Sea spray aerosol formation: Results on the role of different parameters and organic concentrations from bubble bursting experiments

Aerosolization of micro- and nanoplastics via sea spray: Investigating the role of polymer type, size, and concentration, and potential implications for human exposure

Micro- and nanoplastics (MNPs) can enter the atmosphere via sea spray aerosols (SSAs), but the effects of plastic characteristics on the aerosolization process are unclear. Furthermore, the importance of the transport of MNPs via these SSAs as a possible new exposure route for human health remains unknown. The aim of this study was two-fold: (1) to examine if a selection of factors affects aerosolization processes of MNPs, and (2) to estimate human exposure to MNPs via aerosols inhalation. A laboratory-based bubble bursting mechanism, simulating the aerosolization process at sea, was used to investigate the influence of MNP as well as seawater characteristics. To determine the potential human exposure to microplastics via inhalation of SSAs, the results of the laboratory experiments were extrapolated to the field based on sea surface microplastic concentrations and the volume of inhaled aerosols. Enrichment seemed to be influenced by MNP size, concentration and polymer type. With higher enrichment for smaller particles and denser polymers. Experiments with different concentrations showed a larger range of variability but nonetheless lower concentrations seemed to result in higher enrichment, presumably due to lower aggregation. In addition to the MNP characteristics, the type of seawater used seemed to influence the aerosolization process. Our human exposure estimate to microplastic via inhalation of sea spray aerosols shows that in comparison with reported inhaled concentrations in urban and indoor environments, this exposure route seems negligible for microplastics. Following the business-as-usual scenario on plastic production, the daily plastic inhalation in coastal areas in 2100 is estimated to increase but remain far below 1 particle per day. This study shows that aerosolization of MNPs is a new plastic transport pathway to be considered, but in terms of human exposure it seems negligible compared to other more important sources of MNPs, based on current reported environmental concentrations.

Glucose Enhances Salinity-Driven Sea Spray Aerosol Production in Eastern Arctic Waters

Sea spray aerosols (SSA) greatly affect the climate system by scattering solar radiation and acting as seeds for cloud droplet formation. The ecosystems in the Arctic Ocean are rapidly changing due to global warming, and the effects these changes have on the generation of SSA, and thereby clouds and fog formation in this region, are unknown. During the ship-based Arctic Century Expedition, we examined the dependency of forced SSA production on the biogeochemical characteristics of seawater using an on-board temperature-controlled aerosol generation chamber with a plunging jet system. Our results indicate that mainly seawater salinity and organic content influence the production and size distribution of SSA. However, we observed a 2-fold higher SSA production from waters with similar salinity collected north of 81°N compared to samples collected south of this latitude. This variability was not explained by phytoplankton and bacterial abundances or Chlorophyll-a concentration but by the presence of glucose in seawater. The synergic action of sea salt (essential component) and glucose or glucose-rich saccharides (enhancer) accounts for >80% of SSA predictability throughout the cruise. Our results suggest that besides wind speed and salinity, SSA production in Arctic waters is also affected by specific organics released by the microbiota.

Enhanced saccharide enrichment in sea spray aerosols by coupling surface-active fatty acids

The chemical composition of aerosols plays a significant role in aerosol-cloud interactions and, although saccharides make up their largest organic mass fraction, the current process model for understanding sea spray aerosol (SSA) composition struggles to replicate the enrichment of saccharides that has been observed. Here, we simulated the generation of SSA and quantified the enrichment of two soluble saccharides (glucose and trehalose) in SSA with a homemade sea spray aerosol generator. The results of the generation experiments demonstrated that both saccharides, especially trehalose, can promote the generation of SSA, whereas surface-active fatty acids primarily inhibit SSA production due to fewer bubble bursts caused by a large amount of foam accumulation. A significant decrease in surface tension of seawater with the addition of fatty acids was observed, while only a minor decrease was observed for seawater with the addition of only saccharide. Enrichment factors (EFs) of saccharides measured using high performance anion-exchange chromatography (HPAEC) with pulsed amperometric detection (PAD) revealed no enrichment of glucose in submicron SSA, while trehalose showed a slight enrichment. In the presence of surface-active fatty acids on the seawater surface, a significant increase in the enrichment of saccharides in SSA was observed, with glucose and trehalose showing EF of approximately 27-fold and 58-fold, respectively. Besides, this enrichment was accompanied by the accumulation of calcium and magnesium ions. The results presented here suggest that the coupling interaction mechanism of soluble saccharides and surface-active fatty acids on the ocean surface contributes to the enrichment of soluble saccharides in SSA.

High aerosol loading over the Bohai Sea: Long-term trend, potential sources, and impacts on surrounding cities

Air pollution over the oceans has received less attention compared to densely populated urban areas of continents. The Bohai Sea, a semi-enclosed sea in northern China, is surrounded by thirteen industrial cities that have experienced significant improvements in air quality over the past decade. However, the changes in air pollution over the Bohai Sea and its impacts on surrounding cities remain poorly understood. To address this, this study investigated the evolution of air pollution and its chemical composition in the Bohai Sea over four decades, utilizing satellite remote sensing data, reanalysis datasets, emissions inventories, and statistical modeling. Historically, the region has suffered from severe air pollution, resulting from a combination of continental emissions and marine inputs (e.g., sea salt, ports and maritime vessel activities). The aerosol optical depth (AOD) over the sea was higher than the mean levels observed in its surrounding coastal cities. Statistically, 45% of the air masses reaching the Bohai Sea are associated with natural sources (dust- and marine-rich), while the remainder carry anthropogenic pollutants from continental regions. With the exception of Cangzhou city, these coastal cities suffer from air pollutants originating from the Bohai Sea. Cities in the northern region of the sea, spanning from Tianjin to Yingkou, are particularly impacted. The majority of the surrounding cities are affected by a large proportion of anthropogenic aerosol types transported through air masses from the Bohai Sea, including those from biomass burning and industrial activities. These findings emphasize the considerable influence of human-induced sources in the Bohai Sea on neighboring urban areas. Furthermore, being a maritime region, natural sources like sea salt and dust from the sea may also exert a discernible impact on the neighboring environment.

Enrichment of short-chain organic acids transferred to submicron sea spray aerosols

Organic acids, considered to be a substantial component of the marine carbon cycle, can enter the atmosphere through sea spray aerosol (SSA) and further affect the climate. Despite their importance, the distribution and mixing state of organic acids in SSA over the marine boundary layer are poorly understood and therefore need more investigation. Here, we have used ion chromatography (IC) in anion mode to measure short-chain organic acids concentrations in SSA collected throughout a custom-made SSA simulation chamber. The enrichment behavior and morphology of monocarboxylic acids (MAs, C_1-8) and dicarboxylic acids (DAs) in submicron SSA were studied in seawater. We found that with MAs addition, the number concentration and mass concentration of SSA particles decreased gradually for C_5-8 MAs, whereas they weakly varied with DAs addition due to the fact that carboxyl groups at both ends of DAs increased the surface tension of seawater. Moreover, the target compounds in submicron SSA displayed a surface activity-dependent enrichment behavior, where seawater with stronger surface activity, such as that containing MAs with >5 carbons, was more enriched in SSA in comparison to seawater with weaker surface activity. MAs with chain length <5 carbons were slightly enriched in SSA, whereas the enrichment factor (EF) of C_5-8 MAs further increased with increasing chain length. These findings are of utmost importance in further understanding and quantifying the contribution of organic matter to SSA, which is crucial for assessing the atmosphere feedback of the marine carbon cycle. MAIN FINDING OF THE WORK: Surface tension of seawater is the key factor affecting the enrichment of short-chain organic acids in SSA.

Optimisation on the Performance of Bubble-Bursting Atomisation for Minimum Quantity Lubrication with Vegetable Oil Using Computational Fluid Dynamics Simulation

Sustainable and green machining technologies have become a welcomed topic in the manufacturing industries. One of the emerging sustainable technologies is minimum quantity lubrication (MQL). In this study, the optimisation and study of the bubble-bursting atomisation system applied to MQL machining is carried out through the computational fluid dynamics (CFD) simulation approach. Vegetable oil is selected as the cooling lubricant in this study. The performance of the bubble-bursting atomisation system is improved by alternating air inlet velocity and the gap distance between the inlets of bubble production. A velocity of 0.1 ms⁻¹ is suitable for the air at the inlets for the bubble production, whereas 10 ms⁻¹ is suitable for the velocity of the air at the inlet, where the droplets of vegetable oil are guided to the nozzle. Besides that, a 50 mm gap distance between the air inlets for the production of bubbles is able to avoid the occurrence of bubble coalescence. Under these conditions, optimal bubble sizes of 2–3 mm can be achieved, with a higher probability of nano-sized droplets being present in these ranges. Furthermore, a higher rate and smaller size of vegetable oil droplets escaping the atomisation chamber and reaching the machining zone will be generated. Thus, the performance of the MQL machining can be improved.

Molecular size of surfactants affects their degree of enrichment in the sea spray aerosol formation

Sea spray aerosol (SSA), the largest source of natural primary aerosol, plays an important role in atmospheric chemical processes and the earth radiation balance. Its formation process is controlled by many factors. In this study, ethylene glycol (EG) and polyethylene glycol (PEG) with three different molecular weights (200, 400, 600) were used to investigate the influence of molecular size on the properties of submicron SSA produced by plunging jet from an adjustable home-built SSA generator. Different parameters were tested to obtain the optimum experimental conditions. The addition of EG and PEG inhibited the production of SSA and increased the geometric mean diameter (GMD) between 10 and 35 nm. However, PEG with a molecular weight of 600 could promote the production of SSA at higher concentrations, which means that the molecular weight and concentration of the polymer would affect the production efficiency of SSA. Combining with the measurement of surface tension, we found no clear relationship between surface tension and the yield of SSA, due to the properties of the substances themselves. Transmission electron microscopy images show that the addition of EG and PEG could significantly change the structure of salt nuclei in SSA. PEG was significantly enriched in SSA (with enrichment factors within the range 92.9-133.4), and the enrichment was independent of the sampling time, while increasing with the increase of molecular weight. Our results highlight the influence of polymer molecular weight on the properties of SSA, and their importance to improve the accuracy of aerosol emission model parameters.

Mass and number concentration distribution of marine aerosol in the Western Pacific and the influence of continental transport

We quantify for the first time marine aerosol properties and their differences in the offshore and remote ocean in the mid-latitude South Asian waters, low-latitude South Asian waters, and equatorial waters of the Western Pacific Ocean, based on shipboard cruise observations conducted by the Western Pacific Ocean Scientific Observation Network in winter 2018, and further investigate the effects of long-range transport of continental aerosols on the marine environment. During the overall observation period, the average number concentration of particle matter which aerodynamic diameters<2.5 μm (PM_2.5N) was 35.1 ± 87.4 cm^-3 and the mass concentration (PM_2.5M) was 12.3 ± 9.1 μg/m³. The PM_2.5N and PM_2.5M during the continental air mass transport period were 7.2 and 1.3 times higher than those during the non-transport period (109.2 ± 169.3 cm^-3, 15.9 ± 14.9 μg/m³), respectively. Excluding transport period, the average PM_2.5N and PM_2.5M are reduced by 120% and 7%. Coarse mode particle number concentration (PM_2.5-10N) and mass concentration (PM_2.5-10M) are not significantly influenced by continental air masses (only a reduction of 7% and 2%). The variation of marine aerosol concentrations in different latitudes zones is greatly influenced by continental aerosol transport. The offshore PM_2.5M/PM_10M was 30%, 21%, and 22% in the mid-latitude sea of South Asia, a low-latitude sea of South Asia, and the equatorial sea, respectively. In comparison, in the remote ocean, the distribution ratio of PM_2.5M/PM_10M tended to be steady (22%-23%), and the background characteristics of marine aerosols were clearly represented. The aerosol concentration decreases with the increase of wind speed during the transport period, and the wind speed reflects the scavenging effect on aerosol. In the non-transport period, the wind speed at the sea surface promotes the generation of marine aerosols, and the impact in wind speed is strongest in the PM_2.5-PM₅ particle size range.

Non-ignorable contribution of anthropogenic source to aerosols in Arctic Ocean

Arctic Ocean (AO) atmospheric aerosols, which are a factor influencing regional and global climate, have been greatly influenced by an increase in anthropogenic sources. To identify the impact of anthropogenic sources on regional aerosols in the AO and middle and low latitudes (MLO), a single-particle aerosol mass spectrometer was used to count and size aerosols with diameters less than 2.5 μm (PM_2.5) and determine their chemical composition. The mean hourly count of PM_2.5 aerosols was 1639/h in the AO, which was 57.1% lower than that in the MLO. Na_MSA, sulfate, and Na_rich were three major components, which accounted for 74.3% of PM_2.5 aerosols in the AO. The size distribution of PM_2.5 aerosols was unimodal, peaking between 0.42 μm and 1.64 μm. A source apportionment method for single aerosol particles in the Arctic was established using positive matrix factorization (PMF) combined with backward air mass trajectory and principal component analysis (PCA). Three potential sources of aerosols were identified: marine sources; anthropogenic sources; and secondary formation. The largest contribution to aerosols in the AO was from marine sources, accounting for 50.6%. This source was 20.4% higher in the AO than that in the MLO. Secondary formation contributed 19.8% and 36.5% to aerosols in the AO and MLO, respectively. However, the contribution of anthropogenic sources to aerosols was 29.6% in the AO, and this was 3.7% lower than that in the MLO. Our study provides a useful method for identifying sources of aerosols in the Arctic, and the results showed that although marine sources were the largest contributors to aerosols in the AO, the contribution of anthropogenic sources could not be ignored.

The bioaerosols emitted from toilet and wastewater treatment plant: a literature review

The aerosols harboring microorganisms and viruses released from the wastewater system into the air have greatly threatened the health and safety of human beings. The wastewater systems, including toilet and wastewater treatment plant (WWTP), are the major locations of epidemic infections due to the extensive sources of aerosols, as well as multifarious germs and microorganisms. Viruses and microorganisms may transport from both toilet and hospital into municipal pipes and subsequently into WWTP, which accounts for the main source of bioaerosols dispersed in the air of the wastewater system. This review aims to elaborate the generation, transmission, and diffusion processes of bioaerosols at toilet and WWTP. Moreover, the main factors affecting bioaerosol transmission and the corresponding prevention strategies for the airborne and inhaled bioaerosols are also discussed. Collectively, this review highlights the importance of managing bioaerosol occurrence in the wastewater system, which has aroused increasing concern from the public.