Dong, Haisheng Li, Zhaoxin Guo, Yong Zhao
Abstract
Reducing fine particulate nitrate (pNO 3 – ) is critical for further mitigating PM 2.5 pollution in China. However, previous NO x emission reductions have failed to achieve the expected pNO 3 – decreases. The present study reports that pNO 3 – concentration in summer increased by 55.8% and 5.6% at North China Peak (1534 m a.s.l.) from 2007 to 2014 and 2014 to 2021, respectively. pNO 3 – formation enhancement was caused mainly by decreased aerosol acidity due to notable SO 4 2– reduction. pNO 3 – formation changed from a process limited by NH 4 + to one colimited by NO 2 and NH 4 +, suggesting an increased effect of NO x reduction on decreasing pNO 3 – production. Vertical transport represents a significant source of pNO 3 – near the surface, illustrating a percentage as high as 98% recorded during daytime hours and a proportion of 34% in the dark over North China in the simulation scenario during summer 2020. The scheme to reduce NO x emissions by 10% from 2020 to 2025 is predicted to slowly decrease aloft pNO 3 – over North China, which may facilitate further reductions in pNO 3 – concentrations near the surface via vertical transport. The inflection of nitrate chemistry in the top boundary layer suggests an opportunity to accelerate PM 2.5 reduction under projected further emission reductions.