National Science Review, Volume 9, Issue 10 (2022)

The missing base molecules in atmospheric acid–base nucleation

Runlong Cai^1,2, Rujing Yin¹, Chao Yan^2,3, Dongsen Yang⁴, Chenjuan Deng¹, Lubna Dada^2,5, Juha Kangasluoma², Jenni Kontkanen², Roope Halonen⁶, Yan Ma⁴, Xiuhui Zhang⁷, Pauli Paasonen², Tuukka Petäjä², Veli-Matti Kerminen², Yongchun Liu³, Federico Bianchi², Jun Zheng⁴, Lin Wang⁸, Jiming Hao¹, James N. Smith⁹, Neil M. Donahue^10,11, Markku Kulmala^2,∗, Douglas R. Worsnop^2,12 and Jingkun Jiang^1,*

1 State Key Joint Laboratory of Environment Simulation and Pollution Control, School of Environment, Tsinghua University, Beijing 100084, China

2 Institute for Atmospheric and Earth System Research / Physics, Faculty of Science, University of Helsinki, Helsinki 00014, Finland

3 Aerosol and Haze Laboratory, Beijing Advanced Innovation Center for Soft Matter Science and Engineering, Beijing University of Chemical Technology, Beijing 100029, China

4 Collaborative Innovation Center of Atmospheric Environment and Equipment Technology, Nanjing University of Information Science and Technology, Nanjing 210044, China

5 Laboratory of Atmospheric Chemistry, Paul Scherrer Institute, Villigen 5232, Switzerland

6 Center for Joint Quantum Studies and Department of Physics, School of Science, Tianjin University, Tianjin 300350, China

7 Key Laboratory of Cluster Science, Ministry of Education of China, School of Chemistry and Chemical Engineering, Beijing Institute of Technology, Beijing 100081, China

8 Shanghai Key Laboratory of Atmospheric Particle Pollution and Prevention (LAP3 ), Department of Environmental Science and Engineering, Fudan University, Shanghai 200433, China

9 Chemistry Department, University of California, Irvine, CA 92697, USA

10 Center for Atmospheric Particle Studies, Carnegie Mellon University, Pittsburgh, PA 15213, USA

11 Department of Chemistry, Carnegie Mellon University, Pittsburgh, PA 15213, USA

12 Aerodyne Research Inc., Billerica, MA 01821, USA

*Corresponding authors: jiangjk@tsinghua.edu.cn     markku.kulmala@helsinki.fi

Abstract

Transformation of low-volatility gaseous precursors to new particles affects aerosol number concentration, cloud formation and hence the climate. The clustering of acid and base molecules is a major mechanism driving fast nucleation and initial growth of new particles in the atmosphere. However, the acid–base cluster composition, measured using state-of-the-art mass spectrometers, cannot explain the measured high formation rate of new particles. Here we present strong evidence for the existence of base molecules such as amines in the smallest atmospheric sulfuric acid clusters prior to their detection by mass spectrometers. We demonstrate that forming (H₂SO₄)₁(amine)₁ is the rate-limiting step in atmospheric H₂SO₄-amine nucleation and the uptake of (H₂SO₄)₁(amine)₁ is a major pathway for the initial growth of H₂SO₄ clusters. The proposed mechanism is very consistent with measured new particle formation in urban Beijing, in which dimethylamine is the key base for H₂SO₄ nucleation while other bases such as ammonia may contribute to the growth of larger clusters. Our findings further underline the fact that strong amines, even at low concentrations and when undetected in the smallest clusters, can be crucial to particle formation in the planetary boundary layer.