Asian Dust Particles Research Articles

Observational evidence for the non-suppression effect of atmospheric chemical modification on the ice nucleation activity of East Asian dust

Airborne mineral dust triggers ice formation in clouds and alters cloud microphysical properties by acting as ice-nucleating particles (INPs), potentially influencing weather and climate at regional and global scales. Anthropogenic pollution would modify natural mineral dust during the atmospheric transport process. However, the effects of anthropogenic pollution aging on the ice nucleation activity (INA) of mineral dust remain not well-understood. In this study, we investigated the immersion mode ice nucleation properties and particle chemical characterizations of collected size-resolved Asian dust samples (eight particle size classes ranging from 0.18 to 10.0 μm), and testified the chemical modification of aged dust particles via particle chemistry and morphology analyses including the mass concentrations of particulate matter, the water-soluble ion concentrations, the mental element concentrations, and single-particle morphology. The mass fraction of Ca2+ in element Ca and the mean relative mass proportions of supermicron Ca2+ increased by 67.0 % and 3.5–11.2 % in aged Asian dust particles, respectively, suggesting the occurrence of heterogeneous reactions. On the other hand, the total INP concentrations (total NINP) and total ice nucleation active site densities (total ns(T)) were consistent between aged and normal dust particles (0.62–1.18 times) without a statistically significant difference. And the NINP and ns(T) of chemically aged supermicron dust (1.0–10.0 μm) in each particle size class were nearly equal to or slightly higher than those of normal Asian dust, which were 0.70–2.45 times and 0.64–4.34 times at −18 °C, respectively. These results reveal that anthropogenic air pollution does not notably change the INP concentrations and does not impair the INA of Asian dust. Our work provides direct observational evidence and clarifies the non-suppression effect of anthropogenic air pollution on the INA of East Asian dust, advancing the understanding of the ice nucleation of airborne aged mineral dust.

Adhesion of Asian Dust Particles to Verofilcon a Soft Contact Lenses.

Asian dust poses a serious global health hazard. Airborne particles adhering to contact lenses may cause substantial damage to the ocular surface. The recently released one-day disposable silicone hydrogel soft contact lens (SCL), the verofilcon A, has a smooth surface with SMARTSURFACE® technology, which is designed to prevent adhesion of protein components and foreign bodies. The purpose of this study was to verify the protective quality of verofilcon A SCL against adhesion of Asian dust particles to its surface. Verofilcon A and etafilcon A (control lens) SCLs were used (n=16 per group), and 0.2 mL of physiological saline containing 0.01 mg/mL of Asian dust particles was dropped on the surface of SCLs, allowed to stand for 1 hour, shaken for 1 minute, and rinsed three times with saline (after rinsing). In addition, the samples were agitated by a vortex mixer for 1 minute and rinsed three times with saline (after vortex). The number of Asian dust particles adhering to the SCLs and percentage of the surface area occupied by the Asian dust particles was determined before washing, after rinsing, and after vortexing. The number of adherent Asian dust particles was lower on verofilcon A SCL (297 ± 116 after rinsing, and 5 ± 14 after vortexing) than on etafilcon A SCL (523 ± 212 after rinsing, p=0.003, and 378 ± 268 after vortexing, p<0.001). The Asian dust adhesion area was also lower on verofilcon A SCL (3.6 ± 2.3% after rinsing and 0.0 ± 0.1% after vortexing than on etafilcon A (10.2 ± 2.1% after rinsing, p=0.002, and 5.2 ± 3.0% after vortexing, p<0.001). These findings indicate that verofilcon A SCL has the property of low adhesion of Asian dust particles. Verofilcon A SCL can be recommended for SCL wearers during windy and Asian dust days.

Exacerbation of PM2.5 concentration due to unpredictable weak Asian dust storm: A case study of an extraordinarily long-lasting spring haze episode in Seoul, Korea

Severe haze episodes have occurred frequently throughout megacities in East Asia, especially during winter and early spring. Although notable progress has been attained in understanding the causes of severe haze formation, the exacerbation of PM2.5 concentration due to Asian dust has not yet been fully investigated. Here, we investigated the contribution of weak Asian dust particles to PM2.5 concentration during early spring for an extraordinarily long-lasting high PM2.5 episode in Seoul, Korea. PM2.5 concentrations exceeding national criteria (35 μg m−3) were continuously observed from February 27 to March 7, 2019, and can be attributable to the transboundary transported aerosols for the Asian continent under slow eastward-migrating anticyclones. The high-frequency of PM10-2.5 and PM2.5 mass concentrations in the high concentration regime (PM10-2.5 > 30 μg m−3; PM2.5 > 80 μg m−3) suggests that Asian dust particles transported concurrently with anthropogenic pollution aerosols contributed to elevated PM2.5 concentration during this episode. This was also evident from an elevated depolarization ratio (δ532: 0.06–0.13) and aerosol volume concentrations both in coarse and fine modes, which indicates the presence of non-spherical dust particles, from collocated aerosol lidar and optical particle counter measurements. Unlike severe Asian dust episodes (PM10 > 800 μg m−3) in Korea, relatively low Asian dust particle concentrations during high PM2.5 haze episodes have not been accurately predicted and alerted by most air quality forecasting models. This study emphasizes the need for the implementation of a series of dust emission and transport processes for better predictions of PM2.5 concentration during winter-spring high PM2.5 episodes.

Origins of free and combined amino acids in the aerosols at an inland urban site in Japan

A year-round observation of the free amino acids (FAA) and combined amino acids (CAA) in coarse and fine aerosols were conducted at an urban site in Japan. The averaged concentrations of the total FAA and total CAA measured in this study were 149.9 and 237.6 pmolN m−3, respectively, in coarse aerosols, and 177.9 and 562.2 pmolN m−3, respectively, in fine aerosols. The concentrations of the total CAA were higher than those of the total FAA in both mode ranges. The CAA were mainly partitioned into the fine-mode range, whereas the FAA were contained in both mode ranges with a similar concentration level. Only 8.1% of the water-soluble organic nitrogen (WSON) in fine aerosols was explained by these amino acids, although a significant contribution (26.4%) of them to the WSON was found in coarse aerosols. Correlation and factor analyses including these amino acids and other chemical species in the aerosols and gas phase were conducted to discuss potential sources of these amino acids. Plant debris and their associated materials, sea-salt, and Asian dust particles would be important potential sources of the coarse-mode FAA. The most dominant FAA in coarse aerosols was serine that is considered to be derived from sea-salt and Asian dust particles, whereas the other major FAA in coarse aerosols would be from plant debris and associated materials. The coarse-mode CAA can be also considered to be mainly from plant debris and associated materials. Glutamic acid and aspartic acid were dominant in the coarse-mode CAA, and estimated to be from these sources. Significant parts of the fine-mode FAA would be derived from the photochemical aging of the fine-mode CAA in polluted air masses from the Asian continent. Glycine and arginine were dominant in the fine-mode FAA, and estimated to be from the photochemical aging process. The fine-mode CAA is considered to be mainly from both the fossil fuel and biomass burning particles from both the Asian continental and local sources. Glutamic acid and glycine were dominant in the fine-mode CAA, and would be mainly from these sources, especially the Asian continental sources. Serine that is the most dominant compound in the fine-mode CAA, however, is considered to be derived from other unidentified sources.

Size-resolved atmospheric ice-nucleating particles during East Asian dust events

Abstract. Asian dust is an important source of atmospheric ice-nucleating particles (INPs). However, the freezing activity of airborne Asian dust, especially its sensitivity to particle size, is poorly understood. In this study we report the first INP measurement of size-resolved airborne mineral dust collected during East Asian dust events. The measured total INP concentrations in the immersion mode ranged from 10−2 to 102 L−1 in dust events at temperatures between −25 and −5 ∘C. The average contributions of heat-sensitive INPs at three temperatures, −10, −15, and −20 ∘C, were 81±12 %, 70±15 %, and 38±21 %, respectively, suggesting that proteinaceous biological materials have a substantial effect on the ice nucleation properties of Asian airborne mineral dust at high temperatures. The dust particles which originated from China's northwest deserts are more efficient INPs compared to those from northern regions. In general, there was no significant difference in the ice nucleation properties between East Asian dust particles and other regions in the world. An explicit size dependence of both INP concentration and surface ice-active-site density was observed. The nucleation efficiency of dust particles increased with increasing particle size, while the INP concentration first increased rapidly and then leveled, due to the significant decrease in the number concentration of larger particles. A new set of parameterizations for INP activity based on size-resolved nucleation properties of Asian mineral dust particles were developed over an extended temperature range (−35 to −6 ∘C). These size-dependent parameterizations require only particle size distribution as input and can be easily applied in models.

Characteristic time for the scavenging of fine particles due to coagulation with coarse particles

This article suggests an approximate analytical solution for the characteristic time for the mass removal of fine particles due to coagulation scavenging by coarse particles. The characteristic scavenging time is expressed as a function of the mass concentration of coarse particles as well as the mass median diameters (MMDs) and geometric standard deviations of fine and coarse particles. The log-normal method of moments was used to take into account the polydispersity effects. The particle number concentration of coarse particles was found to be the most important factor determining the coagulation-scavenging rate. Sensitivity analyses were conducted to quantify the effects of the particle size distribution parameters. The characteristic scavenging times for three specific cases, urban aerosols, Asian dust particles, and indoor aerosols, are discussed based on the derived solution.

Optical Modeling of Single Asian Dust and Marine Air Particles: A Comparison with Geometric Particle Shapes for Remote Sensing

We compare the optical properties of various geometric shapes with single atmospheric Asian dust and marine background air particles collected at Mauna Loa Observatory. Three-dimensional representations of the particles were acquired with focused ion-beam (FIB) tomography, which involves FIB milling of individual particles followed by imaging and elemental mapping with scanning electron microscopy. Particles were heterogeneous with mainly dolomite or calcite and a minor amount of iron; marine air particles contained gypsum but no iron. Extinction and backscatter fraction were calculated with the discrete dipole approximation method. Geometric shapes were grouped as ellipsoids (sphere, spheroid, ellipsoid), cuboids (cube, square prism, rectangular prism), and pyramids (tetrahedron, triangular pyramid). Each group represented a progression of shapes with 1, 2, or 3 non-identical axes. Most shapes underestimated particle extinction and overestimated the backscatter fraction. Not surprisingly, extinction and the backscatter fraction of the sphere and cube were furthest from those of the particles. While the 3-axis ellipsoid and rectangular prism were closer dimensionally to the particles, extinction and the backscatter fraction for the 2-axis spheroid and square prism, respectively, were often closer to the particles. The extinction and backscatter fraction for the tetrahedron and triangular pyramid were closer on average to the actual particles than were the other shapes. Tetrahedra have the advantage that parameterization of an aerosol model for remote sensing would not require an aspect ratio distribution. Particle surface roughness invariably decreased the backscatter fraction. While surface roughness typically contributes a minor part to overall scattering, in some cases the larger surface area of the tetrahedron and triangular pyramid sufficiently accounted for enhanced forward scattering of particles from surface roughness.

Influence of the morphological change in natural Asian dust during transport: A modeling study for a typical dust event over northern China

The effect of the nonsphericity of mineral dust aerosols on its deposition and transport was investigated based on model simulation for a typical dust event over northern China from April 6 to 12, 2018. The settling velocity related to morphological change in dust size was considered in Nested Air Quality Prediction Modeling System (NAQPMS) to simulate the dust spatial distribution. Comparison of these results with observations showed that the model reproduced the temporal variability in the mass concentration of particles along the dust plume pathway. The most frequently reported aspect ratio (λ) was 1.7 ± 0.2 for Asian dust aerosols. Changing the nonsphericity of the particle from typical prolate ellipsoids (λ = 1.7) to spherical ellipsoids (λ = 1) caused an ~3% decrease in the surface dust concentration on average. For particles with diameters >5 μm, nonsphericity caused a change in the surface dust concentration up to 10%, especially at the periphery of the dust source region. The overall effects on the fine dust (<2.5 μm) were not significant. A sensitivity study using a more extreme nonspherical shape (λ = 2) showed that the differences in PM10 concentration were evident, and the surface dust concentration increased by 15 ± 5% as a result of an ~10% decrease in settling velocity. These results confirmed that the effect of the variability in the nonsphericity of Asian dust particles on their regional transport highly depended on synoptical and pollution conditions, and the adoption of a deposition value that changes over time due to this morphological variability could improve the performance of dust modeling and the assessment of climate effects on a global scale, especially for transboundary processes.

Asian Sand Dust Particles Increased Pneumococcal Biofilm Formation in vitro and Colonization in Human Middle Ear Epithelial Cells and Rat Middle Ear Mucosa.

IntroductionAir pollutants such as Asian sand dust (ASD) and Streptococcus pneumoniae are risk factors for otitis media (OM). In this study, we evaluate the role of ASD in pneumococcal in vitro biofilm growth and colonization on human middle ear epithelium cells (HMEECs) and rat middle ear using the rat OM model.MethodsS. pneumoniae D39 in vitro biofilm growth in the presence of ASD (50–300 μg/ml) was evaluated in metal ion-free BHI medium using CV-microplate assay, colony-forming unit (cfu) counts, resazurin staining, scanning electron microscopy (SEM), and confocal microscopy (CF). Biofilm gene expression analysis was performed using real-time RT-PCR. The effects of ASD or S. pneumoniae individually or on co-treatment on HMEECs were evaluated by detecting HMEEC viability, apoptosis, and reactive oxygen species (ROS) production. In vivo colonization of S. pneumoniae in the presence of ASD was evaluated using the rat OM model, and RNA-Seq was used to evaluate the alterations in gene expression in rat middle ear mucosa.ResultsS. pneumoniae biofilm growth was significantly (P < 0.05) elevated in the presence of ASD. SEM and CF analysis revealed thick and organized pneumococcal biofilms in the presence of ASD (300 μg/ml). However, in the absence of ASD, bacteria were unable to form organized biofilms, the cell size was smaller than normal, and long chain-like structures were formed. Biofilms grown in the presence of ASD showed elevated expression levels of genes involved in biofilm formation (luxS), competence (comA, comB, ciaR), and toxin production (lytA and ply). Prior exposure of HMEECs to ASD, followed by treatment for pneumococci, significantly (P < 0.05) decreased cell viability and increased apoptosis, and ROS production. In vivo experiment results showed significantly (P < 0.05) more than 65% increased bacteria colonization in rat middle ear mucosa in the presence of ASD. The apoptosis, cell death, DNA repair, inflammation and immune response were differentially regulated in three treatments; however, number of genes expressed in co-treatments was higher than single treatment. In co-treatment, antimicrobial protein/peptide-related genes (S100A family, Np4, DEFB family, and RATNP-3B) and OM-related genes (CYLD, SMAD, FBXO11, and CD14) were down regulated, and inflammatory cytokines and interleukins, such as IL1β, and TNF-related gene expression were elevated.ConclusionASD presence increased the generation of pneumococcal biofilms and colonization.

Internal Structure of Asian Dust Particles over the Western North Pacific: Analyses Using Focused Ion Beam and Transmission Electron Microscopy

Mineral dust aerosols, which comprise multiple mineral species, are transported far from their source desert areas to the open ocean. After an Asian dust outflow event was observed over a marine boundary layer in the western North Pacific on February 29, 2012 on research vessel (R/V) Hakuho Maru, two dust particles of about 6 μm diameter were analyzed. First, they were sliced by using a focused ion beam (FIB). Their mineralogical structures and the elemental distribution of their cross-sections were subsequently analyzed with the use of transmission electron microscopy (TEM) and energy-dispersive X ray spectrometry (EDS). These analyses revealed that the dust particles consisted mainly of calcite and silica. Furthermore, Fe-containing domains were found in the submicrometer area surrounded by calcite and silica. A sulfur-containing domain that co-exists with calcium was found in a small domain near the particle surface, but no clear sign of atmospheric aging was found in most of the calcite domain. The inhomogeneous particle structure implies that the dissolution of iron and calcite in dust particles after ocean deposition depends on the physical structures of particles and their degree of aging according to atmospheric conditions during transport. Those factors must be adequately treated when estimating Asian dust effects on marine primary production.

Reactive iron isotope signatures of the East Asian dust particles: Implications for iron cycling in the deep North Pacific

Iron released from wind-blown dust has been widely suggested to be an important nutrient source for oceanic primary productivity. Once introduced into the seawater, the reactive Fe might get dissolved and impart its isotope signature into the water column. Characterization of the reactive iron isotope signatures of eolian dust will thus help to understand the budget of Fe in the global ocean. Yet, there are few systematic studies on the Fe isotope systematics of the dust sources across large spatial scale. Here, we report Fe isotope data from HCl leaching experiment on surficial samples from deserts and loess deposits of different locations spanning >3000 km spatially in east Asia, one of the most important dust source regions. Our data suggest most of the samples have relatively similar leaching signatures (δ56Fe = –0.09±0.07‰, n=9, 2 SD). To understand the kinetics of Fe release during proton promoted leaching of natural particles, a synthetic model taking into account of different dissolution dynamics of easily dissolvable Fe and silicate Fe was developed. The model was tested by continuous leaching of two representative pelagic sediment samples recovered from core LL44-GPC3 in the North Pacific. When introducing only one tunable parameter (i.e., the initial dissolution rate of Fe from hydro(oxides), with other parameters constrained by the dissolution kinetics), the model successfully reproduces leachate δ56Fe evolution and agrees reasonably well with Fe speciation in the studied marine sediment samples. We thus suggest that the leaching process can be well characterized by our kinetic model, while Fe isotopes in the initial leachates of the samples are dominated by endmember composition of the easily dissolvable Fe species. The small but distinct fractionation of Fe isotopes in the desert/loess samples from the parental upper continental silicate materials are suggested to record signatures of the secondary Fe species produced during weathering in the oxic environment. The significantly lighter Fe isotope compositions in the initial leachates of the North Pacific pelagic sediment samples compared to the east Asian desert/loess deposits indicate apparent isotope exchange of the dust reactive components with seawater dissolved species. The sedimentary light reactive Fe isotope signatures in turn point toward the contribution of sources characterized by low δ56Fe to the deep North Pacific and/or preferential uptake of 56Fe by seawater ligands from the dust reactive components particularly at the seawater-sediment interface.

Analysis and Optical Modeling of Individual Heterogeneous Asian Dust Particles Collected at Mauna Loa Observatory.

We have determined optical properties of heterogeneous particles from aerosol samples collected at Hawaii's Mauna Loa Observatory. Back trajectories, satellite imagery, and composition differences among particles from scanning electron microscopy revealed a subset of particles with dolomite or calcite that likely came from Asia. Using focused ion-beam tomography and the discrete dipole approximation, we show how small amounts of an iron phase (oxide or carbonate), or in one case soot, affected extinction and scattering compared with particles of neat dolomite or calcite. We show how particles exhibit a range scattering values due to varying orientations of the inclusion phases. Extinction efficiencies for the heterogeneous particles with dolomite (3.47) and calcite (3.36) were 19% to 21% lower than extinction for marine background air particles (3.72). Extinction for the Asian dust was, however, generally higher than for the neat particles. Compared to iron carbonate, the presence of an absorbing iron oxide affected scattering in Asian dust particles even at the low oxide concentrations studied here (0.6% to 8.1%). Scattering efficiency decreased by <1% with a 1% increase in hematite but by 2% to 5% with magnetite. Asian dust scattered light strongly forward, but backscattering was 56% larger than for the marine background air particles. Backscattering in the Asian dust was also larger with magnetite than hematite. Single scattering albedo for Asian dust with hematite, magnetite, or soot averaged 0.96 ± 0.06 but was as low as 0.72 with a magnetite mass of 5.8%.

Dust particles in free troposphere over Chinese desert region revealed from balloon borne measurements under calm weather conditions

The Taklamakan Desert in China is one of the major source regions for Asian dust particles. All balloon-borne measurements in this report were carried out in Dunhuang, in the Taklamakan Desert, dur...

Long-range-transported bioaerosols captured in snow cover on Mount Tateyama, Japan: impacts of Asian-dust events on airborne bacterial dynamics relating to ice-nucleation activities

Abstract. The westerly wind travelling at high altitudes over eastern Asia transports aerosols from the Asian deserts and urban areas to downwind areas such as Japan. These long-range-transported aerosols include not only mineral particles but also microbial particles (bioaerosols), that impact the ice-cloud formation processes as ice nuclei. However, the detailed relations of airborne bacterial dynamics to ice nucleation in high-elevation aerosols have not been investigated. Here, we used the aerosol particles captured in the snow cover at altitudes of 2450 m on Mt Tateyama to investigate sequential changes in the ice-nucleation activities and bacterial communities in aerosols and elucidate the relationships between the two processes. After stratification of the snow layers formed on the walls of a snow pit on Mt Tateyama, snow samples, including aerosol particles, were collected from 70 layers at the lower (winter accumulation) and upper (spring accumulation) parts of the snow wall. The aerosols recorded in the lower parts mainly came from Siberia (Russia), northern Asia and the Sea of Japan, whereas those in the upper parts showed an increase in Asian dust particles originating from the desert regions and industrial coasts of Asia. The snow samples exhibited high levels of ice nucleation corresponding to the increase in Asian dust particles. Amplicon sequencing analysis using 16S rRNA genes revealed that the bacterial communities in the snow samples predominately included plant associated and marine bacteria (phyla Proteobacteria) during winter, whereas during spring, when dust events arrived frequently, the majority were terrestrial bacteria of phyla Actinobacteria and Firmicutes. The relative abundances of Firmicutes (Bacilli) showed a significant positive relationship with the ice nucleation in snow samples. Presumably, Asian dust events change the airborne bacterial communities over Mt Tateyama and carry terrestrial bacterial populations, which possibly induce ice-nucleation activities, thereby indirectly impacting climate change.

The Effects of Asian Dust for Allergic Symptoms may be Partly Attributed to PAH-Quinone, Secondarily Formed on the Dust Surface – Observational Study in 3 Regions in Japan

Background/Aim: We showed that Asian dust (AD) exposure is associated with increased risk for exacerbations of asthma and allergic symptoms in children or pregnant women in Japan. AD particles contain anthropogenic pollutants such as PAHs. Further, its catalytic effects promote secondary-formation of chemicals, one of which, PAH-quinone is known to generate ROS in human body, which may contribute to allergic diseases. We estimated how much of the effects of AD are attributed to PAH-quinone. Methods: We conducted an observational study for 3,327 pregnant women during spring and fall in 2011-2013 in 3 regions in Japan as an adjunct study of Japan Environment and Children's Study. There, we timely acquired subjects’ daily allergic-symptoms by sending web-based questionnaires on some days for each participant. We also sampled TSP every day, and measured some PAH-quinones by HPLC. We estimated odds ratio (OR) of log-transformed AD per 1SD-change for occurrence of allergic symptom with interaction term of AD and PAH-quinone in the GEE logistic regression model. Results: Both AD and PAH-quinone showed significant associations with allergic symptom. Interaction term of AD and PAH-quinone was significantly larger than 0 (p&lt;.01), and the OR of AD (per log-transformed 1SD change) when log-transformed PAH-quinone is mean, was 1.12 (95%CI: 1.04-1.22), while the OR was 1.34 when log-transformed PAH-quinone is 1SD above the mean. Conclusions: The effect of AD was significantly exacerbated by the presence of PAH-quinone. We may be able to reduce the effects of AD by reducing PAH emissions.

Limited production of sulfate and nitrate on front-associated dust storm particles moving from desert to distant populated areas in northwestern China

Abstract. Sulfate and nitrate compounds can greatly increase the hygroscopicity of mineral particles in the atmosphere and consequently alter the particles' physical and chemical properties. Their uptake on long-distance-transported Asian dust particles within mainland China has been reported to be substantial in previous studies, but the production was very inefficient in other studies. We compared these two salts in particles collected from a synoptic-scale, mid-latitude, cyclone-induced dust storm plume at the Tengger Desert (38.79° N, 105.38° E) and in particles collected in a postfrontal dust plume at an urban site in Xi'an (34.22° N, 108.87° E) when a front-associated dust storm from the Tengger Desert arrived there approximately 700 km downwind. The results showed that the sulfate concentration was not considerably different at the two sites, while the nitrate concentration was slightly larger at the urban site than that at the desert site. The estimated nitrate production rate was 4–5 ng µg−1 of mineral dust per day, which was much less than that in polluted urban air. The adiabatic process of the dust-loading air was suggested to be the reason for the absence of sulfate formation, and the uptake of background HNO3 was suggested to be the reason for the small nitrate production. According to our investigation of the published literature, the significant sulfate and nitrate in dust-storm-associated samples within the continental atmosphere reported in previous studies cannot be confirmed as actually produced on desert dust particles; the contribution from locally emitted and urban mineral particles or from soil-derived sulfate was likely substantial because the weather conditions in those studies indicated that the collection of the samples was started before dust arrival, or the air from which the samples were collected was a mixture of desert dust and locally emitted mineral particles. These results suggest that the production of nitrate and sulfate on dust particles following cold fronts is likely limited when the particles move from the desert to populated areas within the continent. For an accurate quantification of sulfate and nitrate formed on long-distance-transported desert dust particles at downwind populated areas in eastern China, dust collection efforts are indispensable to minimize any possible influence by locally emitted particles or at least to ensure that the samples are collected after dust arrival.

Dust Storms from Degraded Drylands of Asia: Dynamics and Health Impacts

Asian dust events are massive meteorological phenomena during which dust particles from Chinese and Mongolian deserts are blown into the atmosphere and carried by westerly winds across Northeast Asia. Recently, there has been steady increase in both the frequency and the severity of Asian atmospheric dust events. Concern has been expressed regarding the potential health hazards in affected areas. The principal nature of the damage associated with Asian dust events differs between the emission (sandstorm) and downwind (air pollution) regions. In the emission region, the health impacts of dust storms are reflected in the high prevalence of respiratory diseases and severe subjective symptoms. Extreme dust storm events may cause a disaster to happen. In downwind regions such as Japan, analysis of Asian dust particles has shown the presence of ammonium ions, sulfate ions, nitrate ions, and heavy metal compounds that are considered not to originate from soil. Asian dust particles have been thought to adsorb anthropogenic atmospheric pollutants during transport. Therefore, Asian dust events coincide with increases in daily hospital admissions and clinical visits for allergic diseases such as asthma, allergic rhinitis, and conjunctivitis. Although the effect of Asian dust on human health in each region is influenced by a variety of different mechanisms, human activities are partly responsible for such negative effects in many situations. We therefore need to address these environmental problems.

Estimation of the effects of heavy Asian dust on respiratory function by definition type

BackgroundThe adverse effects of Asian dust (AD) on health have been demonstrated in earlier studies, but there is no standardized definition for heavy–AD. This study aimed to examine which definition of heavy–AD has the most adverse effect on respiratory function.MethodsOne–hundred–and–thirty–seven adults with asthma, and 384 school children self-measured their morning peak expiratory flow (PEF). The four definitions of heavy–AD are: (1) the definition provided by the Japan Meteorological Agency (JMA), (2) daily median AD particle level ≥ 0.07 km−1, obtained through light detection and ranging (LIDAR) (3) hourly AD particle level ≥ 0.1 km−1, and (4) hourly level ≥ 0.07 km−1. Linear mixed models were used to estimate the effects of heavy–AD, by definition type, on daily PEF values.ResultsIn adults with asthma, as per the JMA’s definition, significantly reduced PEF were observed on heavy–AD days (lag 0), lag 0–1, and lag 0–3. In school children, after a heavy–AD event, as defined by the JMA, PEF significantly decreased on lag 0–1, lag 0–2, and lag 0–3. However, as per the other definitions, there was no significant decrease in the PEF in the adults and children.ConclusionThe associations between heavy–AD and respiratory function differed between these definitions.

Association between transported Asian dust and outdoor fungal concentration during winter in a rural area of western Japan

BackgroundRecently, Asian dust (AD) has become a serious health problem and several studies have clearly proven that AD can aggravate asthma. However, it remains unclear as to which components of AD have a strong effect on the asthma exacerbation caused by AD exposure. Outdoor fungi can increase emergency department visits and hospitalization for asthma exacerbation and can aggravate asthma symptoms. Therefore, this study was aimed at investigating the relationship between AD and outdoor fungi and determining the potential of fungi to cause airborne particulate matter (PM)-related inflammatory responses.MethodsAirborne PM was collected each day from January 26, 2015 to February 27, 2015. Daily levels of outdoor fungi-associated PM were calculated using a culture-based method. Production of cytokines such as interleukin (IL)-6, IL-8, and tumor necrosis factor (TNF)-α was assessed in THP1 cells stimulated by the collected airborne PM each day.ResultsDaily levels of AD particles were assessed using Light Detection and Ranging and did not correlate with outdoor fungi (r = −0.17, P = 0.94). There was also no association between outdoor fungi and the daily production of IL-6 (r = 0.16, P = 0.37), IL-8 (r = 0.19, P = 0.30), or TNF-α induced by collected PM (r = 0.07, P = 0.70). However, the daily levels of AD particles were significantly associated with IL-6 (r = 0.91, P < 0.0001), IL-8 (r = 0.64, P = 0.0004), and TNF-α (r = 0.72, P < 0.0001) production.ConclusionAD did not increase the acute levels of outdoor fungi and outdoor fungi did not affect the cytokine production induced by airborne PM. These results suggest that outdoor fungi do not have any detectable effect on the asthma exacerbation caused by AD exposure.

Real-time observational evidence of changing Asian dust morphology with the mixing of heavy anthropogenic pollution

Natural mineral dust and heavy anthropogenic pollution and its complex interactions cause significant environmental problems in East Asia. Due to restrictions of observing technique, real-time morphological change in Asian dust particles owing to coating process of anthropogenic pollutants is still statistically unclear. Here, we first used a newly developed, single-particle polarization detector and quantitatively investigate the evolution of the polarization property of backscattering light reflected from dust particle as they were mixing with anthropogenic pollutants in North China. The decrease in observed depolarization ratio is mainly attributed to the decrease of aspect ratio of the dust particles as a result of continuous coating processes. Hygroscopic growth of Calcium nitrate (Ca(NO3)2) on the surface of the dust particles played a vital role, particularly when they are stagnant in the polluted region with high RH conditions. Reliable statistics highlight the significant importance of internally mixed, ‘quasi-spherical’ Asian dust particles, which markedly act as cloud condensation nuclei and exert regional climate change.