Interactive comment on “ Traffic-related air pollution near roadways : discerning local impacts from background ” by Nathan Hilker et al

This study provides three methods to quantify the contribution of local traffic emission to near road measurements and explored the effects of wind speeds and directions on near road pollution. The MS is well written and contains rich and interesting results. However, I worry that the background determined in the paper using method3 may not be a real background, but a characterization of the environment around the road. The authors need to give a clearer view on what they think it means. Below are some specific comments need a response before acceptance.