where( *) is friction velocity in the coal storage piles( *t )is threshold frictionvelocity ( Pi=0 for ( *) ≤ (*t )). Because of the nonlinear form of the erosionpotential function, each erosion event must be treated separately.Emissions of PM10 generated by each event are calculated as the product of k (PM10 = 0.5), erosion potential ( i P ) expressed in g/m2, and the area affected by pile.