Formation of an unprecedented yellow snow episode in Xinjiang on December 1, 2018

On 1 December 2018, a heavy yellow snow fell in Urumqi (87°37'E, 43°47'N) - the largest city of northwest China's Xinjiang province, which was the first case that the yellow snow has been observed in winter. The air parcel trajectories obtained from Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model and the dust surface mass concentration from Modern-Era Retrospective Analysis for Research and Applications Version 2 (MERRA-2) were adopted to identify the potential sources and transport paths of pollutants responsible for this yellow snow episode. The meteorological situation and the European Center for Medium-Range Weather Forecasts (ECMWF) forecast products have been utilized to analyze the supportive meteorological conditions. The results showed that the heavy snow in Urumqi was contaminated by the yellow dust originated in Karamay of Xinjiang province. The strong surface winds in Karamay lifted large amounts of dust into the atmosphere. Then the airborne dusts were transported to Urumqi rapidly by strong low-level winds, where precipitation in connection with the upper trough and the cold front lead to the yellow snow episode. This study can provide important scientific significance for predicting this kind of event (yellow snow).

Origins of black carbon from anthropogenic emissions and open biomass burning transported to Xishuangbanna, Southwest China

Black carbon (BC) has importance regarding aerosol composition, radiative balance, and human exposure. This study adopted a backward-trajectory approach to quantify the origins of BC from anthropogenic emissions (BC_An) and open biomass burning (BC_BB) transported to Xishuangbanna in 2017. Haze months, between haze and clean months, and clean months in Xishuangbanna were defined according to daily PM_2.5 concentrations of >75, 35-75, and <35 µg/m³, respectively. Results showed that the transport efficiency density (TED) of BC transported to Xishuangbanna was controlled by the prevailing winds in different seasons. The yearly contributions to the effective emission intensity of BC_An and BC_BB transported to Xishuangbanna were 52% and 48%, respectively. However, when haze occurred in Xishuangbanna, the average BC_An and BC_BB contributions were 23% and 77%, respectively. This suggests that open biomass burning (BB) becomes the dominant source in haze months. Myanmar, India, and Laos were the dominant source regions of BC transported to Xishuangbanna during haze months, accounting for 59%, 18%, and 13% of the total, respectively. Furthermore, India was identified as the most important source regions of BC_An transported to Xishuangbanna in haze months, accounting for 14%. The two countries making the greatest contributions to BC_BB transported to Xishuangbanna were Myanmar and Laos in haze months, accounting for 55% and 13%, respectively. BC emissions from Xishuangbanna had minimal effects on the results of the present study. It is suggested that open BB in Myanmar and Laos, and anthropogenic emissions in India were responsible for poor air quality in Xishuangbanna.

Ecological restoration can enhance the radiation benefit of sand fixation service: A simulated evidence of Xilingol League, China

Large-scale ecological restoration programs have been initiated globally with the aim of combating desertification and improving ecosystem services, especially for sand fixation service (SF) in arid and semi-arid regions. However, the effectiveness of ecological restoration in the radiation benefit of SF, such as improving air quality, remains not well known. In this study, we selected Xilingol as the study area, investigated the dynamics of SF, and quantified the radiation benefit of SF in downwind areas by employing PM10 concentration as the proxy. The Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model was applied to assess the response of radiation benefit to ecological restoration by designing land use scenarios. Results showed that the SF in Xilingol increased with fluctuation at an average rate of 0.27%/year from 2000 to 2018. Under the effect of ecological restoration, the radiation benefit in the downwind regions was substantially improved, as manifested by a 104.22 μg/m³ reduction in PM10 concentration. The changes in radiation benefit varied greatly across space, and northern and southern Xilingol were hot spots for increased radiation benefit. Based on regional disparity in benefit level, this work could provide a reference to make differentiated cross-regional ecological compensation schemes at the national level.

Cannabis, an emerging aeroallergen in southeastern Spain (Region of Murcia)

The evolution of the behaviour of the Cannabis taxon in the Region of Murcia, Spain, has been analysed (in the cities of Cartagena, 1993-2020; Murcia, 2010-2020; and Lorca, 2010-2020). An attempt has been made to establish the origin of Cannabis pollen in this region to determine whether it is transported locally or from long distances based on air mass origins. Cannabis is an herbaceous, normally dioecious and anemophilous plant, which produces large quantities of pollen grains. It has been widely used for fibre (hemp), bird food (hempseed), essential oils and narcotics. The origin of Cannabis pollen grains has been established by calculating back trajectories at the altitudes of: 750, 1500 and 2500 m above mean sea level (m amsl); 350, 500 and 650 m amsl; and 10, 100 and 250 m amsl, using the HYSPLIT model. Considering this data, 29 days of Cannabis pollen potentially originating in Africa were identified in Cartagena, 19 days in Murcia and 15 days in Lorca. Of the remaining days, the air mass back trajectories showed local or regional pollen origins. These were 83 days in Cartagena, 61 days in Murcia and 57 days in Lorca. The presence of Cannabis in the bioaerosol of the Region of Murcia is irregular, and it is considered a minority pollen type. However, from 2017 to 2020, concentrations increased, with a positive and significant trend of 90% in the Annual Pollen Integral. The pollen season can be defined between June and August. This increase in the concentration of Cannabis pollen grains during this period coincides with an increase in local transport, suggesting the possibility of increased Cannabis cultivation in the study area.

An extensive dust storm impact on air quality on 22 November 2018 in Sydney, Australia, using satellite remote sensing and ground data

Recurrent dust storms represent a significant concern in Australia because of their related hazards and damages since particulate matter (PM) has harmful impacts on the environmental, health and economic sectors. The particulate matter may be released from natural sources and human activities. The major part of natural particulate matter is emitted into the air by wind erosion processes from desert and semi-desert areas at the world scale. A huge dust storm crossed over several areas of New South Wales (NSW), Australia, including the Sydney region on 21-22 November 2018 and decreased the horizontal visibility to less than 1 km for 22 h. This study examined the synoptic weather conditions, and assessed the air quality and identified the source and transport trajectory of the dust storm over Sydney using ground and satellite remote sensing data. PM10 (< 10 μm) concentrations were obtained from selected air quality monitoring sites operated by the Environmental Protection Agency in NSW. The highest hourly concentration of PM10 (578.7 μg/m³) was recorded at Singleton in the Hunter Valley, while concentrations in Sydney ranged from 480 to 385 μg/m³, well above the standard air quality level in Australia (50 μg/m³ per 24 h). The HYSPLIT back trajectories of air parcels suggest that the potential sources of the dust episode originated from the Lake Eyre Basin and northeast South Australia, the Mundi Mundi plains west of Broken Hill, Cobar and the grazing lands and the red sandplains in northwestern NSW. It then travelled towards the east coast. These long-range airflows transported suspended dust particles, raising air quality to hazardous levels (elevated PM10 levels) over most areas of NSW. The results from the HYSPLIT model for dust movement are confirmed by MODIS satellite images. Many areas of NSW experienced this intense dust storm due to northwest wind generated by the low-pressure systems and cold fronts over South Australia and many parts of western NSW as it moved eastward.

Evaluation of pollution indices, health hazards and source identification of heavy metal in dust particles and storm trajectory simulation using HYSPLIT model (Case study: Hendijan center dust, southwest of Iran)

Atmospheric dust is one of the most recent environmental pollutions in Iran. This study examines the concentration of heavy metals and the assessment of environmental and human health risk in the dust samples of Hendijan region as one of the most important centers of wind erosion in the southwestern of Iran. ICP-MSS analysis was performed on 18 samples of fine dust to specify the concentration of heavy metals. Studies showed that the highest concentrations of metals in these fine dust samples belong to Cr, Ni, Zn, Cu, As, Pb and Cd, respectively. Examining fine dust's pollution assessment showed that the highest enrichment and geo-accumulation index belong to As, Ni and Cr metals. Environmental risk assessment shows the low environmental risk of these fine dusts. The hazard quotient in children and adults belongs to Cr, As and Ni, respectively. Human health risk assessment also showed that the highest absorption of metals in both children and adults is through ingestion. The non-carcinogenic risk of heavy metals of dust samples in children is about 9 times more than adults. The highest risk of cancer in the adult group belongs to Ni metal and in the group of children belongs to As and Ni metal. PCA analysis showed that As, Cu, Cd, Cr and Ni are of anthropogenic origin and Zn and Pb are of geogenic origin. The source of the dust phenomenon with the HYSPLIT model and the backward method indicates the tracking of this dust mass through Iraq, and its probable origin was assessed in the centers of northern Iraq and southeastern Syria.

Research on the Temporal and Spatial Characteristics of Air Pollutants in Sichuan Basin

Sichuan Basin is one of the most densely populated areas in China and the world. Human activities have great impact on the air quality. In order to understand the characteristics of overall air pollutants in Sichuan Basin in recent years, we analyzed the concentrations of six air pollutants monitored in 22 cities during the period from January 2015 to December 2020. During the study period, the annual average concentrations of CO, NO2, SO2, PM2.5 and PM10 all showed a clear downward trend, while the ozone concentration was slowly increasing. The spatial patterns of CO and SO2 were similar. High-concentration areas were mainly located in the western plateau of Sichuan Basin, while the concentrations of NO2 and particulate matter were more prominent in the urban agglomerations inside the basin. During the study period, changes of the monthly average concentrations for pollutants (except for O3) conformed to the U-shaped pattern, with the highest in winter and the lowest in summer. In the southern cities of the basin, secondary sources had a higher contribution to the generation of fine particulate matter, while in large cities inside the basin, such as Chengdu and Chongqing, air pollution had a strong correlation with automobile exhaust emissions. The heavy pollution incidents observed in the winter of 2017 were mainly caused by the surrounding plateau terrain with typical stagnant weather conditions. This finding was also supported by the backward trajectory analysis, which showed that the air masses arrived in Chengdu were mainly from the western plateau area of the basin. The results of this study will provide a basis for the government to take measures to improve the air quality in Sichuan Basin.

Spatio-temporal changes of AOD in Xinjiang of China from 2000 to 2019: Which factor is more influential, natural factor or human factor?

Aerosol optical depth (AOD), which represents the optical attenuation, poses a major threat to the production activity, air quality, human health and regional sustainable development of arid and semi-arid areas. To some degree, AOD shows areal air pollution level and possesses obvious spatio-temporal characteristics. However, long-time sequences and detailed AOD information can not be provided due to currently limited monitoring technology. In this paper, a daily AOD product, MODIS-based Multi-angle Implementation of Atmospheric Correction (MAIAC), is deployed to analyze the spatio-temporal characteristics in Xinjiang Uygur Autonomous Region from 2000 to 2019. In addition, the importance of influencing factors for AOD is calculated through Random Forest (RF) Model and the propagation trajectories of pollutants are simulated through Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) Model. Spatio distribution of AOD presents a tendency that AOD value in northern Xinjiang is low while the value in southern Xinjiang is high. Regions with high AOD values are mainly concentrated in Tarim Basin. AOD in southern Xinjiang is the highest, followed by that in eastern Xinjiang and AOD value in northern Xinjiang is the lowest. Seasonal variation of AOD is significant: Spring (0.309) > summer (0.200) > autumn (0.161) > winter (0.158). Average AOD value in Xinjiang is 0.196. AOD appears wavy from 2000 to 2014 with its low inflection point (0.157) appearing in 2005, and then increases, reaching its peak in 2014 (0.223). The obvious downward tendency after 2014 shows that the use of coal to natural gas (NG) conversion project improves the conditions of local environment. According to RF Model, NG contributes most to AOD. HYSPLIT Model reveals that aerosol in southern Xinjiang is related to the short-distant carriage of dust aerosol from the Taklimakan Desert. Aerosol there can affect Inner Mongolia through long-distant transport. Blocked by the Tianshan Mountains, fine dust particles can not cross the Tianshan Mountains to become a factor contributing to AOD in northern Xinjiang.

Characterization of long-range transported bioaerosols in the Central Mediterranean

Airborne bacteria were characterized over a 2-y period via high-throughput massive sequencing of 16S rRNA gene in aerosol samples collected at a background mountain European Monitoring and Evaluation Programme (EMEP) Network site (Monte Martano, Italy) located in the Central Mediterranean area. The air mass origin of nineteen samples was identified by air mass modelling and a detailed chemical analysis was performed. Four main origins (Saharan, North-western, North-eastern, and Regional) were identified, and distinct microbial communities were associated with these air masses. Samples featured a great bacterial diversity with Protobacteria being the most abundant phylum, and Sphingomonas followed by Acidovorax, Acinetobacter and Stenotrophomonas the most abundant genera of the dataset. Bacterial genera including potential human and animal pathogens were more abundant in European and in Regional samples compared to Saharan samples; this stressed the relevance of anthropic impact on bacterial populations transported by air masses that cross densely populated areas. The principal aerosol chemical characteristics and the airborne bacterial communities were correlated by cluster analysis, similarity tests and non-metric multidimensional scaling analysis, explaining most of the variability observed. However, the strong correlation between bacterial community structure and air mass origin hampered the possibility to disentangle the effects of variations in bacterial populations and in dust provenance on variations in chemical variables.

Identification of Long-Range Transport Pathways and Potential Source Regions of PM2.5 and PM10 at Akedala Station, Central Asia

Cluster analyses, potential source contribution function (PSCF) and concentration-weight trajectory (CWT) were used to identify the main transport pathways and potential source regions with hourly PM2.5 and PM10 concentrations in different seasons from January 2017 to December 2019 at Akedala Station, located in northwest China (Central Asia). The annual mean concentrations of PM2.5 and PM10 were 11.63 ± 9.31 and 19.99 ± 14.39 µg/m3, respectively. The air pollution was most polluted in winter, and the dominant part of PM10 (between 54 to 76%) constituted PM2.5 aerosols in Akedala. Particulate pollution in Akedala can be traced back to eastern Kazakhstan, northern Xinjiang, and western Mongolia. The cluster analyses showed that the Akedala atmosphere was mainly affected by air masses transported from the northwest. The PM2.5 and PM10 mainly came with air masses from the central and eastern regions of Kazakhstan, which are characterized by highly industrialized and semi-arid desert areas. In addition, the analyses of the pressure profile of back-trajectories showed that air mass distribution were mainly distributed above 840 hPa. This indicates that PM2.5 and PM10 concentrations were strongly affected by high altitude air masses. According to the results of the PSCF and CWT methods, the main potential source areas of PM2.5 were very similar to those of PM10. In winter and autumn, the main potential source areas with high weighted PSCF values were located in the eastern regions of Kazakhstan, northern Xinjiang, and western Mongolia. These areas contributed the highest PM2.5 concentrations from 25 to 40 µg/m3 and PM10 concentrations from 30 to 60 µg/m3 in these seasons. In spring and summer, the potential source areas with the high weighted PSCF values were distributed in eastern Kazakhstan, northern Xinjiang, the border between northeast Kazakhstan, and southern Russia. These areas contributed the highest PM2.5 concentrations from 10 to 20 µg/m3 and PM10 concentrations from 20 to 60 µg/m3 in these seasons.

Variability of air pollutants, and PM composition and sources at a regional background site in the Balearic Islands: Review of western Mediterranean phenomenology from a 3-year study

The present study discloses the results of a comprehensive 3-years campaign (2010-2012) of air pollution measurements over an regional island background area (Can Llompart-Balearic Islands, Spain), contextualized with other measurements in the western Mediterranean region. Gaseous pollutants and particulate matter fractions were measured in real time; and PM₁₀ and PM₁ daily samples were obtained regularly from which chemical analyses were performed. Furthermore, during three intensive observation periods, real-time concentrations of particle number, black carbon and ammonia were additionally measured. Our results display particular diurnal and seasonal patterns for certain pollutants such as O₃ and particle number concentration. Our study reveals that concentrations of air pollutants and aerosol chemical composition are rather similar all over the central and western Mediterranean basin. The most abundant chemical components in PM₁₀ were mineral dust, followed by organic matter, sea spray and SO₄^2-; in PM₁ organic matter and SO₄^2- dominated, with significant contribution of mineral dust. Furthermore, a source apportionment Positive Matrix Factorization analysis was conducted. Natural sources exert most of the impact on the coarse-mode fraction, while most of fine-mode aerosols are linked to anthropogenic sources coming from local, regional or long range transport emissions. Prevalence of Atlantic air masses in 2010 had a positive effect in air quality, lowering mineral dust, SO₄^2- and EC concentrations. On the contrary, the high incidence of African dust and regional recirculation situations during the 2012 warm season favoured an overall PM load increase governed by mineral dust, SO₄^2- and trace elements associated to dust aerosols. The continuous increase in tourists in the Balearic Islands, and in general all around the Mediterranean, is clearly changing air quality patterns: while urban air pollution has strongly decreased since 2010, such downward trend is less pronounced at the regional scale, thus related to crescent sources such as maritime and air transport.

Anthropogenic and meteorological influences on PM10 metal/semi-metal concentrations: Implications for human health

There is growing interest in investigating the human health risk associated with metals in airborne particulate matter. The objective of this paper is the health risk assessment of Al, Be, Sb, Sn, Ti and Tl in PM₁₀ under different advections of air masses. These metals/semi-metal were studied in samples collected in an area influenced by industrial activities in northern Spain with the aim of analysing the variations in PM₁₀ metal/semi-metal. Elemental concentrations were assessed over a period of one year in terms of air mass origin by means of back trajectories (HYSPLIT), the conditional probability function, polar plots, PM concentration roses, aerosol maps (NAAPs) and receptor modelling. The mean concentrations of Al, Be, Sb, Sn, Ti and Tl were 254, 0.02, 1.30, 1.15, 15.3 and 0.20  ng/m³, respectively, and were within the usual range for suburban stations in Europe. The highest levels were recorded during conditions of regional air mass origin, highlighting the importance of sources not far from the station. Under these circumstances, the renovation of air masses was not produced. The main sources of metals were anthropogenic, mostly related to the use of coal and coke production. In general, the cancer and non-cancer risk values obtained in this study fell within accepted precautionary criteria in all trajectory groups. However, in order to improve air quality and reduce risks to human health, the impact resulting from the joint inhalation of Al, Be, Sb, Sn, Ti and Tl should not be ignored when air masses are fundamentally of regional origin.

Impact of Desert Dust on Air Quality: What is the Meaningfulness of Daily PM Standards in Regions Close to the Sources? The Example of Southern Tunisia

Desert dust is now recognized as a major health hazard. However, there still exists a lack of measurements of desert dust atmospheric loads in regions located in the vicinity of the major desert areas, where a growing part of the world population is living. Dust emission is a sporadic and intense phenomenon so that the classical air quality standards should not be appropriate to reflect the real population exposure to desert dust. In order to give some insight to answer this question, PM10 concentrations were continuously measured at a five-minute time step in southern Tunisia from February 2014 to February 2019. The daily and annual PM10 concentrations were first discussed according to the Tunisian air quality standards: In this relatively remote area, close to dust source, these standards were respected at the annual, but no longer at the daily scale. Measurements performed at a high temporal resolution (five minutes) allowed to discriminate the different situations that led to exceed Tunisian daily standards in southern Tunisia. In particular, intense (five-minute PM10 concentrations up to more than 1500 µg m−3) and short-lived (a few hours) dust outbreaks were regularly observed. This result raises the question of the necessity of defining specific air quality standards at the sub-daily scale in countries affected by intense desert dust outbreaks.

Computing payments for wind erosion prevention service incorporating ecosystem services flow and regional disparity in Yanchi County

Simulating the flows of ecosystem services (ESs) can help understand their spatiotemporal flow paths from generation to use, thereby facilitating payments from beneficiaries to providers of ESs. In this study, an analytical framework incorporated with ES flows and regional disparity was established to compute payments for wind erosion prevention service (WEPS). The results showed that between 2010 and 2015, both the potential and actual wind erosion amounts in Yanchi County decreased considerably, and the total amount of sand fixed by WEPS decreased significantly from 3.71 × 10⁹ kg to 0.08 × 10⁹ kg; additionally, the economic value of the WEPS also decreased from CNY 479.46 million to CNY 10.22 million. Based on the spatiotemporal movements of the physical and economic value flows of the WEPS, this study revealed spatiotemporal relationships between areas providing and benefiting from the WEPS of Yanchi County and provided a direct, scientific basis for decision makers to formulate payment systems for WEPS. The total amount paid for WEPS by beneficiaries in China should theoretically be CNY 38.16 million in 2010 and CNY 1.00 million in 2015 based on the economic value flow of WEPS and the regional disparity coefficient. This framework can provide a scientific and objective basis for establishing horizontal ecological compensation policies.

Contribution of dust in northern China to PM10 concentrations over the Hexi corridor

Four main dust sources and dust events that affected the Hexi Corridor were defined, and the HYSPLIT model was used to trace the dust that originated during the dust episodes of 2015-2017 and to quantify the contributions of dust sources to PM₁₀. On this basis, an algorithm that quantified the contribution of dust sources to PM₁₀ was proposed in this study. The results showed that the main dust sources affecting the Hexi Corridor are generally located in the northern part of Xinjiang, which is mainly dominated by the Gurbantunggut Desert (source A); the Taklimakan and Kumtag Deserts and their surrounding areas (source B); both Qaidam Basins (source C); and the Badain Jaran Desert, Tengger Desert, Hobq Desert, Ulan Buh Desert, and Mu Us Sandy Land and their surrounding areas (source D). The occurrence time of dust and the frequency of PM₁₀ exceeded the daily concentration standards and showed significant characteristics of being high in the spring and low in the autumn. The higher concentration of PM₁₀ in the winter was mainly due to anthropogenic sources from heating process. The contribution of source area D to PM₁₀ concentration was the greatest (42%). Source area B was one of the main dust sources (with a contribution rate of 23%); however, approximately 63% of the dust in this area originates from the Kumtag Desert. The contribution of source area A is lower than that of the study area due to greater precipitation and higher vegetation coverage (22% contribution rate). Source area C has the lowest contribution to the research area due to obstruction by the Qilian Mountain (13% contribution rate).

How to Guarantee the Sustainability of the Wind Prevention and Sand Fixation Service: An Ecosystem Service Flow Perspective

Assessing ecosystem services (ESs) is essential for sustainable development. Ecosystem service flow (ESF) emphasizes the recognition of real ESs beneficiary areas from the perspective of human welfare and establishes a spatiotemporal path between service supply areas (SSAs) and service beneficiary areas (SBAs) to better reflect the relationship between ESs and human welfare, which is conducive to recognize how to guarantee the sustainable supply of ESs. This study simulated the spatiotemporal patterns and flow trajectories of the wind prevention and sand fixation (WPSF) service in Yanchi County based on the Revised Wind Erosion Equation (RWEQ) and the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model, respectively, and constructed an analysis framework for the sustainability of WPSF service from the perspective of ESF. The results indicated that the amount of wind erosion prevented in Yanchi County was 3.71 × 109 kg in 2010 and 0.08 × 109 kg in 2015, with average retention rates of 83.40% and 78.11% and WPSF service values of 479.46 million CNY (Chinese currency; as of 18 July 2018, 6.702 RMB = US $1) and 10.22 million CNY, respectively. The flow trajectories of the WPSF service mostly extended to East Asia, and the densities decreased as the transmission distance increased. The estimated areas of the SBAs of WPSF service in Yanchi County were 1153.2 × 104 km2 in 2010 and 397.2 × 104 km2 in 2015. The grid cells through which many (≥10%) of the trajectories passed were mainly situated in the central part of northern China. The spatiotemporal distribution patterns and flow rates of the physical and value flows of the WPSF service were the same. The SBAs within China accounted for 71.11% in 2010 and 91.32% in 2015, and both maximums occurred in Shaanxi Province. In this research, we identified the actual beneficiaries according to the spatiotemporal distribution of physical and value flows. There were mismatches between the value flow and eco-compensation flow, which was unsustainable. This work can serve as an effective and valid reference for the ecological compensation standard and the formulation of ecological protection measures, which is conducive to regional sustainable development and human welfare.

The Spatio-Temporal Disparities of Areas Benefitting from the Wind Erosion Prevention Service

Ecosystem services are closely linked to human welfare. The flow of ecosystem service can establish spatio-temporal relationships between ecosystem service provision areas (SPAs) and service beneficiary areas (SBAs). In this study, the Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model was used to simulate the spatial flow path of the wind erosion prevention (WEP) service in Yanchi County. The frequency at which the simulated trajectories passed through each grid cell was used as a proxy for spatio-temporal disparities in SBAs, and the distribution of benefitting land cover, population, and gross domestic product (GDP) reflected the effects of the WEP flow. The flow paths of the Yanchi County WEP in 2010 mainly extended to eastern and central China, North Korea, South Korea, Japan, Mongolia, and eastern Russia, and were more intensive and longer in spring and winter than in autumn and winter. The SBAs covered an area of 1153.2 × 10⁴ km² in 2010, with dominant service beneficiary areas (DSBAs) comprising 185.1 × 10⁴ km² and accounting for 16.1% of the total beneficiary area of the year. The areas through which the flow paths passed with a high frequency (≥10%) were mainly located in Shaanxi, Shanxi, Henan, western Shandong, Hebei, Beijing, and northern Hubei, and the spatial scale of these areas varied, demonstrating obvious seasonal changes, and was the largest in spring. The benefitting land cover was mainly cropland across all of the SBAs, with one billion benefitting people (accounting for 77.11% of the total population of China) associated with a gross domestic product (GDP) of 26.8 trillion RMB (Chinese currency; as of 2018-06-22, 6.497 RMB = US $1, accounting for 87.90% of the total GDP of China). Furthermore, the population and socio-economic development in the DSBAs (21 million people and 0.53 trillion RMB GDP) were no longer affected by wind erosion from Yanchi County. This study revealed the spatio-temporal disparities of the SBAs of WEP in Yanchi County from an ecosystem services flow perspective and provides a scientific and effective basis for policymakers to perform standard ecological compensation accounting and to formulate ecological protection policies.

Large Salt Dust Storms Follow a 30-Year Rainfall Cycle in the Mar Chiquita Lake (Córdoba, Argentina)

Starting in 2006, a new source of intense salt dust storms developed in Mar Chiquita (Córdoba, Argentina), the largest saline lake in South America. Storms originate from vast mudflats left by a 30-year expansion-retreat cycle of the lake due to changes in the regional rainfall regime. The annual frequency of salt dust storms correlated with the size of the salt mudflats. Events were restricted to the coldest months, and reached up to 800 km from the source. Occurrence of dust storms was associated with specific surface colors and textures easily identifiable in satellite images. High-emission surfaces were characterized by the presence of sodium sulfate hydrous/anhydrous crystals (mirabilite and thenardite), and a superficial and variable water table, which may result in the periodic development of a characteristic “fluffy” surface derived from salt precipitation-dissolution processes. HYSPLIT model simulation estimates a deposition maximum near the sources (of about 2.5 kg/ha/yr), and a decreasing trend from the emission area outwards, except for the relative secondary maximum modeled over the mountain ranges in southern Bolivia and northern Argentina due to an orographic effect. The 2009 total deposition of salt dust generated in Mar Chiquita was estimated at 6.5 million tons.

Source apportion of atmospheric particulate matter: a joint Eulerian/Lagrangian approach

PM2.5 samples were collected during an annual monitoring campaign (January 2012-January 2013) in the urban area of Naples, one of the major cities in Southern Italy. Samples were collected by means of a standard gravimetric sampler (Tecora Echo model) and characterized from a chemical point of view by ion chromatography. As a result, 143 samples together with their ionic composition have been collected. We extend traditional source apportionment techniques, usually based on multivariate factor analysis, interpreting the chemical analysis results within a Lagrangian framework. The Hybrid Single-Particle Lagrangian Integrated Trajectory Model (HYSPLIT) model was used, providing linkages to the source regions in the upwind areas. Results were analyzed in order to quantify the relative weight of different source types/areas. Model results suggested that PM concentrations are strongly affected not only by local emissions but also by transboundary emissions, especially from the Eastern and Northern European countries and African Saharan dust episodes.

Theoretical and experimental evidences of medium range atmospheric transport processes of polycyclic musk fragrances

This study investigates some aspects of the environmental fate of galaxolide (HHCB) and tonalide (AHTN) musk fragrances, paying particular attention to the phenomenon of atmospheric transport of these substances. The problem was addressed theoretically and experimentally. Firstly, the application of a multimedia model allowed the analysis of their potential atmospheric transport. The obtained results argued in favor of a possible phenomenon of medium range atmospheric transport for both substances. These theoretical findings were supported by the experimental results, which showed their presence both in the fresh fallen snow and in water samples taken from the Frodolfo, a glacial stream that originates from the Forni Glacier (Alps, Northern Italy). Furthermore, the analysis of the air back-trajectories highlighted the prevalence of air masses of local origins that reached the sampling area passing through a densely anthropized area of Northern Italy. Finally, the experimental results discussed here gave evidences of accumulation of these two compounds in the glacier.

Dust storm simulation over Iran using HYSPLIT

Particulate matters have detrimental effects on human health, environment and economic. This pollutant may emit from anthropogenic or natural sources. On global scale, main proportion of natural particulate matter release to the atmosphere because of wind erosion from arid and semi-arid regions. Recently, the amount of dust coming from Arabian countries has dramatically increased, especially dust storms that are affecting western and even central parts of Iran. This phenomenon has caused a lot of environmental problems. Dust source identification and trajectory simulation using numerical techniques are the main aims of this study. HYSPLIT (Hybrid Single Particle Lagrangian Integrated Trajectory) model dust module and trajectory simulation are utilized in this research and two case studies are investigated (in May and June 2010). The base of the HYSPLIT dust module is the PM10 dust storm emission algorithm for desert land use. This methodology is applied to estimate hotspots and trajectories. Due to the results, dust storms started on May 17th and June 7th because of high wind shear (>8.5 m/s) from the western Syrian Desert. The source region limited to 32.50 °N to 33.80 °N and 38.00 °E to 38.80 °E coordinates. Dust plumes lifted and dispersed towards the east and southeast of the sources and reached Ahvaz on May 18th and June 8th. The average of PM10 concentration in these dates reached 625 and 494 μgm3 on Ahvaz monitoring stations, respectively. Moreover, the results gained from the model for dust motion simulation are similar to the MODIS satellite images.

The effect of different transport modes on urban PM(10) levels in two European cities

The aim of the study is to identify transport patterns that may have an important influence on PM10 levels in two European cities, namely Szeged in East-Central Europe and Bucharest in Eastern Europe. 4-Day, 6-hourly three-dimensional (3D) backward trajectories arriving at these locations at 1200 GMT are computed using the HYSPLIT model over a 5-year period from 2004 to 2008. A k-means clustering algorithm using the Mahalanobis metric is applied in order to develop trajectory types. Two statistical indices are used to evaluate and compare exceedances of critical daily PM10 levels corresponding to the trajectory clusters. For Bucharest, the major PM10 transport can be clearly associated with air masses arriving from Central and Southern Europe, as well as the Western Mediterranean. Occasional North African dust intrusions over Romania are also found. For Szeged, Southern Europe with North Africa, Central Europe and Eastern Europe with regions over the West Siberian Plain are the most important sources of PM10. The occasional appearance of North-African-origin dust over Hungary is also detected. A statistical procedure is developed in order to separate medium- and long-range PM10 transport for both cities. Considering the 500 m arrival height, long-range transport plays a higher role in the measured PM10 concentration both for non-rainy and rainy days for Bucharest and Szeged, respectively.

Chemical and microbiological characterization of atmospheric particulate matter during an intense African dust event in Southern Spain

This study presents the results of the physicochemical characterization of particulate matter associated with an important dust event from the Sahara area that occurred in the South of Spain in 2010. The chemical composition of the samples reflected the dominance of the crustal component of sand from the Sahara desert, although the presence of Mo, Ti, and V trace elements indicated that the dust contained industrial material; probably collected in its transport from Africa. Microbial biodiversity associated with the dust was low, but dominated by Firmicutes and Proteobacteria. Some Firmicutes (belonging to the genus Bacillus and Sporosarcina) were cultured on solid and liquid medium, which suggested that the transported microbes were alive or present as spores that germinated under favorable conditions. These cultivable microbes in the form of spores were highly resistant to desiccation, heat, and UV light.

Evaluation of trace elements contamination in cloud/fog water at an elevated mountain site in Northern China

Totally 117 cloud/fog water samples were collected at the summit of Mt. Tai (1534m a.s.l.)-the highest mountain in the Northern China Plain. The results were investigated by a combination of techniques including back trajectory model, regional air quality and dust storm models, satellite observations and Principal Component Analysis. Elemental concentrations were determined by Inductively Coupled Plasma Mass Spectrometry, with stringent quality control measures. Higher elemental concentrations were found at Mt. Tai compared with those reported by other overseas studies. The larger proportions and higher concentrations of toxic elements such as Pb and As in cloud/fog water compared with those in rainwater at Mt. Tai suggests higher potential hazards of cloud/fog water as a source of contamination in polluted areas to the ecosystem. Peak concentrations of trace elements were frequently observed during the onset of cloud/fog events when liquid water contents of cloud/fog water were usually low and large amount of pollutants were accumulated in the ambient air. Inverse relationship between elemental concentrations and liquid water contents were only found in the samples with high electrical conductivities and liquid water contents lower than 0.3gm(-3). Affected mainly by the emissions of steel industries and mining activities, air masses transported from south/southwest of Mt. Tai were frequently associated with higher elemental concentrations. The element Mn is attributed to play an important role in the acidity of cloud/fog water. The composition of cloud/fog water influenced by an Asian dust storm event was reported, which was seldom found in the literature.

Saharan dust contribution to PM₁₀, PM₂.₅ and PM₁ in urban and suburban areas of Rome: a comparison between single-particle SEM-EDS analysis and whole-sample PIXE analysis

From February 15th to April 15th 2009, a period characterised by two episodes of Saharan dust outbreaks in Italy, particulate matter (PM) samples were collected at two stations (urban and suburban) in Rome. Some samples were selected and analysed using the SEM-EDS technique to characterise PM, focussing especially on the mineral contribution. Samples were representative both of days affected by Saharan dust episodes and days without this contribution. Cluster analysis allowed the attribution of each of about 67,000 analysed particles to one of the seven main statistical groups based on their composition. Characteristics of the particulate components identified using SEM-EDS analysis were verified by PIXE analysis carried out on filters collected in a suburban area. Ultimately, the contribution of crustal particles was revealed to be consistently high, highlighting the importance of local and regional mineral contributions, as well as those of Saharan origin. Therefore, quantifying all mineral contributions to resuspended particulate could lead to significant reductions of the PM level also on days not influenced by Saharan dust, thus limiting conditions when PM₁₀ daily limit value (DLV) established by European legislation is exceeded.

Source areas and long-range transport of pollen from continental land to Tenerife (Canary Islands)

The Canary Islands, due to their geographical position, constitute an adequate site for the study of long-range pollen transport from the surrounding land masses. In this study, we analyzed airborne pollen counts at two sites: Santa Cruz de Tenerife (SCO), at sea level corresponding to the marine boundary layer (MBL), and Izaña at 2,367 m.a.s.l. corresponding to the free troposphere (FT), for the years 2006 and 2007. We used three approaches to describe pollen transport: (1) a classification of provenances with an ANOVA test to describe pollen count differences between sectors; (2) a study of special events of high pollen concentrations, taking into consideration the corresponding meteorological synoptic pattern responsible for transport and back trajectories; and (3) a source-receptor model applied to a selection of the pollen taxa to show pollen source areas. Our results indicate several extra-regional pollen transport episodes to Tenerife. The main provenances were: (1) the Mediterranean region, especially the southern Iberian Peninsula and Morocco, through the trade winds in the MBL. These episodes were characterized by the presence of pollen from trees (Casuarina, Olea, Quercus perennial and deciduous types) mixed with pollen from herbs (Artemisia, Chenopodiaceae/Amaranthaceae and Poaceae wild type). (2) The Saharan sector, through transport at the MBL level carrying pollen principally from herbs (Chenopodiaceae-Amaranthaceae, Cyperaceae and Poaceae wild type) and, in one case, Casuarina pollen, uplifted to the free troposphere. And (3) the Sahel, characterized by low pollen concentrations of Arecaceae, Chenopodiaceae-Amaranthaceae, Cyperaceae and Poaceae wild type in sporadic episodes. This research shows that sporadic events of long-range pollen transport need to be taken into consideration in Tenerife as possible responsible agents in respiratory allergy episodes. In particular, it is estimated that 89-97% of annual counts of the highly allergenous Olea originates from extra-regional sources in southern Iberia and northern Africa.

Saharan dust episodes in Italy: influence on PM10 daily limit value (DLV) exceedances and the related synoptic

The relevance of dust outbreaks from the Sahara into Italy was evaluated for the period from 2001 to 2007. To this end, days affected by Saharan dust were recognized at four PM(10) background stations belonging to the Regional Agencies for Environmental Protection (ARPA) monitoring networks (one working in the 2005-2007 period only). The analysis included computation of back trajectories, complemented with satellite images and meteorological charts. Results from other models are also collected for comparison. Saharan Dust contribution to PM(10) was calculated referring to a method developed for Iberian monitoring networks. PM(10) exceeding the daily limit value (DLV) of the European Union air quality standard were reviewed also. The provenience of air masses yielding the exceedances was also recognized, allowing to distinguish the Atlantic-European episodes from the (Atlantic)-Saharan ones. The European episodes are due to anthropogenic pollution that affected mainly northern Italy in winter; instead, the Saharan ones are due to dust outbreaks that affected mainly southern Italy in summer. Central Italy is characterised by a transitional situation that is experienced from north to south. A number of dust affected days with DLV exceedance (from 4 to 108 at the considered stations) were identified and grouped into 55 Saharan dust episodes. Analysis showed that DLV exceedances due to Saharan dust advection vanish at all stations when dust contributions are subtracted. A synoptic analysis based on the meteorological charts was carried out allowing a view of Saharan dust transport into Italy for each meteorological season. Notwithstanding that summer is the season most influenced by Saharan episodes at all of the stations, the analysis showed a low-high system of anomalies on the geopotential height distribution causing south-southwesterly flow carrying dust into Italy during the other seasons.

Aerosol optical depth, aerosol composition and air pollution during summer and winter conditions in Budapest

The dependence of aerosol optical depth (AOD) on air particulate concentrations in the mixing layer height (MLH) was studied in Budapest in July 2003 and January 2004. During the campaigns gaseous (CO, SO(2), NO(x), O(3)), solid components (PM(2.5), PM(10)), as well as ionic species (ammonium, sulfate and nitrate) were measured at several urban and suburban sites. Additional data were collected from the Budapest air quality monitoring network. AOD was measured by a ground-based sun photometer. The mixing layer height and other common meteorological parameters were recorded. A linear relationship was found between the AOD and the columnar aerosol burden; the best linear fit (R(2)=0.96) was obtained for the secondary sulfate aerosol due to its mostly homogeneous spatial distribution and its optically active size range. The linear relationship is less pronounced for the PM(2.5) and PM(10) fractions since local emissions are very heterogeneous in time and space. The results indicate the importance of the mixing layer height in determining pollutant concentrations. During the winter campaign, when the boundary layer decreases to levels in between the altitudes of the sampling stations, measured concentrations showed significant differences due to different local sources and long-range transport. In the MLH time series unexpected nocturnal peaks were observed. The nocturnal increase of the MLH coincided with decreasing concentrations of all pollutants except for ozone; the ozone concentration increase indicates nocturnal vertical mixing between different air layers.