Brake wear from vehicles as an important source of diffuse copper pollution

In this article we show that brake wear from road traffic vehicles is an important source of atmospheric (participate) copper concentrations in Europe. Consequently, brake wear also contributes significantly to deposition fluxes of copper to surface waters. We estimated the copper emission due to brake wear to be 2.4 kiloton per year. For comparison, the official database for Europe (without brake wear) totals 2.6 kiloton per year. In Western Europe the brake wear emissions dominate the total emission of copper. Using the spatially resolved emission data, copper distributions over Europe were calculated with the LOTOS-EUROS model. Without brake wear the model underestimates observed copper concentrations by a factor of 3, which is in accordance with other studies. Including the brake wear emissions largely removes the bias. We find that 75% of the atmospheric copper input in the North Sea may be due to brake wear. We estimate that about 25% of the total copper input in the Dutch part of the North Sea stems from brake wear. Although the estimated brake wear copper emission is associated with a large uncertainty, it significantly improves our understanding of the copper cycle in the environment. © IWA Publishing 2007

Natural sea-salt emissions moderate the climate forcing of anthropogenic nitrate

Natural sea-salt aerosols, when interacting with anthropogenic emissions, can enhance the formation of particulate nitrate. This enhancement has been suggested to increase the direct radiative forcing of nitrate, called the “mass-enhancement effect”. Through a size-resolved dynamic mass transfer modeling approach, we show that interactions with sea salt shift the nitrate from sub- to super-micron-sized particles (“redistribution effect”), and hence this lowers its efficiency for light extinction and reduces its lifetime. The redistribution effect overwhelms the mass-enhancement effect and significantly moderates nitrate cooling; e.g., the nitrate-associated aerosol optical depth can be reduced by 10 %–20 % over European polluted regions during a typical sea-salt event, in contrast to an increase by ∼10 % when only accounting for the mass-enhancement effect. Global model simulations indicate significant redistribution over coastal and offshore regions worldwide. Our study suggests a strong buffering by natural sea-salt aerosols that reduces the climate forcing of anthropogenic nitrate, which had been expected to dominate the aerosol cooling by the end of the century. Comprehensive considerations of this redistribution effect foster better understandings of climate change and nitrogen deposition