Every year thousands of tons of soil-derived dust are transported from deserts in northern China and Mongolia to the North Pacific atmosphere, some of it reaching North America. These large dust storms occur mostly in the spring, and the dust clouds badly affect air quality and visibility in China and regions downwind. They can also carry pollutants such as toxic metals, soot and even bacteria. Windblown desert dust from central Asia travels far and wide, and has been reported in the western USA, British Columbia, Alaska, Greenland and even the French Alps. According to a United Nations Environmental Program report, the frequency and severity of Asian dust storms may now be increasing due to climate warming, droughts and spreading desertification. And as eastern Asia's economy -and air pollution- rapidly grows, the "Trans-Pacific dust express" is becoming a topic of serious concern among environmentalists.
A particularly large Asian dust outbreak event occurred in April 2001. The dust cloud was swiftly blown across the Pacific Ocean. Dust collectors across the USA recorded it, and sunsets reddened as far east as Toronto. As it crossed the southern Yukon, the desert plume dumped an estimated 6000 tons of dust over hundreds of square kilometers, leaving a reddish-brown snow layer in the snows of the St-Elias Mountains. Samples of this snow layer were collected on Mount Logan and analyzed by scientists. They found that they could recognize the chemical composition of the dust and trace back its source to the Gobi desert region of northern China and Mongolia.
Fallout from past Asian dust events is believed to be preserved in layers of ancient glacier ice on Mount Logan. These past dust events can be detected in the ice by greater than normal concentrations of aluminum, silicon or calcium because these elements are abundant in desert dust. Ice cores obtained from the Mount Logan region in 2001-02 are now being analyzed in minute detail. They may soon help to reveal how common and intense such Asian dust events were in past decades and centuries, and to verify if they are indeed becoming more frequent in recent times.
Satellite images of the April 2001 dust cloud moving offshore from Asia, then approaching the Pacific coast of North America. These images were obtained by the the Total Ozone Mapping Spectrometer (TOMS) on board the Earth Probe satellite, an instrument which detects UV-absorbing particles in the atmosphere such as forest fire soot and desert dust.