Sea Salt Aerosol Research Articles

The Effect of Seawater Salinity and Seawater Temperature on Sea Salt Aerosol Production

AbstractTo improve our understanding of the impact of sea salt aerosols (SSA) on the Earth's climate, it is critical to understand the physical mechanisms which determine the size‐resolved SSA production flux. Of the factors affecting SSA emissions, seawater salinity has perhaps received the least attention in the literature and previous studies have produced conflicting results. Here, we present a series of laboratory experiments designed to investigate the role of salinity on aerosol production from artificial seawater using a continuous plunging jet. During these experiments, the aerosol and surface bubble size distributions were monitored while the salinity was decreased from 35 to 0 g kg−1. Three distinct salinity regimes were identified: (a) A high salinity regime, 10–35 g kg−1, where lower salinity resulted in only minor reductions in particle number flux but notable reductions in particle volume flux; (b) an intermediate salinity regime, 5–10 g kg−1, with a local maximum in particle number flux; (c) a low salinity regime, <5 g kg−1, characterized by a rapid decrease in particle number flux at lower salinities and dominated by small particles and larger bubbles. We discuss the implications of our results through comparison of the size‐resolved aerosol flux and the surface bubble population at different salinities. Finally, by varying the seawater temperature at three specific salinities we have also developed a simple parameterization of the particle production flux as a function of seawater temperature and salinity. The range of seawater salinity and temperature studied is representative of the global oceans and lower salinity water bodies such as the Baltic Sea.

A synoptic bridge linking sea salt aerosol concentrations in East Antarctic snowfall to Australian rainfall

Previous research has shown that aerosol sea salt concentrations (Southern Ocean wind proxy) preserved in the Law Dome ice core (East Antarctica) correlate significantly with subtropical eastern Australian rainfall. However, physical mechanisms underpinning this connection have not been established. Here we use synoptic typing to show that an atmospheric bridge links East Antarctica to subtropical eastern Australia. Increased ice core sea salt concentrations and wetter conditions in eastern Australia are associated with a regional, asymmetric contraction of the mid-latitude westerlies. Decreased ice core sea salt concentrations and drier eastern Australia conditions are associated with an equatorward shift in the mid-latitude westerlies, suggesting greater broad-scale control of eastern Australia climate by southern hemisphere variability than previously assumed. This relationship explains double the rainfall variance compared to El Niño-Southern Oscillation during late spring-summer, highlighting the importance of the Law Dome ice core record as a 2000-year proxy of eastern Australia rainfall variability.

Correlation of Stainless Steel Pit Morphology to Humidity-Specific Sea Salt Brine Constituents

Immersion exposures of 304 stainless steel ground to a #4 finish were conducted in brines representative of the chemistry of sea salt aerosols at low (40%) and high (76%) relative humidity (RH). Low-RH-equivalent brines resulted in cross-hatched pits, whereas high-RH-equivalent brines produced ellipsoidal, faceted pits. Distinct surface microcracking was observed to be associated only with cross-hatched pits and appeared to correlate with a high concentration of dissolved carbonate species in low-RH-equivalent solutions while being absent in the high-RH-equivalent brines. Correlating these results to brine composition suggested that the concentrations of MgCl2 and dissolved carbonate species in the brines could, in the presence of machining-induced surface microstructure and residual stress, determine pit morphology in marine atmospheres, thereby potentially impacting stress corrosion cracking susceptibility and lifetime prediction.

Numerical Investigation on the Atomization Characteristics of An Aerosol Spray Nozzle

Inlet air filtration of ships and coastal installations is mainly used to filter out salt aerosol particles, so researches on the inlet filter needs to simulate spray aerosol state in the marine environment. The sea salt aerosol particles have multiple sizes, thus salt aerosol generator should have the ability to produce salt aerosol particles of various diameters. This paper investigates the factors that affect the particle diameter of a salt aerosol generating device. Numerical simulations on the two-phase flow in a salt aerosol nozzle are conducted and the influence of air inlet pressure and droplet mass flow rate on the particle diameter is discovered. The results show that the particle diameter of the aerosol nozzle decreases with the air inlet pressure increasing and the droplet mass flow rate decreasing.

Effects of snow and land modification on an andesite lava aquifer in Chokai volcano, northwestern Japan

Studied regionChokai volcano is composed of low-permeability andesite lava, a snowfall-influenced hydrological setting that has been little studied. Study focusSnowfall there is expected to decrease due to climate change and expanded quarrying along its southern foot. To evaluate the effects of future environmental changes on the groundwater discharged from springs at the feet of lava flows, which is used for agriculture and domestic purposes, we used isotopic, hadrochemical, geologic, meteorological, and topographic information to elucidate the recharge area, major recharge season, and underground flow of spring waters and surface waters at Chokai. New hydrogeological insights for the regionGroundwater and surface water are of NaCl type with high deuterium excess values, indicating a strong contribution of atmospheric deposition of sea salt aerosols during winter. Altitude indicators based on water H and O isotopic compositions and chloride ion concentrations suggest that the foothill springs are recharged mainly on gentle slopes below ∼700 m elevation. This area is generally covered with volcanic sediments, which contain wetlands and perched aquifers that continuously supply groundwater to the underlying lava through fractures and voids without thorough mixing in the lava aquifer. Anticipated decreases in snowfall and the removal of surface rocks may adversely affect not only the foothill springs supplied by snowmelt and the rice cultivation that depends on them, but also the wetland ecosystem.

Sea Salt Aerosol Identification Based on Multispectral Optical Properties and Its Impact on Radiative Forcing over the Ocean

The ground-based measurement of sea salt (SS) aerosol over the ocean requires the massive utilization of satellite-derived aerosol products. In this study, n-order spectral derivatives of aerosol optical depth (AOD) based on wavelength were examined to characterize SS and other aerosol types in terms of their spectral dependence related to their optical properties such as particle size distributions and complex refractive indices. Based on theoretical simulations from the second simulation of a satellite signal in the solar spectrum (6S) model, AOD spectral derivatives of SS were characterized along with other major types including mineral dust (DS), biomass burning (BB), and anthropogenic pollutants (APs). The approach (normalized derivative aerosol index, NDAI) of partitioning aerosol types with intrinsic values of particle size distribution and complex refractive index from normalized first- and second-order derivatives was applied to the datasets from a moderate resolution imaging spectroradiometer (MODIS) as well as by the ground-based aerosol robotic network (AERONET). The results after implementation from multiple sources of data indicated that the proposed approach could be highly effective for identifying and segregating abundant SS from DS, BB, and AP, across an ocean. Consequently, each aerosol’s shortwave radiative forcing and its efficiency could be further estimated in order to predict its impact on the climate.

Molecular dynamics study on the impacts of cations in sea salt aerosol on transport performance of Nafion Membranes for PEMFCs in marine application

The application of polymer electrolyte membrane fuel cells (PEMFCs) in marine industry receives a widespread attention, due to the severe emission regulations. However, cationic contaminants in sea salt aerosol have detrimental effects on the transport performance of polymer electrolyte membranes, which are the core components of PEMFCs. In this study, the effects of K+ and Mg2+ in marine atmosphere on the transport performance of Nafion 117 membranes were evaluated by molecular dynamics simulations. Moreover, the influence of temperature is considered for the first time. The mean square displacements are used to evaluate the diffusion coefficients of water molecules (H2O) and hydronium ions (H3O+). In addition, the effect mechanisms are analyzed using radial distribution functions, water clusters distribution and relative concentration distribution. Results show that the diffusion of H3O+ and H2O is significantly weakened by K+ and Mg2+. Moreover, the impact of Mg2+ is more serious. The difference in the influence of these two kinds of cations on the transport performance of Nafion membranes is discussed by hydrated radius, hydration degree of cations, and the interaction between cations and sulfonic groups. The diffusion coefficients increase significantly with the increase of temperature. The increase of the temperature can also increase the interaction between the cations and the sulfonic groups. In contrast, the interaction between the sulfonic groups and water molecules is decreased.

Description and evaluation of the tropospheric aerosol scheme in the Integrated Forecasting System (IFS-AER, cycle 47R1) of ECMWF

Abstract. This article describes the Integrated Forecasting System aerosol scheme (IFS-AER) used operationally in the IFS cycle 47R1, which was operated by the European Centre for Medium Range Weather Forecasts (ECMWF) in the framework of the Copernicus Atmospheric Monitoring Services (CAMS). It represents an update of the Rémy et al. (2019) article, which described cycle 45R1 of IFS-AER in detail. Here, we detail only the parameterisations of sources and sinks that have been updated since cycle 45R1, as well as recent changes in the configuration used operationally within CAMS. Compared to cycle 45R1, a greater integration of aerosol and chemistry has been achieved. Primary aerosol sources have been updated, with the implementation of new dust and sea salt aerosol emission schemes. New dry and wet deposition parameterisations have also been implemented. Sulfate production rates are now provided by the global chemistry component of IFS. This paper aims to describe most of the updates that have been implemented since cycle 45R1, not just the ones that are used operationally in cycle 47R1; components that are not used operationally will be clearly flagged. Cycle 47R1 of IFS-AER has been evaluated against a wide range of surface and total column observations. The final simulated products, such as particulate matter (PM) and aerosol optical depth (AOD), generally show a significant improvement in skill scores compared to results obtained with cycle 45R1. Similarly, the simulated surface concentration of sulfate, organic matter and sea salt aerosol are improved by cycle 47R1 compared to cycle 45R1. Some biases persist, such as the surface concentrations of nitrate and organic matter being simulated too high. The new wet and dry deposition schemes that have been implemented into cycle 47R1 have a mostly positive impact on simulated AOD, PM and speciated aerosol surface concentration.

Effect of Sea Salt AOT on Precipitation Processes Associated with Red Sea Moisture Flux on Iraq, a Case Study

Sea salt acquires importance in the process of precipitation formation through its hygroscopic nature. and its role in accelerating the droplet formation process within a moisture saturation less than if it was not present. In this work, the maps of precipitation distribution with sea salt aerosol optical thickness (AOT) as well as moisture flux and wind at an altitude of 50 meters were compared. The data of Three rainy cases, characterized by heavy rains and moisture feeding from the Red Sea were selected. They are respectively 13 to 15 November 2018, 1 December 2018, and 27 to 29 January 2019. Cloud top temperature (CTT) data were obtained from Meteosat satellites (Meteosat 9, and 10). Total Precipitable water (TPW) and sea salt (AOT) were obtained from Model projects: a modern-era retrospective analysis for research and applications 2 (MERRA-2). the correlation coefficient (R) was used to test the relation between the variables like Total Precipitable water (TPW), Cloud top temperature (CTT), precipitation, and Sea Salt AOT. The results showed that there is a good correlation between the sea salt AOT and the amount of precipitation. The work also showed the roles that other variables play in the precipitation process. Where the relationships showed values of correlation coefficients about 0,6 to 0,7 between the variables, leading to the enhancement of precipitation.

Study of an Arctic blowing snow-induced bromine explosion event in Ny-Ålesund, Svalbard

Bromine explosion events (BEEs) are important processes that influence the atmospheric oxidation capacity, especially in the polar troposphere during spring. Although sea ice surface is thought to be a significant bromine source, bromine release mechanisms remain unclear. High-resolution ground-based observations of reactive bromine, such as BrO, are important for assessing the potential impacts on tropospheric ozone and evaluating chemical models. However, previous model studies paid little attention to Svalbard, which is surrounded by both open ocean and sea ice. In this paper, we present continuous BrO slant column densities and vertical column densities derived by Multi-Axis Differential Optical Absorption Spectroscopy deployed at Ny-Ålesund (78.92°N, 11.93°E) in March 2017. We focused on one BEE in mid-March, during which the vertical column densities of BrO surged from 4.26 × 1013 molecular cm−2 to the peak at 1.23 × 1014 molecular cm−2 on March 17, surface ozone depleted from a background level of 46.25 parts per billion by volume (ppbv) to 13.9 ppbv. This case study indicates that the BEE was strongly associated with blowing snow induced by the cyclone systems that approached Svalbard from March 14 to 18. By considering meteorological conditions, sea ice coverage, and airmass trajectory history, we demonstrate that sea salt aerosols (SSAs) from blowing snow on sea ice, rather than from open ocean, are attributed to the occurrence of this BEE. Model results from a parallelized-tropospheric offline model of chemistry and transport (p-TOMCAT) indicate that this BEE was mainly triggered by a blowing snow event associated with a low-pressure cyclone system. The concentration of blowing-snow-sourced SSAs surged to peak when the airmass pass across the sea-ice-covered area under high wind speed, which is a critical factor in the process of bromine explosion observed in Ny-Ålesund. Due to the coarse resolution, the possible delayed timing of bromine release from SSA and the model-data discrepancies still exist.

Simulation investigation on the indirect effects due to sea-salt aerosols on the cloud ice during a tropical cyclone

This paper investigated the indirect effects due to sea-salt aerosols on tropical cyclones using the Weather Research and Forecasting model, coupled with a chemistry module (WRF-Chem). The parameterization of sea-salt aerosols in the model was operated. The domain-averaged vertically integrated cloud auto-conversion rates were 0.699 and 0.038 mm/h with and without the inclusion of the aerosol indirect effects, respectively. Cloud ice deposition and mixing ratio were higher with inclusion of indirect effects than without. Conversely, the cloud top temperature at a specified time was lower with indirect effects than without. When indirect effects of aerosols were included, the 0.01 g/kg contour line of the azimuthally and temporally averaged cloud ice mixing ratio increased by about 500 m. Overall, the inclusion of the aerosols indirect effects led to the extension of the cloud tops of tropical cyclones to greater heights.

Acidity of Size-Resolved Sea-Salt Aerosol in a Coastal Urban Area: Comparison of Existing and New Approaches

Aging of sea-salt aerosol and the corresponding phase partitioning behavior of HCl/Cl– were monitored and studied in the Halifax Fog and Air Quality Study (HaliFAQS) field campaign in Canada in the early summer of 2019. Ionic chemical composition of ambient aerosol from total suspended particles (TSPs) to 10 nm was sampled and measured into 14 size ranges, which showed that aerosol at the sampling location was mainly composed of sea-salt constituents with little influence from anthropogenic emissions of secondary inorganic precursors. The size-resolved pH of aged sea-salt aerosol was calculated by Extended Aerosol Inorganic Model (E-AIM) IV and a newly derived method based on the measurement of NH3/NH4+ and HNO3/NO3– or HCl/Cl– coupled phase partitioning behavior. The latter pH calculation method does not require information about the aerosol liquid water content or complete water-soluble ion measurement, compensating for the role of oxidized organics to influence the proton activity. In comparison, E-AIM calculation requires the input of all major hygroscopic species. The size-resolved pH calculated by E-AIM IV generally agrees with the one calculated by NH3–HCl coupled phase partitioning. The sensitivities of HCl and HNO3 phase partitioning to aerosol pH are studied with both observational data and conceptual modeling, which gives evidence that the phase partitioning of HCl is more sensitive and therefore more reflective of aerosol pH changes than HNO3 in sea-salt dominated atmospheres where particles typically have pH > 3. The higher concentration and more reliable measurement also make HCl a more suitable choice to track pH changes in this study.

Temperature and Concentration Affect Particle Size Upon Sublimation of Saline Ice: Implications for Sea Salt Aerosol Production in Polar Regions

AbstractUsing an environmental scanning electron microscope, we quantified for the first time aerosol‐sized salt particles formed during the sublimation of sea ice as a function of temperature and concentration. The sublimation temperature of the ice is a dominating physical factor to determine the size of the residua: Below −20°C, micron‐sized pieces of salt emerge, whereas above the temperature large chunks of salt are detected. Another such aspect influencing the distribution of sizes in salt particles is the concentration: Micron‐sized particles are observed exclusively at salinities below 3.5 psu, while below 0.085 psu particles with a median smaller than 6 μm arise from sea ices at any subzero temperature. Moreover, when a chunk of salt sublimes at less than −30°C to be dried and warmed later, a large number of sub‐micron crystals will appear. We relate our findings to the production of the polar atmospheric sea salt aerosols.

Impacts of Aerosols and Climate Modes on Tropical Cyclone Frequency over the North Indian Ocean: A Statistical Link Approach

Abstract North Indian Ocean (NIO) tropical cyclone activity is strongly influenced by aerosols and climate modes. In this study, we evaluated the impact of aerosols and climate modes on modulating tropical cyclone (TC) frequency over the NIO. A statistical generalized additive model based on Poisson regression was developed to assess their relative impacts. Aerosol optical depth for different compounds simulated by the Goddard Chemistry Aerosol Radiation and Transport model, sunspot number (SN) as solar variability, and eight climate modes—Atlantic meridional mode (AMM), El Niño–Southern Oscillation (ENSO), North Atlantic Oscillation (NAO), Indian Ocean dipole (IOD), Pacific decadal oscillation (PDO), Pacific–North American teleconnection pattern (PNA), Arctic Oscillation (AO), and Antarctic Oscillation (AAO), all based on reanalysis datasets, were analyzed for the 40-yr period 1980–2019. A strong linkage was found between TC activity and the AMM, IOD, and ENSO over the NIO. In addition, black carbon, organic carbon, sea salt, and sulfate aerosols have a significant impact on the cyclone frequency. Among these factors, black carbon, organic carbon, sea salt, and AMM account for the most variance of TCs, and among the other climate modes, IOD contributes more than ENSO. This is the first attempt to have identified this ranked set of aerosols and climate indices according to their relative ability to impact NIO TCs. Possible linkages between the thermodynamic and dynamic effects of aerosols on the Indian monsoon environment and its modifications to the large-scale environmental parameters relevant to TC development, namely, sea surface temperature, vertical wind shear, relative vorticity, and relative humidity during different phases of the climate modes are discussed. Significance Statement Aerosols and climate modes have enormous impact on tropical cyclones (TCs). In this study, we evaluated the impact of aerosols and climate modes that modulate frequency of TCs over the north Indian Ocean. To assess the impact, a statistical generalized additive model based on Poisson regression was developed. A strong linkage was found between TC activity and Atlantic meridional mode, Indian Ocean dipole, and El Niño–Southern Oscillation, whereas other climate modes have no statistical significance. In addition, black carbon, organic carbon, sea salt, and SO4 aerosols have a strong linkage to cyclone frequency. The study postulates that most positive phases of these climate modes are associated with more TCs, while the negative phases are associated with fewer.

Role of Iodine Recycling on Sea-Salt Aerosols in the Global Marine Boundary Layer.

Heterogeneous uptake of hypoiodous acid (HOI), the dominant inorganic iodine species in the marine boundary layer (MBL), on sea‐salt aerosol (SSA) to form iodine monobromide and iodine monochloride has been adopted in models with assumed efficiency. Recently, field measurements have reported a much faster rate of this recycling process than previously assumed in models. Here, we conduct global model simulations to quantify the range of effects of iodine recycling within the MBL, using Conventional, Updated, and Upper‐limit coefficients. When considering the Updated coefficient, iodine recycling significantly enhances gaseous inorganic iodine abundance (∼40%), increases halogen atom production rates (∼40% in I, >100% in Br, and ∼60% in Cl), and reduces oxidant levels (−7% in O3, −2% in OH, and −4% in HO2) compared to the simulation without the process. We appeal for further direct measurements of iodine species, laboratory experiments on the controlling factors, and multiscale simulations of iodine heterogeneous recycling.

Physical and chemical properties of sea salt deliquescent brines as a function of temperature and relative humidity

Thermodynamic modeling has been used to predict chemical compositions of brines formed by the deliquescence of sea salt aerosols. Representative brines have been mixed, and physical and chemical properties have been measured over a range of temperatures. Brine properties are discussed in terms of atmospheric corrosion of austenitic stainless steel, using spent nuclear fuel dry storage canisters as an example. After initial loading with spent fuel, during dry storage, the canisters cool over time, leading to increased surface relative humidities and evolving brine chemistries and properties. These parameters affect corrosion kinetics and damage distributions, and may offer important constraints on the expected timing, rate, and long-term impacts of canister corrosion.

Elucidating the present-day chemical composition, seasonality and source regions of climate-relevant aerosols across the Arctic land surface

The Arctic is warming two to three times faster than the global average, and the role of aerosols is not well constrained. Aerosol number concentrations can be very low in remote environments, rendering local cloud radiative properties highly sensitive to available aerosol. The composition and sources of the climate-relevant aerosols, affecting Arctic cloud formation and altering their microphysics, remain largely elusive due to a lack of harmonized concurrent multi-component, multi-site, and multi-season observations. Here, we present a dataset on the overall chemical composition and seasonal variability of the Arctic total particulate matter (with a size cut at 10 μm, PM10, or without any size cut) at eight observatories representing all Arctic sectors. Our holistic observational approach includes the Russian Arctic, a significant emission source area with less dedicated aerosol monitoring, and extends beyond the more traditionally studied summer period and black carbon/sulfate or fine-mode pollutants. The major airborne Arctic PM components in terms of dry mass are sea salt, secondary (non-sea-salt, nss) sulfate, and organic aerosol (OA), with minor contributions from elemental carbon (EC) and ammonium. We observe substantial spatiotemporal variability in component ratios, such as EC/OA, ammonium/nss-sulfate and OA/nss-sulfate, and fractional contributions to PM. When combined with component-specific back-trajectory analysis to identify marine or terrestrial origins, as well as the companion study by Moschos et al 2022 Nat. Geosci. focusing on OA, the composition analysis provides policy-guiding observational insights into sector-based differences in natural and anthropogenic Arctic aerosol sources. In this regard, we first reveal major source regions of inner-Arctic sea salt, biogenic sulfate, and natural organics, and highlight an underappreciated wintertime source of primary carbonaceous aerosols (EC and OA) in West Siberia, potentially associated with the oil and gas sector. The presented dataset can assist in reducing uncertainties in modelling pan-Arctic aerosol-climate interactions, as the major contributors to yearly aerosol mass can be constrained. These models can then be used to predict the future evolution of individual inner-Arctic atmospheric PM components in light of current and emerging pollution mitigation measures and improved region-specific emission inventories.

Variation and Driving Factor of Aerosol Optical Depth over the South China Sea from 1980 to 2020

Spatial and temporal variation of aerosol optical depth (AOD) and optical depth of different aerosol types derived from the second Modern-Era Retrospective analysis for Research and Applications (MERRA-2) over the South China Sea (SCS) between 1980 and 2020 were studied. AOD distribution showed different characteristics throughout the entire SCS. Sulfate Aerosol Optical Depth (SO4AOD) and Sea Salt Aerosol Optical Depth (SSAOD) mainly contributed to the spatial and temporal variation of AOD over the SCS. A significant increasing trend followed by a decreasing trend of AOD could be observed in the north of the SCS from 1980 to 2020. Mean MERRA-2 AOD between 1980 and 2020 showed that AOD was high in the north and low in the south and that AOD gradually decreased from north to south over the SCS. AOD after 2000 was obviously higher than that of the 1980s and 1990s. Higher AOD appeared in the spring and winter, and low AOD appeared in the summer. The spatial distribution of scattering aerosol optical depth (SAOD) was similar to AOD distribution over the SCS. SO4AOD and SSAOD were obviously higher than black carbon aerosol optical depth (BCAOD), organic carbon aerosol optical depth (OCAOD), and dust aerosol optical depth (DUAOD) over the SCS. SO4AOD accounted for over 50% of total AOD (TAOD) over the north of the SCS, while BCAOD and DUAOD accounted for less than 10% of TAOD over the entire SCS. An obvious annual mean TAOD increase between 1980 and 2007 could be observed over the northern part of the SCS (NSCS), while a TAOD decrease happened from 2008 to 2020 in this region. The correlation coefficient between TAOD and SO4AOD over NSCS from 1980 to 2020 was about 0.93, indicating SO4AOD was the driving factor of TAOD variation in this area. Different AOD variation trends over the different areas of the SCS could be observed during the two periods including 1980–2007 and 2008–2020. AOD increase appeared over most of the SCS during the period from 1980 to 2007, while AOD decrease could be observed over most of the SCS from 2008 to 2020.

Global and Regional Variations and Main Drivers of Aerosol Loadings over Land during 1980–2018

Aerosol particles originated from anthropogenic emissions, volcanic eruptions, biomass burning, and fossil combustion emissions, and their radiative effect is one of the most uncertain factors in climate change. Meanwhile, aerosol particles in fine particle size could also cause irreversible effects on the human respiratory system. This study attempted to analyse the spatial and temporal variations of global aerosol optical depth (AOD, 550 nm) during 1980–2018 using MERRA-2 aerosol reanalysis products and to investigate the effects of natural/anthropogenic emissions of different types of aerosols on AOD values. The results show that the global annual mean AOD values kept high levels with significant fluctuations during 1980–1995 and showed a consistent decreasing and less volatile trend after 1995. Spatially, the AOD values are relatively higher in the Northern Hemisphere than in the Southern Hemisphere, especially in North Africa (0.329), Northern India (0.235), and Eastern China (0.347), because of the intensive natural/anthropogenic aerosol emissions there. The sulphate-based aerosols emitted by biomass burning and anthropogenic emissions are the main types of aerosols worldwide, especially in densely populated and industrialized regions such as East Asia and Europe. Dust aerosols are also the main aerosol type in desert areas. For example, the AOD and AODP values for the Sahara Desert are 0.3178 and 75.32%, respectively. Both black carbon aerosols (BC) and organic carbon aerosols (OC) are primary or secondary from carbon emissions of fossil fuels, biomass burning, and open burning. Thus, the regions with high BC and OC aerosol loadings are mainly located in densely populated or vegetated areas such as East Asia, South Asia, and Central Africa. Sea salt aerosols are mainly found in coastline areas along the warm current pathway. This study could help relevant researchers in the fields of atmospheric science, environmental protection, air pollution, and ecological environment to understand the global spatial–temporal variations and main driving factors of aerosol loadings.

Latitudinal Distribution of Gaseous Elemental Mercury in Tropical Western Pacific: The Role of the Doldrums and the ITCZ.

The role of the tropical western Pacific in the latitudinal distribution of atmospheric mercury is still unclear. In this study, we conducted continuous measurements of gaseous elemental mercury (GEM) in the marine boundary layer (MBL) along a large latitudinal transect (∼60° S to ∼30° N) of the western Pacific, accompanied by measurements of dissolved gaseous mercury (DGM) in the surface seawater. We found that the GEM latitudinal gradient is the most significant in the tropical western Pacific, which to some extent might be attributed to the impact of the doldrums and the Intertropical Convergence Zone (ITCZ) in this area. For the doldrums, calm weather may delay the transport of GEM, facilitating its accumulation in the tropical western Pacific. Furthermore, the regional transport, and low O3 and sea-salt aerosol levels in this area which would not favor the oxidation of GEM in the MBL, would intensify the accumulation of GEM in the tropical western Pacific. For the ITCZ, the vast wet deposition of Hg would drive elevated DGM in the surface seawater, which can increase the evasion flux and may further influence the spatial distribution of GEM. This study provides insight into the role of the tropical western Pacific in the regional atmospheric mercury cycle.