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

Publication type:
Journal article
Metadata:
Abstract
<jats:p>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. While direct evidence for the existence of metastable NAD in the polar stratosphere is still lacking, our experiments add to the wealth of previous laboratory studies that have identified various conditions for the rapid growth of metastable compositions. In the atmosphere, these could be intermediate states that transform into thermodynamically stable NAT on longer timescales in aged PSCs. </jats:p>
Autoren
  • Robert Wagner
  • Alexander D James
  • Victoria L Frankland
  • Ottmar Möhler
  • Benjamin J Murray
  • John MC Plane
  • Harald Saathoff
  • Ralf Weigel
  • Martin Schnaiter
DOI
10.5194/acp-23-6789-2023
eISSN
1680-7324
Ausgabe der Veröffentlichung
12
Zeitschrift
Atmospheric Chemistry and Physics
Sprache
en
Online publication date
2023
Paginierung
6789 - 6811
Status
Published online
Herausgeber
Copernicus GmbH
Herausgeber URL
http://dx.doi.org/10.5194/acp-23-6789-2023
Datum der Datenerfassung
2023
Titel
Particle shapes and infrared extinction spectra of nitric acid dihydrate (NAD) crystals: optical constants of the <i>β</i>-NAD modification
Ausgabe der Zeitschrift
23

Data source: Crossref

Other metadata sources:
Author's licence
CC-BY
Autoren
  • Robert Wagner
  • Alexander D James
  • Victoria L Frankland
  • Ottmar Möhler
  • Benjamin J Murray
  • John MC Plane
  • Harald Saathoff
  • Ralf Weigel
  • Martin Schnaiter
Hosting institution
Universitätsbibliothek Mainz
Sammlungen
  • JGU-Publikationen
Resource version
Published version
DOI
10.5194/acp-23-6789-2023
File(s) embargoed
false
Open access
true
ISSN
1680-7324
Ausgabe der Veröffentlichung
12
Zeitschrift
Atmospheric chemistry and physics
Schlüsselwörter
  • 520 Astronomie
  • 520 Astronomy and allied sciences
  • 530 Physik
  • 530 Physics
Sprache
eng
Open access status
Open Access
Paginierung
6789 - 6811
Datum der Veröffentlichung
2023
Public URL
https://openscience.ub.uni-mainz.de/handle/20.500.12030/10305
Herausgeber
EGU
Datum der Datenerfassung
2024
Datum, an dem der Datensatz öffentlich gemacht wurde
2024
Zugang
Public
Titel
Particle shapes and infrared extinction spectra of nitric acid dihydrate (NAD) crystals : optical constants of the β-NAD modification
Ausgabe der Zeitschrift
23

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particle_shapes_and_infrared_-20240416162025239.pdf

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