Asian dust arriving over North America in significant quantities
By Summit Voice
SUMMIT COUNTY — The desert Southwest isn’t the only source of dust in the atmosphere over Colorado. As much as 64 million tons of dust from minerals, soils, pollutants and other sources cross the ocean from Asia, carried by prevailing west winds, and mix into over North America each year, according to a NASA study published last spring.
That’s just about about equal to the 69 million tons of aerosols produced domestically by natural processes, transportation, and industrial sources. The tiny particles can affect the climate, as well human health if they mix down into the lower atmosphere.
Dust movement is particularly active in spring, when the rise of cyclones and strong mid-latitude westerlies boost particle transport across the Pacific. In addition to the transport from Asia, North America also imports aerosols from Africa and the Middle East.
“This is a crucial step toward better understanding how these tiny but abundant materials move around the planet and impact climate change and air quality,” said Hongbin Yu, lead author and an atmospheric scientist at the University of Maryland and NASA’s Goddard Space Flight Center. Observing aerosols and quantifying their impact on warming or cooling the planet remains one of the most difficult challenges in climate science.
Dust has been identified as a significant factor in Colorado hydrological cycles. In years with significant dust deposition, snow melts earlier. But so far, the imported dust
doesn’t seem to part of that problem.
According to Chris Landry, director of the Silverton-based Center for Snow and Avalanche Studies, most of the dust-on-snow particles that affect Colorado are too large to have made the trans-Pacific journey. Until new research shows otherwise, it’s still reasonable to attribute the primary effects on snow albedo to Colorado Plateau source area dust.
One big question from the past few years of dust-on-snow research is whether the dust storms have become more frequent. The scientists have been cautious in answering that question, citing a lack of historical data, but one of the recent papers published from the research suggests that, since the westward expansion of the United States that began in the mid-19th century, the mountain snow cover of the Colorado River Basin has been subject to five-fold greater dust loading, largely from the Colorado Plateau and Great Basin.
A second study by McKenzie Skiles, with the Department of Geography at UCLA, quantified the direct impacts of dust snow by showing how the darker color absorbs extra energy. The conclusion is that the dust radiative forcing shortens snow cover duration by an astounding 21 to 51 days, while recent melt season temperature increases of 2 to 4 degrees Celsius shorten snow cover by five to 18 days.
The study also showed accelerated timing and rates of snowmelt outflow at the base of the snowpack.
“She also explores the comparative impacts of increases in mean air temperatures on those processes, finding that direct absorption of radiation by dust is already exceeding the spring snowmelt energy budget impacts that 2 and 4 degree C increases in air temperatures (added to the actual measured temperatures at Senator Beck Basin) would have produced,” Landry wrote via email.