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• In Beijing's super sandstorm 2021, 5700 amplicon sequence variants were detected. • Airborne bacteria in sandstorms were compared with the after-storm and haze days. • The sandstorm newly brought 10 pathogenic bacterial genera to the atmosphere. • Small bioaerosols (0.65–1.1 µm) were still suspended after the sandstorm subsided. Sandstorm, which injects generous newly emerging microbes into the atmosphere covering cities, adversely affects the air quality in built environments. However, few studies have examined the change of airborne bacteria during severe sandstorm events. In this work, we analyzed the airborne bacteria during one of the strongest sandstorms in East Asia on March 15th, 2021, which affected large areas of China and Mongolia. The characteristics of the sandstorm were compared with those of the subsequent clean and haze days. The composition of the bacterial community of air samples was investigated using quantitative polymerase chain reaction (qPCR) and high-throughput sequencing technology. During the sandstorm, the particulate matter (PM) concentration and bacterial richness were extremely high (PM 2.5 : 207 µg/m3; PM 10 : 1630 µg/m3; 5700 amplicon sequence variants/m3). In addition, the sandstorm brought 10 pathogenic bacterial genera to the atmosphere, posing a grave hazard to human health. As the sandstorm subsided, small bioaerosols (0.65–1.1 µm) with a similar bacterial community remained suspended in the atmosphere, bringing possible long-lasting health risks. [Display omitted] [ABSTRACT FROM AUTHOR]

Hydroxymethylsulfonate (HMS) is an abundant secondary organic aerosol from aqueous or heterogeneous processes and may be misidentified as sulfate in conventional measurements. High concentrations of HMS have been observed in humid winter and autumn haze in northern China, while its prevalence in other seasons is unclear and the production medium is controversial. In this study, our field measurements in Beijing during the 2021 spring first showed the presence of HMS in PM 2.5 during both haze and sandstorm events despite the different atmospheric conditions. HMS accounted for 0.44% of PM 2.5 during haze periods, higher than the proportion (0.097%) during sandstorms. The sum of HMS and sulfate was also higher during the haze (6.5 μg m−3) than during the sandstorm (2.6 μg m−3), while the HMS/sulfate molar ratio during the haze (0.021) was similar to the value during the sandstorm (0.019). HMS concentration showed a good positive correlation with aerosol water content (AWC), indicating multiphase production. During haze periods, relatively high AWC favored the formation of HMS. In contrast, relative humidity and AWC decreased significantly during sandstorm events, while high pH favored HMS formation. In addition, higher concentrations and proportions of HMS were observed in PM 2.5−10 than in PM 2.5. The presence of HMS in dust particles indicated a heterogeneous formation mechanism of HMS on mineral aerosols. Our findings broaden the prevalence of HMS in aerosols and indicate a new HMS formation mechanism from the perspective of observation. [Display omitted] • Hydroxymethanesulfonate (HMS) existed in PM 2.5 during haze and sandstorm events. • Higher aerosol water content favored HMS formation during haze. • Higher pH favored HMS formation during sandstorms. • HMS was present in PM 2.5−10 and accounted for a higher percentage than in PM 2.5. • Field observations indicated the heterogeneous formation of HMS on mineral aerosols. [ABSTRACT FROM AUTHOR]

The short-, medium- and long-chain chlorinated paraffins (SCCPs, MCCPs, and LCCPs) were measured in outdoor fine particulate matter (PM 2.5) and gas-phases in Xi'an in spring, autumn and winter of 2021, which containing two special events during this time, the sandstorms happened in spring and the COVID-19 epidemic in winter. The CPs concentrations in PM 2.5 were seasonal variated, with spring (mean: 17.5 ng/m3) > autumn (mean: 8.6 ng/m3) > winter (mean: 5.8 ng/m3). The CPs concentrations in gas phases (mean:12.6 ng/m3) were lower than in PM 2.5 in spring, and it showed shorter carbon chain and lower chlorinated CPs dominated in SCCPs in gas phase (C 10 , Cl 5,6) compared with in PM 2.5 (C 11 , Cl 6,7). The absorption was the main mechanism for the partitioning of CP in particle and gaseous phase. The shorter carbon chain CPs (C 10,11 , C 14) with lower chlorinated (Cl 6,7) CPs dominated in SCCPs and MCCPs, while the longer carbon chain (C 25 or C 29) with Cl 6,12 dominated in the LCCPs. So, more researches about the LCCPs should be concerned. Additionally, the CPs concentrations of all samples during the sandstorms in spring were increased 30.4%–136.5% and the proportion of SCCPs was obviously elevated. CPs concentrations obviously decreased during the COVID-19 epidemic in winter, while SCCPs, MCCPs attributed comparable in autumn and winter. Potential source analysis showed that during the sandstorms in spring, atmospheric pollutants were mainly transported over a long distance from northern and northeast of Shaanxi Province, while it was mainly from local emission during the COVID-19 epidemic in winter. The health risk assessment of CPs displayed that there had no or very low inhalation exposure risks of CPs for all age groups, but the younger age groups (younger than 6 years old) should be played more attention for their not fully development of their immune and respiratory systems. [Display omitted] • The sandstorms greatly elevated the chlorinated paraffins levels, especially SCCPs. • CPs decreased in COVID-19 epidemic, with similar compositions as usual. • Shorter-chain and lower chlorinated CPs dominated in gas phase compare to PM 2.5. • The longer carbon chain CPs dominated in the LCCPs, unlike SCCPs and MCCPs. • Absorption mechanism had an important role in atmospheric partitioning of CPs. [ABSTRACT FROM AUTHOR]

Sandstorm is a disastrous weather phenomenon that often occurs in arid and semi-arid areas, endangering the ecological environment and affecting people's lives and property safety seriously. Since the 21st century, the sandstorm weather in the Yellow River Basin has ameliorated obviously. However, the causes of the long-term trends in sandstorms during 21st century were still unknown. In this study, fifteen influencing factors from five aspects: ecology, meteorology, hydrology, geography and man-made were selected to comprehensively analyze the driving mechanism of sandstorm activities in the Yellow River Basin since the 21st century, and the effect of each influencing factor on sandstorm weather was quantified. The results indicated that ecological, meteorological and geographical factors had dominant impacts on the spatio-temporal variation of sandstorms during 2000–2021, while hydrological and human factors played little role in the long-term variation of sandstorms. Sandstorms frequently occurred in semi-desert or grassland or non-high vegetation covered areas in spring. Vegetation coverage, precipitation, surface pressure, surface roughness, and soil moisture content were negatively correlated with sandstorms, while wind speed, friction velocity, evaporation, and soil temperature were positively correlated with sandstorms. Precipitation, runoff, evaporation, soil moisture content, soil temperature, and surface temperature indirectly acted on normalized brightness temperature dust index (NBTDI) and sandstorms by changing soil texture. Normalized Vegetation Index (NDVI) had direct negative effects on NBTDI, while wind speed 10 m (WS10m), slope of sub-gridscale orography (SOSGO), and forecast surface roughness (FSR) had direct positive effects on NBTDI. This study comprehensively revealed the dominant factors and their driving mechanism of sandstorm weather in the Yellow River Basin since the 21st century, which had practical application value for the prevention of sandstorms. [Display omitted] • Spatial heterogeneity existed in sandstorms drives across different regions during 2000–2021. • Precipitation, runoff, evaporation, soil moisture, and temperature indirectly affect sandstorms through soil texture. • SP, NDVI, ST, E, R and WS10m on the long-term change of sandstorm were more important. • Vegetation, evaporation, runoff, slope negatively affect sandstorms; wind, temperature positively. [ABSTRACT FROM AUTHOR]

Mineral dust particles play an important role in the formation of secondary inorganic aerosols, which largely contribute to haze pollution in China. During this study, a haze episode (haze days) and a typical haze process mixed with sandstorm (sandy haze days) were observed in Zhengzhou with a series of high-time-resolution monitoring instruments from November 22 to December 8, 2018. Concentrations of PM 10 and crustal elements clearly increased in the sandy haze days. Concentrations of gaseous pollutants, metallic elements emitted from anthropogenic sources, nitrate, and ammonium during sandy haze days were slightly lower than those during the haze days but still obviously higher than those during the non-haze days. The sulfate concentrations, the sulfate fractions in PM 2.5 , and the sulfur oxidation ratios significantly increased in the sandy haze days. Heterogeneous reactions dominated the conversion of SO 2 during the haze and sandy haze days. Enhanced SO 2 conversion during the sandy haze days may be attributed to the high concentrations of transition metal ions from the sandstorm when the values of relative humidity (RH) were in 30%–70%, and high O 3 at certain time points. Gas-phase NO 2 oxidation reactions were the main pathways for nitrate formation. In the sandy haze days, higher nitrogen oxidation ratio (NOR) at daytime may be associated with higher RH and lower temperature than those in the haze days, which facilitate the gas-to-particle partitioning of nitrate; higher NOR values at night may be attributed to the higher O 3 concentrations, which promoted the formation of N 2 O 5. Image 1 [ABSTRACT FROM AUTHOR]

[Display omitted] • The sandstorms presented a trend of decreasing first and then increasing. • The sandstorms mainly occurred in spring (92.4%) and winter (5.6%). • Hot spots of sandstorms were concentrated in the Loess Plateau and desert area. • In the future, sandstorm will become more frequent, in line with past trends. Sandstorm, as a disastrous weather phenomenon, seriously threatens the ecological environment and human health. In this study, the normalized brightness temperature dust index (NBTDI) data set of sandstorms in Yellow River Basin, China during 2000–2021 was constructed. Based on this, the temporal and spatial distribution pattern of sandstorms in the Yellow River Basin in the 21st century was analyzed. The variation trend of NBTDI in the past 22 years was discussed. The results showed that the interannual variation of sandstorms in the 21st century weakened first and then intensified. From the perspective of seasonal variation, sandstorm events occurred most frequently in spring (92.4%), followed by winter (5.6%), and occasionally in summer and autumn. In space, the distribution of sandstorms in the Yellow River Basin had obvious spatial heterogeneity. The central location of the sandstorm in the Yellow River Basin moved slightly to the north, but all of them were concentrated on desert areas. This was caused by the combination of unique geographical location and meteorological factors. The natural climate was closely related to the occurrence of sandstorms. The variation trend of long time-series NBTDI indicated that there were long memories between 22 years of sandstorms. NBTDI had an increasing trend in the long time series. In the future, sandstorms will become more frequent, in line with past trends. This study provides important data support for comprehensive understanding of extreme sandstorm weather, and has important significance for large-scale and long-term monitoring of sandstorm weather. [ABSTRACT FROM AUTHOR]

Air quality has significantly improved in China; however, new challenges emerge when dust weather is combined with haze pollution during spring in northern China. On March 15, 2021, an extremely severe sandstorm occurred in Beijing, with hourly maximum PM 10 and PM 2.5 concentrations reaching 5267.7 μg m−3 and 963.9 μg m−3, respectively. Continuous sandstorm events usually lead to complicated pollution status in spring. Three pollution types were identified disregarding the time sequence throughout March. The secondary formation type was dominant, with high ratios of PM 2.5 /PM 10 (mean 74%) and PM 1 /PM 2.5 (mean 52%). This suggests that secondary transformations are the primary cause of heavy pollution, even during the dry seasons. Sandstorm type resulted in dramatic PM 10 levels, with a noticeable decrease in PM 2.5 /PM 10 levels (27%), although PM 2.5 levels remain high. The transitional pollution type was distinguished by an independent increase in PM 10 levels, although PM 2.5 and PM 1 levels differed from the PM 10 levels. Throughout March, the sulfur oxidation rate varied considerably, with high levels during most periods (mean 0.52). A strong correlation indicated that relative humidity was the primary variable promoting the formation of secondary sulfate. Sandstorms promote heterogeneous reactions by providing abundant reaction surfaces from mineral particles, therefore aggravating secondary pollution. The sandstorm air mass from the northwest passing through the sand sources of Mongolia carried not only crustal matter but also organic components, such as bioaerosols, resulting in a sharp increase in the organic carbon in PM 2.5. [Display omitted] • Three types of air pollution were identified: secondary formation, sandstorm and transitional pollution. • Haze mixed with sandstorms caused more severe air pollution in Beijing. • Air masses from Mongolia with high bioaerosol burden led to increased organic carbon concentrations. [ABSTRACT FROM AUTHOR]

The present study addresses an intense sandstorm event over the Persian Gulf and its transport over the Arabian Sea region and the Indian sub-continent using satellite observations and measurements. MODIS data are used to analyze the temporal variation of the dust events that occurred from 17 to 24 March 2012 with the strongest intensity on 20 March over the Arabian Sea. MODIS images are examined to provide an independent assessment of dust presence and plume location and its migration over the Arabian Sea to the Indian sub-continent. Dust enhancement and dust detection procedure is attempted to demarcate the dust event. Dust source, formation, transportation path, and dissipation is studied using source-back-tracking, surface wind, and surface pressure, wind speed and direction, geo-potential height for different pressure level, and remote sensing methods. Finally, an attempt is made to investigate the impact of super sandstorm on the Arabian Sea by studying sea surface temperature and chlorophyll a variability during the events. It is noted that sea surface temperature is decreased and chlorophyll a concentration increased during the post-event period. The present study demonstrates the use of remote sensing data and geospatial techniques in detecting and mapping of dust events and monitoring dust transport along specific regional transport pathways over land and ocean. [ABSTRACT FROM AUTHOR]

Abstract: This study reports findings on observed visibility reductions and associated concentrations of mineral dust from a detailed Australian case study. An understanding of the relationship between visibility and dust concentration is of considerable utility for wind erosion and aeolian dust research because it allows visibility data, which are available from thousands of weather observation stations worldwide, to be converted into dust concentrations. Until now, this application of visibility data for wind erosion/dust studies has been constrained by the scarcity of direct measurements of co-incident dust concentration and visibility measurements. While dust concentrations are available from high volume air samplers, these time-averaged data cannot be directly correlated with instantaneous visibility records from meteorological observations. This study presents a new method for deriving instantaneous values of total suspended dust from time averaged (filter-based) samples, through reference to high resolution PM10 data. The development and testing of the model is presented here as well as a discussion of the derived expression in relation to other visibility-dust concentration predictive curves. The current study is significant because the visibility-dust concentration relationship produced is based on visibility observations made 10–100 km from the dust sources. This distance from source makes the derived relationship appropriate for a greater number of visibility recording stations than widely-used previous relationships based on observations made directly at eroding sources. Testing of the new formula performance against observed total suspended dust concentrations demonstrates that the model predicts dust concentration relatively well (r 2 = 0.6) from visibility. When considered alongside previous studies, the new relationship fits into the continuum of visibility-dust concentration outcomes existing for increasing distance-from-source. This highlights the important influence that distance to source has on the visibility-dust concentration relationship. [Copyright &y& Elsevier]

Sandstorms are natural climate calamities causing severe weather changes and health problems. The sandstorm allied issues are of significant apprehension worldwide, mainly in the present pandemic. This study aims to examine the "sandstorm impact on environmental pollution particulate matter (PM 2.5), carbon monoxide (CO), ozone (O3), and daily new cases and deaths due to Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2)" in Kuwait. The two incidences of sandstorms occurred in Kuwait, dated 13 March 2021 and 13 June 2021. The data on "PM 2.5 , CO, NO2, and O3, and SARS-CoV-2 cases and deaths" were documented three weeks before and after both incidences of the sandstorm. For the first incidence, the data was recorded from 18 February to 12 March 2021; and from 13 March to 2 April 2021. However, for the second incidence of sandstorms, data were documented from 23 May to 12 June 2021; and from 13 June to 3 July 2021. The daily "PM 2.5 , CO, NO2, and O3 levels" were recorded from "Air Quality Index-AQI, metrological web, and data on COVID-19 daily cases and deaths were recorded from the World Health Organization". After the first and second sandstorm incidence, the air contaminants PM 2.5 was increased by 26.62%, CO 22.08%, and O3 increased 18.10% compared to before the sandstorm. SARS-CoV-2 cases were markedly amplified by (21.25%), and deaths were increased by (61.32%) after the sandstorm. Sandstorm events increase air pollutants PM2.5, CO, and O3 levels, and these pollutants increase the SARS-COV-2 daily cases and deaths in Kuwait. The findings have a meaningful memorandum to healthcare representatives to advise the public about the health hazards of the sandstorm and its linkage with SARS-CoV-2 cases and deaths. [ABSTRACT FROM AUTHOR]

Abstract: The effects of blowing dust on transport operations are often mentioned as one of the significant impacts of aeolian processes on human welfare. However, few studies have been presented to demonstrate this impact. This research examined official air traffic incident reports in Australia for inclusively 1969–2010 to characterise the hazard of blowing dust to aviation in the country, the first such study of its kind. For the 42 year record, 61 incidents were identified (mean 1.4 per annum), with the large majority occurring in the first half of the 1970s. Only 20% of incidents occurred from 1984 onwards. Australian dust activity has not decreased over time, and the reduction in incidents is partly explained by improvements in aviation technology. The centralisation of Air Traffic Control operations to major coastal cities may however have reduced pilot reporting of dust-induced aviation incidents. By type of dust activity, dust storms were associated with nearly half of the reported incidents and dust hazes produced around a quarter. Only 5% of incidents resulted in any physical damage to aircraft and only one case involving personal injury was reported. The majority of the adverse effects on aviation due to dust (nearly 60% of reported incidents) were related to difficulties for navigation and completion of scheduled journey. Since aircraft damage and bodily harm were rare, the impact of dust in Australia is mostly that of inconvenience and associated raised economic costs. From 1990, the temporal pattern of incidents does not show any significant increase despite several intensely dusty years associated with recent droughts. This suggests that Australian aviation safety may be relatively resistant to the adverse effects of atmospheric dust as a hazard. [Copyright &y& Elsevier]

Abstract: Objective: Arid areas in the Arabian Peninsula are one of the largest sources of global dust, yet there is no data on the impact of this on human health. This study aimed to investigate the impact of dust storms on hospital admissions due to asthma and all respiratory diseases over a period of 5years in Kuwait. Methods: A population-based retrospective time series study of daily emergency asthma admissions and admissions due to respiratory causes in public hospitals in Kuwait was analyzed in relation to dust storm events. Dust storm days were defined as the mean daily PM10 >200μg/m3 based on measurements obtained from all six monitoring sites in the country. Findings: During the five-year study period, 569 (33.6%) days had dust storm events and they were significantly associated with an increased risk of same-day asthma and respiratory admission, adjusted relative risk of 1.07 (95% CI: 1.02–1.12) and 1.06 (95% CI: 1.04–1.08), respectively. This was particularly evident among children. Conclusion: Dust storms have a significant impact on respiratory and asthma admissions. Evidence is more convincing and robust compared to that from other geographical settings which highlights the importance of public health measures to protect people''s health during dust storms and reduce the burden on health services due to dust events. [Copyright &y& Elsevier]

Abstract: The Mie theory and Rayleigh approximation are two basic methods to study the EM scattering of uncharged spherical particle, and when the particle radius is much smaller than the incident wavelength, they are equivalent, but whether the Rayleigh approximation is still equivalent to Mie theory when we use them to calculate the EM scattering of small charged particle, there is still no any report published to discuss this problem. In this paper we make some comparisons between Mie theory and Rayleigh approximation to solve the EM scattering of partially electrification spherical particles. The results showed that the Mie theory would be more suitable to calculate the scattering of charged spherical particles. [Copyright &y& Elsevier]

An empirical method is used to estimate the aerosol direct radiative forcing (ADRF) over 20oN − 40oN regions from March 2000 to March 2019. The ADRF is calculated as the difference between the cloud-free sky and clean-sky (non-aerosol) radiative fluxes, which are fitted to an exponential function of the aerosol optical depth (AOD). The regional averaged ADRFs are negative (cooling effect) at the surface (SUR) and the top of atmosphere (TOA) and positive (warming effect) in the atmosphere (ATM). The spatial and temporal distributions of ADRF are closely linked to the spatio-temporal distributions of AOD. Higher AOD and stronger ADRF are found in spring (March to May) and summer (June to August). ADRFs are larger in regions with frequent sandstorm outbreaks and rapid economic growth since 2000 than other regions. The uncertainty of ADRF due to data source is 1.12 W/m2 at the surface and 0.91 W/m2 at the TOA according to the stochastic error propagation function. The ADRFs in our study regions show statistically significant but different changes of −0.074 W/m2 /year and 0.1 W/m2 /year at the surface during 2000 to 2009 and 2010 to 2019, respectively. Recent trend analysis also shows that the reduced aerosol contributes to the increasing short-wave flux about 0.32 W/m2 under the background of the global warming during the period from 2000 to 2019 in our study area, which indicates that it may alter the pattern of atmospheric circulation or enhance the global warming effect. • An empirical method is used to estimate the aerosol direct radiative forcing (ADRF). • ADRF spatial distribution is highly related to sandstorm & anthropogenic activities. • ADRFs show increasing cooling effect (−0.074 W/m2/year) at the surface in 2000–2009. • ADRFs show decreasing cooling effect (0.10 W/m2/year) at the surface in 2010–2019. • Reduced aerosol cooling effect contributes to further warming over the study region. [ABSTRACT FROM AUTHOR]

Abstract: With the warming and drying of climate and desertification, sandstorms are occurring on a more frequent basis. In China, high-frequency regions of sandstorms tend to correspond with the spring wheat regions between the end of February and the end of March. During March to May each year, when sandstorms frequently occur, the seedlings of spring wheat are young and susceptible to being uprooted by the winds. There is not enough plant coverage or root depth at this early stage to hold the soil from the fierce winds. As a result, the young plant life is destroyed and leaving the top soil susceptible to being blown about when in the path of high-frequency regions of sandstorms. By contrast, the seeding time of winter wheat is about September–October corresponding to lowest-frequency period of sandstorms. From the end of February to the middle of March, the winter wheat begins to turn green (ahead of 10 day than grass). During March to May when sandstorm frequently occurs, the winter wheat has come into a mature tillering or jointing stage. By then, the leaf area index is 1–4 and height is up to 20–50 cm, by which the loose soil is more compacted and covered with the fledging wheat. The result is that the energy of the air current is gradually dissipated and the wind speed near the ground is greatly weakened. So, without bare uncovered soil being whipped by powerful winds, the resulting sandstorms are greatly mitigated or weakened. After investigating the trend of global warming, the geological history-forming mechanism of sandstorms and their temporal–spatial distributions, and test for the last few years, the result is that by replacing spring wheat with winter wheat in high-frequency sandstorm regions, the damages of sandstorm are greatly reduced. Thus, by significantly increasing the vegetal cover time of ground during the windy season, one can alleviate the hazard index of sandstorms, which is a social, ecological and economic favorable result. [Copyright &y& Elsevier]

A large share of future solar energy plants is going to be located in desert environments where the involved aging effects of the installed components still exhibit a lack of knowledge. The acquired data within this project is considered of high interest for plant developers because for the first time representative samples were exposed at three heights above ground (1.2, 2.4 and 3.6 m) and varying orientations at a Moroccan site which is known to exhibit significant sandstorm activity for 12 months. Additionally, the present wind velocities and directions were measured. It could be concluded, that the strongest reflectance losses are detected on the samples which are orientated towards the directions from which the maximum wind velocities were measured, even though their frequency was three orders of magnitude smaller than the frequency of intermediate winds. Furthermore, an explicit height dependence of the erosion effects with increasing distance from the ground is demonstrated. Analysis of the horizontal inclination angles showed that the reflectors exposed at 90° experienced twice the damage that was measured at the reflectors exposed at 45°. This is in line with theoretical assumptions and results from laboratory experiments dealing with the dependence of erosion effects on the impact angle. • Outdoor exposure of CSP mirrors at a site of frequent sandstorm occurrence. • Exposure accompanied by meteorological and geological data acquisition. • Analysis of erosion damage in dependence of wind velocity and direction. • Analysis of erosion damage in dependence of height above ground. • Analysis of erosion damage in dependence of horizontal inclination angle. [ABSTRACT FROM AUTHOR]

• Investigating 3-D behavior of sand particles in the presence of a rigid wall barrier. • Specify effect of wind speed and sand diameter on the design of rigid wall barrier. • Determine relation between the shelter distance and the barrier height. • Determine the proper distance of rigid wall barriers along the railway tracks. Wind flow moves sand particles in a gas–solid multiphase environment by application of lifting and thrusting forces. This study uses the Reynolds-averaged Navier–Stokes equations and the dense discrete phase method-kinetic theory of granular flow. The study also uses Eulerian and Lagrangian models to simulate air and sand particles, respectively. The goal is to numerically study the behavior of sand particles in the presence of a rigid wall barrier to determine the relationship between the shelter distance (the safe distance after the barrier to prevent sand particle deposition) and the barrier height at different wind speeds. Therefore, sand particles with different mean diameters and mass distributions on the eastern railway line (Tabas), Iran, are examined under different wind speeds. The results indicate that the particles will be deposited at a certain distance after the barrier given their size and wind speed. Accordingly, increasing the diameter of the particles will decrease the shelter distance after the barrier, while increasing the wind speed will increase this distance. Finally, from the discussion of the location of railway tracks around the rigid wall barrier, it is found that a minimum height of 1.2 m is required to create a 17-meter shelter distance, by taking into considerations sandstorms in the eastern Iran. The results can be used to determine the proper distance of rigid wall barriers in desert areas according to specific sand diameter distribution and wind speeds. [ABSTRACT FROM AUTHOR]

• Mixed haze was composed of regional transport, secondary conversion, and sandstorm. • N 2 O 5 hydrolysis at high relative humidity was the driving factor for high PM 2.5. • Sandstorm with low PM 2.5 /PM 10 ratios (<30%) is responsible for high PM 10. In the Northern China Plain (NCP), extreme haze events with high concentrations of fine particles occur frequently during the winter but rarely occur in autumn. In this study, we present a synthetic analysis of particulate constituents during the historically polluted transition period of autumn–winter in 2018, revealing that mixed-type haze episodes are the result of regional transport, homogeneous/heterogeneous conversion, and sandstorm influences. The hydrolysis process of N 2 O 5 at higher relative humidity levels (>70%), which feature an enhanced nitrate oxidation ratio (0.30–0.70) and NO 3 − concentration (>60 μg m−3), was the driving factor for high PM 2.5 mass concentrations during the observation periods. The long-distance transport of sandstorms, characterized by decreasing PM 2.5 /PM 10 ratios (<30%) from the north/northwest, is the most important factor for the explosive growth of PM 10 concentration. These results can help us gain a comprehensive understanding of haze formation and highlight the importance of nitrate chemistry in the aqueous phase. The results suggest that persistent NO x emission reduction measures must be made to better achieve air quality standards in Beijing and the NCP region. [ABSTRACT FROM AUTHOR]