Aerosol constituents and their spatial distribution in the free troposphere of coastal Antarctic regions

Hara, Keiichiro; Iwasaka, Yasunobu; Wada, Makoto; Ihara, Tatsuo; Shiba, Hirokazu; Osada, Kazuo; Yamanouchi, Takashi

doi:10.1029/2005jd006591

Cited by 20 publications

(24 citation statements)

References 57 publications

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“…Previous aerosol volatility measurements in the AFT deduced that sulfate is the primary component of nanoparticle populations and speculated that biologically produced DMS is the primary precursor (e.g. Iwasaka et al, 1985;Hara et al, 2006). However, composition measurements have not been conclusive.…”

Section: Discussionmentioning

confidence: 88%

Unexpectedly high ultrafine aerosol concentrations above East Antarctic sea ice

et al. 2016

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Abstract. Better characterisation of aerosol processes in pristine, natural environments, such as Antarctica, have recently been shown to lead to the largest reduction in uncertainties in our understanding of radiative forcing. Our understanding of aerosols in the Antarctic region is currently based on measurements that are often limited to boundary layer air masses at spatially sparse coastal and continental research stations, with only a handful of studies in the vast sea-ice region. In this paper, the first observational study of sub-micron aerosols in the East Antarctic sea ice region is presented. Measurements were conducted aboard the icebreaker Aurora Australis in spring 2012 and found that boundary layer condensation nuclei (CN 3 ) concentrations exhibited a fivefold increase moving across the polar front, with mean polar cell concentrations of 1130 cm −3 -higher than any observed elsewhere in the Antarctic and Southern Ocean region. The absence of evidence for aerosol growth suggested that nucleation was unlikely to be local. Air parcel trajectories indicated significant influence from the free troposphere above the Antarctic continent, implicating this as the likely nucleation region for surface aerosol, a similar conclusion to previous Antarctic aerosol studies. The highest aerosol concentrations were found to correlate with low-pressure systems, suggesting that the passage of cyclones provided an accelerated pathway, delivering air masses quickly from the free troposphere to the surface. After descent from the Antarctic free troposphere, trajectories suggest that sea-ice boundary layer air masses travelled equatorward into the low-albedo Southern Ocean region, transporting with them emissions and these aerosol nuclei which, after growth, may potentially impact on the region's radiative balance. The high aerosol concentrations and their transport pathways described here, could help reduce the discrepancy currently present between simulations and observations of cloud and aerosol over the Southern Ocean.

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Section: Discussionmentioning

confidence: 88%

Unexpectedly high ultrafine aerosol concentrations above East Antarctic sea ice

et al. 2016

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“…In addition, the derivation of J hom allows for estimation of ice particle production rates from derived homogeneous nucleation according to P ice hom = J hom ·V particle , where V particle is the amount of total liquid volume of aerosol per cm 3 of air. We assume sea salt concentrations, estimated here from field observations of aerosol particle concentrations in the free troposphere as 10 cm −3 (Cziczo et al, 2004;Ikegami et al, , 2004Brock et al, 2011;Hara et al, 2006), with mean dry diameter of 200 nm and a wet diameter of 480 nm at 90 % RH (Zhang et al, 2005;Lewis and Schwartz, 2006), and applying J hom = 10 6 cm −3 s −1 at a temperature of 215 K (Fig. 3), P ice hom could reach 0.035 ice particles L −1 (air) min −1 .…”

Section: Homogeneous Ice Nucleationmentioning

confidence: 99%

Ice nucleation from aqueous NaCl droplets with and without marine diatoms

2011

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Abstract. Ice formation in the atmosphere by homogeneous and heterogeneous nucleation is one of the least understood processes in cloud microphysics and climate. Here we describe our investigation of the marine environment as a potential source of atmospheric IN by experimentally observing homogeneous ice nucleation from aqueous NaCl droplets and comparing against heterogeneous ice nucleation from aqueous NaCl droplets containing intact and fragmented diatoms. Homogeneous and heterogeneous ice nucleation are studied as a function of temperature and water activity, a w . Additional analyses are presented on the dependence of diatom surface area and aqueous volume on heterogeneous freezing temperatures, ice nucleation rates, ω het , ice nucleation rate coefficients, J het , and differential and cumulative ice nuclei spectra, k(T ) and K(T ), respectively. Homogeneous freezing temperatures and corresponding nucleation rate coefficients are in agreement with the water activity based homogeneous ice nucleation theory within experimental and predictive uncertainties. Our results confirm, as predicted by classical nucleation theory, that a stochastic interpretation can be used to describe the homogeneous ice nucleation process. Heterogeneous ice nucleation initiated by intact and fragmented diatoms can be adequately represented by a modified water activity based ice nucleation theory. A horizontal shift in water activity, a w,het = 0.2303, of the ice melting curve can describe median heterogeneous freezing temperatures. Individual freezing temperatures showed no dependence on available diatom surface area and aqueous volume. Determined at median diatom freezing temperatures for a w from 0.8 to −4.1 ×10 4 cm −2 . The experimentally derived ice nucleation rates and nuclei spectra allow us to estimate ice particle production which we subsequently use for a comparison with observed ice crystal concentrations typically found in cirrus and polar marine mixed-phase clouds. Differences in application of time-dependent and time-independent analyses to predict ice particle production are discussed.

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“…These previous works indicated (1) aerosol enhancement in free troposphere immediately after cyclone passing (Yamanouchi et al, 1999), (2) appearance of a CN-enhanced layer in lower free troposphere , and (3) transport of sea-salt particles and mineral particles from mid-latitudes through the free troposphere (Yamazaki et al, 1989;Hara et al, 2006). Vertical and seasonal distributions of the aerosol number concentration and constituents in the upper atmosphere, however, are poorly known for Antarctic regions because aerosol measurements in the free troposphere over Antarctica are limited.…”

Section: Introductionmentioning

confidence: 99%

“…They have also been made at inland stations: Dome-F (77 • 19 S 39 • 42 E) , Kohnen (75 • 00 S 00 • 04 E) (Weller et al, 2007), Concordia (75 • S, 123 • E) (Jourdain et al, 2008), and at the South Pole (Amundsen Scott) (90 • S) (Bodhaine, 1995). Some investigations have pointed out the likelihood of aerosol transport through the free troposphere (e.g., Hara et al, 2006) and new particle formation in the free troposphere (Ito et al, 1993;Koponen et al, 2002). Recent works suggested that black carbon, derived mostly from biomass burning, was transported to Antarctic coasts (Fiebig et al, 2009;Hara et al, 2010).…”

Section: Introductionmentioning

confidence: 99%

“…Previous aerosol measurements in the upper atmosphere of Antarctic regions were conducted using (1) airplanes (Iwasaka et al, 1985;Yamazaki et al, 1989;Yamanouchi et al, 1999;Wada et al, 2001;Hara et al, 2006;, (2) balloon-borne particle counters (i.e., aerosol sonde) (Ito et al, 1986;Hayashi, 2001), and (3) tethered balloons (Rankin and Wolff, 2002). These previous works indicated (1) aerosol enhancement in free troposphere immediately after cyclone passing (Yamanouchi et al, 1999), (2) appearance of a CN-enhanced layer in lower free troposphere , and (3) transport of sea-salt particles and mineral particles from mid-latitudes through the free troposphere (Yamazaki et al, 1989;Hara et al, 2006).…”

Section: Introductionmentioning

confidence: 99%

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Seasonal variations and vertical features of aerosol particles in the Antarctic troposphere

et al. 2011

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Abstract. Tethered balloon-borne aerosol measurements were conducted at Syowa Station, Antarctica during the 46th Japanese Antarctic expedition (2005)(2006). The CN concentration reached a maximum in the summer, although the number concentrations of fine particles (D p >0.3 µm) and coarse particles (D p >2.0 µm) increased during the winterspring. The CN concentration was 30-2200 cm −3 near the surface (surface -500 m) and 7-7250 cm −3 in the lower free troposphere (>1500 m). During the austral summer, higher CN concentration was often observed in the lower free troposphere, where the number concentrations in fine and coarse modes were remarkably lower. The frequent appearance of higher CN concentrations in the free troposphere relative to continuous aerosol measurements at the ground strongly suggests that new particle formation is more likely to occur in the lower free troposphere in Antarctic regions. Seasonal variations of size distribution of fine-coarse particles show that the contribution of the coarse mode was greater in the winterspring than in summer because of the dominance of sea-salt particles in the winter-spring. The number concentrations of fine and coarse particles were high in air masses from the ocean and mid-latitudes. Particularly, aerosol enhancement was observed not only in the boundary layer, but also in the lower free troposphere during and immediately after Antarctic haze events occurring in May, July and September.

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Aerosol constituents and their spatial distribution in the free troposphere of coastal Antarctic regions

Cited by 20 publications

References 57 publications

Unexpectedly high ultrafine aerosol concentrations above East Antarctic sea ice

Unexpectedly high ultrafine aerosol concentrations above East Antarctic sea ice

Ice nucleation from aqueous NaCl droplets with and without marine diatoms

Seasonal variations and vertical features of aerosol particles in the Antarctic troposphere

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