Abstract. 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.
Supplementary material to "Marine organic matter in the remote environment of the Cape Verde Islands – An introduction and overview to the MarParCloud campaign"
