Teflon 37 mm Millipore filters with a pore size of 0.45 m (Fisher Scientific, FHLP03700, Waltham, MA) were used. A SKC button sampler (SKC Inc., 225–360, Eighty Four, PA) with a curved multi-orificed inlet for all suspended PM smaller than 100 m in aerodynamic diameter at an air flow of 4.0 l/min was used to collect inhalable PM.