Spring Dust Research Articles

Seasonal ambient particulate matter and population health outcomes among communities impacted by road dust in British Columbia, Canada

ABSTRACTIn recent years, many air quality monitoring programs have favored measurement of particles less than 2.5 µm (PM2.5) over particles less than 10 µm (PM10) in light of evidence that health impacts are mostly from the fine fraction. However, the coarse fraction (PM10-2.5) may have independent health impacts that support continued measurement of PM10 in some areas, such as those affected by road dust. The objective of this study was to evaluate the associations between different measures of daily PM exposure and two daily indicators of population health in seven communities in British Columbia, Canada, where road dust is an ongoing concern. The measures of exposure were PM10, PM2.5, PM10-2.5, PM2.5 adjusted for PM10-2.5, and PM10-2.5 adjusted for PM2.5. The indicators of population health were dispensations of the respiratory reliever medication salbutamol sulfate and nonaccidental mortality. This study followed a time-series design using Poisson regression over a 2003–2015 study period, with analyses stratified by three seasons: residential woodsmoke in winter; road dust in spring; and wildfire smoke in summer. A random-effects meta-analysis was conducted to establish a pooled estimate. Overall, an interquartile range increase in daily PM10-2.5 was associated with a 3.6% [1.6, 5.6] increase in nonaccidental mortality during the road dust season, which was reduced to 3.1% [0.8, 5.4] after adjustment for PM2.5. The adjusted coarse fraction had no effect on salbutamol dispensations in any season. However, an interquartile range increase in PM2.5 was associated with a 2.7% [2.0, 3.4] increase in dispensations during the wildfire season. These analyses suggest different impacts of different PM fractions by season, with a robust association between the coarse fraction and nonaccidental mortality in communities and periods affected by road dust. We recommend that PM10 monitoring networks be maintained in these communities to provide feedback for future dust mitigation programs.Implications: There was a significant association between daily concentrations of the coarse fraction and nonaccidental mortality during the road dust season, even after adjustment for the fine fraction. The acute and chronic health effects associated with exposure to the coarse fraction remain unclear, which supports the maintenance of PM10 monitoring networks to allow for further research in communities affected by sources such as road dust.

The dual effect of vegetation green-up date and strong wind on the return period of spring dust storms

Vegetation phenology changes have been widely applied in the disaster risk assessments of the spring dust storms, and vegetation green-up date shifts have a strong influence on dust storms. However, the effect of earlier vegetation green-up dates due to climate warming on the evaluation of dust storms return periods remains an important, but poorly understood issue. In this study, we evaluate the spring dust storm return period (February to June) in Inner Mongolia, Northern China, using 165 observations of severe spring dust storm events from 16 weather stations, and regional vegetation green-up dates as an integrated factor from NDVI (Normalized Difference Vegetation Index), covering a period from 1982 to 2007, by building the bivariate Copula model. We found that the joint return period showed better fitting results than without considering the integrated factor when the actual dust storm return period is longer than 2years. Also, for extremely severe dust storm events, the gap between simulation result and actual return period can be narrowed up to 0.4888years by using integrated factor. Furthermore, the risk map based on the return period results shows that the Mandula, Zhurihe, Sunitezuoqi, Narenbaolige stations are identified as high risk areas. In this study area, land surface is extensively covered by grasses and shrubs, vegetation green-up date can play a significant role in restraining spring dust storm outbreaks. Therefore, we suggest that Copula method can become a useful tool for joint return period evaluation and risk analysis of severe dust storms.

Frequency of spring dust weather in North China linked to sea ice variability in the Barents Sea

The link between winter sea ice cover in the Barents Sea (SICBS) and the frequency of spring dust weather over North China (DWFNC) is investigated. It is found that year-to-year variability of SICBS and DWFNC are strongly correlated for the period 1996–2014 with a correlation coefficient of −0.65, whereas the correlation between SICBS and DWFNC is not statistically significant for the periods 1980–2014 and 1980–1995. During 1996–2014, low winter SICBS is associated with decreased snow cover over western Siberia (SCWS) in both winter and spring, which is also supported by a strengthening relationship between winter SICBS and spring SCWS since the mid-1990s. This leads to changes in atmospheric circulation and climate conditions that are favorable for increased frequency of dust weather events over North China. Our further analysis suggests that the interannual variability of the standard deviation of SICBS has intensified and the center of actions has moved eastward to the north Barents Sea and Kara Sea since the mid-1990s. Such change may easily induce stronger and southward stationary Rossby wave train propagation, influencing the dust-related atmospheric circulation (strengthened East Asian subtropical jet, increased cyclogenesis, and larger atmospheric thermal instability). Thus interannual variation of winter SICBS plays an increasingly important role in dust-related climate conditions over North China, which might serve as a new precursor for the prediction of spring dust activity in North China.

Classifying Aerosols Based on Fuzzy Clustering and Their Optical and Microphysical Properties Study in Beijing, China

Classification of Beijing aerosol is carried out based on clustering optical properties obtained from three Aerosol Robotic Network (AERONET) sites. The fuzzy c-mean (FCM) clustering algorithm is used to classify fourteen-year (2001–2014) observations, totally of 6,732 records, into six aerosol types. They are identified as fine particle nonabsorbing, two kinds of fine particle moderately absorbing (fine-MA1 and fine-MA2), fine particle highly absorbing, polluted dust, and desert dust aerosol. These aerosol types exhibit obvious optical characteristics difference. While five of them show similarities with aerosol types identified elsewhere, the polluted dust aerosol has no comparable prototype. Then the membership degree, a significant parameter provided by fuzzy clustering, is used to analyze internal variation of optical properties of each aerosol type. Finally, temporal variations of aerosol types are investigated. The dominant aerosol types are polluted dust and desert dust in spring, fine particle nonabsorbing aerosol in summer, and fine particle highly absorbing aerosol in winter. The fine particle moderately absorbing aerosol occurs during the whole year. Optical properties of the six types can also be used for radiative forcing estimation and satellite aerosol retrieval. Additionally, methodology of this study can be applied to identify aerosol types on a global scale.

Particle size traces modern Saharan dust transport and deposition across the equatorial North Atlantic

Abstract. Mineral dust has a large impact on regional and global climate, depending on its particle size. Especially in the Atlantic Ocean downwind of the Sahara, the largest dust source on earth, the effects can be substantial but are poorly understood. This study focuses on seasonal and spatial variations in particle size of Saharan dust deposition across the Atlantic Ocean, using an array of submarine sediment traps moored along a transect at 12° N. We show that the particle size decreases downwind with increased distance from the Saharan source, due to higher gravitational settling velocities of coarse particles in the atmosphere. Modal grain sizes vary between 4 and 32 µm throughout the different seasons and at five locations along the transect. This is much coarser than previously suggested and incorporated into climate models. In addition, seasonal changes are prominent, with coarser dust in summer and finer dust in winter and spring. Such seasonal changes are caused by transport at higher altitudes and at greater wind velocities during summer than in winter. Also, the latitudinal migration of the dust cloud, associated with the Intertropical Convergence Zone, causes seasonal differences in deposition as the summer dust cloud is located more to the north and more directly above the sampled transect. Furthermore, increased precipitation and more frequent dust storms in summer coincide with coarser dust deposition. Our findings contribute to understanding Saharan dust transport and deposition relevant for the interpretation of sedimentary records for climate reconstructions, as well as for global and regional models for improved prediction of future climate.

Association between Ambient Air Pollution and Emergency Room Visits for Respiratory Diseases in Spring Dust Storm Season in Lanzhou, China.

Background: Air pollution has become a major global public health problem. A number of studies have confirmed the association between air pollutants and emergency room (ER) visits for respiratory diseases in developed countries and some Asian countries, but little evidence has been seen in Western China. This study aims to concentrate on this region. Methods: A time-series analysis was used to examine the specific effects of major air pollutants (PM10, SO2 and NO2) on ER visits for respiratory diseases from 2007 to 2011 in the severely polluted city of Lanzhou. We examined the effects of air pollutants for stratified groups by age and gender, accounting for the modifying effect of dust storms in spring to test the possible interaction. Results: Significant associations were found between outdoor air pollution concentrations and respiratory diseases, as expressed by daily ER visits in Lanzhou in the spring dust season. The association between air pollution and ER visits appeared to be more evident on dust days than non-dust days. Relative risks (RRs) and 95% CIs per 10 µg/m3 increase in 3-day PM10 (L3), 5-day SO2 (L5), and the average of current and previous 2-day NO2 (L01) were 1.140 (1.071–1.214), 1.080 (0.967–1.205), and 1.298 (1.158–1.454), respectively, on dust days. More significant associations between PM10, SO2 and NO2 and ER visits were found on dust days for elderly females, elderly males and adult males, respectively. Conclusions: This study strengthens the evidence of dust-exacerbated ER visits for respiratory diseases in Lanzhou.

SEASON OF DELTAMETHRIN APPLICATION AFFECTS FLEA AND PLAGUE CONTROL IN WHITE-TAILED PRAIRIE DOG (CYNOMYS LEUCURUS) COLONIES, COLORADO, USA.

In 2008 and 2009, we evaluated the duration of prophylactic deltamethrin treatments in white-tailed prairie dog ( Cynomys leucurus ) colonies and compared effects of autumn or spring dust application in suppressing flea numbers and plague. Plague occurred before and during our experiment. Overall, flea abundance tended to increase from May or June to September, but it was affected by deltamethrin treatment and plague dynamics. Success in trapping prairie dogs (animals caught/trap days) declined between June and September at all study sites. However, by September trap success on dusted sites (19%; 95% confidence interval [CI] 16-22%) was about 15-fold greater than on undusted control sites (1%; CI 0.3-4%; P≤0.0001). Applying deltamethrin dust as early as 12 mo prior seemed to afford some protection to prairie dogs. Our data showed that dusting even a portion of a prairie dog colony can prolong its persistence despite epizootic plague. Autumn dusting may offer advantages over spring in suppressing overwinter or early-spring flea activity, but timing should be adjusted to precede the annual decline in aboveground activity for hibernating prairie dog species. Large colony complexes or collections of occupied but fragmented habitat may benefit from dusting some sites in spring and others in autumn to maximize flea suppression in a portion of the complex or habitat year-round.

Earlier onset of the spring fine dust season in the southwestern United States

AbstractParticulate matter (PM)2.5 dust concentrations (mineral particles with aerodynamic diameters less than 2.5 µm) typically peak in spring and early summer at rural and remote sites across the southwestern United States. Trend analyses indicate that springtime regional mean PM2.5 dust concentrations have increased from 1995 to 2014, especially in March (5.4% yr−1, p < 0.01). This increase reflects an earlier onset of the spring dust season across the Southwest by 1 to 2 weeks over the 20 year time period. March dust concentrations were strongly correlated with the Pacific Decadal Oscillation index (r = −0.65, p < 0.01), which was mostly in its negative phase from 2007 to 2014, during which the region was drier, windier, and less vegetated. The positive spring trend and its association with large‐scale climate variability have several important implications for visibility, particulate matter, health effects, and the hydrologic cycle in the region.

Variability in Dust Observed over China Using A-Train CALIOP Instrument

Patterns of dust aerosol variation over China are analyzed using A-Train CALIOP and precipitation, soil moisture, and vegetation coverage datasets during the period of 2007 and 2014. Spatially, dust is mostly prominent over northwestern China, with the highest and most widespread dust activities being in Taklimakan Desert. Dust is generally distributed across the atmosphere up to 5 km altitude, with a peak of DAFOD around 3 km. The dust layer has a significant geographical and seasonal drifting, with higher altitude in spring and summer and dust source regions (between 3 km and 5 km). Additionally, single dust layer is more often observed in a vertical column. Temporally, high amounts of dust aerosol (C-DAFOD as high as 0.08) experienced in spring subsequently continuous decrease until the spring of next year. The correlation coefficients between the latitude averaged column integrated dust aerosol feature optical depth (C-DAFOD) and precipitation, soil moisture, and vegetation coverage are −0.65, −0.81, and −0.77, respectively. The correlation coefficients of seasonal mean C-DAFOD with the three factors are −0.15, −0.67, and −0.35, respectively. The analysis showed dust and the other three factors are negatively correlated. Overall, dust over China shows considerable spatial, temporal, and vertical variations.

Spatial and temporal variations of spring dust emissions in northern China over the last 30 years

Abstract Dust emissions caused by wind erosion have significant impacts on land degradation, air quality, and climate change. Dust from the arid and semiarid regions of China is a main contributor to atmospheric dust aerosols in East Asia, and their impacts can stretch far beyond the territory of China. Spatial-temporal patterns of dust emissions in China over the last several decades, however, are still lacking, especially during the spring season. In this study, we simulated the spatial-temporal dynamics of spring dust emissions from 1982 to 2011 in arid and semi-arid areas of China using the Integrated Wind Erosion Modeling System. Results showed that the most severe dust emission events occurred in the Taklimakan Desert, Badain Jaran Desert, Tengger Desert, and Ulan Buh Desert. Over the last three decades, the magnitude of spring dust emissions generally decreased at the regional scale, with an annual spring dust emission of ∼401.10 Tg. Among different vegetation types, the highest annual spring dust emission occurred in the desert steppes (∼163.95 Tg), followed by the deserts (∼103.26 Tg). The dust emission intensity in the desert steppes and the deserts was ∼150.83 kg km −2 ·yr −1 and ∼205.46 kg km −2 ·yr −1 , respectively. The spatial patterns of the inter-decadal variation are related to climate change and human activities. Mitigation strategies such as returning farmland to grassland, fenced grazing, and adequate grass harvesting, must be taken to prevent further soil losses and grassland degradation in northern China.

A New Perspective on Understanding the Reduced Spring Dust Storm Frequency in Inner Mongolia, China

Spatiotemporal patterns of dust storms are affected by climate change through changes in convective instability, regional meteorological characteristics, and local sediment supply. Linking dust storm dynamics to climate change helps the understanding of what controls the initiation of dust storms, and assists the prediction of future dust storm occurrence. This study examines the temporal dynamics of spring dust storms in Inner Mongolia, a major dust source area in East Asia. We found that severe spring dust storms have significantly declined from 1954 to 2007. Four dust storm types showed similar decreasing trends from 2001 to 2012. This change in spring dust storm dynamics is attributed to the shift in vegetation green-up dates based on the analysis of a satellite derived vegetation index. Earlier vegetation green-up has a dampening effect on spring dust storms. Suitable environmental conditions for vegetation green-up hinder the emergence of dust storms. This study expands our understanding of the dynamics of spring dust storms in the changing climate through a new perspective on vegetation phenology in the spring.

Long-term trend and spatiotemporal variations of haze over China by satellite observations from 1979 to 2013

With the fast development of economy and industry in the past thirty years, many large cities in the eastern and southwestern areas of China are experiencing increased haze events and atmospheric pollution, which causes significant impacts on the regional environment, human health, and even climate. The long-term trend and spatiotemporal variations of haze over China during recent 30 years are investigated using TOMS AAI products. In addition, the heavy haze events that occurred in January 2013 over eastern China are explored using AAI products from TOU on board FY-3A. Validation results show that satellite AAI products can be used for haze monitoring since it is sensitive to the carbonaceous aerosol, which is one of the main components of haze. In China, the high AAI values (>1.0) mainly located in the main four areas with intense anthropogenic activities, except for the desert region in Northwestern China. In the eastern and northeastern region, AAI peaks dominate in spring before 2005 since those areas were always affected by dust in spring. However, after 2005, AAI peaks appear in winter over eastern China because of haze. Moreover, in the northeastern region, AAI peaks dominate in winter with a secondary peak in spring because this area is affected by both dust and haze. In the southern region, the AAI peaks always dominate in spring since the high-level air pollution often occur in spring, but a decreasing trend is acquired during recent ten years. Over eastern China and northeastern China, AAI shows an increasing trend during recent 30 years in winter, which reveals that the haze over these areas is strengthen. A case study result shows that the heavy haze events occurred in January 2013 in eastern China can be clearly identified from the AAI products of TOU/FY-3A. The daily coverage area with AAI > 3.0 peaks at five periods at this time, i.e. Jan. 7–8, Jan. 13, Jan. 18, Jan. 23, and, Jan. 28–29, which agrees well with the haze events recorded by in-situ measurements.

From dust to dust: Quaternary wind erosion of the Mu Us Desert and Loess Plateau, China

The Ordos Basin of China encompasses the Mu Us Desert in the northwest and the Chinese Loess Plateau to the south and east. The boundary between the mostly internally drained Mu Us Desert and fluvially incised Loess Plateau is an erosional escarpment, up to 400 m in relief, composed of Quaternary loess. Linear ridges, with lengths of ∼10 2 –10 3 m, are formed in Cretaceous- Quaternary strata throughout the basin. Ridge orientations are generally parallel to near-surface wind vectors in the Ordos Basin during modern winter and spring dust storms. Our observations suggest that the Loess Plateau previously extended farther to the north and west of its modern windward escarpment margin and has been partially reworked by eolian processes. The linear topography, Mu Us Desert internal drainage, and escarpment retreat are all attributed to wind erosion, the aerial extent of which expanded southeastward in China in response to Quaternary amplification of Northern Hemisphere glaciation.

Regional variability in dust‐on‐snow processes and impacts in the Upper Colorado River Basin

AbstractDust deposition onto mountain snow cover in the Upper Colorado River Basin frequently occurs in the spring when wind speeds and dust emission peaks on the nearby Colorado Plateau. Dust loading has increased since the intensive settlement in the western USA in the mid 1880s. The effects of dust‐on‐snow have been well studied at Senator Beck Basin Study Area (SBBSA) in the San Juan Mountains, CO, the first high‐altitude area of contact for predominantly southwesterly winds transporting dust from the southern Colorado Plateau. To capture variability in dust transport from the broader Colorado Plateau and dust deposition across a larger area of the Colorado River water sources, an additional study plot was established in 2009 on Grand Mesa, 150 km to the north of SBBSA in west central, CO. Here, we compare the 4‐year (2010–2013) dust source, deposition, and radiative forcing records at Grand Mesa Study Plot (GMSP) and Swamp Angel Study Plot (SASP), SBBSA's subalpine study plot. The study plots have similar site elevations/environments and differ mainly in the amount of dust deposited and ensuing impacts. At SASP, end of year dust concentrations ranged from 0.83 mg g−1 to 4.80 mg g−1, and daily mean spring dust radiative forcing ranged from 50–65 W m−2, advancing melt by 24–49 days. At GMSP, which received 1.0 mg g−1 less dust per season on average, spring radiative forcings of 32–50 W m−2 advanced melt by 15–30 days. Remote sensing imagery showed that observed dust events were frequently associated with dust emission from the southern Colorado Plateau. Dust from these sources generally passed south of GMSP, and back trajectory footprints modelled for observed dust events were commonly more westerly and northerly for GMSP relative to SASP. These factors suggest that although the southern Colorado Plateau contains important dust sources, dust contributions from other dust sources contribute to dust loading in this region, and likely account for the majority of dust loading at GMSP. Copyright © 2015 John Wiley & Sons, Ltd.

Spatiotemporal variability in dust observed over the Sinkiang and Inner Mongolia regions of Northern China

This study presents a detailed analysis of the spatiotemporal variability in dust observed over Sinkiang and Inner Mongolia in Northern China from 2005 to 2008. The relationships between airborne dust (observed by OMI–AI and MODIS–AOD), the normalized difference vegetation index (NDVI), monthly total precipitation (MTP) and surface wind speed (SWS) are investigated. The results show that the spatial distribution of airborne dust distinctly decreases from west to east across Northern China; this pattern is opposite to that of the NDVI and MTP. Both Sinkiang and Inner Mongolia experience high amounts of airborne dust in spring, with the highest values in April. The two regions also had different dust variabilities. In Sinkiang, three major dust regions were identified, with airborne dust mainly distributed in regions with NDVI values between 0 and 0.1, SWS values between 2 and 5m/s, and a MTP of less than 5mm. In addition, the temporal variation in airborne dust exhibits both positive and negative correlations with the NDVI, MTP and SWS. However, over Inner Mongolia, five high–dust regions were confirmed, with airborne dust generally distributed in the areas with NDVI values between 0 and 0.4, SWS values between 3 and 6m/s, and a MTP of less than 10mm. The time series of airborne dust is negatively correlated with the NDVI and MTP but strongly and positively correlated with the SWS. In addition, the temporal pattern of the AOD in Sinkiang is essentially controlled by dust activity, whereas it may be influenced by anthropogenic emissions in Inner Mongolia. Overall, the spatiotemporal variabilities in dust over Sinkiang and Inner Mongolia are not identical, although both regions are important sources of dust in East Asia.

Characteristics and Seasonal Variations of Carbonaceous Species in PM2.5 in Taiyuan, China

Seasonal characteristics of PM2.5, organic carbon (OC) and elemental carbon (EC) were studied in Taiyuan from 2009 to 2010. PM2.5 samples were collected by pre-baked quartz filters with high-volume air sampler, and then OC and EC were analyzed by thermal/optical reflectance method. The annual average concentrations of PM2.5, OC and EC were 220.2, 37.4 and 19.6 µg/m3 respectively, which were higher than those in most regions in China. Total carbonaceous aerosol (TCA) accounted for more than one third of the total PM2.5 mass. The levels of PM2.5, OC and EC were the highest in winter, followed by spring, fall and summer. OC and EC were well correlated in summer compared with other seasons, indicating the presence of other additional sources such as biomass burning in fall, coal combustion for heating in winter and dust in spring. Higher OC/EC ratios in winter might be primarily attributed to the significant increase of direct emission of OC as a result of coal and biomass combustion, and also cooling effect of carbonaceous aerosols due to low temperature and stagnated atmospheric condition. These results showed that the pollution of carbonaceous particles in Taiyuan was serious, and might be an inducing factor of dust haze, especially in winter.

Climatic controls on the interannual to decadal variability in Saudi Arabian dust activity: Toward the development of a seasonal dust prediction model

AbstractThe observed climatic controls on springtime and summertime Saudi Arabian dust activities during 1975–2012 are analyzed, leading to development of a seasonal dust prediction model. According to empirical orthogonal function analysis, dust storm frequency exhibits a dominantly homogeneous pattern across Saudi Arabia, with distinct interannual and decadal variability. The previously identified positive trend in remotely sensed aerosol optical depth since 2000 is shown to be a segment of the decadal oscillation in dust activity, according to long‐duration station record. Regression and correlation analyses reveal that the interannual variability in Saudi Arabian dust storm frequency is regulated by springtime rainfall across the Arabian Peninsula and summertime Shamal wind intensity. The key drivers of Saudi Arabian dust storm variability are identified. Winter‐to‐spring La Niña enhances subsequent spring dust activity by decreasing rainfall across the country's primary dust source region, the Rub' al Khali Desert. A relatively cool tropical Indian Ocean favors frequent summer dust storms by producing an anomalously anticyclonic circulation over the central Arabian Peninsula, which enhances the Shamal wind. Decadal variability in Saudi Arabian dust storm frequency is associated with North African rainfall and Sahel vegetation, which regulate African dust emissions and transport to Saudi Arabia. Mediterranean sea surface temperatures (SSTs) also regulate decadal dust variability, likely through their influence on Sahel rainfall and Shamal intensity. Using antecedent‐accumulated rainfall over the Arabian Peninsula and North Africa, and Mediterranean SSTs, as low‐frequency predictors, and tropical eastern Pacific and tropical Indian Ocean SSTs as high‐frequency predictors, Saudi Arabia's seasonal dust activity is well predicted.

Land surface memory effects on dust emission in a Mongolian temperate grassland

AbstractAeolian processes in temperate grasslands are unique in that the plant growth‐decay cycle, soil moisture/snowpack dynamics, and induced grazing interactively affect seasonal and interannual variations of dust emission. This study uses process‐based ecosystem model DAYCENT and unique saltation flux measurements to (1) identify primary land surface factors that control dust emission with soil moisture and vegetation components (live grasses, standing dead grasses, and litter) in a Mongolian grassland and (2) test the dead‐leaf hypothesis proposed by previous observational studies that correlates plant biomass in summer and dust events the following spring. In general, the DAYCENT model realistically simulates seasonal and interannual variations of the vegetation components and soil moisture that were captured by field observations during 2003–2010. Then, the land surface components are correlated with measured daily saltation flux in the springs of 2008–2009 and the frequency of monthly dusty days during March–June 2002–2010. Results show that dust emission had a similar amplitude of significant correlation with wind speed and a combination of all land surface components, which demonstrates a memory of the preceding year. The memory analysis reveals that vegetation and soil moisture anomalies during spring dust emission are significantly autocorrelated with the preceding year's (autumn) corresponding anomalies, which were controlled by rainfall during a given summer. Most importantly, of the vegetation components, the standing dead grasses had the strongest memory and simultaneous correlation with spring dust emission, suggesting the validity of the dead‐leaf hypothesis.

Synoptic characteristics of spring dust days over northern Saudi Arabia

This study describes the synoptic features associated with spring dust cases over northern Saudi Arabia. Dust cases were detected and classified using the values and distribution of the aerosol index (AI) from the total ozone mapping spectrometer (TOMS) satellites. The classes were narrow spread, moderate spread, and wide spread. In addition, the dust types observed at the surface weather stations during the detected cases were used to describe the distributions of various dust types over northern Saudi Arabia. The results demonstrate that the eastern side of the region experiences considerably more dust storms than non-dust-storm types (haze, etc.), whereas the western side near the Red Sea is only influenced by a limited number of dust-type observations. Moreover, a synoptic analysis of the classes shows that increases in the class strength produce a synoptic feature in which the pressure decreases within the western high-pressure ridge and eastern low-pressure system; as a result, the low-pressure trough that typically affects the northern Arabian Peninsula extends northward. Additionally, the maximum winds at 250 hPa decrease and shift northward, the stability and instability between 1000 and 850 hPa increase, and the stability between 850 and 500 hPa decreases. At 500 hPa, the northern cyclone weakens, and the southern anticyclone strengthens. As a result, the northern trough weakens, the ridge shifts northward, and the geopotential height gradient and wind velocities decrease. In general, these features represent the atmospheric conditions that increase the severity of dust cases over this region.

Characteristics, seasonality and sources of inorganic ions and trace metals in North-east Asian aerosols

Environmental context Atmospheric aerosols affect the Earth’s climate system and can cause adverse effects on human health depending on their loading and chemical composition. This study presents the chemical characteristics and seasonality of inorganic ions and trace metals in atmospheric aerosols from Sapporo, northern Japan, and explores their possible sources. The work is relevant for our understanding of atmospheric composition and climate change. Abstract To better understand the characteristics, seasonality and sources of inorganic aerosols in North-east Asia, we studied total suspended particulate samples collected in Sapporo, northern Japan for inorganic ions and trace metals over a 1-year period. SO42– was found as the most abundant ionic species, which accounted for on average 43±15% of the measured total ionic mass followed by Cl–≈NO3–≈Na+. Among the metals determined, Ca was found as the most abundant (45±5.2% of the measured total metals) followed by Fe. Temporal variations of methanesulfonate (MS–) and SO42– showed a clear seasonal pattern with a maximum in summer followed by spring. Cl–, NO3–, NH4+ and K+ showed increasing trends from mid autumn to winter. Na+, Ca2+ and Mg2+ and crustal metals (Al, Ca, Fe, Ti and Mn) peaked in early spring. Na+ and Mg2+ and Ni, Cu and As were abundant in autumn whereas Zn was in spring. However, Cd and Pb did not show any seasonality. Based on comparisons of such seasonal trends with those of organic tracers as well as the air mass trajectories, we infer that the seasonality in inorganic aerosols in the North-east Asian atmosphere is mainly controlled by their season-specific source(s): soil dust in early spring, biogenic emissions in spring–summer, microbial activities in autumn and forest fires and biomass burning in autumn–winter. However, contributions from anthropogenic sources are significant in all seasons. This study also suggests that fungal spores partly contribute to some trace metals (i.e. Ni, Cu and As) whereas pollen contributes to Zn in aerosols.