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.

Global transport of perfluoroalkyl acids via sea spray aerosol

Johansson, J.H.; Salter, M.E.; Navarro, J-C.A.; Leck, C.; Nilsson, E.D.; Cousins, I.T.
2019 | SU

SETAC Europe 29th Annual Meeting | May 30, 2019 | Helsinki, Finland

Concerns of young protesters are justified

Gregor Hagedorn; Peter Kalmus; Michael Mann; Sara Vicca; Joke Van den Berge; Jean-Pascal van Ypersele; Dominique Bourg; Jan Rotmans; Roope Kaaronen; Stefan Rahmstorf; Helga Kromp-Kolb; Gottfried Kirchengast; Reto Knutti; Sonia I. Seneviratne; Philippe Thalmann; Raven Cretney; Alison Green; Kevin Anderson; Martin Hedberg; Douglas Nilsson; Amita Kuttner; Katharine Hayhoe
2019 | Science | 364 (6436) (139-140)

Global transport of perfluoralkyl acids via sea spray aerosol

2019 | Environ. Sci.-Process Impacts | 21 (4) (635-649)

Perfluoroalkyl acids (PFAAs) are persistent organic pollutants found throughout the world's oceans. Previous
research suggests that long-range atmospheric transport of these substances may be substantial. However,
it remains unclear what the main sources of PFAAs to the atmosphere are. We have used a laboratory sea
spray chamber to study water-to-air transfer of 11 PFAAs via sea spray aerosol (SSA). We observed significant
enrichment of all PFAAs relative to sodium in the SSA generated. The highest enrichment was observed in
aerosols with aerodynamic diameter < 1.6 mm, which had aerosol PFAA concentrations up to 62 000 times
higher than the PFAA water concentrations in the chamber. In surface microlayer samples collected from
the sea spray chamber, the enrichment of the substances investigated was orders of magnitude smaller
than the enrichment observed in the aerosols. In experiments with mixtures of structural isomers,
a lower contribution of branched PFAA isomers was observed in the surface microlayer compared to the
bulk water. However, no clear trend was observed in the comparison of structural isomers in SSA and
bulk water. Using the measured enrichment factors of perfluorooctanoic acid and perfluorooctane
sulfonic acid versus sodium we have estimated global annual emissions of these substances to the
atmosphere via SSA as well as their global annual deposition to land areas. Our experiments suggest that
SSA may currently be an important source of these substances to the atmosphere and, over certain
areas, to terrestrial environments.

Interactions between the atmosphere, cryosphere and ecosystems at northern high latitudes

Michael Boy; Erik S. Thomson; Juan-C. Acosta Navarro; Olafur Amalds; Ekaterina Batchvarova; Jaana K. Bäck; Frank Berninger; Merete Bilde; Pavla Dagsson Waldhuserova; Dimistri Castaréde; Maryam Dalirian; Gerrit de Leeuw; Monika Wittman; Ella-Maria Duplissy (nèe Kyrö); J. Duplissy; A. M. L. Ekman; Keyan Fang; Jean-Charlet Gallet; Marianne Glasius; Sven-Erik Gryning; Henrik Grythe; Hans-Christen Hansson; Margareta Hansson; Elisabeth Isaksson; Trond Iverson; Ingibjörg Jónsdottir; Ville Kasurinen; Alf Kirkevåg; Atte Korhola; Radovan Krejci; Jon Egill Kristjansson; Hanna K. Lappalainen; Antti Lauri; Matti Leppäranta; Heikki Livhvainen: Risto Makkonon; Andreas Massling; Outi Meinander; E Douglas Nilsson; Haraldur Ólofsson; Jan B. C. Pettersson; Nonne L. Prisle; Ilona Riipinen; Pontus Roldin; Meri Ruppel; Matt Edward Salter; Maria Sand; Ovind Seland; Heikki Seppä; Henrik Skov; Joanna Soares; Andreas Stohl; Johan Ström; Jonas Svensson; Erik Swietlicki; Ksenia Tabakova; Thorstur Torsteinsson; Aki Virkula; Gesa A. Weyhenmeyer; Yusheng Wu; Paul Zieger; Markku Kulmala
2019 | Atmos. Chem. Phys. | 19 (2015-2061)

The Nordic Centre of Excellence CRAICC (Cryosphere–Atmosphere Interactions in a Changing Arctic Climate), funded by NordForsk in the years 2011–2016, is the largest joint Nordic research and innovation initiative to date, aiming to strengthen research and innovation regarding climate change issues in the Nordic region. CRAICC gathered more than 100 scientists from all Nordic countries in a virtual centre with the objectives of identifying and quantifying the major processes controlling Arctic warming and related feedback mechanisms, outlining strategies to mitigate Arctic warming, and developing Nordic Earth system modelling with a focus on short-lived climate forcers (SLCFs), including natural and anthropogenic aerosols.

The outcome of CRAICC is reflected in more than 150 peer-reviewed scientific publications, most of which are in the CRAICC special issue of the journal Atmospheric Chemistry and Physics. This paper presents an overview of the main scientific topics investigated in the centre and provides the reader with a state-of-the-art comprehensive summary of what has been achieved in CRAICC with links to the particular publications for further detail. Faced with a vast amount of scientific discovery, we do not claim to completely summarize the results from CRAICC within this paper, but rather concentrate here on the main results which are related to feedback loops in climate change–cryosphere interactions that affect Arctic amplification.

Calcium enrichment in sea spray aerosol particles

Salter, M.; Hamacher-Barth, E.; Leck, C.; Werner, J.; Johnson, C.; Riipinen, I.; Nilsson, D.; Zieger, P.
2016 | Geophys Res Lett

Sea spray aerosol particles are an integral part of the Earth's radiation budget. To date, the inorganic composition of nascent sea spray aerosol particles have widely been assumed to be equivalent to the inorganic composition of seawater. Here we challenge this assumption using a laboratory sea spray chamber containing both natural and artificial seawater, as well as with ambient aerosol samples collected over the central Arctic Ocean during summer. We observe significant enrichment of calcium in submicrometer (<1μm in diameter) sea spray aerosol particles when particles are generated from both seawater sources in the laboratory as well as in the ambient aerosols samples. We also observe a tendency for increasing calcium enrichment with decreasing particle size. Our results suggest that calcium enrichment in sea spray aerosol particles may be environmentally significant with implications for our understanding of sea spray aerosol, its impact on Earth's climate, as well as the chemistry of the marine atmosphere.

An empirically derived inorganic sea spray source function incorporating sea surface temperature

Salter, M. E.; Zieger, P.; Acosta Navarro, J. C.; Grythe, H.; Kirkevag, A.; Rosati, B.; Riipinen, I.; Nilsson, E. D.
2015 | Atmos. Chem. Phys. | 15 (11047-11066)

We have developed an inorganic sea spray source function that is based upon state-of-the-art measurements of sea spray aerosol production using a temperature-controlled plunging jet sea spray aerosol chamber. The size-resolved particle production was measured between 0.01 and 10 μm dry diameter. Particle production decreased non-linearly with increasing seawater temperature (between −1 and 30 °C) similar to previous findings. In addition, we observed that the particle effective radius, as well as the particle surface, particle volume and particle mass, increased with increasing seawater temperature due to increased production of particles with dry diameters greater than 1 μm. By combining these measurements with the volume of air entrained by the plunging jet we have determined the size-resolved particle flux as a function of air entrainment. Through the use of existing parameterisations of air entrainment as a function of wind speed, we were subsequently able to scale our laboratory measurements of particle production to wind speed. By scaling in this way we avoid some of the difficulties associated with defining the "white area" of the laboratory whitecap – a contentious issue when relating laboratory measurements of particle production to oceanic whitecaps using the more frequently applied whitecap method.

The here-derived inorganic sea spray source function was implemented in a Lagrangian particle dispersion model (FLEXPART – FLEXible PARTicle dispersion model). An estimated annual global flux of inorganic sea spray aerosol of 5.9 ± 0.2 Pg yr−1 was derived that is close to the median of estimates from the same model using a wide range of existing sea spray source functions. When using the source function derived here, the model also showed good skill in predicting measurements of Na+ concentration at a number of field sites further underlining the validity of our source function.

In a final step, the sensitivity of a large-scale model (NorESM – the Norwegian Earth System Model) to our new source function was tested. Compared to the previously implemented parameterisation, a clear decrease of sea spray aerosol number flux and increase in aerosol residence time was observed, especially over the Southern Ocean. At the same time an increase in aerosol optical depth due to an increase in the number of particles with optically relevant sizes was found. That there were noticeable regional differences may have important implications for aerosol optical properties and number concentrations, subsequently also affecting the indirect radiative forcing by non-sea spray anthropogenic aerosols.

Seawater mesocosm experiments in the Arctic uncover differential transfer of marine bacteria to aerosols

Fahlgren, C.; Gomez-Consarnau, L.; Zabori, J.; Lindh, MV.; Krejci, R.; Martensson, EM.; Nilsson, D.; Pinhassi, J.
2015 | Environ. Microbiol. | 7 (3) (460-470)

Biogenic aerosols critically control atmospheric processes. However, although bacteria constitute major portions of living matter in seawater, bacterial aerosolization from oceanic surface layers remains poorly understood. We analysed bacterial diversity in seawater and experimentally generated aerosols from three Kongsfjorden sites, Svalbard. Construction of 16S rRNA gene clone libraries from paired seawater and aerosol samples resulted in 1294 sequences clustering into 149 bacterial and 34 phytoplankton operational taxonomic units (OTUs). Bacterial communities in aerosols differed greatly from corresponding seawater communities in three out of four experiments. Dominant populations of both seawater and aerosols were Flavobacteriia, Alphaproteobacteria and Gammaproteobacteria. Across the entire dataset, most OTUs from seawater could also be found in aerosols; in each experiment, however, several OTUs were either selectively enriched in aerosols or little aerosolized. Notably, a SAR11 clade OTU was consistently abundant in the seawater, but was recorded in significantly lower proportions in aerosols. A strikingly high proportion of colony-forming bacteria were pigmented in aerosols compared with seawater, suggesting that selection during aerosolization contributes to explaining elevated proportions of pigmented bacteria frequently observed in atmospheric samples. Our findings imply that atmospheric processes could be considerably influenced by spatiotemporal variations in the aerosolization efficiency of different marine bacteria.

On the seawater temperature dependence of the sea spray aerosol generated by a continuous plunging jet

Salter, ME; Nilsson, ED; Butcher, A; Bilde, M
2014 | J. Geophys. Res.-Atmos. | 119 (14) (9052-9072)
air-entrainment , breaking waves , bubble entrainment , energy-dissipation , gas entrainment , oceanic whitecaps , simulation tank , size distributions , surface tension , water temperature

Breaking waves on the ocean surface produce bubbles which, upon bursting, deliver seawater constituents into the atmosphere as sea spray aerosol particles. One way of investigating this process in the laboratory is to generate a bubble plume by a continuous plunging jet. We performed a series of laboratory experiments to elucidate the role of seawater temperature on aerosol production from artificial seawater free from organic contamination using a plunging jet. The seawater temperature was varied from -1.3 degrees C to 30.1 degrees C, while the volume of air entrained by the jet, surface bubble size distributions, and size distribution of the aerosol particles produced was monitored. We observed that the volume of air entrained decreased as the seawater temperature was increased. The number of surface bubbles with film radius smaller than 2 mm decreased nonlinearly with seawater temperature. This decrease was coincident with a substantial reduction in particle production. The number concentrations of particles with dry diameter less than similar to 1 mu m decreased substantially as the seawater temperature was increased from -1.3 degrees C to similar to 9 degrees C. With further increase in seawater temperature (up to 30 degrees C), a small increase in the number concentration of larger particles (dry diameter >similar to 0.3 mu m) was observed. Based on these observations, we infer that as seawater temperature increases, the process of bubble fragmentation changes, resulting in decreased air entrainment by the plunging jet, as well as the number of bubbles with film radius smaller than 2 mm. This again results in decreased particle production with increasing seawater temperature.

Heated submicron particle fluxes using an optical particle counter in urban environment.

Vogt, M.; Johansson, C.; Mårtensson, M.; Struthers, H.; Ahlm, L.; Nilsson, E. D.
2013 | Atmos. Chem. Phys. | 13 (3087-3096)

From May 2008 to March 2009 aerosol emissions were measured using the eddy covariance method covering the size range 0.25 to 2.5 μm diameter (Dp) from a 105 m tower, in central Stockholm, Sweden. Supporting chemical aerosol data were collected at roof and street level. Results show that the inorganic fraction of sulfate, nitrate, ammonium and sea salt accounts for approximately 15% of the total aerosol mass < 1 μm Dp (PM1) with water soluble soil contributing 11% and water insoluble soil 47%. Carbonaceous compounds were at the most 27% of PM1 mass. It was found that heating the air from the tower to 200 °C resulted in the loss of approximately 60% of the aerosol volume at 0.25 μm Dp whereas only 40% of the aerosol volume was removed at 0.6 μm Dp. Further heating to 300 °C caused very little additional losses <0.6 μm Dp. The chemical analysis did not include carbonaceous compounds, but based on the difference between the total mass concentration and the sum of the analyzed non-carbonaceous materials, it can be assumed that the non-volatile particulate material (heated to 300 °C) consists mainly of carbonaceous compounds, including elemental carbon. Furthermore, it was found that the non-volatile particle fraction <0.6 μm Dp correlated (r2 = 0.4) with the BC concentration at roof level in the city, supporting the assumption that the non-volatile material consists of carbonaceous compounds. The average diurnal cycles of the BC emissions from road traffic (as inferred from the ratio of the incremental concentrations of nitrogen oxides (NOx) and BC measured on a densely trafficked street) and the fluxes of non-volatile material at tower level are in close agreement, suggesting a traffic source of BC. We have estimated the emission factors (EFs) for non-volatile particles <0.6 μm Dp to be 2.4 ± 1.4 mg veh−1 km−1 based on either CO2 fluxes or traffic activity data. Light (LDV) and heavy duty vehicle (HDV) EFs were estimated using multiple linear regression and reveal that for non-volatile particulate matter in the 0.25 to 0.6 μm Dp range, the EFHDV is approximately twice as high as the EFLDV, the difference not being statistically significant.

Comparison between summertime and wintertime Arctic Ocean primary marine aerosol properties

Zabori, J.; Krejci, R.; Ström, J.; Vaattovaara, P.; Ekman, A.M.L.; Salter, M.; Mårtensson, E.M.; Nilsson, E.D.
2013 | Atmos. Chem. Phys. | 13 (4783-4799)

Climate-induced changes in sea salt aerosol number emissions: 1870 to 2100

Struthers, H., A.; Ekman, M. L.; Glantz, P.; Iversen, T.; Kirkevåg, A.; Seland, Ø.; Mårtensson, E. M.; Noone, K.; Nilsson, E. D.
2013 | J. Geophys. Res.-Atmos. | 118 (1-13)

Contact information

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Geovetenskapens Hus,
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Arrheniuslaboratoriet, Svante Arrhenius väg 16, Stockholm (Unit for Analytical and Toxicological Chemistry)

Mailing address:
Department of Environmental Science and Analytical Chemistry (ACES)
Stockholm University
106 91 Stockholm

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