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Nitric acid concentrations near the tropical tropopause: Implications for the properties of tropical nitric acid trihydrate clouds
Author(s) -
Jensen Eric,
Drdla Katja
Publication year - 2002
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2002gl015190
Subject(s) - tropopause , nitric acid , extinction (optical mineralogy) , nat , aerosol , atmospheric sciences , lightning (connector) , air mass (solar energy) , mixing ratio , chemistry , analytical chemistry (journal) , troposphere , mineralogy , meteorology , physics , environmental chemistry , inorganic chemistry , power (physics) , boundary layer , quantum mechanics , thermodynamics
In situ measurements of NO y , NO x , and temperature confirm that nitric acid trihydrate (NAT) particles could form at the tropical tropopause. The HNO 3 mixing ratio near the tropical tropopause is typically no larger than about 0.2–0.3 ppbv, and the corresponding equilibrium mass of nitric acid trihydrate (NAT) is no larger than 0.3 μg m −3 . Considerably larger NAT condensed masses are required to explain the HALOE extinctions; however, localized regions of enhanced HNO 3 produced by oxidation of lightning‐generated NO might exist. NAT layers would only be identified as clouds by SAGE II if the particle diameters are in the optimum range of about 0.6 to 2 μm and the condensed NAT mass is larger than about 0.2 μg m −3 . The SAGE II extinction ratio measurements (0.5 μm/1.0 μm) cannot distinguish NAT clouds from mixtures of optically thin ice clouds and background aerosols.