Refinement of national-scale heavy metal load estimations in road runoff based on field measurements

This paper estimates the traffic-related heavy metal emissions and rainfall–runoff loads in Hungary for 2008 using the results of two rainfall–runoff sampling programs. Based on the metal concentrations found in runoff samples, distinct Cu/Zn ratios are identified for urban and motorway traffic. The former being higher than the latter reflects the effect of more frequent brake application. Runoff Cu/Zn values from field samples are compared to those from various estimation scenarios to evaluate the latter and it is found that, as a rule-of-thumb, about 25% of the emitted brake wear material becomes entrained by rainfall–runoff. Based on the comparison of Pb/Cu ratios derived from the load estimation and the road runoff samples, the Pb emissions appear to be underestimated by an order of magnitude.

Research highlights
► Using Hungarian data, the paper shows that traffic dynamics strongly influence emissions and road runoff loads of Cu and Zn.
► The paper identifies the characteristic Cu/Zn ratios for urban and motorway runoff.
► A quarter of emitted brake wear material becomes entrained by rainfall–runoff.