R. D. Blatherwick

Infrared Solar Spectroscopic Measurements of Free Tropospheric CO, C2H6, and HCN above Mauna Loa, Hawaii: Seasonal Variations and Evidence for Enhanced Emissions from the Southeast Asian Tropical Fires of 1997-1998

High spectral resolution (0.003/ cm) infrared solar absorption measurements of CO, C2H6, and HCN have been recorded at the Network for the Detection of Stratospheric Change station on Mauna Loa, Hawaii, (19.5 deg N, 155.6 deg W, altitude 3.4 km). The observations were obtained on over 250 days between August 1995 and February 1998. Column measurements are reported for the 3.4 - 16 km altitude region, which corresponds approximately to the free troposphere above the station. Average CO mixing ratios computed for this layer have been compared with flask sampling CO measurements obtained in situ at the station during the same time period. Both show asymmetrical seasonal cycles superimposed on significant variability. The first two years of observations exhibit a broad January-April maximum and a sharper CO minimum during late summer. The C2H6 and CO 3.4 - 16 km columns were highly correlated throughout the observing period with the C2H6/CO slope intermediate between higher and lower values derived from similar infrared spectroscopic measurements at 32 deg N and 45 deg S latitude, respectively. Variable enhancements in CO, C2H6, and particularly HCN were observed beginning in about September 1997. The maximum HCN free tropospheric monthly mean column observed in November 1997 corresponds to an average 3.4 - 16 km mixing ratio of 0.7 ppbv (1 ppbv = 10(exp -9) per unit volume), more than a factor of 3 above the background level. The HCN enhancements continued through the end of the observational series. Back-trajectory calculations suggest that the emissions originated at low northern latitudes in southeast Asia. Surface CO mixing ratios and the C2H6 tropospheric columns measured during the same time also showed anomalous autumn 1997 maxima. The intense and widespread tropical wild fires that burned during 3 the strong El Nino warm phase of 1997-1998 are the likely source of the elevated emission products.

The ν1, 2ν2, and ν3 interacting bands of 14N16O2: Line positions and intensities

Abstract High-resolution Fourier transform spectra have been used in the 1200–1850 cm −1 spectral region to measure the positions of lines with K a = 0–15 for the ν 1 and ν 3 bands of 14 N 16 O 2 , as well as lines with K a = 0, 1, 2, and 6 for the 2 ν 2 band up to very high N values. The spin-rotation energy levels were very satisfactorily reproduced using a theoretical model which takes explicitly into account both the Coriolis interactions between the spin-rotation levels of the (001) vibrational state with those of (100) and (020), and the spin-rotation resonances in each vibrational state. In this analysis, precise band centers and rotational, spin-rotation, and coupling constants were obtained for the triad {(100), (020), (001)} of interacting states for 14 N 16 O 2 . In addition, using a large set of individual line intensities we have determined precisely the ν 1 , 2 ν 2 , and ν 3 transition moment operators of 14 N 16 O 2 . Finally, a comprehensive list of line positions and intensities of the interacting ν 1 , 2 ν 2 , and ν 3 bands of 14 N 16 O 2 has been generated.

Mt. Pinatubo SO2 Column Measurements From Mauna Loa

Absorption features of the v1 band of SO2 have been identified in high resolution infrared solar absorption spectra recorded from Mauna Loa, Hawaii, on July 9 and 12, 1991, shortly after the arrival of the first eruption plume from the Mt. Pinatubo volcano in the Phillipines. A total SO2 vertical column amount of (5.1 ± 0.5) × 1016 molecules cm−2 on July 9 has been retrieved based on nonlinear least-squares spectral fittings of 9 selected SO2 absorption features with an updated set of SO2 spectral parameters. A SO2 total column upper limit of 0.9 × 1016 molecules cm−2 deduced from measurements on September 20–24, 1991, is consistent with the dispersion of the SO2 cloud and the rapid conversion of the SO2 vapor into volcanic aerosol particles.

High resolution solar spectrometer system for measuring atmospheric constituents

A mid IR Michelson interferometer capable of obtaining 0.002-cm(-1) resolution solar spectra has been developed for balloon use. The interferometer is based on the Bomem self-aligning instrument, and is equipped with a solar tracking system, telemetry, and recording systems, as well as temperature control and gondola orientation. The interferometer has made two successful flights in the 7-14 microm (700-1300-cm(-1)) interval up to 40 km. The basic systems are described and sample spectra are presented.

New analysis of the ν6 band of H2O2: The (n, τ) = (0, 1), (1, 1), (2, 1), (0, 3), and (1, 3) torsional subbands

Abstract The ν 6 band of H 2 O 2 has been recorded at a resolution of 0.002 cm −1 by means of Fourier transform spectroscopy in the spectral region 1190–1330 cm −1 . The ( n , τ ) = (0, 1), (1, 1), (2, 1), (0, 3), and (1, 3) torsional subbands have been extensively analyzed leading to a large and precise set of torsion-rotation energy levels for the v 6 = 1 vibrational state. Numerous resonances have been observed and are discussed. For the ( n , τ ) = (0, 3), (1, 3) rotational levels the resonances are mainly due to the v 2 = 1 vibrational state whereas for the ( n , τ ) = (0, 1), (1, 1), and (2, 1) rotational levels, the v 3 = 1 vibrational state and/or the ground state is also involved. For the ( n , τ ) = (0, 3), and (1, 3) torsional states it has been possible to satisfactorily fit the experimental energies using a Hamiltonian which takes simultaneously into account both the interactions between the torsional states within the v 6 = 1 state and the v -off diagonal ( v 6 = 1 ↔ v 2 = 1) interaction between the levels of the v 6 = 1 and v 2 = 1 vibrational states. As very few data are available concerning the v 3 = 1 vibrational state it has not been possible to perform a similar calculation for the ( n , τ ) = (0, 1), (1, 1), and (2, 1) torsional states and the least-squares fit was performed taking into account only the resonances within the v 6 = 1 state and neglecting the resonances with the other vibrational states. Finally, using the ( n , τ ) = (0, 1), (1, 1), (2, 1), (0, 3), and (1, 3) torsional band centers the cis - and trans -barrier heights of the v 6 = 1 vibrational state have been estimated.

Spectroscopic line parameters for the nu6 band of carbonyl fluoride

New measurements and analysis of high resolution(0.0025 cm(-1)) laboratory spectra of the carbonyl fluoride v6 band are described. The data are used to generate line parameters suitable for high resolution atmospheric studies.

Infrared methane spectra between 1120 cm −1 and 1800 cm −1 : a new atlas

A new atlas of CH(4) lines in the 1120-1800-cm(-1) region has been generated, based on laboratory spectra taken with a Nicolet interferometer at 0.06-cm(-1) resolution with 635-cm path length at pressures of 0.98 Torr, 4.86 Torr, and 19.97 Torr. A compilation of line positions and line intensities includes 1339 CH(4) lines, several hundred of which have not been previously observed.

Smearing of interferograms in Fourier transform spectroscopy

The effects of changing spectral radiance during the scan of an interferometer on the spectra obtained from the interferogram are considered. For well-behaved variations the integrated radiance and base line are the same as at the zero path difference of the interferometer. The changes in the appearance of spectral features are hardly changed beyond a few resolution elements from the changing features.

Correlation relationships of stratospheric molecular constituents from high spectral resolution, ground‐based infrared solar absorption spectra

Comparisons of chemically active species with chemically inert tracers are useful to quantify transport and mixing and assess the accuracy of model predictions. We report measurements of chemically active species and chemically inert tracers in the stratosphere derived from the analysis of infrared solar absorption spectra recorded with a ground-based Fourier transform spectrometer operated typically at 0.005- to 0.01-cm−1 spectral resolution. The measurements were recorded from Kitt Peak in southern Arizona (latitude 31.9°N, 111.6°W, 2.09 km altitude). Time series of N2O, CH4, O3, and HNO3 vertical profiles have been retrieved from measurements in microwindows. From these results, correlations between N2O and CH4 stratospheric mixing ratios and between O3 and HNO3 lower stratospheric mixing ratios have been derived. The measured correlations between N2O versus CH4 mixing ratios are compact and show little variability with respect to season in quantitative agreement with Atmospheric Trace Molecule Spectroscopy Experiment (ATMOS) spring and autumn measurements recorded near the same latitude. Lower stratospheric O3 versus HNO3 mixing ratios measured during low to moderate aerosol loading time periods also show a compact relations though the HNO3/O3 slope is a factor of 2 lower than obtained from November 1994 ATMOS measurements near the same latitude. We also compare Kitt Peak and ATMOS N2O versus CH4 and O3 versus HNO3 relations obtained by averaging the measurements over two broad stratospheric layers. This comparison avoids bias from the a priori profiles and the limited vertical resolution of the ground-based observations.

Quantification of HCl from high-resolution, ground-based, infrared solar spectra in the 3000 cm-1 region

Recent ground-based infrared solar spectra at 0.02 cm-1 resolution in the 3000 cm-1 region have been analysed for the atmospheric content of HCl. Nonlinear spectral least-squares fitting applied to spectra obtained at several zenith angles show little sensitivity of the results to tropospheric HCl but provide an accurate measurement of the total column amount.