The observation of nitric acid-containing particles in the tropical lower stratosphere

P. J. Popp (1, 2) , T. P. Marcy (1, 2) , E. J. Jensen (3) , B. Kärcher (4) , D. W. Fahey (1) , R. S. Gao (1) , T. L. Thompson (1) , K. H. Rosenlof (1) , E. C. Richard (1, 2) , R. L. Herman (5) , E. M. Weinstock (6) , J. B. Smith (6) , R. D. May (7) , H. Vömel (8) , J. C. Wilson (9) , A. J. Heymsfield (10) , M. J. Mahoney (5) , A. M. Thompson (11)

1 NOAA Aeronomy Laboratory
2 CIRES - Cooperative Institute for Research in Environmental Sciences
3 ARC - NASA Ames Research Center
4 IPA - DLR Institut für Physik der Atmosphäre = DLR Institute of Atmospheric Physics
5 JPL - Jet Propulsion Laboratory
6 Atmospheric Research Project [Cambridge]
7 MayComm Instruments
8 CMDL - NOAA Climate Monitoring and Diagnostics Laboratory
9 Department of Engineering
10 MMM - Mesoscale and Microscale Meteorology Division
11 PennState Meteorology Department

Airborne in situ measurements over the eastern Pacific Ocean in January 2004 have revealed a new category of nitric acid (HNO₃)-containing particles in the tropical lower stratosphere. These particles are most likely composed of nitric acid trihydrate (NAT). They were intermittently observed in a narrow layer above the tropopause (18±0.1 km) and over a broad geographic extent (>1100 km). In contrast to the background liquid sulfate aerosol, these particles are solid, much larger (1.7?4.7 µm vs. 0.1 µm in diameter), and significantly less abundant (<10^-4 cm^-3 vs. 10 cm^-3). Microphysical trajectory models suggest that the NAT particles grow over a 6?14 day period in supersaturated air that remains close to the tropical tropopause and might be a common feature in the tropics. The small number density of these particles implies a highly selective or slow nucleation process. Understanding the formation of solid NAT particles in the tropics could improve our understanding of stratospheric nucleation processes and, therefore, dehydration and denitrification.

Domaines: Océan, Atmosphère

P. J. Popp, T. P. Marcy, E. J. Jensen, B. Kärcher, D. W. Fahey, et al.. The observation of nitric acid-containing particles in the tropical lower stratosphere. Atmospheric Chemistry and Physics Discussions, 2005, 5 (5), pp.10097-10124. ⟨hal-00301855⟩