Open AccessChemical NO x budget in the upper troposphere over the tropical South Pacific
Author(s) -
Schultz Martin G.,
Jacob Daniel J.,
Bradshaw John D.,
Sandholm Scott T.,
Dibb Jack E.,
Talbot Robert W.,
Singh Hanwant B.
Publication year - 2000
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/1999jd900994
Subject(s) - troposphere , chemical transport model , atmospheric sciences , stratosphere , aerosol , environmental science , tropics , altitude (triangle) , chemical evolution , chemical composition , climatology , meteorology , chemistry , physics , geology , stars , geometry , mathematics , organic chemistry , astronomy , fishery , biology
The chemical NO x budget in the upper troposphere over the tropical South Pacific is analyzed using aircraft measurements made at 6–12 km altitude in September 1996 during the Global Tropospheric Experiment (GTE) Pacific Exploratory Mission (PEM) Tropics A campaign. Chemical loss and production rates of NO x along the aircraft flight tracks are calculated with a photochemical model constrained by observations. Calculations using a standard chemical mechanism show a large missing source for NO x ; chemical loss exceeds chemical production by a factor of 2.4 on average. Similar or greater NO x budget imbalances have been reported in analyses of data from previous field studies. Ammonium aerosol concentrations in PEM‐Tropics A generally exceeded sulfate on a charge equivalent basis, and relative humidities were low (median 25% relative to ice). This implies that the aerosol could be dry in which case N 2 O 5 hydrolysis would be suppressed as a sink for NO x . Suppression of NO 2 O 5 hydrolysis and adoption of new measurements of the reaction rate constants for NO 2 + OH + M and HNO 3 + OH reduces the median chemical imbalance in the NO x budget for PEM‐Tropics A from 2.4 to 1.9. The remaining imbalance cannot be easily explained from known chemistry or long‐range transport of primary NO x and may imply a major gap in our understanding of the chemical cycling of NO x in the free troposphere.