Modeling Erosion of Particulate Matter

A U.S. Department of Agriculture (USDA) scientist and his research partners have combined models of wind erosion and regional climate patterns to simulate the sources and dispersion of particulate matter—such as tiny bits of soil and other substances—blowing in dust storms around Mexico City.

People who inhale particulates with a diameter of 10 micrometers or less (PM10) can develop respiratory problems, so public health officials are anxious to predict how these airborne pollutants are dispersed over time.

Agricultural Research Service (ARS) soil scientist John Tatarko, who works at the agency's Engineering and Wind Erosion Research Unit in Manhattan, Kan., collaborated with scientists at the National Autonomous University of Mexico on this research. ARS is USDA's chief intramural scientific research agency.

The team combined two existing models to explore how wind erodes PM10 from farm fields and dry lakebeds around Mexico City, where poor air quality is an ongoing concern. The first model was the Wind Erosion Prediction System (WEPS), which was developed by ARS scientists to simulate rates of soil loss, PM10 emissions and other data for specific erosion events.

The other model, developed at the Karlsruhe Institute of Technology in Germany, was the Multiscale Climate and Chemistry Model (MCCM). It combines information about weather conditions and other factors to produce estimates of the transport of air pollutants. The combined model system was called MCCM-WEPS.

The researchers collected field data on four dust storms around Mexico City during the dry season. Then they compared PM10 erosion rates from these storms with MCCM-WEPS simulations of erosion rates for the same storms.

The team found that the simulated rates produced by MCCM-WEPS generally aligned with the PM10 erosion rates that had been measured from the dust storms and accurately simulated the PM10 dispersion down wind. The model also suggested that the horizontal transport of PM10 accelerates when wind currents mix and form low pressure systems, which prompts the upward movement of the particulates. These combined findings all indicate that wind erosion is a major cause of high PM10 concentrations in Mexico City.

Results from this research, which were published in 2010 in Aeolian Research, support the USDA priority of responding to climate change.