Diel cycle of sea spray aerosol concentration

Sea spray aerosol (SSA) formation have a major role in the climate system, but measurements at a global-scale of this micro-scale process are highly challenging. We measured high-resolution temporal patterns of SSA number concentration over the Atlantic Ocean, Caribbean Sea, and the Pacific Ocean covering over 42,000 km. We discovered a ubiquitous 24-hour rhythm to the SSA number concentration, with concentrations increasing after sunrise, remaining higher during the day, and returning to predawn values after sunset. The presence of dominating continental aerosol transport can mask the SSA cycle. We did not find significant links between the diel cycle of SSA number concentration and diel variations of surface winds, atmospheric physical properties, radiation, pollution, nor oceanic physical properties. However, the daily mean sea surface temperature positively correlated with the magnitude of the day-to-nighttime increase in SSA concentration. Parallel diel patterns in particle sizes were also detected in near-surface waters attributed to variations in the size of particles smaller than ~1 µm. These variations may point to microbial day-to-night modulation of bubble-bursting dynamics as a possible cause of the SSA cycle.


nature research | reporting summary
April 2020 Field-specific reporting Please select the one below that is the best fit for your research. If you are not sure, read the appropriate sections before making your selection. Did the study involve field work?

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Measurements of marine aerosol size distributions across the Atlantic Ocean, the Caribbean Sea, and the Pacific Ocean, along side meteorological data, surface ocean physical properties and approximate size of marine particles.
The atmospheric marine boundary layer and the ocean surface We took the raw counts (per minute) measured by the particle counter. The raw counts can be assumed to follow a Poisson distribution, therefore their standard deviation, "=#!, where µ is the mean. We sampled for 282 days, and therfore had over 1,000,000 sample points. The sample points were devided then into 24hr periods. We belive this amount of data is sufficient to draw conclusions as normally sea expeditions last about 30 days or less.
For the aerosol filters we sampled for periods of about 12 hours with a flow of 30 lpm. We decided to sample for 12 hour periods to try to differenciate between night and day. The AC-S data recorded data every minute. The instrument was turned off if the algae conceantrtion was too high (e.g., near Japan).
Data was collected with an optical particle counter (OPC; EDM-180 GRIMM Aerosol Technik Ainring GmbH & Co. KG, Ainring, Germany), for continuous aerosol size distribution measurements (from 0.25 -32 µm, sorted into 31 bins), and a custom-made aerosol filter system consisting of four 47mm filter holders and one vacuum pump (Diaphragm pump ME 16 NT, VACUUBRAND BmbH & Co KG, Wertheim, Germany) were installed aboard R/V Tara. Two separate inlets, located next to each other, were constructed out of conductive tubing of 1.9 cm inner diameter and a funnel (allowing the collection of all diameters) and mounted on the rear backstay of Tara. For the Atlantic Ocean measurements, from Lorient, France to Miami, U.S.A., the inlet was installed half way up the backstay (~15m asl) and after Miami, the inlet was relocated to the top of the backstay (~27m asl).The instruments were installed in the sail boat and left running independently, with researchers and crew members checking them continuously. The collected filters were changed every 12 hours by J. Michel Flores. The meteorological data was collected with the weather station on board Tara and operated by Meteo France (Station Bathos II, Météo France). For the water measurements, the inline system consisted of a Sea-Bird Electronics SBE45 MicroTSG for measurements of sea surface temperature (SST) and salinity and an AC-S spectrophotometer (WET Labs, Inc.) measuring hyperspectral particulate absorption (ap) and particulate attenuation (cp) with a~4 nm resolution, and an ECO-BB3 (WetLabs Inc.) set in a BB-box of~4.5 L measuring particulate backscattering at three wavelength (470 nm, 532 nm and 650 nm), altogether mounted in an autonomous setup.
Pictures of the ocean-atmosphere state were taken with a GoPro camera installed at portside; the GoPro took one picutre every minute. Long rains periods were anotated in the log sheet with permanent markers.
The expedition began on 28 May 2016 from Lorient, France, and finished the first year of the campaign on June 17, 2017, in Whangarei, New Zealand. The expedition was design to sample coral reefs, the island stop overs were design for the coral reef research. The aerosol instrumentation ran, for the most part, continuously regardless of the stop over.
The data was checked for pollution periods, all periods recognized as pollution (e.g., by engine exhaust), were excluded from the analysis.
Given it is filed data, in order for another group to be able to reproduce our findings, we clearly marked the route and dates of the expedition and the instrumentation as well. We calibrated the optical particle counter before the expedition and in the Island of Guam about 8 months into the expedition. We believe that with this information the measurements can be reproduced by any other research vessel.
Randomization of the optical particle counter data and the AC-S is not relevant for this study. We did continuous measurements in the marine boundary layer and the ocean surface where several scientist and crew members were involved to check the optical particle counter and the AC-S were running without errors. For the aerosol filters all scientist and crew members followedg a specific protocol to change the filters. The initial and final times (in UTC) of sampling were written in a log sheet and a and a random barcode was given to it. To analyze the aerosol filters in the SEM, we first identified the two week period to be analyzed, then the filters were analyzed by randomly taken a filter, which were labeled with different barcodes, after the analysis of the filters were done, they were assingned to the appropriate date written in the log sheets.
Not relevant, we performed continuous measurements of marine aerosols and the surface of the ocean. For the aerosol filter measurements, a protocol was written for any researcher on board or crew member to follow. This involved labeling the collected filter and a log sheet where initial and final times, in UTC, were written for each filter. Later, to analyze the filters the log sheets were used to find the relevant dates. We also did a handling blank every few days.