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How frequent is new particle formation over the remote temperate/boreal forest?
  • Meinrat Andreae,
  • Tracey Andreae,
  • Florian Ditas
Meinrat Andreae
Max Planck Institute for Chemistry

Corresponding Author:m.andreae@mpic.de

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Tracey Andreae
Max Planck Institute for Chemistry
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Florian Ditas
Max Planck Institute for Chemistry
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Abstract

The frequency and intensity of new particle formation (NPF) over remote forest regions in the temperate and boreal zones, and thus the importance of NPF for the aerosol budget and life cycle in the pristine atmosphere, remains controversial. Whereas NPF has been shown to occur relatively frequently at several sites in Scandinavia [1], it was found to be nearly absent at a mid-continental site in Siberia [2]. To explore this issue further, we made measurements of aerosol size distributions between 10 and 300 nm diameter at two remote sites in the transition region between temperate and boreal forest in British Columbia, Canada. The measurements covered 23 days during the month of June 2019, at the time when NPF typically reaches its seasonal maximum in remote mid-latitude regions. These are the first such measurements on the North American continent. Although the sites were only 150 km apart, there were dramatic differences in NPF frequency and intensity between them. At the Eagle Lake site, NPF occurred almost daily and nucleation mode particle concentrations reached above 5000 cm-3. In contrast, at the Nazko River site, there were only 6 NPF events in 11 days and nucleation mode particle concentrations reached only about 800 cm-3. The reasons for this difference are under investigation. They may include airmass origins, pre-existing aerosols, density of forest cover in the surrounding regions, and proximity to the Pacific coast. Our results suggest that measurement campaigns in the remote forest regions of North America to investigate the role of NPF with a more comprehensive set of instrumentation are essential for a deeper scientific understanding of this important process. [1] Nieminen et al., Atmos. Chem. Phys. 18 (2018) 14737-14756. [2] Wiedensohler et al., Atmospheric Environment, 200 (2019) 167-169.