Characterization of submicron aerosols over the Yellow Sea measured onboard the Gisang 1 research vessel in the spring of 2018 and 2019
Minsu ParkSeong Soo YumNajin KimM. JeongHee-Jung YooJeong Eun KimJoonhyoung ParkMeehye LeeMinyoung SungJoonyoung Ahn
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Cloud condensation nuclei
Supersaturation
Sea spray
Research vessel
Sea salt aerosol
Asian Dust
The influence of aerosol particles on the Earth's climate is a major driver of scientific uncertainty in assessing future conditions. The importance of aerosols in their role as cloud condensation nuclei (CCN) and ice nuclei (IN), known as the Aerosol Indirect Effect, is most poorly understood. The number concentration of CCN available to nucleate droplets can have important influences on cloud albedo, lifetime, and propensity to form precipitation. Natural sources are of particular importance, since the absolute influence of aerosols on cloud properties is highly sensitive to background concentrations of CCN before anthropogenic emissions. Chemical studies of sea spray aerosol (SSA) particles, the second most abundant type of natural aerosol globally, were conducted to better understand the influence of marine organic matter on CCN activity. While direct chemical measurements of aerosol particles with diameter (d) > 500 nm indicated that the production mechanism of SSA controls particle composition, especially with respect to the amount of organic matter transferred across the air-sea interface. CCN activity studies, on the other hand, showed a weak dependence on seawater organic matter concentration. The extent to which organic matter and sea salt were externally mixed for particles with d < 100 nm more strongly affected CCN activity than the overall volume fraction of organic matter in the population. Secondary aerosol formation, which was observed to be associated specifically with phytoplankton senescence in laboratory experiments, could be an additional means of influencing marine clouds. Secondary aerosol were less CCN-active than SSA particles, but growth of secondary particles led to their contribution to CCN concentrations, and could potentially affect the formation of marine stratus clouds. Orographic clouds also form in pristine marine air masses over the Sierra Nevada Mountains. Below the marine clouds, highly CCN-active aerosols were redistributed by a barrier jet during winter storms and could influence rainfall in some regions of California. Overall, these studies show that chemistry is closely linked to climate through cloud droplet nucleation, and that studies of fundamental chemistry stemming from the complex systems described in this work could yield marked advances in scientific understanding of the indirect effect
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Atmospheric aerosols in clean remote oceanic regions contribute significantly to the global albedo through the formation of haze and cloud layers; however, the relative importance of 'primary' wind-produced sea-spray over secondary (gas-to-particle conversion) sulphate in forming marine clouds remains unclear. Here we report on marine aerosols (PM1) over the Southern Ocean around Antarctica, in terms of their physical, chemical, and cloud droplet activation properties. Two predominant pristine air masses and aerosol populations were encountered: modified continental Antarctic (cAA) comprising predominantly sulphate with minimal sea-salt contribution and maritime Polar (mP) comprising sulphate plus sea-salt. We estimate that in cAA air, 75% of the CCN are activated into cloud droplets while in mP air, 37% are activated into droplets, for corresponding peak supersaturation ranges of 0.37-0.45% and 0.19-0.31%, respectively. When realistic marine boundary layer cloud supersaturations are considered (e.g. ~0.2-0.3%), sea-salt CCN contributed 2-13% of the activated nuclei in the cAA air and 8-51% for the marine air for surface-level wind speed < 16 m s-1. At higher wind speeds, primary marine aerosol can even contribute up to 100% of the activated CCN, for corresponding peak supersaturations as high as 0.32%.
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Abstract. This work estimates the primary marine organic aerosol global emission source and its impact on cloud condensation nuclei (CCN) concentrations by implementing an organic sea spray source function into a series of global aerosol simulations. The source function assumes that a fraction of the sea spray emissions, depending on the local chlorophyll concentration, is organic matter in place of sea salt. Effect on CCN concentrations (at 0.2% supersaturation) is modeled using the Two-Moment Aerosol Sectional (TOMAS) microphysics algorithm coupled to the GISS II-prime general circulation model. The presence of organics affects CCN activity in competing ways: by reducing the amount of solute available in the particle and decreasing surface tension of CCN. To model surfactant effects, surface tension depression data from seawater samples taken near the Georgia coast were applied as a function of carbon concentrations. A global marine organic aerosol emission rate of 17.7 Tg C yr−1 is estimated from the simulations. Marine organics exert a localized influence on CCN(0.2%) concentrations, decreasing regional concentrations by no more than 5% and by less than 0.5% over most of the globe, assuming direct replacement of sea salt aerosol with organic aerosol. The decrease in CCN concentrations results from the fact that the decrease in particle solute concentration outweighs the organic surfactant effects. The low sensitivity of CCN(0.2%) to the marine organic emissions is likely due to the small compositional changes: the mass fraction of OA in accumulation mode aerosol increases by only ~15% in a biologically active region of the Southern Ocean. To test the sensitivity to uncertainty in the sea spray emissions process, we relax the assumption that sea spray aerosol number and mass remain fixed and instead can add to sea spray emissions rather than replace existing sea salt. In these simulations, we find that marine organic aerosol can increase CCN by up to 50% in the Southern Ocean and 3.7% globally during the austral summer. This vast difference in CCN impact highlights the need for further observational exploration of the sea spray aerosol emission process as well as evaluation and development of model parameterizations.
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Abstract The effect of sub‐cloud aerosol on cloud droplet concentration was explored over the north Atlantic and east Pacific under a variety of low and high wind speed conditions. A relationship of the form of D = 197{1 ‐ exp(‐6.13 × 10 3 * A )} was found to fit best the relationship between cloud droplet concentration ( D ; cm ‐3 ) and sub‐cloud aerosol concentration ( A ; cm ‐3 ) under low to moderate wind conditions. A few noticeable deviations from this relationship were observed which occurred under moderate to high wind speed condition. Under these high wind conditions, sea‐salt aerosol provided the primary source of cloud nuclei due to their higher nucleation activity and larger sizes, even under sulphate‐rich conditions. Simple model simulations reveal that the activation of sea‐salt nuclei suppresses the peak supersaturation reached in cloud, and thus inhibits the activation of smaller sulphate nuclei into cloud droplets. A multi‐component aerosol‐droplet parametrization for use in general circulation models is developed to allow prediction of cloud droplet concentration as a function of sea‐salt and non‐sea‐salt‐(nss) sulphate nuclei. The effects of enhancing an existing nss‐sulphate cloud condensation nuclei (CCN) population with sea‐salt nuclei are to reduce the number of cloud droplets activated under high (polluted) sulphate conditions and to increase the cloud droplet concentration under low (clean) sulphate conditions. The presence of sea‐salt CCN reduces the influence of nss‐sulphate CCN on cloud droplet concentrations, and thus is likely to reduce the predicted effect of nss‐sulphate indirect radiative forcing.
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Sea spray aerosols (SSA) represent one of the largest sources of atmospheric particles since over two-thirds of the Earth’s surface is covered by oceans. They play an important role in climate and atmospheric chemistry, however, despite this a series of knowledge gaps hinder us from constraining their relevance. One critical question is why the physicochemical properties of nascent particles generated in the laboratory are so different from those measured in the ambient marine atmosphere. For example, a series of studies have highlighted that SSA generated in the laboratory exhibit essentially the same ability to act as cloud condensation nuclei as inorganic sea salt, regardless of the amounts of organic substances present in the seawater from which they were generated (e.g., Collins et al., 2016). This is in stark contrast to observations of ambient marine aerosols - their ability to act as cloud condensation nuclei is often significantly reduced in comparison (Swietlicki et al., 2000).To address this discrepancy, we prepared a novel experimental setup in which we deployed a chemical ionisation mass spectrometer (CIMS) with an Aim inlet in a setup together with a sea spray simulation chamber, an oxidative flow reactor (OFR), and a differential mobility particle sizer (DMPS) at Graciosa Island, Azores, in the eastern north Atlantic Ocean during summer 2022 as a part of the AGENA campaign.We used freshly-sampled ocean water to generate SSA that were aged in an OFR for an equivalent period of 3 to 3.5 days in the atmosphere. We recorded the gas-phase chemical composition of nascent and aged aerosols using the AIM-CIMS with multiple reagent ions, collected filter samples for offline analysis of the particle-phase chemical composition, and used a DMPS to compare the particle size distribution and concentration.The first results of our study show that the volatile organic compounds released from the sampled ocean water considerably nucleate when they are oxidized in the OFR. Furthermore, the chemical analysis of these gases reveals an increase in the concentration of DMS oxidation products, such as methane sulfonic acid, when the nascent SSAs along with the gases in the tank headspace are exposed to oxidants in the OFR. However, we did not observe any substantial differences in the concentration and size distribution of the accumulation and larger-mode particles for primary and aged SSA. This could be attributed to extensive nucleation taking place in the OFR. It is possible that in the real world, these VOCs would rather condense on the primary SSA than form new particles.In this presentation we will compare the properties of ambient SSA particles in the Eastern North Atlantic and those generated and aged with our experimental setup using real seawater in an attempt to address the discrepancy.Collins, D. B., et al., Geophys. Res. Lett. 2016, 43 (18), 9975-9983.Swietlicki, E., et al., Tellus B: Chemical and Physical Meteorology 2000, 52 (2), 201-227
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Abstract. This work quantifies the primary marine organic aerosol global emission source and its impact on cloud condensation nuclei (CCN) concentrations by implementing an organic sea spray source function into a series of global aerosol simulations. The source function assumes that a fraction of the sea spray emissions, depending on the local chlorophyll concentration, is organic matter in place of NaCl. Effect on CCN concentrations (at 0.2% supersaturation) is modeled using the Two-Moment Aerosol Sectional (TOMAS) microphysics algorithm coupled to the GISS II-prime general circulation model. The presence of organics affects CCN activity in competing ways: by reducing the amount of solute available in the particle and decreasing surface tension of CCN. To model surfactant effects, surface tension depression data from seawater samples taken near the Georgia coast were applied as a function of carbon concentrations. A global marine organic aerosol emission rate of 17.7 Tg C yr−1 is estimated from the simulations. Marine organics exert a localized influence on CCN(0.2%) concentrations, decreasing regional concentrations by no more than 5% and by less than 0.5% over most of the globe. The decrease in CCN concentrations results from the fact that the decrease in particle solute concentration outweighs the organic surfactant effects. The low sensitivity of CCN(0.2%) to the marine organic emissions is likely due to the small compositional changes: the mass fraction of OA in accumulation mode aerosol increases by only 15% in a biologically active region of the Southern Ocean.
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