Half of the Particulate Pollution in North America Comes from Other Continents
Atmospheric particles can travel thousands of miles downwind and impact the environment in other regions, found lead researcher Hongbin Yu of the University of Maryland, and his team. This could offset emission controls in North America and suggests there are more factors affecting domestic pollution than the Environmental Protection Agency has accounted for.
"People have been concerned about how an emerging Asian economy and increased manmade pollution will influence North American air quality and climate, but we found that dust makes large contributions here," says Yu, an associate research scientist in UMD's Earth System Science Interdisciplinary Center (ESSIC). "So we cannot just focus on pollution. We need to consider dust."
The study, which provides the first satellite-measurement-based estimate of the amount of airborne particles that come to North America from overseas, shows this migrating dust usually comes in at high altitudes and in the United States is most likely to affect upper atmospheric conditions.
Most of the pollution migrating into the North American atmosphere is not industrial emissions but dust from Asia, Africa and the Middle East, Yu found. Out of the total annual accumulation of foreign aerosols, 87.5 percent is dust from across the Pacific, 6.25 percent is comprised of combustion aerosols from the same region and 6.25 percent is Saharan dust from across the Atlantic.
The researchers say the EPA is aware that foreign pollution affects U.S. air, but it is unclear on the amount of imported aerosols, Yu says. The study revealed that much of the dust migration occurs at high altitudes and is unlikely to affect the air we breathe.
Current satellite sensor technology allows scientists to track aerosol plumes across the ocean and measure their composition and particle characteristics. The 3-D satellite measurements can distinguish dust from other types of aerosols such as those released from burning biomass and fuel. While dust and combustion aerosol migration occurs year round, it is heightened in the spring due to strong seasonal wind patterns and extra-tropical cyclones.
UMD climate scientist Antonio (Tony) Busalacchi, who is chairman of the Joint Scientific Committee for the World Climate Research Programme and chairman of the Board on Atmospheric Sciences and Climate of the U.S. National Academy of Sciences/National Research Council, says one of the most interesting points Yu and his coauthors make in their study is that even a reduction of industrial emissions by the emerging economies of Asia could be overwhelmed by an increase in dust emissions due to changes in meteorological conditions and potential desertification.