Long-Term Efficiencies of Dust Suppressants to Reduce PM₁₀ Emissions from Unpaved Roads

A 14-month study was undertaken to assess the long-term efficiencies of four dust suppressants (i.e., biocatalyst stabilizer, polymer emulsion, petroleum emulsion with polymer, and nonhazardous crude-oil-containing materials) to reduce the emission of PM₁₀ from public unpaved roads. PM₁₀ emission rates were calculated for each test section and for an untreated section for comparison purposes. Emission rates were determined from PM₁₀ concentrations measured from 1.25 m to 9 m upwind and downwind of the road and above its surface. Calculated emission factors ranged between zero and 1,361 g-PM₁₀/vehicle kilometer traveled (VKT) (average uncertainty = ±35 g-PM₁₀/ VKT) for the four types applied. One week after application, suppressant efficiencies ranged between 33% and 100% for the four types applied. After 8-12 months of exposure to weathering and 4,900-6,400 vehicle passes, the suppressant efficiencies ranged from zero to 95%. Roadway surface properties associated with low-emitting, well-suppressed surfaces are (1) surface silt loading and (2) strength and flexibility of suppressant material as a surface layer or cover. Suppressants that create surface conditions resistant to brittle failure are less prone to deterioration and more likely to increase long-term reduction efficiency for PM₁₀ emissions on unpaved roads.