In April 2012, a dust storm that originated in China and Mongolia took a six­day journey across more than ten thousand kilometers of sea and open land to Arizona in the United States. The cloud was so dense that it seemed as if the sun were setting early. At least one person thought a volcano had erupted.

　　Although traveling dust storms are nothing new, the dust now often contains chemical or metallic substances that contribute to respiratory illnesses (呼吸道疾病) and damage the environment. At present, a group of researchers in Asia is studying aerosol particles and their effects on the environment - and they have plenty of dust to work with.

　　Dust storms are one of the repercussions (后果) of humans messing around with Mother Nature. Although they are a natural phenomenon, dust storms have been occurring more often, at shorter intervals, and with greater force in recent years, and human activity is the cause.

　　It is a fact that excessive herding of animals and exploitation of grasslands are responsible for the majority of dust storms. This means that dust storms are largely a result of human actions; in other words, they are controllable.

　　Section_ⅠIntroduction & Reading - Pre­reading