Vortex‐Wide Detection of Large Aspherical NAT Particles in the Arctic Winter 2011/12 Stratosphere

Woiwode, Wolfgang; Höpfner, Michael; Bi, Lei; Khosrawi, Farahnaz; Santee, M. L.

doi:10.1029/2019gl084145

Cited by 7 publications

(8 citation statements)

References 72 publications

(127 reference statements)

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“…(2014) and Woiwode et al. (2014; 2016; 2019) suggest that NAT particles may be highly aspherical. The following section summarizes findings made from in situ and remote sensing particle measurements in the last decade.…”

Section: Formation Pathways and Particle Characteristicsmentioning

confidence: 98%

“…Recently, the baseline of the spectrum (i.e., when trace gas signatures are neglected, see Woiwode et al, 2019, Figure 1) from 817.5 to 961 cm −1 was utilized to define a simple detection method sensitive to highly aspherical β-NAT populations with volume-equivalent median radii of 3-7 μm. 10.1029/2020RG000702…”

Section: Evidence For Highly Aspherical β-Nat Particlesmentioning

confidence: 99%

“…Based on an analysis of airborne observations, Woiwode et al (2016) proposed that this modified NAT feature is an indicator of the presence of highly aspherical β-NAT particles (see also Section 3.2.1). Recently, a simple detection method sensitive to this modified step-like feature and considering also the distinct scattering pattern toward higher wave numbers was successfully applied for vortex-wide detection of large aspherical β-NAT in the Arctic winter 2011/12 (Woiwode et al, 2019). However, this modified NAT feature (hence the presence of large aspherical NAT particles) is not considered in the current MIPAS PSC composition algorithm.…”

Section: Mipasmentioning

confidence: 99%

“…Recently, the baseline of the spectrum (i.e., when trace gas signatures are neglected, see Woiwode et al., 2019, Figure 1) from 817.5 to 961 cm −1 was utilized to define a simple detection method sensitive to highly aspherical β ‐NAT populations with volume‐equivalent median radii of 3–7 μm. Underlying size distributions are compatible with in situ observations of large HNO 3 ‐containing particles reported in the literature (compare Molleker et al., 2014, references therein) and available HNO 3 .…”

Section: Formation Pathways and Particle Characteristicsmentioning

confidence: 99%

See 3 more Smart Citations

Polar Stratospheric Clouds: Satellite Observations, Processes, and Role in Ozone Depletion

Tritscher

Pitts

Poole

et al. 2021

Reviews of Geophysics

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Polar stratospheric clouds (PSCs) play important roles in stratospheric ozone depletion during winter and spring at high latitudes (e.g., the Antarctic ozone hole). PSC particles provide sites for heterogeneous reactions that convert stable chlorine reservoir species to radicals that destroy ozone catalytically. PSCs also prolong ozone depletion by delaying chlorine deactivation through the removal of gas-phase HNO 3 and H 2 O by sedimentation of large nitric acid trihydrate (NAT) and ice particles. Contemporary observations by the spaceborne instruments Michelson Interferometer for Passive Atmospheric Sounding (MIPAS), Microwave Limb Sounder (MLS), and Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) have provided an unprecedented polar vortex-wide climatological view of PSC occurrence and composition in both hemispheres. These data have spurred advances in our understanding of PSC formation and related dynamical processes, especially the firm evidence of widespread heterogeneous nucleation of both NAT and ice PSC particles, perhaps on nuclei of meteoritic origin. Heterogeneous chlorine activation appears to be well understood. Reaction coefficients on/in liquid droplets have been measured accurately, and while uncertainties remain for reactions on solid NAT and ice particles, they are considered relatively unimportant since under most conditions chlorine activation occurs on/in liquid droplets. There have been notable advances in the ability of chemical transport and chemistry-climate models to reproduce PSC temporal/spatial distributions and composition observed from space. Continued spaceborne PSC observations will facilitate further improvements in the representation of PSC processes in global models and enable more accurate projections of the evolution of polar ozone and the global ozone layer as climate changes.Plain Language Summary Polar stratospheric clouds (PSCs) occur during winter and early spring in the polar stratosphere, when temperatures are low enough to enable cloud formation despite the extremely dry conditions. Ground-based PSC sightings date back to the late 19th century, but they were little more than a scientific curiosity until the discovery of the Antarctic ozone hole in 1985. Soon thereafter, it was shown that PSCs play a crucial role in converting stable halogen (mainly chlorine) species of anthropogenic origin into reactive gases that rapidly destroy ozone. Considerable progress was made over the next two decades in quantifying these processes through laboratory studies, field campaigns, and limited spaceborne observations. We are now reaping the benefits of new PSC observations over the entire polar regions from three complementary 21st century spaceborne instruments. This study reviews these instruments and highlights new findings on PSC occurrence and composition. These datasets have also triggered advances in understanding how PSCs form and the influence of atmospheric dynamics, as well as improvements in how detailed cloud processes are approximated in global models. Thi...

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Section: Formation Pathways and Particle Characteristicsmentioning

confidence: 98%

Section: Evidence For Highly Aspherical β-Nat Particlesmentioning

confidence: 99%

Section: Mipasmentioning

confidence: 99%

Section: Formation Pathways and Particle Characteristicsmentioning

confidence: 99%

See 2 more Smart Citations

Polar Stratospheric Clouds: Satellite Observations, Processes, and Role in Ozone Depletion

Tritscher

Pitts

Poole

et al. 2021

Reviews of Geophysics

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“…There seems to be a systematic difference between WACCM and MIPAS in this year, though, maybe due to a lower precision of the instrument at that time (Piccolo and Dudhia, 2007). The Arctic winter 2011/2012 was characterized by an early breakdown of the polar vortex at the end of December (Roy and Kuttippurath, 2022), but there is some evidence of large NAT particles during the cold 150 period during December 2011 (Woiwode et al, 2019). This is why the HNO 3 distributions change in WACCM and probably large NAT particles play a larger role in determining the distributions for that year, see Fig.…”

Section: Ozonesondesmentioning

confidence: 99%

Effects of denitrification on the distributions of trace gas abundances in the polar regions: a model-data comparison

Weimer

Kinnison

Wilka

et al. 2022

Preprint

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Abstract. Polar stratospheric clouds (PSCs) play a key role in the polar chemistry of the stratosphere. Nitric acid trihydrate (NAT) particles have been shown to lead to denitrification of the lower stratosphere. While the existence of large NAT particles (NAT "rocks") has been verified by many measurements especially in the Northern Hemisphere (NH), most current chemistry-climate models use simplified parametrizations, often based on evaluations in the Southern Hemisphere where the polar vortex is stable enough that accounting for NAT rocks is not as important as in the NH. Here, we evaluate the probability density functions of various gaseous species in the polar vortex using one such model, the Whole Atmosphere Community Climate Model (WACCM), and compare these with measurements by the Michelson Interferometer for Passive Atmospheric Sounding onboard the Environmental Satellite (MIPAS/Envisat) and two ozonesonde stations for a range of years and in both hemispheres. Using the maximum difference between the distributions of MIPAS and WACCM as a measure of coherence, we find better agreement for HNO3 when reducing the NAT number density from the standard value of 10−2 used in this model to 5 × 10−4 cm−3 for almost all spring seasons during the MIPAS period in both hemispheres. The distributions of ClONO2 and O3 are not greatly affected by the NAT density. The average difference of WACCM to ozonesondes supports the need to reduce the NAT number density in the model. Therefore, this study suggests to use a NAT number density of 5 × 10−4 cm−3 for future simulations with WACCM.

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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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Vortex‐Wide Detection of Large Aspherical NAT Particles in the Arctic Winter 2011/12 Stratosphere

Cited by 7 publications

References 72 publications

Polar Stratospheric Clouds: Satellite Observations, Processes, and Role in Ozone Depletion

Polar Stratospheric Clouds: Satellite Observations, Processes, and Role in Ozone Depletion

Effects of denitrification on the distributions of trace gas abundances in the polar regions: a model-data comparison

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

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