Marine Aerosol Research Articles

Unraveling the sources of atmospheric organic aerosols over the Arabian Sea: Insights from the stable carbon and nitrogen isotopic composition

The isotopic composition of stable carbon (δ13C) and nitrogen (δ15N) in marine aerosols influenced by the continental outflows are useful proxies for understanding the aging and secondary formation processes. Every winter, the haze pollutants transported from South Asia significantly affect the chemical composition of marine atmospheric boundary layer of the Arabian Sea. Here, we assessed the δ13C of total carbon (TC) and δ15N of total nitrogen (TN) in marine aerosols collected over the Arabian Sea during a winter cruise (6–24 December 2018). TC (2.1–13.4 μg m−3) is strongly correlated with TN (0.9–5.0 μg m−3), likely because of their common source-emissions, biomass burning and fossil-fuel combustion in the Indo-Gangetic Plain and South Asia (corroborated by backward-air mass trajectories and satellite fire counts). Besides, the linear relationship between the mass ratios of water-soluble organic carbon (WSOC) to TC (0.04–0.65) and δ13CTC (−25.1‰ to −22.9‰) underscores the importance of aging process. This means oxidation of organic aerosols during transport not only influences the WSOC levels but also affects their δ13CTC. Likewise, the prevalent inverse linear relationship between the equivalent mass ratio of (NH4+/non-sea-salt- or nss-SO42−) and δ15NTN (+15.3‰ to +25.1‰) emphasizes the overall significance of neutralization reactions between major acidic ([nss-SO42−] ≫ [NO3−]) and alkaline species (NH4+) in aerosols. Higher δ15NTN values in winter than the spring inter-monsoon clearly emphasizes the significance of the anthropogenic combustion sources (i.e., biomass burning) in the South Asian outflow. A comparison of δ13CTC and δ15NTN with the source emissions revealed that crop-residue burning emissions followed by the coal fired power plants mostly dictate the atmospheric abundance of organic aerosols in the wider South Asian outflow.

Review on Per- and Poly-Fluoroalkyl Substances’ (PFASs’) Pollution Characteristics and Possible Sources in Surface Water and Precipitation of China

In recent years, due to the production and use of per- and poly-fluoroalkyl substances (PFASs), the research on the pollution characteristics and sources of PFASs in surface water and precipitation in China has attracted increasing attention. In this study, the related published articles with sampling years from 2010 to 2020 were reviewed, and the concentration levels, composition characteristics and possible sources of PFASs in surface water (rivers and lakes) and precipitation in China were summarized, including those in the Tibetan Plateau region. The results show that the concentrations of PFASs in surface water in different areas of China vary greatly, ranging from 0.775 to 1.06 × 106 ng/L. The production processes of fluorinated manufacturing facilities (FMFs) and sewage discharge from wastewater treatment plants (WWTPS) were the main sources of PFASs in surface water in China, and the concentrations of PFASs in water flowing through cities with high urbanization increased significantly compared with those before water flowed through cities with high urbanization. The compositions of PFASs in surface water gradually changed from long-chain PFASs, such as per-fluoro-octanoic acid (PFOA) and per-fluoro-octanesulfonic acid (PFOS) to short-chain PFASs, such as per-fluorobutanoic acid (PFBA), per-fluorobutanesulfonic acid (PFBS), perfluorohexanoic acid (PFHxA) and per-fluoropentanoic acid (PFPeA). The concentrations of PFASs in precipitation in China ranged from 4.2 to 191 ng/L, which were lower than those of surface water. The precipitation concentrations were relatively high around a fluorination factory and in areas with high urbanization levels. PFASs were detected in the surface water and precipitation in the Tibetan Plateau (TP), which is the global “roof of the world”, but the concentrations were low (0.115–6.34 ng/L and 0.115–1.24 ng/L, respectively). Local human activities and surface runoff were the main sources of PFASs in the surface water of the Tibetan Plateau. In addition, under the influence of the Southeast Asian monsoon in summers, marine aerosols from the Indian Ocean and air pollutants from human activities in Southeast Asia and South Asia will also enter the water bodies through dry and wet depositions. With the melting of glaciers caused by global warming, the concentration of PFASs in the surface water of the TP was higher than that before the melting of glaciers flowed into the surface water of the TP. Generally, this study summarized the existing research progress of PFAS studies on surface water and precipitation in China and identified the research gaps, which deepened the researchers’ understanding of this field and provided scientific support for related research in the future. The concentrations of PFASs in the water bodies after flowing through FMFs were significantly higher than those before water flowed through FMFs, so the discharge of the FMF production process was one of the main sources of PFASs in surface water.

Brown carbon from biomass burning imposes strong circum-Arctic warming

Brown carbon from biomass burning imposes strong circum-Arctic warming

Gas-phase catalytic hydration of I2O5 in the polluted coastal regions: Reaction mechanisms and atmospheric implications

Marine aerosols play an important role in the global aerosol system. In polluted coastal regions, ultra-fine particles have been recognized to be related to iodine-containing species and is more serious due to the impact of atmospheric pollutants. Many previous studies have identified iodine pentoxide (I2O5, IP) to be the key species in new particles formation (NPF) in marine regions, but the role of IP in the polluted coastal atmosphere is far to be fully understood. Considering the high humidity and concentrations of pollutants in the polluted coastal regions, the gas-phase hydration of IP catalyzed by sulfuric acid (SA), nitric acid (NA), dimethylamine (DMA), and ammonia (A) have been investigated at DLPNO-CCSD(T)//ωB97X-D/aug-cc-pVTZ + aug-cc-pVTZ-PP with ECP28MDF (for iodine) level of theory. The results show that the hydration of IP involves a significant energy barrier of 22.33 kcal/mol, while the pollutants SA, NA, DMA, and A all could catalyze the hydration of IP. Especially, with SA and DMA as catalysts, the hydration reactions of IP present extremely low barriers and high rate constants. It is suggested that IP is unstable under the catalysis of SA and DMA to generate iodic acid, which is the key component in NPF in marine regions. Thus, the catalytic hydration of IP is very likely to trigger the formation of iodine-containing particles. Our research provides a clear picture of the catalytic hydration of IP as well as theoretical guidance for NPF in the polluted coastal atmosphere.

Analysis of the atmospheric visibility influencing factors under sea-land breeze circulation.

Factors influencing atmospheric visibility (VIS) in coastal areas are more complex than those for inland and far oceans owing to the complex circulation and aerosol sources. This study analyzed the factors influencing VIS under sea-land breeze circulation (SLBC) for different external aerosol sources based on field survey data in southern Chinese coastal areas. First, SLBC characteristics observed during the experiment period showed that on SLBC days, sea breeze occurs more frequently (∼50%) than land breeze (∼27%), and the wind speed (WS) is generally small, with a mean sea and land breeze WSs of ∼2.18 m/s and ∼2.38 m/s, respectively. Then, analysis of factors influencing VIS was conducted for different land/sea breeze conditions and external aerosol source conditions indicated by the HYSPLIT4 model simulations. Results showed that the aerosol particle number concentration (PNC) and relative humidity (RH) both had negative correlations with VIS, while only very weak relationships between WS and VIS were found, possibly due to small WSs on SLBC days or because local aerosols were not pure marine aerosols. Further two-factor analysis of VIS showed that the power-law function relating VIS with PNC in each RH bin ranges from ∼-0.3 to ∼-1.5, and VIS exhibited sharper exponential decline with increasing PNC under high RH. A new method of retrieving aerosol-extinction hygroscopic growth factor (fext) with the measured VIS, RH, and PNC was developed to investigate the optical hygroscopic growth property of aerosols. Results show that aerosols in the study area have similar fext under different land/sea breeze and external aerosol source conditions; the deliquescence RH of aerosols is ∼60%, suggesting that mainly polluted marine aerosol was observed during experiments in this area.

On the Speciation of Iodine in Marine Aerosol.

We have compiled and analyzed a comprehensive data set of field observations of iodine speciation in marine aerosol. The soluble iodine content of fine aerosol (PM1) is dominated by soluble organic iodine (SOI; ∼50%) and iodide (∼30%), while the coarse fraction is dominated by iodate (∼50%), with nonnegligible amounts of iodide (∼20%). The SOI fraction shows an equatorial maximum and minima coinciding with the ocean “deserts,” which suggests a link between soluble iodine speciation in aerosol and ocean productivity. Among the major aerosol ions, organic anions and non‐sea‐salt sulfate show positive correlations with SOI in PM1. Alkali cations are positively correlated to iodate and negatively correlated with SOI and iodide in coarse aerosol. These relationships suggest that under acidic conditions iodate is reduced to HOI, which reacts with organic matter to form SOI, a possible source of iodide. In less acidic sea‐salt or dust‐rich coarse aerosols, HOI oxidation to iodate and reaction with organic matter likely compete.

Global estimation of clear-sky shortwave aerosol direct radiative effects based on CALIPSO observations

ABSTRACT The total and individual aerosol direct radiative effects (ADREs) were estimated for clear-sky conditions using Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) observations and radiative transfer model. In this study, a parametric sensitivity analysis was performed for the Santa Barbara DISORT Atmospheric Radiative Transfer model using a global sensitivity analysis method. Uncertainties in the ADREs due to aerosol optical properties and surface albedo errors were evaluated. The single-scattering albedo and asymmetry factor for marine, dust, pollution, and smoke aerosols required for the model calculations were obtained from the classified AErosol RObotic NETwork observations. The estimated average global ADREs and errors at the top-of-atmosphere (TOA) and the surface were −2.36 ± 0.54 and −4.78 ± 2.2 Wm−2, respectively. In regions with higher dust, pollution, and smoke aerosol loading, the ADREs exhibited significant seasonal variability. In the Sahara and Arabian deserts, during the June-July-August season with higher dust aerosol loading, the seasonal average ADREs in the region were −3.23 and −21.37 Wm−2 at the TOA and surface, respectively. In the Indian region, during the March–April–May season with higher pollution aerosol loading, the ADREs were −10.33 and −28.04 Wm−2 at the TOA and surface, respectively. In Southern Africa, the smoke aerosol with a single-scattering albedo of 0.87 caused negative radiative effects at the TOA, and during the September-October-November season with higher smoke aerosol loading, the seasonal average ADREs were −2.34 and −6.36 Wm−2 at the TOA and surface, respectively.

Effects of energy structure differences on chemical compositions and respiratory health of PM2.5 during late autumn and winter in China

To understand the influence of the energy structure (including solid fuel and clean energy) on air pollution, two comprehensive measurement campaigns were conducted in Baoding and Shanghai in late autumn and winter during 2017–2018. The chemical compositions, driving factors, regional transport of pollutants, and potential respiratory disease (RD) health risks of PM2.5 for Baoding and Shanghai were analyzed. The results showed that the concentration of PM2.5 in Baoding (156.9 ± 139.8 μg m−3) was 2.6 times of that in Shanghai (60.9 ± 45.9 μg m−3). The most important contributor to PM2.5 in Baoding was organic matter (OM), while inorganic aerosols accounted for major fractions of PM2.5 in Shanghai. Positive matrix factorization (PMF) results indicated that coal combustion (CC; 39%) accounted for the most in Baoding, followed by secondary aerosols (21%), biomass burning (BB; 20%), industrial emissions (14%), dust (3%), and vehicle exhaust (2%). However, the average contribution in Shanghai followed the order: secondary aerosols (44%), vehicle exhaust (36%), dust (11%), marine aerosols (6%), and BB (3%). The evolution of source contributions at different pollution levels revealed that haze episodes in Baoding and Shanghai were triggered by CC and secondary formation, respectively; however, the air quality on clean days in Baoding and Shanghai was affected mostly by BB and vehicle emissions, respectively. Potential source contribution function (PSCF) results suggested that CC in Baoding was primarily from local emissions, while BB was primarily from local and regional transport. Vehicle exhaust and secondary aerosols in Shanghai were mainly from local emissions and regional transport. The number of RD deaths related to haze episodes in Baoding and Shanghai were 215 (95% CI: 109, 319) and 76 (95% CI: 11, 135), respectively. This research also emphasized the importance of further attention to the usage of coal in Baoding and vehicle emissions in Shanghai.

Hydrogeochemical analysis and identification of solute sources in the meltwater of Chaturangi glacier, Garhwal Himalaya, India

This paper presents an insight on major ion chemistry and identification of solute sources in meltwater of Chaturangi glacier throughout the ablation period 2015 and 2016. The results indicate that meltwater is slightly acidic with Ca–HCO3 and Mg–HCO3 dominated hydrochemical facies. In meltwater, Ca2+ and HCO3− are the most dominant cation and anion, respectively. The Water Quality Index values show that the quality of meltwater is good for both the ablation seasons. An important factor governing the quality of water is the residence time for dissolving minerals from the rocks. Mineralogy of surrounding rocks and Gibbs plot suggest that the meltwater ionic concentration is mostly controlled by weathering of rocks with slight contribution from atmospheric aerosols. For meltwater, the average equivalent ratios of Na/Cl and K/Cl were calculated as 3.36 ± 1.29 and 2.29 ± 0.62 in 2015 and 1.39 ± 0.6 and 0.8 ± 0.2 in 2016, which are considerably higher than the marine aerosols (Na/Cl = 0.85 and K/Cl = 0.017), it also confirmed the less contribution of atmospheric input in meltwater. The petrographic analysis of surrounding rocks indicate positive relationship among the cations (Ca2+, Mg2+, Na+ and K+) and mineral abundance. Our observations suggest that the bedrock mineralogy and weathering reactions together with amount and composition of atmospheric inputs are the main sources of ions, dissolved in the glacier meltwater. It might be due to rate of chemical reaction which leads decomposition of rocks and leaching of minerals into the meltwater. Additionally, the geology of the area plays a significant as the influence of geology and climate on water quality is observed by the quantity and types of dissolved materials and amount of the sediment carried by the streams. The elevated proportion of Ca + Mg in total cations and high Ca + Mg/(Na + K ratios, 1.47 ± 0.14 in the year 2015 and 1.44 ± 0.28 in 2016 clearly reveal that the ionic composition is primarily controlled by carbonate weathering and partly by silicate weathering. Further, the low Na + K/TZ− ratio (0.41 ± 0.02) and (0.22 ± 0.05) in 2015 and 2016, respectively also supports that carbonate weathering is main geochemical process controlling the hydrochemistry of meltwater. In addition, the ion denudation rate was calculated for both the years. The results show that the cation denudation rate of meltwater was 32.84 and 22.30 ton/km2/ablation during 2015 and 2016, respectively, whereas the anion denudation rate was found to be 205.43 in 2015 and 170.24 ton/km2/ablation in 2016.

Mapping gaseous dimethylamine, trimethylamine, ammonia, and their particulate counterparts in marine atmospheres of China’s marginal seas – Part 2: Spatiotemporal heterogeneity, causes, and hypothesis

Abstract. Spatiotemporal heterogeneities in the concentrations of alkaline gases and their particulate counterparts in the marine atmosphere over China's marginal seas were investigated in terms of causes and chemical conversion during two winter cruise campaigns, using semi-continuous measurements made by an onboard URG-9000D Ambient Ion Monitor-Ion Chromatograph (AIM-IC, Thermo Fisher). During the cruise campaign over the East China Sea from 27 December 2019 to 6 January 2020, the concentrations of gas-phase atmospheric trimethylamine (TMAgas) varied by approximately 1 order of magnitude, with an average (± standard deviation) of 0.10±0.04 µg m−3 corresponding to a mixing ratio of 26±17 pptv. Corresponding mean values were 0.037±0.011 µg m−3 (14±5 pptv in mixing ratio) over the Yellow Sea during the period from 7 to 16 January 2020 and 0.031±0.009 µg m−3 (12±4 pptv in mixing ratio) over the Yellow Sea and Bohai Sea from 9 to 22 December 2019. By contrast, the simultaneously observed concentrations of TMA in PM2.5, detected as TMAH+, over the East China Sea were 0.098±0.069 µg m−3 and substantially smaller than the 0.28±0.18 µg m−3 observed over the Yellow Sea and Bohai Sea from 9 to 22 December 2019. A significant correlation between TMAgas and particulate TMAH+ was observed over the East China Sea, but no correlation was found over the Yellow Sea and Bohai Sea. Proportional or disproportional variations in concentrations of TMAgas with particulate TMAH+ over the sea zones were probably attributed to the difference in the enrichment of TMAH+ in the sea surface microlayer. In addition, spatiotemporal heterogeneities in concentrations of atmospheric ammonia (NH3gas), atmospheric dimethylamine (DMAgas), and DMA in PM2.5, detected as DMAH+, were investigated. Case analyses were performed to illustrate the formation and chemical conversion of particulate aminium ions in marine aerosols. Finally, we hypothesized the release of basic gases and particulate counterparts from the ocean to the atmosphere, together with the secondary formation of DMAH+ and chemical conversion of TMAH+, in the marine atmosphere.

Observed Relationships Between Cloud Droplet Effective Radius and Biogenic Gas Concentrations in Summertime Marine Stratocumulus Over the Eastern North Atlantic

AbstractBiogenic gases are a prominent component of the summertime marine boundary layer (MBL) over the Eastern North Atlantic. One of these gases, dimethyl sulfide (DMS), can produce sulfate cloud condensation nuclei (CCN) that, in theory, can brighten clouds through photolysis, and produces a reaction product, methane sulfonic acid (MSA). It is also possible that DMS can interact with sea‐salt or other marine aerosols changing their CCN activation spectrum, which could also modify cloud microphysical structure. Data collected aboard the G1 aircraft during the Aerosol Cloud Experiment Eastern North Atlantic (ACE‐ENA) in well‐mixed and decoupled marine boundary layers (MBLs) were used to examine relationships between the cloud droplet effective radii, , and the concentrations of DMS and MSA in constant cloud liquid water content (LWC) bins. A weak but statistically significant negative correlation was observed between CCN concentration and in most LWC bins, regardless of the source of the CCN, while a weak but statistically significant positive correlation between and DMS was observed. No correlation between the cloud droplet number concentration and DMS was found. The presence of MSA indicated that DMS‐to‐sulfate photolysis was likely occurring, but data sparsity prevented a statistically significant conclusion regarding the relationship between MSA and . Data sparsity in decoupled conditions also prevented statistically significant conclusions. To properly address biogenic gas impacts on cloud microphysics, it is recommended that aircraft data be supplemented by long‐term biogenic gas measurements at the surface in marine locations with appropriate remote and in‐situ cloud sensing capabilities, and the analysis limited to well‐mixed MBL's.

South-hemispheric marine aerosol Hg and S isotope compositions reveal different oxidation pathways

Particle-bound mercury (PBM) records the oxidation of elemental mercury, of which the main oxidation pathways (Brž/Clž/OHž/O3) remain unclear, especially in the Southern-Hemisphere. Here, we present latitudinal covariations of Hg and S-isotopic anomalies in cross-hemispheric marine aerosols that evidence an equator-to-poleward transition of Hg oxidants from OHž/O3 in tropics to Brž/Clž in polar regions highlighting thus the presence of distinct oxidation processes producing PBM. The correlations between Hg, S and O-isotopic compositions measured in PBM, sulfates and nitrates respectively within the aerosols highlight the implication of common oxidants in their formations at different latitudes. Our results open a new window to better quantify the present-day atmospheric Hg, S and N budgets and to evaluate the influences of aerosols on climate and ecosystems once the isotopic fractionations associated to each process have been determined.

Extension of the AIOMFAC model by iodine and carbonate species: applications for aerosol acidity and cloud droplet activation

Abstract. Iodine and carbonate species are important components in marine and dust aerosols, respectively. The non-ideal interactions between these species and other inorganic and organic compounds within aqueous particle phases affect hygroscopicity, acidity, and gas–particle partitioning of semivolatile components. In this work, we present an extended version of the Aerosol Inorganic–Organic Mixtures Functional groups Activity Coefficients (AIOMFAC) model by incorporating the ions I−, IO3-, HCO3-, CO32-, OH−, and CO2(aq) as new species. First, AIOMFAC ion interaction parameters for aqueous solutions were determined based on available thermodynamic data, such as water activity, mean molal activity coefficients, solubility, and vapor–liquid equilibrium measurements. Second, the interaction parameters for the new ions and various organic functional groups were optimized based on experimental data or, where data are scarce, alternative estimation methods such as multiple linear regression or a simple substitution by analogy approach. Additional bulk water activity and electrodynamic balance measurements were carried out to augment the database for the AIOMFAC parameter fit. While not optimal, we show that the use of alternative parameter estimation methods enables physically sound predictions and offers the benefit of a more broadly applicable model. Our implementation of the aqueous carbonate–bicarbonate–CO2(aq) system accounts for the associated temperature-dependent dissociation equilibria explicitly and enables closed- or open-system computations with respect to carbon dioxide equilibration with the gas phase. We discuss different numerical approaches for solving the coupled equilibrium conditions and highlight critical considerations when extremely acidic or basic mixtures are encountered. The fitted AIOMFAC model performance for inorganic aqueous systems is considered excellent over the whole range of mixture compositions where reference data are available. Moreover, the model provides physically meaningful predictions of water activity under highly concentrated conditions. For organic–inorganic mixtures involving new species, the model–measurement agreement is found to be good in most cases, especially at equilibrium relative humidities above ∼ 70 %; reasons for deviations are discussed. Several applications of the extended model are shown and discussed, including the effects of ignoring the auto-dissociation of water in carbonate systems, the effects of mixing bisulfate and bicarbonate compounds in closed- or open-system scenarios on pH and solution speciation, and the prediction of critical cloud condensation nucleus activation of NaI or Na2CO3 particles mixed with suberic acid.

Type‐Dependent Impact of Aerosols on Precipitation Associated With Deep Convective Cloud Over East Asia

AbstractAerosol‐cloud‐precipitation interactions represent one of the most significant uncertainties in climate simulation and projection. In particular, the impact of aerosols on precipitation is highly uncertain due to limited and conflicting observational evidence. A major challenge is to distinguish the effects of different types of aerosols on precipitation associated with deep convective clouds, which produces most of the precipitation in East Asia. Here, we use 9‐yr observations from multiple satellite‐borne sensors and find that the occurrent frequency of heavy rain increases while that of light rain decreases with the increase of aerosol optical depth (AOD) for dust and polluted continental aerosol types. For average hourly precipitation amount, elevated smoke tends to suppress deep convective precipitation, while dust and polluted continental aerosols enhance precipitation mainly through the invigoration of deep convection. The invigoration effect is more significant for clouds with higher cloud base temperature (CBT), while no significant invigoration is observed when CBT is <12°C. A great contrast is found for the response of average hourly precipitation amount to aerosols over ocean and land. While the prevailing continental aerosol types other than smoke increase precipitation, the marine aerosols first enhance and then inhibit precipitation with the increase of AOD. Moreover, our analysis indicates that the above‐mentioned enhancement and inhibition effects on precipitation are mainly caused by aerosols themselves, rather than by the covariation of meteorological factors. These observed relationships between different aerosol types and precipitation frequency and amount provide valuable constraints on the model forecasting of precipitation.

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 (PM2.5N) was 35.1 ± 87.4 cm−3 and the mass concentration (PM2.5M) was 12.3 ± 9.1 μg/m3. The PM2.5N and PM2.5M 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 PM2.5N and PM2.5M are reduced by 120% and 7%. Coarse mode particle number concentration (PM2.5–10N) and mass concentration (PM2.5–10M) 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 PM2.5M/PM10M 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 PM2.5M/PM10M 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 PM2.5–PM5 particle size range.

Analysis and Sources Identification of Atmospheric PM10 and Its Cation and Anion Contents in Makkah, Saudi Arabia

In this paper, atmospheric water-soluble cation and anion contents of PM10 are analysed in Makkah, Saudi Arabia. PM10 samples were collected at five sites for a whole year. PM10 concentrations (µg/m3) ranged from 82.11 to 739.61 at Aziziyah, 65.37 to 421.71 at Sanaiyah, 25.20 to 466.60 at Misfalah, 52.56 to 507.23 at Abdeyah, and 40.91 to 471.99 at Askan. Both daily and annual averaged PM10 concentrations exceeded WHO and Saudi Arabia national air quality limits. Daily averaged PM10 concentration exceeded the national air quality limits of 340 µg/m3, 32% of the time at Aziziyah, 8% of the time at Sanaiyah, and 6% of the time at the other three sites. On average, the cations and anions made a 37.81% contribution to the PM10 concentrations. SO42−, NO3−, Ca2+, Na+, and Cl− contributed 50.25%, 16.43%, 12.11%, 11.12%, and 8.70% to the total ion concentrations, respectively. The minor ions (F−, Br−, Mg2+, NO2−, and PO43−) contributed just over 1% to the ion mass. Four principal components explained 89% variations in PM10 concentrations. Four major emission sources were identified: (a) Road traffic, including emission from the exhaust, wear-and-tear, and the resuspension of dust particles (F−, SO42−, NO3−, Ca2+, Na+, Mg+, Br−, Cl−, NO2−, PO43−); (b) Mineral dust (Cl−, F−, Na+, Ca2+, Mg2+, PO43−); (c) Industries and construction–demolition work (F−, SO42−, Ca2+, Mg2+); and (d) Seaspray and marine aerosols (Cl−, Br−, Mg2+, Na+). Future work would include an analysis of the metal contents of PM10 and their spatiotemporal variability in Makkah.

Sources of airborne particulate matter-bound metals and spatial-seasonal variability of health risk potentials in four large cities, South Korea

Fifteen airborne particulate matter-bound metals were analyzed at 14 sites in four large cities (Seoul, Incheon, Busan, Daegu) in South Korea, between August 2013 and June 2017. Among the seven sources resolved by positive matrix factorization, soil dust and marine aerosol accounted for the largest and second largest portions in the three cities; however, in Seoul, soil dust and traffic occupied the largest and the second largest, respectively. Non-carcinogenic risk assessed by inhalation of eight metals (Cd, Co, Ni, Pb, As, Al, Mn, and V) was greater than the hazard index (HI) of 1 at four sites located at or near the industrial complexes. Cumulative incremental lifetime cancer risk (ILCR) due to exposure to five metals (Cd, Co, Ni, Pb, and As) exceeded the 10−6 cancer benchmark at 14 sites and 10−5 at six sites, which includes four sites with HI greater than 1. The largest contributor to ILCR was coal combustion in Seoul, Incheon, and Daegu, and industry sources in Busan. Moreover, industry sources were the largest contributors to non-carcinogenic risk in Seoul, Busan, and Daegu, and soil dust was in Incheon. Incheon had the highest HI in spring because of the higher contribution of soil dust sources than in other seasons. The higher ILCR in Incheon in spring and winter and higher ILCR and HI in Daegu in autumn were mainly due to the influence of industry or coal combustion sources. Statistically significant differences in the ILCR and HI values among the sampling sites in Busan and Daegu resulted from the higher contribution of industry sources at a certain site in the respective city.

Marine aerosol properties over the Southern Ocean in relation to the wintertime meteorological conditions

Abstract. Given the vast expanse of oceans on our planet, marine aerosols (and sea salt in particular) play an important role in the climate system via multitude of direct and indirect effects. The efficacy of their net impact, however, depends strongly on the local meteorological conditions that influence their physical, optical and chemical properties. Understanding the coupling between aerosol properties and meteorological conditions is therefore important. It has been historically difficult to statistically quantify this coupling over larger oceanic areas due to the lack of suitable observations, leading to large uncertainties in the representation of aerosol processes in climate models. Perhaps no other region shows higher uncertainties in the representation of marine aerosols and their effects than the Southern Ocean. During winter the Southern Ocean boundary layer is dominated by sea salt emissions. Here, using 10 years of austral winter period (June, July and August, 2007–2016) space-based aerosol profiling by CALIOP-CALIPSO in combination with meteorological reanalysis data, we investigated the sensitivity of marine aerosol properties over the Southern Ocean (40–65∘ S) to various meteorological parameters, such as vertical relative humidity (RH), surface wind speed and sea surface temperature (SST) in terms of joint histograms. The sensitivity study is done for the climatological conditions and for the enhanced cyclonic and anticyclonic conditions in order to understand the impact of large-scale atmospheric circulation on the aerosol properties. We find a clear demarcation in the 532 nm aerosol backscatter and extinction at RH around 60 %, irrespective of the state of the atmosphere. The backscatter and extinction increase at higher relative humidity as a function of surface wind speed. This is mainly because of the water uptake by the wind-driven sea salt aerosols at high RH near the ocean surface resulting in an increase in size, which is confirmed by the decreased depolarization for the wet aerosols. An increase in aerosol backscatter and extinction is observed during the anticyclonic conditions compared to cyclonic conditions for the higher wind speeds and relative humidity, mainly due to aerosols being confined to the boundary layer, and their proximity to the ocean surface facilitates the growth of the particles. We further find a very weak dependency of aerosol backscatter on SSTs at lower wind speeds. However, when the winds are stronger than about 12 m s−1, the backscattering coefficient generally increases with SST. When aerosol properties are investigated in terms of aerosol verticality and in relation to meteorological parameters, it is seen that the aerosol backscatter values in the free troposphere (pressure &lt;850 hPa) are much lower than in the boundary layer, irrespective of the RH and the three weather states. This indicates that the local emissions from the ocean surface make the dominant contribution to aerosol loads over the Southern Ocean. A clear separation of particulate depolarization is observed in the free and lower troposphere, more prominent in the climatological mean and the cyclonic states. For RH &gt; 60 %, low depolarization values are noticeable in the lower troposphere, which is an indication of the dominance of water-coated and mostly spherical sea salt particles. For RH &lt; 60 %, there are instances when the aerosol depolarization increases in the boundary layer; this is more prominent in the mean and anticyclonic cases, which can be associated with the presence of drier aerosol particles. Based on the joint histograms investigated here, we provide third-degree polynomials to obtain aerosol extinction and backscatter as a function of wind speed and relative humidity. Additionally, backscattering coefficient is also expressed jointly in terms of wind speed and sea surface temperature. Furthermore, depolarization is expressed as a function of relative humidity. These fitting functions would be useful to test and improve the parameterizations of sea salt aerosols in the climate models. We also note some limitations of our study. For example, interpreting the verticality of aerosol properties (especially depolarization) in relation to the meteorological conditions in the free and upper troposphere (pressure &lt;850 hPa) was challenging. Furthermore, we do not see any direct evidence of sudden crystallization (efflorescence), deliquescence or hysteresis effects of the aerosols. Observing such effects will likely require a targeted investigation of individual cases considering tracer transport, rather than the statistical sensitivity study that entails temporally and geographically averaged large data sets.

On the role of aerosols in the production of orographically-induced extreme rainfall in near-maritime environments

The present study aims at disentangling the role of marine aerosols in extreme precipitation events of orographic nature over near-maritime locations. Being the hazardous character of these events mainly associated to runoffs and river floodings, their destructive potential makes them subjects of special interest. In pursuit of a deep understanding on the development mechanisms of such events, this study reproduces the conditions and development of an event ranging from 20 to 27 of December 2009 that took place in Southern Spain. During this event, a series of Atlantic fronts swept the southernmost part of the Iberian Peninsula which, along with water vapor entrainment in the form of an atmospheric river, produced rainfall accumulations up to 900 mm in some specific mountainous locations. With this purpose, a number of simulations are conducted to study the microphysical processes and aerosol-cloud interactions governing the rain production. The WRF model is utilized with two different configurations of the Morrison double-moment microphysics scheme: (1) with prescribed type and concentrations of aerosols (PA); and (2) a setup in which a chemistry module is coupled to the meteorological core (Interactive Aerosols, IA), allowing for the consideration of prognostic aerosol concentrations and other relevant aspects such as the hygroscopicity and dry size of the different chemical species. According to the validation performed with a database constructed from measurements of rain gauges, results show that using prognostic aerosols concentrations for natural aerosols, namely sea salt and dust, improves the model's skill for reproducing extreme rainfall with respect to the setup using the default aerosols distribution prescribed in the WRF-alone simulations. Additionally, IA simulations increase windward precipitation and reduce leeward rainfall, thus largely amplifying the spatial variability of precipitation along the direction of the moisture flux. Besides, it is observed that this effect is independent of the model resolution. Consequently, it is concluded that a realistic aerosols concentration, along with a detailed treatment of both the size and hygroscopic properties of aerosols, have a crucial impact on the microphysical processes involved in this type of orographically-induced extreme precipitation events. Specifically, under a regime of low concentration of cloud condensation nuclei originating from natural aerosols, the formed cloud droplets are more prone to grow to precipitating size, thus enhancing the auto-conversion rate.

The Sea Spray Chemistry and Particle Evolution study (SeaSCAPE): overview and experimental methods.

Marine aerosols strongly influence climate through their interactions with solar radiation and clouds. However, significant questions remain regarding the influences of biological activity and seawater chemistry on the flux, chemical composition, and climate-relevant properties of marine aerosols and gases. Wave channels, a traditional tool of physical oceanography, have been adapted for large-scale ocean-atmosphere mesocosm experiments in the laboratory. These experiments enable the study of aerosols under controlled conditions which isolate the marine system from atmospheric anthropogenic and terrestrial influences. Here, we present an overview of the 2019 Sea Spray Chemistry and Particle Evolution (SeaSCAPE) study, which was conducted in an 11 800 L wave channel which was modified to facilitate atmospheric measurements. The SeaSCAPE campaign sought to determine the influence of biological activity in seawater on the production of primary sea spray aerosols, volatile organic compounds (VOCs), and secondary marine aerosols. Notably, the SeaSCAPE experiment also focused on understanding how photooxidative aging processes transform the composition of marine aerosols. In addition to a broad range of aerosol, gas, and seawater measurements, we present key results which highlight the experimental capabilities during the campaign, including the phytoplankton bloom dynamics, VOC production, and the effects of photochemical aging on aerosol production, morphology, and chemical composition. Additionally, we discuss the modifications made to the wave channel to improve aerosol production and reduce background contamination, as well as subsequent characterization experiments. The SeaSCAPE experiment provides unique insight into the connections between marine biology, atmospheric chemistry, and climate-relevant aerosol properties, and demonstrates how an ocean-atmosphere-interaction facility can be used to isolate and study reactions in the marine atmosphere in the laboratory under more controlled conditions.