Concentration ratio of copper to antimony in dust - an indicator for brake dust?

Sources for antimony in road dust is abrasion of brake pads and brake linings and organic antimony compounds used as additives in grease and oil. Copper is also contained in brake linings and pads, but it is also contained in tire tread. Additionally, copper is released by wear and abrasion of parts made of copper, bronze and brass. In literature, the ratio of the concentration of copper to antimony is used as an indicator for the presence of brake dust in road dust. A ratio of around 5:1 is an indicator of brake-related particles, while the typical crustal ratio of the two metals is around 125:1. Reported values of the ratio for road dust samples are in the range of 20:1. Literature data of the size-dependent concentrations copper and antimony in road dust result in a ratio of copper to antimony of about 10:1 for the fine size fractions while for the coarse size fraction the ratio is higher. This result supports how reliable the ratio is as an indicator for brake dust in road dust.