A 3D study on the amplification of regional haze and particle growth by local emissions

Wei Du,Kaspar R Daellenbach,Yuying Wang,Yele Sun,Federico Bianchi,Leena Järvi,Yuehui He ,Yongchun Liu,Weiqi Xu,Weigang Wang,Zhanqing Li,Guiqian Tang,Tuukka Petäj̈ä ,Maofa Ge,Lei Yao,Tom Kokkonen ,Xueshun Chen,Yingjie Zhang,Jing Cai,Pingqing Fu,Zifa Wang,Wei Zhou,Xueling Cheng,Simo Hakala,Qiaozhi Zha,Qingqing Wang,Pauli Paasonen,Markku Kulmala,Douglas R Worsnop,Biwu Chu,Wei Nie,Chao Yan,Mona Kurppa,Jian Zhao,Conghui Xie,Lubna Dada,Veli‐Matti Kerminen

doi:10.1038/s41612-020-00156-5

Abstract

The role of new particle formation (NPF) events and their contribution to haze formation through subsequent growth in polluted megacities is still controversial. To improve the understanding of the sources, meteorological conditions, and chemistry behind air pollution, we performed simultaneous measurements of aerosol composition and particle number size distributions at ground level and at 260 m in central Beijing, China, during a total of 4 months in 2015–2017. Our measurements show a pronounced decoupling of gas-to-particle conversion between the two heights, leading to different haze processes in terms of particle size distributions and chemical compositions. The development of haze was initiated by the growth of freshly formed particles at both heights, whereas the more severe haze at ground level was connected directly to local primary particles and gaseous precursors leading to higher particle growth rates. The particle growth creates a feedback loop, in which a further development of haze increases the atmospheric stability, which in turn strengthens the persisting apparent decoupling between the two heights and increases the severity of haze at ground level. Moreover, we complemented our field observations with model analyses, which suggest that the growth of NPF-originated particles accounted up to ∼60% of the accumulation mode particles in the Beijing–Tianjin–Hebei area during haze conditions. The results suggest that a reduction in anthropogenic gaseous precursors, suppressing particle growth, is a critical step for alleviating haze although the number concentration of freshly formed particles (3–40 nm) via NPF does not reduce after emission controls.

Highlights

Air pollution episodes, characterized by high aerosol particle loading, are one of the major environmental challenges in China as they profoundly impact the climate, visibility, and human health[1]
By observing the different behavior of the particles at ground level and at 260 m, we hypothesized that a decoupling in terms of particle number size distribution and chemical composition between the two heights is probable
We observed significant differences in the particle chemical compositions and number size distribution between the 260 m height and ground level, even when the mixing layer height

Summary

Introduction

Air pollution episodes, characterized by high aerosol particle loading, are one of the major environmental challenges in China as they profoundly impact the climate, visibility, and human health[1]. We observed that differences in the particle number size distribution and chemical composition between the two heights became more obvious with an increasing PM1 loading at the ground level (Fig. 2 and Supplementary Fig. 5)[26].

Results

Conclusion