Biogenic particles formed in the Himalaya as an important source of free tropospheric aerosols

F. Bianchi (1) , H. Junninen (1) , A. Bigi (2) , V. Sinclair (1) , L. Dada (1) , C. Hoyle (3) , Q. Zha (1) , L. Yao (1) , L. Ahonen (1) , P. Bonasoni (4) , S. Buenrostro Mazon (1) , M. Hutterli (5) , P. Laj (1, 4, 6) , K. Lehtipalo (1, 7) , J. Kangasluoma (1) , V.-M. Kerminen (1) , J. Kontkanen (1) , A. Marinoni (4) , S. Mirme (8) , U. Molteni (3) , T. Petäjä (1) , M. Riva (9) , Clémence Rose (1, 10) , K. Sellegri (10) , C. Yan (1) , D. Worsnop (1, 11) , M. Kulmala (1, 12) , U. Baltensperger (3) , J. Dommen (3)

1 INAR - Institute for Atmospheric and Earth System Research
2 University of Modena and Reggio Emilia
3 LAC - Laboratory of Atmospheric Chemistry [Paul Scherrer Institute]
4 ISAC - CNR Institute of Atmospheric Sciences and Climate
5 Tofwerk AG
6 IGE - Institut des Géosciences de l’Environnement
7 FMI - Finnish Meteorological Institute
8 University of Tartu
9 CARE - IRCELYON-Catalytic and Atmospheric Reactivity for the Environment
10 LaMP - Laboratoire de Météorologie Physique
11 Aerodyne Research Inc.
12 Beijing University of Chemical Technology

Aerosols of biogenic and anthropogenic origin affect the total radiative forcing of global climate. Poor knowledge of the pre-industrial aerosol concentration and composition, in particular of particles formed directly in the atmosphere from gaseous precursors, constitutes a large uncertainty in the anthropogenic radiative forcing. Investigations of new particle formation at pre-industrial-like conditions can contribute to the reduction of this uncertainty. Here we present observations taken at the remote Nepal Climate Observatory Pyramid station at 5,079 m above sea level, a few kilometres from the summit of Everest. We show that up-valley winds funnel gaseous aerosol precursors to higher altitudes. During this transport, these are oxidized into compounds of very low volatility, which rapidly form a large number of aerosol particles. These are then transported into the free troposphere, which suggests that the whole Himalayan region may act as an ‘aerosol factory’ and contribute substantially to the free tropospheric aerosol population. Aerosol production in this region occurs mainly via organic precursors of biogenic origin with little evidence of the involvement of anthropogenic pollutants. This process is therefore likely to be essentially unchanged since the pre-industrial period, and may have been one of the major sources that contributes to the upper tropospheric aerosol population during that time.

Domaines: Physique Atmosphérique et Océanique [physics.ao-ph]; Océan, Atmosphère; Météorologie

F. Bianchi, H. Junninen, A. Bigi, V. Sinclair, L. Dada, et al.. Biogenic particles formed in the Himalaya as an important source of free tropospheric aerosols. Nature Geoscience, 2020, ⟨10.1038/s41561-020-00661-5⟩. ⟨hal-03052798⟩