Infrared transmittance spectra of polar stratospheric clouds

Lecours, Michael J.; Bernath, Peter F.; Boone, C. D.; Crouse, Jeff

doi:10.1016/j.jqsrt.2022.108406

Cited by 11 publications

(9 citation statements)

References 36 publications

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“…In satellite-and aircraft-based infrared measurements, however, only -NAT has been clearly identified, e.g. by its signature at 820 cm -1 (Höpfner et al, 2006;Woiwode et al, 2016;Woiwode et al, 2019;Lecours et al, 2022;Lecours et al, 2023). The new data set of optical constants for -NAD clearly does not question this assignment, since the 2(NO3 -) mode in -NAD is located at 812 cm -1 .…”

Section: Discussionmentioning

confidence: 88%

“…The distinctive PSC spectral signature at a wavenumber of 820 cm -1 , corresponding to the 2 symmetric deformation mode of the NO3ion (Spang and Remedios, 2003), could be best matched by refractive index data for -NAT (Höpfner et al, 2006). The -NAT phase was also identified in broadband infrared transmittance spectra recorded between 4400 and 750 cm -1 with the Fourier transform spectrometer on board the Atmospheric Chemistry Experiment (ACE) satellite (Lecours et al, 2022;Lecours et al, 2023).…”

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confidence: 82%

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Particle shapes and infrared extinction spectra of nitric acid dihydrate crystals: Optical constants of the β-NAD modification

Wagner

James

Frankland

et al. 2023

Preprint

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Abstract. Satellite- and aircraft-based mid-infrared measurements of polar stratospheric clouds (PSCs) have provided spectroscopic evidence for the presence of β-NAT (nitric acid trihydrate) particles. Metastable nitric acid hydrate phases such as α-NAT and α-NAD (nitric acid dihydrate) have been frequently observed in laboratory experiments, but not yet detected as a constituent of PSCs in atmospheric measurements. As for the β-NAD modification, its formation was first observed in X-ray diffraction measurements when the low-temperature α-NAD phase was warmed to a temperature above 210 K. Its infrared spectrum has been reported, but so far no optical constants have been derived that could be used as input for infrared retrievals of PSC composition. In this work, we show that β-NAD particles were efficiently formed in isothermal, heterogeneous crystallisation experiments at 190 K from supercooled HNO3/H2O solution droplets containing an embedded mineral dust or meteoric smoke particle analogue. An inversion algorithm based on a T-matrix optical model was used to derive for the first time the mid-infrared complex refractive indices of the β-NAD modification from the measured extinction spectrum of the particles. In contrast to the heterogeneous crystallisation experiments, the α-NAD phase was formed when the HNO3/H2O solution droplets did not contain a solid nucleus and crystallised homogeneously. Using a light scattering detector that recorded two-dimensional scattering patterns of the crystallised NAD particles, we were able to determine predominant shapes of the α- and β-NAD crystals. We found that α-NAD grew into elongated, needle-shaped crystals, while β-NAD particles were compact in shape. This agrees with previously reported images of α- and β-NAD particles grown on the cryo-stage of an Environmental Scanning Electron Microscope.

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Section: Discussionmentioning

confidence: 88%

mentioning

confidence: 82%

Particle shapes and infrared extinction spectra of nitric acid dihydrate crystals: Optical constants of the β-NAD modification

Wagner

James

Frankland

et al. 2023

Preprint

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“…The sulfate feature loses intensity as the sulfuric acid weight percent decreases; when the 1,120 cm −1 feature fully disappears from the spectrum the PSC is classified as SNA. Ice is easily identifiable by the two upward features near 1,000 cm −1 and 3,550 cm −1 , and in some ice spectra (Figure 4 in L23) the libration mode around 780 cm −1 can also be observed.…”

Section: Methodsmentioning

confidence: 97%

“…Briefly, beta‐NAT can be identified by the diagnostic feature at 820 cm −1 , the unique doublet in the OH stretching region at 3,200 cm −1 and 3,350 cm −1 and a broad slanted feature around 1,380 cm −1 ; see Figure 1 in L23. STS (Figure 3 in L23) and SNA (Figure 2 in L23) both have a broad singlet feature in the OH region which makes it easy to distinguish from NAT. There are three distinct features in STS: a sulfate band at 1,120 cm −1 and nitric acid features at 1,420 cm −1 and 1,720 cm −1 .…”

Section: Methodsmentioning

confidence: 99%

“…As the temperature in the stratosphere cools during polar winter, sulfate aerosols in the Junge layer (Junge et al, 1961) begin to uptake gas-phase water and nitric acid to form STS, thereby increasing the size (Carslaw et al, 1997) and lowering the fraction of sulfuric acid in the aerosol. If temperature is low enough, the relative amount of sulfuric acid can drop to ∼1% by weight such that the aerosol is predominately composed of supercooled nitric acid and water (SNA) (Carslaw et al, 1997;Kim et al, 2006;Lecours et al, 2023;Lowe & MacKenzie, 2008). NATs are thermodynamically stable below 195 K, STS will begin to form from binary solutions (H 2 O/H 2 SO 4 ) when temperatures drop below the dew point, around 192 K, and solid ice particles will form below the ice frost point of 188 K (Carslaw et al, 1994(Carslaw et al, , 1997Peter & Grooß, 2011).…”

Section: Introductionmentioning

confidence: 99%

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Antarctic Polar Stratospheric Cloud Analysis of ACE‐FTS Data From 2005 to 2023

Lecours,

Boone,

Bernath

2024

JGR Atmospheres

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We present an analysis of Antarctic polar winters from 2005 to 2023 as observed by the Atmospheric Chemistry Experiment (ACE). The unique broad band infrared spectral features in ACE “residual” spectra are used to classify the spectra of polar aerosols by composition into polar stratospheric clouds (PSCs) and sulfate aerosols. The spectra of PSCs are further classified into nitric acid trihydrate, supercooled ternary solutions, supercooled nitric acid, ice‐mix, and mixtures of PSCs. A breakdown of PSC composition is presented for each year. Antarctic winter seasons with unusual compositions are: 2011, in which volcanic ash mixed with PSCs was observed from July to August; 2019, which experienced a stratospheric warming event; 2020, the PSC season following the Australian Black Summer pyrocumulonimbus event; and 2023, which had unusually large sulfate aerosols following the Honga‐Tonga Honga Ha'apai eruption of 2022.

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