The dust in the Sahara Dust Stream consists mainly of tiny minerals that were once rocks. Typically, as the dust stream passes through the Canary Islands of Spain, which lie hundreds of miles downwind of the desert's source, most of the dust that falls is less than 20 microns in diameter, half the size of particles that can be seen with the naked eye on Earth. As the dust crosses the ocean to reach the Caribbean Sea, it falls even finer - less than 10 microns - and many of the remaining fragments are even smaller. The prevailing northeasterly trade winds tend to blow the dust into the Atlantic rather than north to Europe.

So most of the time, strong northeasterly trade winds at low and mid latitudes can pull this dust into the Atlantic Ocean and toward the Americas, even reaching the U.S. Gulf Coast. But sometimes the dust spreads to other places as well. As meteorologist Marshall Shepherd notes, at least a few times a year, persistent winds from the south push Saharan dust into Europe - when the fine dust of the Sahara Desert is lifted aloft by strong winds, it enters the Hadley circulation, which rises at the equator and sinks in the subtropics When the fine dust from the Sahara desert is lifted to high altitudes by strong winds, it enters the Hadley circulation, which rises at the equator and sinks in the subtropics, and is transported northward with the circulation, thus catching the mid-latitude westerly "express" and drifting toward Europe. If dust particles are lifted by strong air currents into the upper troposphere or even into the stratosphere, they can be transported even farther and can even have a global impact. Dust can both warm and cool the Earth. When plumes of light-colored dust are over the oceans, they reflect incoming heat from the sun that would otherwise be absorbed by the dark ocean surface. But when dust collects on otherwise bright surfaces such as snow or ice, it does the opposite, absorbing solar heat and accelerating ice melting.

The Amazon rainforest contains approximately 80,000 species of plants, with each square kilometer containing an average of 90,790 metric tons of living plants, which support at least 2.5 million species of insects, as well as tens of thousands of other animals, making it the most species-diverse place on Earth.

Rainforests are among the most biologically productive places in the world, but the soils that anchor forest trees in their proper place are known to be low in certain elements essential for growth, especially phosphorus. Much of the soil in the basin is insufficient to support the abundant life that grows from it, and a key feature of rainforest habitats - rainfall - picks up any unused phosphorus almost as quickly as it appears. Rain and flooding wash away large amounts of phosphorus from the soil, a fertilizing nutrient that is critical to plant growth.

How did the Amazon's biological richness emerge from such poor soil? Some teams of scientists suspect that the answer may lie in the tiny dust they know has been floating in the Atlantic Ocean for millions of years. They know that this dust contains phosphorus. in 2015, one team calculated that the hottest deserts are actually interconnected with the largest rainforests, a transcontinental dust journey. The phosphorus in this dust essentially fills the gap between the phosphorus needed by the rainforests and the phosphorus content of their severely depleted soils, as the wind transports about 22,000 tons of phosphorus from the Sahara desert each year. The Amazon rainforest is also home to a variety of other aerosols, such as smoke and biological particles containing substances such as bacteria, fungi, spores, and pollen.

Without this dust, one of the most biodiverse places on Earth would not be so rich. "It's a small world," says NASA researcher Hongbin Yu, a meteorologist at the University of Maryland, "and we're all connected."

In June 2020, a "Godzilla" dust plume crosses the Atlantic Ocean from the Sahara, the largest and hottest desert on Earth, to North America. While this dramatic dust flow made headlines, NASA scientists combined satellite data and computer models to predict that due to climate change and warming oceans, Africa's annual dust plume will actually be reduced to a 20,000-year minimum over the next century.

As the dust covered the Caribbean Sea and darkened skies over several southeastern U.S. states, several meteorologists called the event "historic." Dust concentrations in the atmosphere over the Atlantic Ocean on June 20 were higher than on any day since 2003. AOD is a unitless measure of how much light is prevented from passing through the atmosphere by particles in the air. A few days later, the ground-based AERONET sensor at Ragged Point, Barbados, recorded the highest AOD value ever recorded at the site since 1996.

As the dust moves through the ocean, the larger particles are shed first, leaving behind mainly finer particles, which are especially problematic for human health. According to Yu Hongbin, an atmospheric scientist at NASA's Goddard Space Flight Center, it weighed more than 24 million tons, enough to fill hundreds of Olympic-size swimming pools. The "Godzilla" dust flow reduced air quality in the Caribbean basin to dangerous levels, and about 40 percent of stations in the southern U.S. exceeded the EPA air quality for dust inhalation, especially harmful to children, the elderly and people with respiratory conditions such as asthma.

"East African winds export dust from Africa to the Atlantic region. Then the North Atlantic subtropical high pressure, a high-pressure system located over the subtropical North Atlantic, can further transport it to the Caribbean. Once the dust reaches the Caribbean, the Caribbean low-level rapids - which is another system - along with the subtropical high pressure can further transport the dust from the Caribbean to the United States.

Weather experts say storms in the Sahara desert about 2,000 miles away are usually responsible for raising dust that blows toward Britain. The winds currently arriving in the country are part of a belt of warm air that is expected to bring unusually warm temperatures in the coming days, followed by rain in some areas. Experts say "blood rain" occurs in Britain several times a year. It is more common in southern Europe, such as Spain and southern France, near the Sahara desert. But it can travel greater distances and fall in areas such as Scandinavia.

"Blood rain" is a term used for rain that carries sand from the desert. It looks red when it rains, and when it does, it leaves a thin layer of dust, which can also be red, hence the name. It is capable of coating houses, cars and garden furniture. "The different colors of sand in the Sahara desert mean that the rain and the color of the coating it leaves behind can vary," said weather expert Philip Eden. "It can be slightly red, but it's very rare. It's more likely to be sandy or brown. It's not as spectacular as it sounds."

The red rain begins to fall in the middle of the monsoon and continues this way off and on for weeks. The color is so intense that it can stain clothes. Green, yellow, brown and black rainfall has also been reported. Investigations suggest that the rain was red because the wind blew up the dust of the Arabian Peninsula. Although another theory explored even suggested that some form of life had fallen from the sky. At the time, physicist Godfrey Lewis of Mahatma Gandhi University in Kottayam reportedly concluded that the rain left behind a sample that did not contain dust, but had a "clear biological appearance".

The aerosol model CAM considers five major types of atmospheric aerosols, including black carbon, organic carbon, sulfate, sea salt and dust (Gong et al., 2002; 2003), and the distribution spectrum of various aerosol particles is divided into 12 scales from 0.01 μm to 40.96 μm in diameter. CAM considers the main atmospheric aerosol processes such as aerosol emission, transport, chemical transformation, and wet and dry deposition, and combines them with a microphysical cloud module to address the interaction of aerosols with cloud precipitation.

Observational studies have found that dust aerosols from Africa are transported northeastward across Eurasia, but dust aerosols from this pathway (including dust from Arabia and Central Asia) are often combined with dust aerosols from East Asia to be transported out of Asia as Asian pollutants and possibly across the Pacific ( McKendry et al., 2007; Chin et al., 2007). Both the long-range transport of dust from African desert source areas and Arabia and Central Asia directly affect the atmospheric environment in East Asia, while the trans-Asian-European transport of dust aerosols remains to be studied and understood, especially the contribution of trans-Asian-European transport of dust to atmospheric aerosols in East Asia, compared to the mid-latitude trans-Pacific transport and low-latitude trans-Atlantic transport of dust aerosols in the Northern Hemisphere. In this study, the aerosol simulation experiment of GCM CAM3.1 is used to analyze and assess the impact of dust aerosol transport across Asia and Europe from African, Arabian and Central Asian deserts on the atmospheric environment of East Asia.

Based on the analysis of the spatial and temporal distribution of dust storms, floating dust, 850 hPa wind field and winter and summer aerosol index (AI) at 300 meteorological stations in North Africa from 1997 to 2016, we investigated their long-range transport paths and obtained the following conclusions.

This study concluded that there are two main transport paths of dust and sand in North Africa, I and II, which start from Algeria, go eastward to the Mediterranean Sea, Egypt and Sudan, then turn to the Sahel and travel from east to west to the Atlantic Ocean; II starts from Algeria, travels southward to Mauritania, and then travels westward to the Atlantic Ocean. There are four branches in the transmission path I, 1 from Egypt continues eastward; 2 from Algeria, northeastward to the Mediterranean Sea or southern Europe; 3 from Niger and central Chad, southward across the Sahel to the Gulf of Guinea, then westward to the Atlantic Ocean; 4 from northern Sudan southeastward to the Red Sea; the branches 3 and 4 occur in winter and summer, respectively.

Dust source areas can also be identified from satellite TOMS AI data, e.g. Brooks et al identified the Horn of Africa, southern Egypt, the Nubian Desert in northern Sudan, and the Bodleian Depression as important dust source areas, with other minor dust source areas located south of the Atlas Mountains in northern Algeria, the eastern Libyan desert, and Prospero and Washington further identified the Bodleian Depression as a major dust source area. [Mahowald argued that the shrinkage of Lake Chad resulted in the exposure of nearly 20,000 km2 of lake sediments, resulting in the exposure of nearly 20,000 km2 of lake sediments. Mahowald suggested that the Lake Chad source is a potentially important source area for dust emissions in North Africa due to the reduction in Lake Chad area, but some researchers have suggested that the contribution of the Lake Chad source may be insignificant compared to the Bodleian Depression, which is about 700 km north of Lake Chad . Dust source areas can also be identified through dust emissions in dust value simulations, e.g., Mokhtari et al. used ALADIN combined with ORILAM aerosol scheme to simulate the annual average dust emissions in the Sahara region from 2006 to 2010, and the simulations showed that the Bodleian depression had the highest average annual dust flux (2 kg·m-2·year-1 ), followed by the central Niger. followed by central Niger (400-600 g·m-2·year-1), the western and eastern Great Desert of Algeria (200-400 g·m-2·year-1), the Western Sahara coast, central Mali and Mauritania (200-400 g·m-2·year-1), southeastern Libya and Sudan (100-200 g·m-2·year-1), Egypt and Libya. 1), and along the border between Egypt and Libya (100-200 g·m-2·year-1). Evan et al, using satellite, infrared imager (SEVIRI), and dust models, concluded that 82% of dust emissions in North Africa originate from the Sahel region at 15-20°N, with most of the dust emissions coming from the Bodri Depression (64% ± 16%) and the leeward depressions of the Ayr and Hogar Mountains (13% ± 3%). However, the simulated dust emissions are subject to large uncertainties, e.g., the total annual dust emissions in North Africa simulated by different models vary from a minimum of 580 Tg·year-1 to a maximum of 1430 Tg·year-1, which is nearly a factor of one. At the same time, the spatial variation of dust emissions simulated by different sand initiation scenarios is also observed.

The highest concentrations of dust particles were observed east of the Balerik Islands, northwestern Italy, Switzerland, southeastern France and western Austria. Skies have turned orange in many areas. As tonight's winds continue to push Saharan dust north and east, it could reach the Benelux, central Germany, the Czech Republic and Hungary by Sunday morning. Weather models cover this event well, with the highest Saharan dust concentrations this Saturday in the western Alps, eastern France and southern Germany. On Sunday, dust particles may be detected in (eastward moving) northern and northeastern Germany, south-central Poland and Ukraine. It may not be surprising to see some Saharan dust particles in parts of the Benelux and England.

In combination with the 850hPa wind field, there is a good correspondence between the transport of dust storms and the distribution of floating dust. In northern North Africa (north of 30°N), westerly or northwesterly winds prevail throughout the year, a characteristic airflow that allows the transport of North African dust to the Mediterranean [59]; in the east, a very pronounced north-south flow is present throughout the year from 25 to 32°N before shifting to northeasterly winds south of 25°N Saharan dust storms occur mainly in spring in the eastern Mediterranean basin; however, dusty events can also be observed in summer particularly during the first half of the year. Eastern Mediterranean dust events are associated with atmospheric depressions that move eastward. Two different types of low pressure systems can be distinguished in the daily analysis: the Sharav cyclone and the mid-latitude Mediterranean cyclone (Figures 7a and 7b). The shallow Sharav cyclone forms on the southern side of the Atlas Mountains due to the steep temperature gradient between the heated continent and the cooler ocean. Mediterranean cyclones are formed by polar frontal disturbances enhanced by the complex geomorphology of the Mediterranean region. Both types of Eastern Mediterranean dust-laden atmospheric circulation have a fairly strong latitudinal wind component, with a maximum westerly flow of 12 m/s due to their eastward drift. backward trajectories clearly indicate the dominance of latitudinal winds over the meridional flow (Fig. 7c).

The dust deposited on the snow surface darkens the snow surface by 40%, so it absorbs more solar radiation and melts at a higher rate. These two effects have led to the extreme reduction in snow observed in early 2021. The study also suggests that the dust and nutrients contained therein may have contributed to the growth of red algae on the snow surface, a phenomenon that was seen in the Alps in 2021. Based on the pioneering framework established by Schotterer et al. (1985), Wagenbach & Geis (1989), Schwikowski et al. (1995) and Lugauer et al. (1998) on the transport of Saharan dust to the European Alps, our study contributes to the understanding of aerosol transport to the CG region by using a novel ultra-high resolution, continuously sampled, two-millennium, subannual dust record from the 2013 collection of cores (Bohleber et al., 2018). Previous studies of the 2013 CG ice cores have produced reliable ice core chronologies by combining annual layer counts with previously known layers and newly discovered volcanic ash layers (More et al. 2017; Luongo et al. 2017; Bohleber et al. 2018; Loveluck et al. 2018). Based on annual layer counts and cryptotephra analyses, the CG record is traceable to at least 1 C.E. at 61 m (abs) depth, with the potential for further expansion (Bohleber et al., 2018; Loveluck et al., 2018).

The strength of the prevailing westerly winds varies with the polar cyclone. In winter, as the cyclone reaches its maximum strength, the prevailing westerlies intensify and are positioned to the south. Aerosols are brought into the territory of western Russia under the influence of the Mongolian-Siberian high pressure that is coiled in East Asia. The East Asian winter winds originate in the Siberian region where winter temperatures are low, and the build-up process is rapid and creates strong northwesterly winds in the lower troposphere along the East Asia-Pacific coast. (Ding, Yihui et al.; Chang and Lu). The East Asian winter winds and the changes of Siberian high pressure have significant effects on the winter weather and climate in northern Eurasia, East Asia and even the whole Northern Hemisphere (Cohen et al., 2001; Gong and Ho, 2002; Chernokulsky et al.) When the East Asian winter winds are strong, the northern part of Asia and Europe are prone to cold wave outbreaks, and the East Asian region including China In East Asia, including northern China, Japan, Korea, and North Korea, cold air is likely to affect the region, and catastrophic weather such as low temperature, cold wave, snowstorm, and dust storm often occur.

Figure 2 shows the distribution of the difference of sea level pressure field and 850 hPa wind field between the high AOD year and low AOD year (average of high AOD year minus average of low AOD year). The difference between the sea level pressure field in the high and low AOD years is not obvious in the center of Siberian high pressure, i.e., near Mongolia, indicating that the intensity of Siberian high pressure is not the main reason for the high or low AOD in the northern region from 2001 to 2013. However, in the high AOD year, the sea level pressure field has a significant distribution of negative anomalies in the western part of Mongolia and a significant distribution of positive anomalies in the northeast of China to the vicinity of Japan, and the areas that have passed the 90% confidence test are marked by white crosses. This indicates that the change of east-west position of Siberian high pressure may be the main reason for the high or low AOD in the northern region in winter. When the position of Siberian high pressure is westward, the winter AOD in the northern region tends to be low; when the position of Siberian high pressure is eastward, the winter AOD in the northern region tends to be high. From the difference distribution of 850 hPa wind field, it can be seen that there are abnormal southeasterly winds in the 850 hPa wind field in the northern region in the year of high AOD, indicating that the prevailing northwesterly winds in the northern region in winter weaken in the year of high AOD, resulting in the weakening of dry and cold air from the Siberian region, and the diffusion of pollutants in the northern region downwind is also inhibited, resulting in the high concentration of pollutants in the northern region.

In the case of strong cold air in the Arctic, cold waves (blowing northwesterly winds) carry sand and dust southward to the territory of China. A cold wave is a weather event in which cold air from high latitudes invades the middle and low latitudes on a large scale, causing severe cooling. Cold waves are also often accompanied by catastrophic weather such as high winds, dust storms and blizzards. Inner Mongolia is located in the northern border of the motherland, bounded by 37° 24′~ 53° 23′ N. This zone is also the active zone of the northern frontal zone, where cold and warm air frequently converge and cold waves are frequent. With the transit of cold fronts, November 27, 2021 17:00 (Beijing time) from Hulunbeier City, the western and northern Xilinguole League began to appear cooling, followed by different degrees of cooling across the region. The average daily temperature of 63.1% of weather stations in the region dropped by ≥10.0 °C within 48 h on 1-3, and 42.9% of weather stations dropped by ≥10.0 °C on 2-4 (Figure 1), of which more than half of the weather stations in Chifeng had a temperature drop of 14.0 °C or more. It reached the standard of extra strong cold wave. The maximum process cooling in Xilinguole League West WuZhuMuchin Banner, 22.7 ° C. In summary, the process is a region-wide cold wave weather process, part of the region to reach the standard of a very strong cold wave.

Beijing is located in the North China Plain, surrounded by mountains on three sides, and has a topographic feature of high in the north and low in the south, which makes it extremely easy for pollution to accumulate in the area when unfavorable meteorological conditions occur. Sand and dust are affected by the topography at the intersection of the second and third terrain steps in China to settle in the regional area of Beijing.

Research content and analysis methods

1. Research content

Through the collection of atmospheric dry deposition and PM25 samples in Beijing, the morphology and components of atmospheric particulate matter were observed and studied by using transmission electron microscopy and X-ray diffraction methods; meanwhile, the elemental composition was measured and analyzed by ICP-MS method, combined with the analysis of atmospheric dry deposition fluxes and the geographical conditions around the collection site in Beijing, to find the similarities and differences of aerosol sources by comparing the Sahara desert particulate matter.

Atmospheric aerosol samples were collected from different locations from the second ring to suburban areas of Beijing under hazy and non-hazy weather, and the concentrations of the main organic pollutants were analyzed and measured. The sources of each pollutant and their contributions were inferred by concentration analysis, geographical variation analysis and numerical analysis methods. Meanwhile, C-N isotope analysis was used to analyze the C-ratio of organic pollutants in PM25 samples to determine the C and N sources of atmospheric samples. The conclusions of the two methods of concentration analysis and isotope analysis were corroborated and discussed with each other, and comparative analyses were conducted in terms of spatial differences and climatic differences to determine the sources and contribution rates of organic pollutants in PM25 in Beijing hazy atmosphere and to infer the causes of hazy weather formation in Beijing.

2. Overview of the sampling area

The sampling area is located on the roof of Building 7 of the Central Academy of Fine Arts, No. 8 Huajiardi South Street, Chaoyang District, Beijing. The geographical coordinates are 39°58′48″ latitude and 116°27′33″ east longitude.

The sampling area has a warm-temperate monsoonal continental semi-humid and semi-dry early climate with four distinct seasons and obvious changes in dryness, wetness, coldness and warmth. In winter, controlled by Siberia and Mongolia high pressure, low temperature and snow, more windy weather than the dominant wind direction is northwest (see Figure 3-1 for the rose wind map of Beijing), summer by the human land low pressure and Pacific high pressure, hot and less windy, more rainfall, the annual average temperature is 108 ℃, the sampling area is affected by the reservoir, the average temperature in the summer period is 3 ℃ below the urban area.

3. Sample collection and pre-treatment

A dust collection chamber was used to collect monthly atmospheric dry deposition, which was a 30 cm high, 15 cm circumference acrylic plastic and metal device (Fig.). During the sampling process, the chamber was placed 5 m above the ground surface and away from daily human activities to reduce the impact of dust on sample collection. During sampling, a small amount of 20% glycol solution was added to the chamber to prevent secondary dust generation from the collected dry deposition. The sampling period was from December 2011

From December 2011 to December 2021, dry deposition was collected once a day, and a total of 10 atmospheric dry deposition samples were collected (some samples were discarded due to the collection of rainwater).

PM2s samples were collected using a medium flow rate atmospheric sampler (Qingdao Laoying 2030 Figure 3-3) with a sampling flow rate of 100 L/min and a sampling time of 24 h. PM25 samples were collected using 88 mm diameter quartz filter membranes, which were roasted in a 450°C muffle furnace for 8 h before sampling to remove volatile and organic substances. Ten samples were collected at the sampling sites from November 27, 2021 to December 7, 2021, with a total of 103 valid particulate matter samples.