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EPA regulates dust, formally described as particulate matter, under anti-pollution laws. E.P.A. is considering either keeping the current limit, set in 1987, on exposure to dust or lowering it. A periodic review of the dust rule has led outside scientists to suggest a stricter limit.  Dust regulation is aimed at microscopic particles that can be inhaled and cause serious health problems such as difficult breathing and irregular heartbeat. Sand and particles larger than 10 microns in diameter are not regulated. By comparison, a human hair is about 70 microns in diameter. Particles regulated by the E.P.A. can come from construction sites, fields, unpaved roads, power plants, cars and industry.

Studies by the Desert Research Institute have shown that anthropogenic fugitive dust emissions contribute on the order of 5-20% of PM2.5 (particles with an aerodynamic diameter less than 2.5 um) and 40-60% of PM10 (particles with an aerodynamic diameter less than 10 um) in urban areas that either have been or potentially may be unable to attain the National Ambient Air Quality Standards (NAAQS) for PM2.5 and/or PM10. On the other hand, air quality models suggest vastly higher contributions from current fugitive dust emission inventories, with contributions ranging from 50-80% for PM2.5 and 70-90% for PM10.

Unpaved rural roads are a source of pollution. Erosion of unpaved roadways occurs when soil particles are loosened and carried away from the roadway base, ditch, or road bank by water, wind, traffic, or other transport means. Exposed soils, high runoff velocities and volumes, sandy or silty soil types, and poor compaction increase the potential for erosion.

EPA is not requiring the control of dust from every unpaved road. In fact, unpaved roads do not need to be stabilized unless vehicles drive on them 250 times a day or more. This equals about 3 cars every 5 minutes over a 7-hour period or 2 cars every 5 minutes over a 10 1/2-hour workday.

Four United States representatives have introduced legislation that would temporarily ban the E.P.A. from changing the dust rule. A quarter of the members of the House signed a letter to Jackson on March 29 opposing stricter limits. (EcoSeed, 4/21/2011, Assessing the Anthropogenic Fugitive Dust Emission Inventory and Temporal Allocation using an Updated Speciation of Particulate Matter, EPA Dust)