Composition and Chemistry
Measurement of HO2NO2 in the free troposphere during the Intercontinental Chemical Transport Experiment–North America 2004
Article first published online: 10 FEB 2007
Copyright 2007 by the American Geophysical Union.
Journal of Geophysical Research: Atmospheres (1984–2012)
Volume 112, Issue D12, 27 June 2007
How to Cite
2007), Measurement of HO2NO2 in the free troposphere during the Intercontinental Chemical Transport Experiment–North America 2004, J. Geophys. Res., 112, D12S01, doi:10.1029/2006JD007676., et al. (
- Issue published online: 10 FEB 2007
- Article first published online: 10 FEB 2007
- Manuscript Accepted: 14 NOV 2006
- Manuscript Revised: 20 OCT 2006
- Manuscript Received: 20 JUN 2006
- pernitric acid;
- upper troposphere;
 The first direct in situ measurements of HO2NO2 in the upper troposphere were performed from the NASA DC-8 during the Intercontinental Chemical Transport Experiment–North America 2004 with a chemical ionization mass spectrometer (CIMS). These measurements provide an independent diagnostic of HOx chemistry in the free troposphere and complement direct observations of HOx, because of the dual dependency of HO2NO2 on HOx and NOx. On average, the highest HO2NO2 mixing ratio of 76 pptv (median = 77 pptv, σ = 39 pptv) was observed at altitudes of 8–9 km. Simple steady state calculations of HO2NO2, constrained by measurements of HOx, NOx, and J values, are in good agreement (slope = 0.90, R2 = 0.60, and z = 5.5–7.5 km) with measurements in the midtroposphere where thermal decomposition is the major loss process. Above 8 km the calculated steady state HO2NO2 is in poor agreement with observed values (R2 = 0.20) and is typically larger by a factor of 2.4. Conversely, steady state calculations using model-derived HOx show reasonable agreement with the observed HO2NO2 in both the midtroposphere (slope = 0.96, intercept = 7.0, and R2 = 0.63) and upper troposphere (slope = 0.80, intercept = 32.2, and R2 = 0.58). These results indicate that observed HO2 and HO2NO2 are in poor agreement in the upper troposphere but that HO2NO2 levels are consistent with current photochemical theory.