Although these results cannot be projected at the overall urban
atmosphere, since the tunnel conditions magnify the impact of
non-exhaust emissions, e.g. resuspension, and refer to peculiar
traffic flowconditions, they raise awarning on our ability to control
emissions. In the near future, non-exhaust emissions (road dust
resuspension, road surface abrasion, brake, clutch and tyre wear)
are expected to dominate the remaining traffic-related PM emissions,
mostly due to the steep decrease in exhaust emissions, which
are heavily regulated, while non-exhaust emissions are not yet
affected by regulation standards (Denier van der Gon et al., 2013).