On the dustiest days in the western United States, 40 percent of the grime blows in from Asia. And fine particles can travel all the way around the world from Africa’s Sahara Desert. These unwanted visitors show up in a new model of dust imports developed by researchers from Harvard and the National Aeronautics and Space Administration (NASA). The findings have important implications for air pollution and climate change.
The Asian dust invasion is heaviest in the western states in spring. It moves on into the eastern U.S., but in much lower quantities. The traveling grime is mobilized by strong winds blowing over deserts or dry lakes and streambeds. “Most of the dust is from natural sources and falls out close to its source,” notes Daniel Jacob, a professor of atmospheric chemistry and environmental engineering at Harvard. “But fine dust can be transported over long distances: from Asia to North America, and from North Africa to Florida, and all the way around the world to Canada and the U.S.”
The grit is a health problem. A study done by other investigators, at the Harvard School of Public Health, concludes that an increase of particulate air pollution increases the risk of early death for people with diabetes, chronic obstructive lung disease, congestive heart failure, and inflammatory ailments like rheumatoid arthritis and lupus. Fine mineral dust is so damaging because it can penetrate much deeper into the lungs than larger particles.
Jacob worked with graduate student T. Duncan Fairlie and research associate Rokjin Park to build a computer model for estimating the impact of dust from Asia. They tested the model’s accuracy with measurements from a NASA aircraft mission over the Pacific led by Jacob in 2001. The results were compared with dust records from Japan, various Pacific Islands, and air quality observing stations in the United States.
The model simulates the highs and lows of dust flow. Following the largest flow in spring, things quiet down in summer. Then a second, less active peak blows dust around in the fall. Winter is quiet.
North African dust imports peak during summer months in Florida and along the Gulf Coast. It adds haze in the Great Smoky Mountains, the Appalachians, and other East Coast locations.