Validation of HNO3, ClONO2, and N2O5 from the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS)

M. A. Wolff, T. Kerzenmacher, K. Strong, K. A. Walker, M. Toohey, E. Dupuy, P. F. Bernath, C. D. Boone, S. Brohede, V. Catoire, T. von Clarmann, M. Coffey (+32 others)
2008 Atmospheric Chemistry and Physics Discussions  
The Atmospheric Chemistry Experiment (ACE) satellite was launched on 12 August 2003. Its two instruments measure vertical profiles of over 30 atmospheric trace gases by analyzing solar occultation spectra in the ultraviolet/visible and infrared wavelength regions. The reservoir gases HNO 3 , ClONO 2 , and N 2 O 5 are three of the key species 5 provided by the primary instrument, the ACE Fourier Transform Spectrometer (ACE-FTS). This paper describes the ACE-FTS version 2.2 data products,
more » ... a products, including the N 2 O 5 update, for the three species and presents validation comparisons with available observations. We have compared volume mixing ratio (VMR) profiles of HNO 3 , ClONO 2 , and N 2 O 5 with measurements by other satellite instruments (SMR, MLS, MIPAS), air-10 craft measurements (ASUR), and single balloon-flights (SPIRALE, FIRS-2). Partial columns of HNO 3 and ClONO 2 were also compared with measurements by groundbased Fourier Transform Infrared (FTIR) spectrometers. Overall the quality of the ACE-FTS v2.2 HNO 3 VMR profiles is good from 18 to 35 km. For the statistical satellite comparisons, the mean absolute differences are generally within ±1 ppbv (±20%) 15 from 18 to 35 km. For MIPAS and MLS comparisons only, mean relative differences lie within ±10% between 10 and 36 km. ACE-FTS HNO 3 partial columns (∼15-30 km) show a slight negative bias of −1.3% relative to the ground-based FTIRs at latitudes ranging from 77.8 • S-76.5 • N. Good agreement between ACE-FTS ClONO 2 and MI-PAS, using the Institut für Meteorologie und Klimaforschung and Instituto de Astrofísica 20 de Andalucía (IMK-IAA) data processor is seen. Mean absolute differences are typically within ±0.01 ppbv between 16 and 27 km and less than +0.09 ppbv between 27 and 34 km. The ClONO 2 partial column comparisons show varying degrees of agreement, depending on the location and the quality of the FTIR measurements. Good agreement was found for the comparisons with the midlatitude Jungfraujoch partial 25 columns for which the mean relative difference is 4.7%. ACE-FTS N 2 O 5 has a low bias relative to MIPAS IMK-IAA, reaching −0.25 ppbv at the altitude of the N 2 O 5 maximum (around 30 km). Mean absolute differences at lower altitudes (16-27 km) are typically 2431 ACPD Abstract Introduction Conclusions References Tables Figures ◭ ◮ ◭ ◮ Back Close Full Screen / Esc Printer-friendly Version Interactive Discussion EGU −0.05 ppbv for MIPAS nighttime and ±0.02 ppbv for MIPAS daytime measurements. 1 Introduction This is one of two papers describing the validation of NO y species measured by the Atmospheric Chemistry Experiment (ACE) through comparisons with coincident measurements. The total reactive nitrogen, or NO y , family consists of NO x (NO + NO 2 ) + 5 all oxidized nitrogen species: [NO y ] = [NO] + [NO 2 ] + [NO 3 ] + [HNO 3 ] + [HNO 4 ] + [ClONO 2 ] + [BrONO 2 ] + 2[N 2 O 5 ]. (1) The ACE-Fourier Transform Spectrometer (ACE-FTS) measures all of these species, with the exception of NO 3 and BrONO 2 (Bernath et al., 2005), while the ACE-10 Measurement of Aerosol Extinction in the Stratosphere and Troposphere Retrieved by Occultation (ACE-MAESTRO) also measures NO 2 (McElroy et al., 2007). The species NO, NO 2 , HNO 3 , ClONO 2 , and N 2 O 5 are five of the 14 primary target species for the ACE mission, while HNO 4 is a research product. In this study, the quality of the ACE-FTS version 2.2 nitric acid (HNO 3 ), chlorine nitrate (ClONO 2 ), and ACE-FTS version 15 2.2 dinitrogen pentoxide (N 2 O 5 ) update is assessed prior to its public release. A companion paper by Kerzenmacher et al. (2007) provides an assessment of the ACE-FTS v2.2 nitric oxide (NO) and nitrogen dioxide (NO 2 ), and of the ACE-MAESTRO v1.2 NO 2 . Validation of ACE-FTS v2.2 measurements of nitrous oxide (N 2 O), the source gas for NO y , is discussed by Strong et al. (2007). 20 The three molecules HNO 3 , ClONO 2 , and N 2 O 5 are important reservoir species for nitrogen and chlorine in the stratosphere and therefore play an important role in stratospheric ozone chemistry. They can sequester the more reactive NO x species, thereby reducing ozone destruction via fast catalytic cycles (Solomon, 1999; Brasseur and Solomon, 2005). NO x /NO y partitioning is largely determined by ozone and aerosol 25 2432 ACPD Abstract Introduction Conclusions References Tables Figures ◭ ◮ ◭ ◮ Back Close Full Screen / Esc Printer-friendly Version Interactive Discussion EGU concentrations (e.g., Salawitch et al., 1994; Solomon et al., 1996) . HNO 3 is the dominant form of NO y in the lower stratosphere, and is produced from NO x by the reaction: where M is a third body that remains unchanged under the reaction. HNO 3 is chemi-5 cally destroyed by photolysis and oxidation by OH: Both processes make comparable contributions to HNO 3 loss in the lower stratosphere. At higher altitudes, Reaction (R3) becomes gradually more important and dominates 10 the HNO 3 loss mechanisms in the upper stratosphere (Dessler, 2000). ClONO 2 is also produced from NO x by reaction with ClO: and is photolyzed at ultraviolet wavelengths to create either Cl + NO 3 , or ClO + NO 2 . N 2 O 5 is created through the reaction: Because of the extremely low abundances of NO 3 during the day, this process occurs at night (Dessler, 2000). N 2 O 5 is mainly destroyed by photolysis (more than 90%) and collisional decomposition, to generate NO 3 and either NO 2 or NO + O. During polar winter, the conversion of NO x and ClO to HNO 3 , ClONO 2 , and N 2 O 5 20 reduces the chemical destruction of ozone. However, in the presence of polar stratospheric clouds (PSCs), ClONO 2 and N 2 O 5 can undergo heterogeneous reactions with H 2 O and HCl to create HNO 3 and release chlorine into chemically active forms. HNO 3 2433 ACPD Abstract Introduction Conclusions References Tables Figures ◭ ◮ ◭ ◮ Back Close Full Screen / Esc Printer-friendly Version Interactive Discussion EGU can, in turn, be removed from the gas phase through sequestration on the PSCs, and subsequently lost through sedimentation of large PSC particles. This process of denitrification effectively removes NO y from the stratosphere, thereby suppressing Reaction (R4), and redistributes it to lower altitudes where the PSCs evaporate (e.g., Toon et al., 1986; Waibel et al., 1999) . Hydrolysis of N 2 O 5 can also occur on sulphuric 5 25 trieved by the Cryogenic Limb Array Etalon Spectrometer (CLAES) (Roche et al.
doi:10.5194/acpd-8-2429-2008 fatcat:vtjmp2z5c5avrnvngaxo7yyqoa