Measurement report: New particle formation events observed during the COALA-2020 campaign

Abstract

Aerosols play an important role in atmospheric processes influencing cloud formation, scattering and absorbing solar radiation and affecting trace gases through chemical reactions occurring in and on aerosol particles. Ultimately, aerosols affect the radiative balance of the Earth, modifying climate. A large fraction of aerosols is formed through chemical reactions following gas-to-particulate processes in the atmosphere: nucleation and growth. Biogenic secondary organic aerosols (BSOAs) are formed when plant-produced volatile organic compounds (VOCs) react in the atmosphere through gas-phase oxidation. One of the highest biogenic VOC (BVOC)-emitting regions in the world is Southeast Australia due to the high density of Eucalyptus species. The Characterizing Organics and Aerosol Loading over Australia (COALA)-2020 (Characterizing Organics and Aerosol Loading over Australia) campaign worked towards gaining a better understanding of biogenic VOCs in quasi-pristine conditions in the atmosphere and their role in particle formation. The observations showed a highly reactive atmosphere with frequent new particle formation (NPF) occurring (42 % d with data), often associated with pollution plumes. Analysis of NPF events suggested that SO2 plumes likely triggered particle formation, while particle growth depended on available VOCs and hydroxyl radicals, and the presence of multiple SO2 intrusions promoted the growth of smaller clusters. Nighttime NPF events coincided with monoterpene ozonolysis but were rare. These findings highlight the significant role of biogenic VOCs in driving NPF and secondary organic aerosol (SOA) formation in Southeast Australia. The COALA-2020 campaign provided valuable insights into local atmospheric chemistry and its potential impact on regional air quality and climate. However, longer-term observations are crucial to understand seasonal variations, trends, and extreme events.