Effect of nucleation on icy pebble growth in protoplanetary discs

Katrin Ros; Anders Johansen; Ilona Riipinen; Daniel Schlesinger
2019 | Astron Astrophys | 629 (A65)

Solid particles in protoplanetary discs can grow by direct vapour deposition outside of ice lines. The presence of microscopic silicate particles may nevertheless hinder growth into large pebbles, since the available vapour is deposited predominantly on the small grains that dominate the total surface area. Experiments on heterogeneous ice nucleation, performed to understand ice clouds in the Martian atmosphere, show that the formation of a new ice layer on a silicate surface requires a substantially higher water vapour pressure than the deposition of water vapour on an existing ice surface. In this paper, we investigate how the difference in partial vapour pressure needed for deposition of vapour on water ice versus heterogeneous ice nucleation on silicate grains influences particle growth close to the water ice line. We developed and tested a dynamical 1D deposition and sublimation model, where we include radial drift, sedimentation, and diffusion in a turbulent protoplanetary disc. We find that vapour is deposited predominantly on already ice-covered particles, since the vapour pressure exterior of the ice line is too low for heterogeneous nucleation on bare silicate grains. Icy particles can thus grow to centimetre-sized pebbles in a narrow region around the ice line, whereas silicate particles stay dust-sized and diffuse out over the disc. The inhibition of heterogeneous ice nucleation results in a preferential region for growth into planetesimals close to the ice line where we find large icy pebbles. The suppression of heterogeneous ice nucleation on silicate grains may also be the mechanism behind some of the observed dark rings around ice lines in protoplanetary discs, as the presence of large ice pebbles outside ice lines leads to a decrease in the opacity there.

Using land-based stations for air–sea interaction studies

Rutgersson, A.; Pettersson, H.; Nilsson, E.; Bergström, H.; Wallin, M. B.; Nilsson, E. D.; Sahlée, E.; Wu., L.; Mårtensson, E. M.
2019 | Tellus | A (in press)

In situ measurements representing the marine atmosphere and air–sea interaction
are taken at ships, buoys, stationary moorings and land-based towers, where
each observation platform has structural restrictions. Air–sea fluxes are often
small, and due to the limitations of the sensors, several corrections are applied.
Land-based towers are convenient for long-term observations, but one critical
aspect is the representativeness of marine conditions. Hence, a careful analysis
of the sites and the data is necessary. Based on the concept of flux footprint, we
suggest defining flux data from land-based marine micrometeorological sites in
categories depending on the type of land influence:
1) CAT1: Marine data representing open sea,
2) CAT2: Disturbed wave field resulting in physical properties different
from open sea conditions and heterogeneity of water properties in the footprint
region, and
3) CAT3: Mixed land–sea footprint, very heterogeneous conditions and
possible active carbon production/consumption.
Characterization of data would be beneficial for combined analyses using
several sites in coastal and marginal seas and evaluation/comparison of
properties and dynamics. Aerosol fluxes are a useful contribution to
characterizing a marine micrometeorological field station; for most conditions,
they change sign between land and sea sectors.
Measured fluxes from the land-based marine station Östergarnsholm are used as
an example of a land-based marine site to evaluate the categories and to present
an example of differences between open sea and coastal conditions.
At the Östergarnsholm site the surface drag is larger for CAT2 and CAT3 than
for CAT1 when wind speed is below 10 m/s. The heat and humidity fluxes show
a distinctive distinguished seasonal cycle; latent heat flux is larger for CAT2 and
CAT3 compared to CAT1. The flux of carbon dioxide is large from the coastal
and land–sea sectors, showing a large seasonal cycle and significant variability (compared to the open sea sector). Aerosol fluxes are partly dominated by sea
spray emissions comparable to those observed at other open sea conditions.

Plant roots increase both decomposition and stable organic matter formation in boreal forest soil

Adamczyk B.; Sietö, O.-M.; Straková P.; Prommer J.; Wild B.; Hagner M.; Pihlatie M.; Fritze H.; Richter A.; Heinonsalo J.
2019 | Nat. Commun. | 10

A global view on the effect of water uptake on aerosol particle light scattering

Burgos, M., Andrews, E., Titos, G., Alados-Arboledas, L., Baltensperger, U., Day, D., Jefferson, A., Kalivitis, N., Mihalopoulos, N., Sherman, J., Sun, J., Weingartner, E., Zieger, P.
2019 | Sci. Data | 6 (157) (1-19)

A reference dataset of multi-wavelength particle light scattering and hemispheric backscattering coefficients for different relative humidities (RH) between RH = 30 and 95% and wavelengths between λ = 450 nm and 700 nm is described in this work. Tandem-humidified nephelometer measurements from 26 ground-based sites around the globe, covering multiple aerosol types, have been re-analysed and harmonized into a single dataset. The dataset includes multi-annual measurements from long-term monitoring sites as well as short-term field campaign data. The result is a unique collection of RH-dependent aerosol light scattering properties, presented as a function of size cut. This dataset is important for climate and atmospheric model-measurement inter-comparisons, as a means to improve model performance, and may be useful for satellite and remote sensing evaluation using surface-based, in-situ measurements.

Children’s exposure to perfluoroalkyl acids – a modelling approach

Balk, F.G.P.; Winkens Pütz, K.; Ribbenstedt, A.; Gomis, M.I.; Filipovic, M.; Cousins, I.T.
2019 | Environ. Sci.-Process Impacts | XX (XXX-XXX)

Let us empower the WFD to prevent risks of chemical pollution in European rivers and lakes

Brack, W.; Ait-Aissa, S.; Altenburger, R.; Cousins, I.T.; Dulio, V.; Escher, B.; Focks, A.; Ginebreda, A.; Hering, D.; Hilscherová, K.; Hollender, J.; Hollert, H.; Kortenkamp, A.; López de Alda, M.; Posthuma, L.; Schymanski, E.; Segner, H.; Slobodnik, J.
2019 | Environ Sci Eur | 31 (47) (1-3)

Bioaccumulation Potential of CPs in Aquatic Organisms: Uptake and Depuration in Daphnia magna

Castro, M.; Sobek, A.; Yuan, B.; Breitholtz, M
2019 | Environ. Sci. Technol. | 53 (9533-9541)

Microbial carbon and nitrogen cycling responses to drought and temperature in differently managed mountain grasslands

Fuchslueger L.; Wild B.; Mooshammer M.; Takriti M.; Kienzl S.; Knoltsch A.; Hofhansl F.; Bahn M.; Richter A.
2019 | Soil Biol. Biochem. | 135 (144-153)

Prospects for finding Junge variability-lifetime relationships for micropollutants in the Danube river

Coll, C.; Lindim, C.; Sobek, A.; Sohn, M.D.; MacLeod, M.
2019 | Environ. Sci.-Process Impacts

Temporal Changes in Concentrations of Lead and Other Trace Metals in Free-Ranging Eurasian Eagle Owls Bubo bubo in Sweden

Björn Helander; Marcus Sundbom; Agneta A. Runkel; Anders Bignert
2019 | Arch. Environ. Contam. Toxicol.

Patterns of lead and other trace metals were examined in 122 Eurasian eagle owls Bubo bubo found dead in Sweden in the period 1978–2013. Environmental lead (Pb) has decreased over recent decades from reduced anthropogenic emissions but mortality by Pb poisoning is still frequently reported for avian raptors and scavengers exposed to Pb ammunition. One objective here was to determine if Pb concentrations in a nocturnal non-scavenging raptor follow the general decline observed in other biota. Pb concentration in owl liver was significantly correlated with body weight, sex, latitude, longitude and season. Pb showed a significant decreasing trend towards north and west. Starved birds had significantly higher concentrations. Total Pb concentrations in liver averaged 0.179 μg g−1 dry weight (median 0.103) and decreased by 5.6% per year 1978–2013, or 5.3% after adjustment for confounding factors, similar to trends in other species. Among 14 other trace elements only antimony and arsenic showed decreasing trends. Lead isotope ratios 206Pb/207Pb and 208Pb/207Pb increased from 1.138 and 2.408 in 1978–1985 to 1.170 and 2.435 in 2010–2013, respectively, demonstrating that the decreasing Pb concentration in eagle owl is related to the phase-out of leaded gasoline in Europe, where Pb additives had much lower isotope ratios than natural lead in Swedish soils. Only one incidence of suspected Pb poisoning (40.7 μg g−1 in liver) was observed indicating that poisoning from ingestion of metallic lead is rare (< 1%) in eagle owl in Sweden, in contrast to what has been reported for eagles.

Future Carbon Emission From Boreal and Permafrost Lakes Are Sensitive to Catchment Organic Carbon Loads

Bayer, T. K.; Gustafsson, E.; Brakebusch, M.; Beer, C.
2019 | J. Geophys. Res.-Biogeosci. | 124 (7) (1827-1848)

Environmental Risk of Metal Contamination in Sediments of Tropical Reservoirs

Quadra, G., R.; Lino, A.; Sobek, A.; Malm, O.; Barros, N.; Guida, Y.; Thomaz, J.; Mendonça, R.; Cardoso, S.; Estrada, C.; Rust, F.; Roland, F.
2019 | Bull Environ Contam Toxicol | 103 (292-301)

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