Brake wear particulate matter emissions

Current particulate matter (PM) emission factor models estimate brake wear particulate matter emission rates using data derived from asbestos brakes. However, most brake pads are now produced from nonasbestos materials. Littl e work has been performed on emissions from brakes using these materials. T herefore, a brake wear study was performed using seven brake pad formulatio ns that were in high volume use in 1998. Included were semi-metallic brakes ; brakes using potassium titanate fibers, and brakes using aramid fibers. B rakes were tested on a brake dynamometer under four wear conditions. On ave rage, 35% of the brake pad mass loss was emitted as airborne PM. The observ ed wear rates correspond to vehicle emission rates of 5.1-14.1 mg/mi. On av erage, 86 and 63% of the airborne PM was smaller than 10 mum in diameter (P M10) or 2.5 mum in diameter (PM2.5), respectively. The large number of part icles observed in some wear tests was attributed to condensation, a process that is highly dependent on dilution condition. Analysis of airborne PM sh owed very few inhalable fibers. On average, 18% of the airborne PM was carb onaceous material. Elemental analysis indicated that metallic species toget her with silicon, phosphorus, sulfur, and chlorine accounted for most of th e remaining mass. Estimates of brake wear PM10 and PM2.5 emission rates fro m light-duty vehicles are made from brake dynanometer wear tests.