|【Yellow sand or Dust and sandstorm】|
Yellow sand or Dust and sandstorm
The Dust and sandstorm (DSS) phenomenon occurs when fine soil particles are scooped up to thousands of meters by wind from arid areas, such as the Taklamakan Desert and Gobi Desert in northwest China and the Loess Plateau in inland China, and from semi-arid areas, as well. The sand particles are carried airborne on westerly winds and are deposited across the coastlines of China, Korean peninsula, and Japan. Such phenomenon mainly happens during the spring season thus, it is considered a kind of "spring haze". It has been observed especially in the western part of Japan. Lately, DSS particles have passed over the eastern part and have reached even the northernmost tip of the main island of Japan. This occurrence starts in February and peaks in April. In recent years, it is observed frequently in Japan and it is recorded over 300 days a year at 108 locations (Japan, Referred to the data from the Ministry of the Environment). In Beijing, China, the amount of deposition is about 15 tons/ km2 a month whereas, it is estimated at 1-5 tons/ km2 a year in Japan
DSS brings about harmful influences on the agricultural production of crops because of the soil acidification it effects. When present in the environment, it poses a significant health hazard to the people. Furthermore, the sand particles remain suspended in the atmosphere and affects global climate (Japan, Referred to the data from the National Institute for Environmental Studies). Above all, unprecedented sandstorms have occurred in Central Asia for three years since 2000, and the generated DSS is transported to East Asia. The DSS phenomenon sometimes disrupts elementary schools in the cities of Beijing and Seoul in China and South Korea, respectively, which results in temporary suspension of classes. In Japan, it indicates an important influence and is now a prevailing concern in Mongolia.
Although the DSS problem is a common challenge among the northeast Asian countries, the quantity and grade of the damage depend on the distance from the source region. In countries which are near the source region, DSS causes collapse of trees, destruction of factory products, soiling of cars and laundries, and most importantly it is the cause of the disappearance and worse, death of the residents as well as buried institutions and railway tracks. Moreover, although there is a difference in the degree of accumulation, DSS has caused the most massive damage on the agricultural sector, airline flight cancellation and traffic jam because of the reduced visibility, and especially respiratory and ocular disorders in the people's health.
In China, the history of the DSS phenomenon dates back as early as 1,150 B C. Since 174, the problem has also been described in South Korea. In Japan, DSS has been observed since old times. DSS is conventionally understood as a natural phenomenon, wherein the sand is carried from the Yellow River valley or deserts. In recent years, it is said to have come from the degradation of land by overgrazing and farmland conversion and from desertification. Hence, it is pointed out that DSS is an anthropogenic process.
The DSS particles that reach Japan are the types which predominate in the coarse particle region and are approximately 4μｍ in size (4-10μｍ in Beijing, China). They demonstrate the typical feature of a natural soil particle. The following minerals can be extracted from DSS; rock-forming minerals, such as quartz and feldspar and clay minerals, such as mica and kaolinite. Aside from minerals, sulfate, nitric, and ammonium ions are included. Astonishingly, these compounds come from natural sources, as well. In addition, anthropogenic air contaminants are mixed with DSS particles while being conveyed by wind. It is said that the fine DSS particles, which are not visible to the naked eye, have traversed the Pacific Ocean and have reached the West Coast in the United States. Therefore, deposition on the Pacific Ocean along the way is inevitable.
To date, Light Detection and Ranging (LIDAR) is used for the surveillance of DSS and its level of visibility, in addition to the measurement of suspended particles matter (SPM) less than 10μｍ in size. LIDAR utilizes laser light instead of electromagnetic wave. It is a Remote Sensing Method which measures DSS passing through the air on the ground.
The effects of DSS are not, however, strictly negative. DSS contains many constituents similar to soil and it shows a little basic character. Therefore, DSS particles can help neutralize acid rain because it is rich in calcium carbonate, which negates the acidity of gases generated by the exhausts from cars and factories. It relation to the global warming issue, it slows down the rate of warming by absorbing the emitted sulfur dioxide when coal is burned. Subsequently, it turns the gas into sulfur mist which reflects the sunlight thereby effectively cooling the atmosphere. Additionally, its mineral content benefits the marine environment by supplying minerals to the planktons, which are fundamental components of the food chain. Ecological balance has been preserved for a long time. If this is taken into consideration, the DSS phenomenon can be regarded as an anthropogenic environmental problem, which sets off the depletion of forests, land degradation, and desertification, and not a mere seasonal phenomenon. In order to restore the balance in nature, holistic treatment is deemed necessary.
DSS is a transboundary environmental problem. In order to implement effective researches and measures, cooperation among relevant countries is required. Forestalling the generation of DSS promptly and understanding of the movement and development of the process requires maintenance of the observation network, which has been conducted in large range from the northwest part of China to Japan islands. In Japan, the duration that the DSS concentrates in the atmosphere is calculated by a computer and the results form a DSS model to conduct prediction and verification. Then the data are utilized as prediction activities of the Meteorological Agency. China has been working on the reduction of bare lands by restoration of natural vegetation to prevent land degradation, prevention of soil erosion and travel of sand by building windbreak forest and developing environmental capacity of the land.