Particles worn away from automobile brake linings and tires continue to be major sources of potentially toxic metal emissions in urban areas despite new regulations and auto industry efforts to reduce the use of the metals, according to a new study scheduled for the 1 August issue of the journal Environmental Science & Technology.
In the study, David S. T. Hjortenkrans and colleagues compared metal emissions from brake linings and tires to other metal emission sources in Stockholm during 1995 and from 1998-2005.
During this period, copper and zinc emissions from brake linings remained relatively unchanged at high levels that make them a major source of these metals, the researchers said. Brake linings were also a source of another toxic metal, antimony. By contrast, lead and cadmium emissions from brake linings decreased by one-tenth during this period.
The study found that emissions of many metals (Cr, Cu, Ni, Pb, and (probably) Sb) declined between 1995 and 2005, as manufacturers reduced metal concentrations in tire treads. Tires, however, remained one of the largest sources of zinc and an important source of cadmium.
Emissions from the road traffic sector accounted for approximately 50% or more of total toxic metal emissions, depending upon the metal, in Stockholm.
As Stockholm represents a rather average city in most respects, the results from this study may be relevant for many other urban areas.
“Metal Emissions from Brake Linings and Tires: Case Studies of Stockholm, Sweden 1995/1998 and 2005”; David S. T. Hjortenkrans, Bo G. Bergbäck, and Agneta V. Häggerud;; Environ. Sci. Technol., ASAP Article 10.1021/es070198o S0013-936X(07)00198-8