Seawater Aerosol Research Articles

Long‐term atmospheric corrosion rates of Zn55Al‐coated steel

AbstractHot‐dip Zn55Al‐coated steel samples have been exposed for up to 6 years at 11 different weathering sites, including marine, marine‐industrial, acid‐rain and dry atmospheres. From the mass loss measurements, Zn55Al metallic coating showed globally long‐term good corrosion resistance in all weathering conditions compared with hot‐dip Zn‐0.2Al‐coated steel (Z). Yet, weaker performance was observed on Zn55Al in high SO2 polluted atmosphere, particularly when combined with seawater aerosols. This is explained by a more acidic surface condition linked to high SO2. Although the extent of corrosion in this phase was different at the different sites, the final corrosion products formed after 6 years were rather similar at all sites. This consists of hydrous aluminium sulphate or hydrous aluminium hydroxy sulphate and, probably also a smaller amount of sulphate‐containing zinc corrosion products or Al/Zn products.

The Effect of a Hot Humid Climate on Corrosion of Reinforced Concrete

The expansion of economic cooperation with countries located in areas with hot, humid climates and the construction of reinforced concrete buildings and structures in coastal zones of non–freezing seas poses the task of assessing the impact of climate on the corrosive state of reinforced concrete structures, primarily carbonation of concrete and seawater aerosol containing chlorides. The effect of low negative temperature is not considered in this work. The data on the carbonation of concrete under conditions of increased insolation and the action of sea salt aerosol are summarized, mainly using the example of the hot humid climate of Cuba for further development of research, and subsequently the development of standards for protection against corrosion and carbonation of concrete and steel reinforcement in areas with a tropical climate. Based on the results of a survey of the condition of reinforced concrete structures and structures manufactured and erected in Cuba, as well as the results of observations, the results of an analysis of aggressive environmental factors of the Republic of Cuba affecting the corrosion of reinforced concrete structures, the results of studies of concrete carbonation and the effects of sea salt aerosol are presented. When designing and building structures on the seashore by domestic organizations in countries with hot, humid climates, the aggressive effects of seawater aerosol and accelerated carbonation of concrete, which reduce the durability of reinforced concrete structures, should be taken into account.

Evaporative Cooling Does Not Prevent Vertical Dispersion of Effervescent Seawater Aerosol for Brightening Clouds.

Marine cloud brightening (MCB) is a potential intervention to mitigate the effects of climate change by increasing the reflectance of low-level maritime clouds, including those over the Great Barrier Reef. The technique involves dispersing a plume of submicrometer seawater droplets over the ocean, which evaporate, generating nanosized sea-salt aerosols (SSAs) that disperse through the atmosphere with some fraction incorporated into clouds. Droplet evaporation, which occurs in the immediate vicinity (meters to tens of meters) of the source, has been theorized to produce a negatively buoyant plume hindering the mixing of the sea-salt aerosol to cloud height and compromising the effectiveness of MCB. We characterized in situ for the first time the nearfield aerosol dispersion from a point source of atomized seawater produced using the effervescent technique. We observed consistent vertical mixing of the plume up to 150 ± 5 m height at 1 km downwind. The extent of vertical dispersion was influenced by wind velocity and atmospheric stability. We found no evidence that negative buoyancy due to the evaporation of the 0.068 kg/s water fraction significantly suppressed vertical mixing. Our results can be attributed to the small droplet sizes generated by the effervescent spray technology and associated low flow rates required to generate around 1014 droplets s-1. We estimate that, for a hypothetical implementation producing up to 1016 s-1 similarly sized SSAs, evaporative cooling is unlikely to significantly suppress the vertical dispersion of aerosol for MCB.

Time series of δ26Mg variability in precipitation of north‐west Germany

AbstractThis study presents δ26Mg values, Mg2+ concentrations, δ18O and δ2H values of monthly collected rain and snow samples between 2014 and 2017 from north‐west Germany. The δ26Mg values of snow are similar to those of rain. Unlike δ18O and δ2H, neither δ26Mgprecipitation values nor Mg2+ concentrations display a relationship with air temperature. In contrast, δ26Mgprecipitation values and Mg2+ concentrations are correlated with precipitation amount. As previously suggested by other studies but now based on a larger data set, it is proposed that the δ26Mg values and Mg2+ concentrations are affected by the mineralogical composition and amount of airborne dust. Consequently, a small number of random precipitation samples cannot represent the complex processes influencing the δ26Mgprecipitation values. δ26Mgprecipitation can be used to differentiate between seawater aerosols, carbonate and silicate dust. Silicate dust is typified by higher Mg concentrations and δ26Mg values compared to carbonate dust. Concerning carbonates, dolostone dust has higher Mg concentrations and δ26Mg values, while limestone dust is Mg‐lean with lower δ26Mg values. Dust of anthropogenic origin in the region can come from active limestone and dolostone quarries, surface mining of siliciclastics, and agriculture on silicate‐rich soils. Although dust of this mineralogy can also be of natural origin, most natural dust consists of airborne silicates transported by wind systems from the Sahara to Europe. Higher δ26Mgprecipitation values would indicate silicate or dolostone dust influx. Lower δ26Mgprecipitation values suggest lower dust concentrations and a predominantly calcitic dust mineralogy. It appears that δ26Mgprecipitation is most probably influenced by changes in weather conditions and natural and anthropogenic dust origin. This study implies that δ26Mgprecipitation is a potential proxy for dust mineralogy and fluxes. Nevertheless, further research should include the determination of atmospheric dust mineralogy and their fractions as well as air mass back trajectory analysis to identify the source(s) of dust.

Study of the corrosion resistance of aluminum alloy AMg6 and steel 12Kh18N10T in conditions of loading under the impact of environmental factors

Stress corrosion cracking is one of the most dangerous types of corrosion damage in metallic materials. We present the results of studying the impact of environmental factors on the susceptibility of AMg6 aluminum alloy and 12Kh18N10T stainless steel to stress corrosion cracking under four-point bending. Tests of loaded samples were carried out in laboratory and field conditions of the moderately warm climate of the coastal zone over a period of six months. The samples were examined daily with fixation of the time to their destruction and upon completion of the tests the appearance of the samples and the depth of intergranular corrosion on microsections were assessed. A 3D relief was constructed using macro photography of the surface with the determination of the depth of corrosion foci. We also carried out a comparative analysis of the frequency of stress-induced destruction of steel samples of various grades both in atmospheric and laboratory conditions. It is shown that in atmospheric conditions characterized by the presence of dust particles acting as concentrators for the formation of corrosion foci, the aggressiveness of the corrosive effect of the environment increases, whereas the general corrosion resistance of materials decreases. The most pronounced effect of the environment was recorded in AMg6 alloy samples when exposed under a ventilated canopy in conditions of periodic spraying of seawater aerosols. The depth of surface corrosion damage was up to 0.1 mm. When the test samples were exposed under other conditions (salt fog chamber and louvered storage) the corrosion damage was absent. The results obtained can be used to predict the corrosion resistance of the products made of AMG6 alloy and 12Kh18N10T steel when operated in conditions of loading under the impact of environmental factors.

Assessment of the water quality of groundwater in Bohai Rim and the controlling factors—a case study of northern Shandong Peninsula, north China

This study collected 184 groundwater (GW) samples from 92 wells during the dry and wet seasons, respectively to understand the hydrochemical characteristics, water quality, and risk of GW nitrate (NO3−) to human health in northern Shandong Peninsula (NSP), China. The results showed that GW in the NSP is weakly alkaline and classified as hard fresh water. The mean concentration of NO3− in GW exceeded 100 mg·L−1, total hardness exceeded 450 mg·L−1, and total dissolved solids (TDS) was less than 1000 mg·L−1. A Piper diagram showed that the water chemistry of GW in the NSP was mainly of the SO4·Cl-Ca·Mg type. A Gibbs diagram and ion ratio analysis indicated that the weathering of silicate rocks and agricultural production were the dominant factors affecting the hydrochemical characteristics of GW in the NSP, with cation exchange, dissolution of salt rock, and weathering of carbonate rock also making contributions. Na+ and Cl− in GW are significantly affected by seawater aerosols in coastal areas. During the wet season, the hydrodynamic conditions of the aquifer are improved, agricultural activities are strengthened, and GW becomes generally homogenized. The water quality index classified the GW quality of the NSP as mainly of medium quality. There was a relatively consistent spatial distribution of water quality during different periods. Water samples of poor water quality were mainly distributed in the lower reaches of the Huangshui River. In addition, total hardness and NO3− concentrations were the main variables affecting the quality of GW in the NSP. The assessment of the risk NO3− in GW in the NSP to human health through the ingestion of drinking water demonstrated a significant risk (infants > children > adults). These results indicate the need for local management measures to reduce the potential health risks of GW quality in the NSP.

Leading edge erosion of wind turbines: Effect of solid airborne particles and rain on operational wind farms

AbstractLeading edge erosion (LEE) affects almost all wind turbines, reducing their annual energy production and lifetime profitability. This study presents results of an investigation into 18 operational wind farms to assess the validity of the current literature consensus surrounding LEE. Much of the historical research focuses on rain erosion, implying that this is the predominant causal factor. However, this study showed that the impact of excessive airborne particles from seawater aerosols or from adverse local environments such as nearby quarries greatly increases the levels of LEE. Current testing of leading edge protection coatings or tapes is based on a rain erosion resistivity test, which does little to prove its ability to withstand solid particle erosion and may drive coating design in the wrong direction. Furthermore, it was shown that there is little correlation between test results and actual field performance. A method of monitoring the expected level of erosion on an operational wind turbine due to rain erosion is also presented. Finally, the energy losses associated with LEE on an operational wind farm are examined, with the average annual energy production dropping by 1.8% due to medium levels of erosion, with the worst affected turbine experiencing losses of 4.9%.

Boron toxicity in higher plants: an update.

In this review, emphasis is given to the most recent updates about morpho-anatomical, physiological, biochemical and molecular responses adopted by plants to cope with B excess. Boron (B) is a unique micronutrient for plants given that the range of B concentration from its essentiality to toxicity is extremely narrow, and also because it occurs as an uncharged molecule (boric acid) which can pass lipid bilayers without any degree of controls, as occurs for other ionic nutrients. Boron frequently exceeds the plant's requirement in arid and semiarid environments due to poor drainage, and in agricultural soils close to coastal areas due to the intrusion of B-rich seawater in fresh aquifer or because of dispersion of seawater aerosol. Global releases of elemental B through weathering, volcanic and geothermal processes are also relevant in enriching B concentration in some areas. Considerable progress has been made in understanding how plants react to B toxicity and relevant efforts have been made to investigate: (I) B uptake and in planta partitioning, (II) physiological, biochemical, and molecular changes induced by B excess, with particular emphasis to the effects on the photosynthetic process, the B-triggered oxidative stress and responses of the antioxidant apparatus to B toxicity, and finally (III) mechanisms of B tolerance. Recent findings addressing the effects of B toxicity are reviewed here, intending to clarify the effect of B excess and to propose new perspectives aimed at driving future researches on the topic.

Identification of ornamental shrubs tolerant to saline aerosol for coastal urban and peri-urban greening

Salt spray can be an important abiotic stress that strongly influences plant survival and species distribution. Much of the research conducted on salinity tolerance concerns saline soil or saline irrigation, but little research focuses on plant exposure to salt spray in the absence of saline irrigation conditions. The aim of this study was to investigate the effects of seawater aerosol on fifteen ornamental shrubs diffuse in the Mediterranean environment. Plants of the fifteen ornamental shrubs were subjected to twice a week nebulisation treatments with synthetic seawater solution for eight weeks. Among the 15 species studied, four were selected as models, one as a sensitive species (Viburnum tinus), two as intermediate species (Murraya paniculata and Polygala myrtifolia), and one as a tolerant species (Raphiolepis umbellata). The following morphological parameters were monitored: the fresh and dry weight of shoots and roots, leaf area, leaf number, leaf damage, specific leaf area (SLA), chlorophyll content and ion content. The relative water content (RWC), leaf gas exchange and chlorophyll a fluorescence were monitored during the entire experimental period. The species exposed to the seawater solution showed different physiological and morphological responses. The treatment led to a decrease of biomass, leaf area and number in M. paniculata. The gas exchanges were affected by the stress conditions, indicating the defence mechanism activated against the salt stress. The leaf damage increased with the exposure to the seawater aerosol and the greatest damage was found in V. tinus. In P. myrtifolia, a decrease in the chlorophyll a fluorescence was observed. The salt spray treatments enhanced the correlation between chlorophyll a fluorescence and WUE.

Effect of seawater aerosol on leaves of six plant species potentially useful for ornamental purposes in coastal areas

Aerosol marine strongly affects the growth and development of urban, garden and landscape plants. Few studies have focused on the effects of sodium chloride on plant growth, which is usually applied through irrigation water or substrate media. Even less information is available on the eco-physiological responses of plants to marine aerosol. The aim of this work was to evaluate the physiological responses of different plant species to seawater nebulisation treatments. Plant species that are commonly used along sea fronts were selected as being potentially useful for the study. Plants were bought from a local nursery and included: Acacia cultriformis, Callistemon citrinus, Carissa edulis microphylla, Gaura lindheimeri, Jasminum sambac, Westringia fruticosa. Plants were placed in a randomised block design in a greenhouse and treated for 5 s with seawater or irrigation water (control) using a nebulisation system once every day for 77 days. In the seawater aerosol-treated plants, the following parameters were monitored: leaf area damage using an image analysis tool, chlorophyll a fluorescence, hormonal changes and cation concentrations. We found that seawater aerosol treatment leads to: (i) leaf necrosis; (ii) chlorophyll loss; and (iii) a decrease in chlorophyll a fluorescence. The ion exclusion mechanism might have played a key role in the tolerance mechanism. Ethylene production increased in all species as a good biomarker and the strong increase in ABA content in the sensitive species may play a role in the plant's adaptation to stress. The chlorophyll a fluorescence parameters such as Fv/Fm and the performance index were the most affected by treatment and led to a screening sensitive ( A. cultriformis and G. lindheimeri) and tolerant ( W. fruticosa) species.

Heterogeneous loss of HO 2 by KCl, synthetic sea salt, and natural seawater aerosol particles

The HO 2 uptake to aerosol particles is potentially significant sink for the HO 2 radical in the marine atmosphere. To assess the heterogeneous loss of HO 2 on marine aerosol particles, we have investigated the uptake coefficients ( γ) of HO 2 for submicron aerosol particles of KCl, synthetic sea salt, and natural seawater under ambient conditions (760 Torr and 296 ± 2 K) using an aerosol flow tube (AFT) coupled with a chemical conversion/laser-induced fluorescence (CC/LIF) technique. γ values determined for dry and wet aerosols of KCl were 0.02 ± 0.01 and 0.07 ± 0.03 at 66% and 75% RH, respectively, while γ values for those doped with CuSO 4 was 0.55 ± 0.19 at 75% RH. γ values determined for synthetic sea-salt particles were 0.07 ± 0.03, 0.12 ± 0.04 and 0.13 ± 0.04 at 35%, 50%, 75% RH, respectively, while γ values for natural seawater particles were 0.10 ± 0.03, 0.11 ± 0.02 and 0.10 ± 0.03 at 35%, 50%, 75% RH, respectively. We recommend a HO 2 uptake coefficient in marine areas of 0.1 for modeling and estimated the contribution of heterogeneous loss of HO 2 by sea-salt aerosol particles in marine areas using a box model. Our box-model simulations suggested that daytime maximum HO 2 concentrations decreased to 87–94% of the values without heterogeneous loss.

The effect of varying levels of surfactant on the reactive uptake of N<sub>2</sub>O<sub>5</sub> to aqueous aerosol

Abstract. Recent observations have detected surface active organics in atmospheric aerosols. We have studied the reaction of N2O5 on aqueous natural seawater and NaCl aerosols as a function of sodium dodecyl sulfate (SDS) concentration to test the effect of varying levels of surfactant on gas-aerosol reaction rates. SDS was chosen as a proxy for naturally occurring long chain monocarboxylic acid molecules, such as palmitic or stearic acid, because of its solubility in water and well-characterized surface properties. Experiments were performed using a newly constructed aerosol flow tube coupled to a chemical ionization mass spectrometer for monitoring the gas phase, and a differential mobility analyzer/condensation particle counter for determining aerosol surface area. We find that the presence of ~3.5wt% SDS in the aerosol, which corresponds to a monolayer surface coverage of ~2×1014 molecules cm-2, suppresses the N2O5 reaction probability, γN2O5, by approximately a factor of ten, independent of relative humidity. Consistent with this observation is a similar reduction in the rate of ClNO2 product generation measured simultaneously. However, the product yield remains nearly constant under all conditions. The degree of suppression is strongly dependent on SDS content in the aerosol, with no discernable effect at 0.1wt% SDS, but significant suppression at what we predict to be submonolayer coverages with 0.3–0.6wt% SDS on NaCl and natural seawater aerosols, respectively.

Computational assessment of a proposed technique for global warming mitigation via albedo-enhancement of marine stratocumulus clouds

A simplified version of the model of marine stratocumulus clouds developed by Bower, Jones and Choularton [Bower, K.N., Jones, A., and Choularton, T.W., 1999. A modeling study of aerosol processing by stratocumulus clouds and its impact on GCM parameterisations of cloud and aerosol. Atmospheric Research, Vol. 50, Nos. 3–4, The Great Dun Fell Experiment, 1995-special issue, 317–344.] was used to examine the sensitivity of the albedo-enhancement global warming mitigation scheme proposed by Latham [Latham, J., 1990. Control of global warming? Nature 347, 339–340; Latham, J., 2002. Amelioration of global warming by controlled enhancement of the albedo and longevity of low-level maritime clouds. Atmos. Sci. Letters (doi:10.1006/Asle.2002.0048).] to the cloud and environmental aerosol characteristics, as well as those of the seawater aerosol of salt-mass m s and number concentration Δ N, which–under the scheme–are advertently introduced into the clouds. Values of albedo-change Δ A and droplet number concentration N d were calculated for a wide range of values of m s, Δ N, updraught speed W, cloud thickness Δ Z and cloud-base temperature T B: for three measured aerosol spectra, corresponding to ambient air of negligible, moderate and high levels of pollution. Our choices of parameter value ranges were determined by the extent of their applicability to the mitigation scheme, whose current formulation is still somewhat preliminary, thus rendering unwarranted in this study the utilisation of refinements incorporated into other stratocumulus models. In agreement with earlier studies: (1) Δ A was found to be very sensitive to Δ N and (within certain constraints) insensitive to changes in m s, W, Δ Z and T B; (2) Δ A was greatest for clouds formed in pure air and least for highly polluted air. In many situations considered to be within the ambit of the mitigation scheme, the calculated Δ A values exceeded those estimated by earlier workers as being necessary to produce a cooling sufficient to compensate, globally, for the warming resulting from a doubling of the atmospheric carbon dioxide concentration. Our calculations provide quantitative support for the physical viability of the mitigation scheme and offer new insights into its technological requirements.

The influence of weathering process on riverine osmium isotopes in a basaltic terrain

This study presents Os isotope and comprehensive major and trace element data for the dissolved load, suspended particulates and bedload for Icelandic rivers, draining predominantly basaltic catchments that range in age from historic to ca. 12 Ma. Hydrothermal waters and precipitation have also been analysed. Both Os and Re concentrations are greater in the suspended load than the bedload, while Re / Os ratios are lower, suggesting that both elements are concentrated in weathering resistant minerals. Despite this elemental fractionation the suspended particulates and bedload for each river yield indistinguishable 187Os / 188Os isotope compositions that range from 0.136 to 0.292. In contrast, the dissolved load (< 0.2 μm filtered) often possesses a significantly more radiogenic Os isotope composition than the corresponding suspended or bed load with 187Os / 188Os ratios ranging from 0.15 to 1.04. The isotope and elemental data for the dissolved load can be explained in terms of an unradiogenic contribution from congruent basalt weathering (and/or hydrothermal input) and a radiogenic contribution that arises from two distinct processes. For the glacier-fed rivers there is a covariation between 187Os / 188Os and the extent of glacial cover in the catchment, and this is most readily explained by the entrainment of seawater aerosols into precipitation and subsequent glacial melting. While for direct-runoff (and spring-fed rivers) there is a covariation between 187Os/ 188Os and the age of the bedrock in the catchment, that cannot be explained by congruent weathering of old basalt. Calculations indicate that those direct-runoff rivers with radiogenic 187Os/ 188Os values are also undersaturated with respect to the primary basalt minerals olivine, pyroxene and plagioclase, indicating that these phases are unstable and prone to preferential dissolution. Published Re–Os isotope data indicate that the same phases possess exceptionally high 187Re / 188Os ratios and thus evolve to radiogenic 187Os/ 188Os compositions in very short time intervals. Taken together, these results indicate that incongruent (preferential) weathering of certain primary basalt minerals can impart a radiogenic Os isotope composition to the dissolved riverine load. Nevertheless, overall the Os isotope signal to the Oceans from Icelandic rivers is little affected because rivers with unradiogenic 187Os/ 188Os values and a high discharge dominate the Os flux.

Boron isotopic composition of atmospheric precipitations and liquid–vapour fractionations

Boron isotope compositions (δ 11B) and B concentrations of rains and snows were studied in order to characterize the sources and fractionation processes during the boron atmospheric cycle. The 11B/ 10B ratios of instantaneous and cumulative rains and snows from coastal and continental sites show a large range of variations, from −1.5 ± 0.4 to +26.0 ± 0.5‰ and from −10.2 ± 0.5 to +34.4 ± 0.2‰, respectively. Boron concentrations in rains and snows vary between 0.1 and 3.0 ppb. All these precipitation samples are enriched in 10B compared to the ocean value (δ 11B = +39.5‰). An empirical rain-vapour isotopic fractionation of +31‰ is estimated from three largely independent methods. The deduced seawater–vapour fractionation is +25.5‰, with the difference between the rain and seawater fractionations principally reflecting changes in the speciation of boron in the liquid with ∼100% B(OH) 3 present in precipitations. A boron meteoric water line, δD = 2.6δ 11B − 133, is proposed which describes the relationship between δD and δ 11B in many, but not all, precipitations. Boron isotopic compositions of precipitations can be related to that of the seawater reservoir by the seawater–vapour fractionation and one or more of (1) the rain-vapour isotopic fractionation, (2) evolution of the δ 11B value of the atmospheric vapour reservoir via condensation–precipitation processes (Rayleigh distillation process), (3) any contribution of vapour from the evaporation of seawater aerosols, and (4) any contribution from particulate matter, principally sea salt, continental dust and, perhaps more regionally, anthropogenic sources (burning of biomass and fossil fuels). From the δ 11B values of continental precipitations, a sea salt contribution cannot be more than a percent or so of the total B in precipitation over these areas.

Magnesium Sulfate Aerosols Studied by FTIR Spectroscopy: Hygroscopic Properties, Supersaturated Structures, and Implications for Seawater Aerosols

Supersaturated MgSO4 aerosols and dilute MgSO4 solutions were studied by FTIR spectroscopic techniques (i.e., aerosol flow tube (AFT) and attenuated total reflection (ATR)). The hygroscopic properties of MgSO4 aerosols were investigated with results in good agreement with previous measurements by a scanning electrodynamic balance (SEDB). Well-defined spectral evolutions with changing relative humidity (RH) for the v3 band of SO4(2-) and the water O-H stretching envelope could be directly related to the observed hygroscopic properties of MgSO4 aerosols. When the RH decreased from approximately 55 to approximately 40%, the v1 band of SO4(2-) in supersaturated MgSO4 aerosols was observed to transform from a sharp peak at approximately 983 cm(-1) into a wide band at approximately 1005 cm(-1). The sharp peak at approximately 983 cm(-1) was mainly assigned to such associated complexes of Mg2+ and SO4(2-) as double solvent-separated ion pairs (2SIPs), solvent-shared ion pairs (SIPs), and simple contact ion pairs (CIPs) in supersaturated MgSO4 aerosols, while the wide band at approximately 1005 cm(-1) was due to polymeric CIPs chains, probably the main component of gels formed in MgSO4 aerosols at low RHs. Relating to this v1 band transformation, the peak position of the v(3) band was first shown to be a sensitive indicator of CIPs formation, spanning across approximately 40 cm(-1) on the formation of polymeric CIPs chains, which could also be supported by aerosol composition analysis in the form of water-to-solute molar ratios (WSR). In the water O-H stretching envelope, the absorbance intensities at 3371 and 3251 cm(-1) were selected to represent contributions from weak and strong hydrogen bonds, respectively. The absorbance intensity ratio changing with RH of 3371 to 3251 cm(-1) could be related to the previous observations with the v1 and v3 bands of SO4(2-). As a result, the formation of CIPs with various structures in large amounts was supposed to significantly weaken hydrogen bonds in supersaturated MgSO4 aerosols, while 2SIPs and SIPs were not expected to have similar effects even when occurring in abundance. In comparison with MgSO4 aerosols, the peak positions of the v3 band of SO4(2-) in artificial seawater aerosols implied that the MgSO4 component should be contained as gels or concentrated solutions in the fissures of microcrystals of sea salts for freshly formed seawater aerosols at low RHs.

N2O5 Reaction on Submicron Sea Salt Aerosol: Kinetics, Products, and the Effect of Surface Active Organics

The reaction of N(2)O(5) on sea salt aerosol is a sink for atmospheric nitrogen oxides and a source of the Cl radical. We present room-temperature measurements of the N(2)O(5) loss rate on submicron artificial seawater (ASW) aerosol, performed with an entrained aerosol flow tube coupled to a chemical ionization mass spectrometer, as a function of aerosol phase (aqueous or partially crystalline), liquid water content, and size. We also present an analysis of the product growth kinetics showing that ClNO(2) is produced at a rate equal to N(2)O(5) loss, with an estimated lower limit yield of 50% at 50% relative humidity (RH). The reaction probability for N(2)O(5), gamma(N(2)(O)(5)), depends strongly on the particle phase, being 0.005 +/- 0.004 on partially crystalline ASW aerosol at 30% RH and 0.03 +/- 0.008 on aqueous ASW aerosol at 65% RH. At 50% RH, N(2)O(5) loss is relatively insensitive to particle size for radii greater than 100 nm, and gamma(N(2)(O)(5)) displays a statistically insignificant increase from 0.022 to approximately 0.03 for aqueous ASW aerosol over the RH range of 43-70%. We find that the presence of millimolar levels of hexanoic acid in the aerosol bulk decreases the gamma(N(2)(O)(5)) at 70% RH by a factor of 3-4 from approximately 0.025 to 0.008 +/- 0.004. This reduction is likely due to the partitioning of hexanoic acid to the gas-aerosol interface at a surface coverage that we estimate to be equivalent to a monolayer. This result is the first evidence that a monolayer coating of aqueous organic surfactant can slow the reactive uptake of atmospheric trace gases to aerosol.

Infrared spectroscopy of model tropospheric aerosols as a function of relative humidity: Observation of deliquescence and crystallization

The infrared extinction spectra of model tropospheric aerosols, (NH4)2SO4, NH4HSO4, NaCl, and artificial seawater, have been measured as a function of relative humidity. Experimentally, submicron‐sized aerosol particles are spectroscopically monitored as they flow at atmospheric pressure on a 30‐s timescale through a room temperature infrared absorption cell. By monitoring absorption features due to either constituent ions or water molecules, we infer both the physical phase and, to some degree, the chemical composition of the aerosol particles. It is observed that (1) solid (NH4) SO4 and NaCl aerosol particles exhibit deliquescence at 79±1% and 75±1% relative humidity, respectively, very close to their thermodynamic values; (2) (NH4)2SO4 and NaCl liquid particles exhibit crystallization at relative humidities of 33±2% and 43±2%, respectively, well below their deliquescence points; (3) NH4HSO4 aqueous aerosol particles remain in the liquid state to relative humidities as low as 2%, far below the thermodynamic deliquescence humidity of 39%; and (4) artificial seawater aerosol particles show strong H2O absorption features at low relative humidities, arising either because the particle has not crystallized or because solid hydrates of Mg2+ salts have formed. These observations illustrate the extent to which water will be present in the aerosol condensed phase in both laboratory experiments and in the atmosphere. Specifically, for (NH4)2SO4 and NaCl particles, the water content is expected to be low at relative humidities below the crystallization point, whereas the aerosol particles will be liquid at higher relative humidities. NH4HSO4 and artificial seawater aerosols will both contain significant quantities of water down to very low relative humidities, present either as a liquid or possibly as hydrates of Mg2+ in the case of artificial seawater. By adding gas‐phase D2O to NH4HSO4 and artificial seawater aerosols at low relative humidity, condensed phase D2O features appear in the spectra, indicating facile exchange of water between the gas‐phase and the particles. Conversely, aerosols with low water content, such as solid NaCl, do not exhibit condensed‐phase D2O features in the presence of gas‐phase D2O.

Influences on Concentration Measurements of Liquid Aerosols by Laser-Induced Breakdown Spectroscopy

Results are presented for laser-induced breakdown spectroscopy (LIBS) as a method for measuring salt concentrations in seawater aerosol droplets. An excimer laser, operating at high pulse energy with KrF gas (λ = 248 nm) produces laser-induced breakdown plasmas in an aerosol spray. Emission lines of Na and H are monitored with an optical multichannel analyzer to characterize the plasma spatially and temporally. Studies of temporally resolved atomic line emissions from the plasma determine the optimum time for gating of the detector to be 2–4 μs after the excimer laser pulse arrives in the probe volume. Spatially resolved measurements of atomic emission line intensities are studied by positioning a stream of monodisperse droplets at various locations relative to the measurement probe volume. The electron temperature of the plasma is estimated to be 12,600 ± 4600 K, averaged over 1700 measurements during a 100-ns interval 2 μs after breakdown. Calibration curves are presented relating the Na(I) 589-nm to Hα 656.3-nm intensity ratio as a function of Na concentration, ranging from 100 to 10,000 ppm. Limits of detection for Na by the current method under the experimental conditions are estimated to be approximately 165 ppm for monodisperse sprays and 925 ppm for one case involving a polydisperse spray. Droplet diameter strongly influences the observed emission intensity ratio.

Phytotoxicity of sea-water aerosols on forest plants with special reference to the role of surfactants

Experiments were conducted in a wind tunnel to investigate the impact of synthetic sea-water aerosols, with or without the addition of sodium linear-alkylbenzene-sulfonate (LAS), a common pollutant of sea-water, on young plants of Pinus pinea and Quercus ilex. LAS had a minor direct toxic effect, but its presence was correlated with a greater absorbance of salts into leaf tissues. Sodium was the principal noxious agent in Q. ilex; in P. pinea the contributions of sodium and chloride were not different. Potassium levels decreased in both species as a consequence of saline stress; the levels of calcium and magnesium did not show any major variation. By using a gradient of LAS concentrations in sea-water (from 0 to 240 ppm), it was possible to identify a significant linear regression for sodium and chloride absorbed by the leaves. Total free amino acid content was significantly increased by the saline treatment in P. pinea and a consistent accumulation of proline took place; no such metabolic changes were observed in Q. ilex, which proved to be more salt stress tolerant. An exposure for 10 days of plants to 110 ppb SO 2 (a concentration which does not cause any macroscopic injury) before and/or after the spray induced a significant increase in toxicity of the saline treatment.