Post‐Mount Pinatubo eruption ground‐based infrared stratospheric column measurements of HNO3, NO, and NO2 and their comparison with model calculations

Curtis P Rinsland,E Mahieu,R Zander,C J Scott,L S Chiou,P Demoulin,D K Weisenstein,M K W Ko

doi:10.1029/2002jd002965

Curtis P Rinsland, E Mahieu + Show 6 more

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https://doi.org/10.1029/2002jd002965

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Abstract

Infrared solar spectra recorded between July 1991 to March 1992 and November 2002 with the Fourier transform spectrometer on Kitt Peak (31.9°N latitude, 111.6°W longitude, 2.09 km altitude) have been analyzed to retrieve stratospheric columns of HNO3, NO, and NO2. The measurements cover a decade time span following the June 1991 Mount Pinatubo volcanic eruption and were recorded typically at 0.01 cm−1 spectral resolution. The measured HNO3 stratospheric column shows a 20% decline from 9.16 × 1015 molecules cm−2 from the first observation in March 1992 to 7.40 × 1015 molecules cm−2 at the start of 1996 reaching a broad minimum of 6.95 × 1015 molecules cm−2 thereafter. Normalized daytime NO and NO2 stratospheric column trends for the full post‐Pinatubo eruption time period equal (+1.56 ± 0.45)% yr−1, 1 sigma, and (+0.52 ± 0.32)% yr−1, 1 sigma, respectively. The long‐term trends are superimposed on seasonal cycles with ∼10% relative amplitudes with respect to mean values, winter maxima for HNO3 and summer maxima for NO and NO2. The measurements have been compared with two‐dimensional model calculations utilizing version 6.1 Stratospheric Aerosol and Gas Experiment (SAGE) II sulfate aerosol surface area density measurements through 1999 and extended to the end of the time series by repeating the 1999 values. The model‐calculated HNO3, NO, and NO2 stratospheric column time series agree with the measurements to within ∼8% after taking into account the vertical sensitivity of the ground‐based measurements. The consistency between the measured and model‐calculated stratospheric time series confirms the decreased impact on stratospheric reactive nitrogen chemistry of the key heterogeneous reaction that converts reactive nitrogen to its less active reservoir form as the lower‐stratospheric aerosol surface area density declined by a factor of ∼20 after the eruption maximum.

Highlights

[2] A key heterogeneous reaction on sulfuric acid aerosol surfaces converts dinitrogen pentoxide (N2O5) to nitric acid (HNO3): N2O5 þ H2O ! HNO3 þ HNO3
The largest changes are observed for HNO3 with an overall decline of 20% from 9.16 Â 1015 molecules cmÀ2 at the time of first observation in March 1992 to 7.40 Â 1015 molecules cmÀ2 at the start of 1996 reaching a broad minimum of 6.95 Â 1015 molecules cmÀ2, 25% below the first post-Pinatubo observation by the end of the time series
[38] The measurements and model time series have been compared with 2-D model calculations utilizing version 6.1 Stratospheric Aerosol and Gas Experiment (SAGE) II aerosol surface area density profiles through 1999 and extended to the end of the measurement time series by repeating the 1999 values, retaining the seasonal cycle

Summary

Introduction

[2] A key heterogeneous reaction on sulfuric acid aerosol surfaces converts dinitrogen pentoxide (N2O5) to nitric acid (HNO3): N2O5 þ H2O ! HNO3 þ HNO3. McLinden et al [2001] used a combination of a photochemical box and three-dimensional transport model to reinterpret the same Lauder NO2 time series They attributed only half of the NO2 increase as directly due to the rise in N2O at the surface, with the remainder of the NO2 rise caused by ozone changes, the impact of increased halogens on odd-nitrogen partitioning, and changes in aerosol loading. Average stratospheric columns of HNO3, NO, and NO2 are reported taking into account the vertical sensitivity of the measurements based on averaging kernels These results are compared with two-dimensional chemistry-transport model calculations based on version 6.1 Stratospheric Aerosol and Gas Experiment (SAGE) II monthly average aerosol surface area densities through 1999 [Yue, 1999] with all boundary conditions specified by the ‘‘ab baseline’’ trend scenario for World Meteorological Organization (WMO) [2003], including the trends of N2O, CH4, chlorofluorocarbons, chlorine, and bromine species as a function of time.

Analysis Method

Measurement Results

Discussion

Findings

10. Summary and Conclusions