Ambient concentrations of ice-forming particles measured during ship expeditions are collected and summarised with the aim of determining the spatial distribution and variability in ice nuclei in ...oceanic regions.
The presented data from literature and previously unpublished data from over 23 months of ship-based measurements stretch from the Arctic to the Southern Ocean and include a circumnavigation of Antarctica. In comparison to continental observations, ship-based measurements of ambient ice nuclei show 1 to 2 orders of magnitude lower mean concentrations. To quantify the geographical variability in oceanic areas, the concentration range of potential ice nuclei in different climate zones is analysed by meridionally dividing the expedition tracks into tropical, temperate and polar climate zones. We find that concentrations of ice nuclei in these meridional zones follow temperature spectra with similar slopes but vary in absolute concentration. Typically, the frequency with which specific concentrations of ice nuclei are observed at a certain temperature follows a log-normal distribution. A consequence of the log-normal distribution is that the mean concentration is higher than the most frequently measured concentration. Finally, the potential contribution of ship exhaust to the measured ice nuclei concentration on board research vessels is analysed as function of temperature. We find a sharp onset of the influence at approximately −36 ∘C but none at warmer temperatures that could bias ship-based measurements.
Mechanisms behind the phenomenon of Arctic amplification are widely discussed. To contribute to this debate, the (AC)(3) project was established in 2016 (www.ac3-tr.de/). It comprises modeling and ...data analysis efforts as well as observational elements. The project has assembled a wealth of ground-based, airborne, shipborne, and satellite data of physical, chemical, and meteorological properties of the Arctic atmosphere, cryosphere, and upper ocean that are available for the Arctic climate research community. Short-term changes and indications of long-term trends in Arctic climate parameters have been detected using existing and new data. For example, a distinct atmospheric moistening, an increase of regional storm activities, an amplified winter warming in the Svalbard and North Pole regions, and a decrease of sea ice thickness in the Fram Strait and of snow depth on sea ice have been identified. A positive trend of tropospheric bromine monoxide (BrO) column densities during polar spring was verified. Local marine/biogenic sources for cloud condensation nuclei and ice nucleating particles were found. Atmospheric-ocean and radiative transfer models were advanced by applying new parameterizations of surface albedo, cloud droplet activation, convective plumes and related processes over leads, and turbulent transfer coefficients for stable surface layers. Four modes of the surface radiative energy budget were explored and reproduced by simulations. To advance the future synthesis of the results, cross-cutting activities are being developed aiming to answer key questions in four focus areas: lapse rate feedback, surface processes, Arctic mixed-phase clouds, and airmass transport and transformation.
In a warming Arctic the increased occurrence of new
particle formation (NPF) is believed to originate from the declining ice
coverage during summertime. Understanding the physico-chemical properties ...of
newly formed particles, as well as mechanisms that control both particle
formation and growth in this pristine environment, is important for
interpreting aerosol–cloud interactions, to which the Arctic climate can be
highly sensitive. In this investigation, we present the analysis of NPF and
growth in the high summer Arctic. The measurements were made on-board
research vessel Polarstern during the PS106 Arctic expedition. Four
distinctive NPF and subsequent particle growth events were observed, during
which particle (diameter in a range 10–50 nm) number concentrations
increased from background values of approx. 40 up to 4000 cm−3. Based
on particle formation and growth rates, as well as hygroscopicity of
nucleation and the Aitken mode particles, we distinguished two different
types of NPF events. First, some NPF events were favored by negative ions,
resulting in more-hygroscopic nucleation mode particles and suggesting
sulfuric acid as a precursor gas. Second, other NPF events resulted in
less-hygroscopic particles, indicating the influence of organic vapors on
particle formation and growth. To test the climatic relevance of NPF and its
influence on the cloud condensation nuclei (CCN) budget in the Arctic, we
applied a zero-dimensional, adiabatic cloud parcel model. At an updraft
velocity of 0.1 m s−1, the particle number size distribution (PNSD)
generated during nucleation processes resulted in an increase in the CCN
number concentration by a factor of 2 to 5 compared to the background CCN
concentrations. This result was confirmed by the directly measured CCN
number concentrations. Although particles did not grow beyond 50 nm in
diameter and the activated fraction of 15–50 nm particles was on average
below 10 %, it could be shown that the sheer number of particles produced
by the nucleation process is enough to significantly influence the
background CCN number concentration. This implies that NPF can be an important
source of CCN in the Arctic. However, more studies should be conducted in
the future to understand mechanisms of NPF, sources of precursor gases and
condensable vapors, as well as the role of the aged nucleation mode
particles in Arctic cloud formation.
Transparent exopolymer particles (TEPs) exhibit the properties of gels and are ubiquitously found in the world oceans. TEPs may enter the atmosphere as part of sea-spray aerosol. Here, we report ...number concentrations of TEPs with a diameter 4.5 µm, hence covering a part of the supermicron particle range, in ambient aerosol and cloud water samples from the tropical Atlantic Ocean as well as in generated aerosol particles using a plunging waterfall tank that was filled with the ambient seawater. The ambient TEP concentrations ranged between 7x10.sup.2 and 3x10.sup.4 #TEP m.sup.-3 in the aerosol particles and correlations with sodium (Na.sup.+) and calcium (Ca.sup.2+) (R.sup.2 =0.5) suggested some contribution via bubble bursting. Cloud water TEP concentrations were between 4x10.sup.6 and 9x10.sup.6 #TEP L.sup.-1 and, according to the measured cloud liquid water content, corresponding to equivalent air concentrations of 2-4x10.sup.3 #TEP m.sup.-3.
In the marine environment, measurements of lipids as representative species
within different lipid classes have been performed to characterize their
oceanic sources and their transfer from the ocean ...into the atmosphere to
marine aerosol particles. The set of lipid classes includes hydrocarbons
(HC); fatty acid methyl esters (ME); free fatty acids (FFA); alcohols (ALC);
1,3-diacylglycerols (1,3 DG); 1,2-diacylglycerols (1,2 DG);
monoacylglycerols (MG); wax esters (WE); triacylglycerols (TG); and
phospholipids (PP) including phosphatidylglycerols (PG),
phosphatidylethanolamine (PE), phosphatidylcholines (PC), as well as
glycolipids (GL) which cover sulfoquinovosyldiacylglycerols (SQDG),
monogalactosyl-diacylglycerols (MGDG), digalactosyldiacylglycerols (DGDG)
and sterols (ST). These introduced lipid classes have been analyzed in the
dissolved and particulate fraction of seawater, differentiating between
underlying water (ULW) and the sea surface microlayer (SML) on the one hand.
On the other hand, they have been examined on ambient submicrometer aerosol
particle samples (PM1) which were collected at the Cape Verde
Atmospheric Observatory (CVAO) by applying concerted measurements. These
different lipids are found in all marine compartments but in different
compositions. Along the campaign, certain variabilities are observed for the
concentration of dissolved (∑DLULW: 39.8–128.5 µg L−1, ∑DLSML: 55.7–121.5 µg L−1) and
particulate (∑PLULW: 36.4–93.5 µg L−1, ∑PLSML: 61.0–118.1 µg L−1) lipids in the seawater of the
tropical North Atlantic Ocean. Only slight SML enrichments are observed for
the lipids with an enrichment factor EFSML of 1.1–1.4 (DL) and 1.0–1.7
(PL). On PM1 aerosol particles, a total lipid concentration between
75.2–219.5 ng m−3 (averaged: 119.9 ng m−3) is measured. As also
bacteria – besides phytoplankton sources – influence the lipid
concentrations in seawater and on the aerosol particles, the lipid abundance
cannot be exclusively explained by the phytoplankton tracer
(chlorophyll a). The concentration and enrichment of lipids in the SML are
not related to physicochemical properties which describe the surface
activity. On the aerosol particles, an EFaer (the enrichment factor on
the submicrometer aerosol particles compared to the SML) between 9×104–7×105 is observed. Regarding the individual lipid
groups on the aerosol particles, a statistically significant correlation
(R2=0.45, p=0.028) was found between EFaer and
lipophilicity (expressed by the KOW value), which was not present for
the SML. But simple physicochemical descriptors are overall not sufficient
to fully explain the transfer of lipids. As our findings show that
additional processes such as formation and degradation influence the
ocean–atmosphere transfer of both OM in general and of lipids in particular,
they have to be considered in OM transfer models. Moreover, our data suggest
that the extent of the enrichment of the lipid class constituents on the
aerosol particles might be related to the distribution of the lipid within
the bubble–air–water interface. The lipids TG and ALC which are preferably
arranged within the bubble interface are transferred to the aerosol
particles to the highest extent. Finally, the connection between ice
nucleation particles (INPs) in seawater, which are already active at higher
temperatures (−10 to −15 ∘C), and the lipid classes
PE and FFA suggests that lipids formed in the ocean have the potential to
contribute to (biogenic) INP activity when transferred into the atmosphere.
In the framework of the MarParCloud (Marine biological production, organic aerosol particles and marine clouds: a Process Chain) project, measurements were carried out on the islands of Cabo Verde ...(a.k.a. Cape Verde) to investigate the abundance, properties and sources of aerosol particles in general, and cloud condensation nuclei (CCN) in particular, both close to sea level and at the cloud level. A thorough comparison of particle number concentration (PNC), particle number size distribution (PNSD) and CCN number concentration (NCCN) at the Cape Verde Atmospheric Observatory (CVAO, sea-level station) and Monte Verde (MV, cloud-level station) reveals that during times without clouds the aerosols at CVAO and MV are similar and the boundary layer is generally well mixed. Therefore, data obtained at CVAO can be used to describe the aerosol particles at cloud level. Cloud events were observed at MV during roughly 58 % of the time, and during these events a large fraction of particles was activated to cloud droplets. A trimodal parameterization method was deployed to characterize PNC at CVAO. Based on number concentrations in different aerosol modes, four well-separable types of PNSDs were found, which were named the marine type, mixture type, dust type1 and dust type2. Aerosol particles differ depending on their origins. When the air masses came from the Atlantic Ocean, sea spray can be assumed to be one source for particles besides new particle formation. For these air masses, PNSDs featured the lowest number concentration in Aitken, accumulation and coarse modes. Particle number concentrations for sea spray aerosol (SSA, i.e., the coarse mode for these air masses) accounted for about 3.7 % of NCCN,0.30 % (CCN number concentration at 0.30 % supersaturation) and about 1.1 % to 4.4 % of Ntotal (total particle number concentration). When the air masses came from the Sahara, we observed enhanced Aitken, accumulation and coarse mode particle number concentrations and overall increased NCCN; NCCN,0.30 % during the strongest observed dust periods is about 2.5 times higher than that during marine periods. However, the particle hygroscopicity parameter κ for these two most different periods shows no significant difference and is generally similar, independent of air mass. Overall, κ averaged 0.28, suggesting the presence of organic material in particles. This is consistent with previous model work and field measurements. There is a slight increase in κ with increasing particle size, indicating the addition of soluble, likely inorganic, material during cloud processing.
Ice-nucleating particles (INPs) initiate the primary ice formation in clouds at temperatures above ca. −38 ∘C and have an impact on precipitation formation, cloud optical properties, and cloud ...persistence. Despite their roles in both weather and climate, INPs are not well characterized, especially in remote regions such as the Arctic.
We present results from a ship-based campaign to the European Arctic during May to July 2017. We deployed a filter sampler and a continuous-flow diffusion chamber for offline and online INP analyses, respectively. We also investigated the ice nucleation properties of samples from different environmental compartments, i.e., the sea surface microlayer (SML), the bulk seawater (BSW), and fog water.
Concentrations of INPs (NINP) in the air vary between 2 to 3 orders of magnitudes at any particular temperature and are, except for the temperatures above −10 ∘C and below −32 ∘C, lower than in midlatitudes. In these temperature ranges, INP concentrations are the same or even higher than in the midlatitudes.
By heating of the filter samples to 95 ∘C for 1 h, we found a significant reduction in ice nucleation activity, i.e., indications that the INPs active at warmer temperatures are biogenic. At colder temperatures the INP population was likely dominated by mineral dust.
The SML was found to be enriched in INPs compared to the BSW in almost all samples. The enrichment factor (EF) varied mostly between 1 and 10, but EFs as high as 94.97 were also observed. Filtration of the seawater samples with 0.2 µm syringe filters led to a significant reduction in ice activity, indicating the INPs are larger and/or are associated with particles larger than 0.2 µm. A closure study showed that aerosolization of SML and/or seawater alone cannot explain the observed airborne NINP unless significant enrichment of INP by a factor of 105 takes place during the transfer from the ocean surface to the atmosphere.
In the fog water samples with −3.47 ∘C, we observed the highest freezing onset of any sample. A closure study connecting NINP in fog water and the ambient NINP derived from the filter samples shows good agreement of the concentrations in both compartments, which indicates that INPs in the air are likely all activated into fog droplets during fog events.
In a case study, we considered a situation during which the ship was located in the marginal sea ice zone and NINP levels in air and the SML were highest in the temperature range above −10 ∘C. Chlorophyll a measurements by satellite remote sensing point towards the waters in the investigated region being biologically active. Similar slopes in the temperature spectra suggested a connection between the INP populations in the SML and the air. Air mass history had no influence on the observed airborne INP population. Therefore, we conclude that during the case study collected airborne INPs originated from a local biogenic probably marine source.
The project MarParCloud (Marine biological production, organic
aerosol Particles and marine Clouds: a process
chain) aims to improve our understanding of the genesis, modification and
impact of ...marine organic matter (OM) from its biological production, to
its export to marine aerosol particles and, finally, to its ability to
act as ice-nucleating particles (INPs) and cloud condensation nuclei (CCN). A
field campaign at the Cape Verde Atmospheric Observatory (CVAO) in the
tropics in September–October 2017 formed the core of this project that was
jointly performed with the project MARSU (MARine atmospheric
Science Unravelled). A suite of chemical,
physical, biological and meteorological techniques was applied, and
comprehensive measurements of bulk water, the sea surface microlayer (SML),
cloud water and ambient aerosol particles collected at a ground-based and a
mountain station took place. Key variables comprised the chemical characterization of the atmospherically
relevant OM components in the ocean and the atmosphere as well as
measurements of INPs and CCN. Moreover, bacterial cell counts, mercury
species and trace gases were analyzed. To interpret the results, the
measurements were accompanied by various auxiliary parameters such as air
mass back-trajectory analysis, vertical atmospheric profile analysis, cloud
observations and pigment measurements in seawater. Additional modeling
studies supported the experimental analysis. During the campaign, the CVAO exhibited marine air masses with low and
partly moderate dust influences. The marine boundary layer was well mixed as
indicated by an almost uniform particle number size distribution within the
boundary layer. Lipid biomarkers were present in the aerosol particles in
typical concentrations of marine background conditions. Accumulation- and
coarse-mode particles served as CCN and were efficiently transferred to the
cloud water. The ascent of ocean-derived compounds, such as sea salt and
sugar-like compounds, to the cloud level, as derived from chemical analysis
and atmospheric transfer modeling results, denotes an influence of marine
emissions on cloud formation. Organic nitrogen compounds (free amino acids)
were enriched by several orders of magnitude in submicron aerosol particles
and in cloud water compared to seawater. However, INP measurements also indicated
a significant contribution of other non-marine sources to the local INP
concentration, as (biologically active) INPs were mainly present in
supermicron aerosol particles that are not suggested to undergo strong
enrichment during ocean–atmosphere transfer. In addition, the number of CCN
at the supersaturation of 0.30 % was about 2.5 times higher during dust
periods compared to marine periods. Lipids, sugar-like compounds, UV-absorbing (UV: ultraviolet) humic-like substances and low-molecular-weight neutral components
were important organic compounds in the seawater, and highly surface-active
lipids were enriched within the SML. The selective enrichment of specific
organic compounds in the SML needs to be studied in further detail and
implemented in an OM source function for emission modeling to better
understand transfer patterns, the mechanisms of marine OM transformation in the
atmosphere and the role of additional sources. In summary, when looking at particulate mass, we see oceanic compounds
transferred to the atmospheric aerosol and to the cloud level, while from a
perspective of particle number concentrations, sea spray aerosol (i.e.,
primary marine aerosol) contributions to both CCN and INPs are rather
limited.
Marine aerosol particles are an important part of the natural aerosol systems
and might have a significant impact on the global climate and biological
cycle. It is widely accepted that truly pristine ...marine conditions are
difficult to find over the ocean. However, the influence of continental and
anthropogenic emissions on the marine boundary layer (MBL) aerosol is still
less understood and non-quantitative, causing uncertainties in the estimation
of the climate effect of marine aerosols. This study presents a detailed
chemical characterization of the MBL aerosol as well as the source
apportionment of the organic aerosol (OA) composition. The data set covers
the Atlantic Ocean from 53∘ N to 53∘ S, based on four
open-ocean cruises in 2011 and 2012. The aerosol particle composition was
measured with a high-resolution time-of-flight aerosol mass
spectrometer (HR-ToF-AMS), which indicated that sub-micrometer aerosol
particles over the Atlantic Ocean are mainly composed of sulfates (50 %
of the particle mass concentration), organics (21 %) and sea salt
(12 %). OA has been apportioned into five factors, including three
factors linked to marine sources and two with continental and/or
anthropogenic origins. The marine oxygenated OA (MOOA, 16 % of the total
OA mass) and marine nitrogen-containing OA (MNOA, 16 %) are identified as
marine secondary products with gaseous biogenic precursors dimethyl sulfide
(DMS) or amines. Marine hydrocarbon-like OA (MHOA, 19 %) was attributed
to the primary emissions from the Atlantic Ocean. The factor for the
anthropogenic oxygenated OA (Anth-OOA, 19 %) is related to continental
long-range transport. Represented by the combustion oxygenated OA (Comb-OOA),
aged combustion emissions from maritime traffic and wild fires in Africa
contributed, on average, a large fraction to the total OA mass (30 %).
This study provides the important finding that long-range transport was found
to contribute averagely 49 % of the submicron OA mass over the Atlantic
Ocean. This is almost equal to that from marine sources (51 %).
Furthermore, a detailed latitudinal distribution of OA source contributions
showed that DMS oxidation contributed markedly to the OA over the South
Atlantic during spring, while continental-related long-range transport
largely influenced the marine atmosphere near Europe and western and central
Africa (15∘ N to 15∘ S). In addition, supported by a solid
correlation between marine tracer methanesulfonic acid (MSA) and the
DMS-oxidation OA (MOOA, R2>0.85), this study suggests that
the DMS-related secondary organic aerosol (SOA) over the Atlantic Ocean could
be estimated by MSA and a scaling factor of 1.79, especially in spring.
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