On the effect of polluted air on health. Is it more gradual, or more immediate?
The main factors of urban air pollution are nitric oxides, carbon monoxide, and what is called in german "Feinstaub" (very small carbon-rich particles from diesel exhaust). However, do not forget heavy metals: street dust is especially metal-rich and is swept into the soil near the streets where children and farmed plants can take it up. Lead is a heavy metal that can be breathed in with the air. Last not least noise over a certain threshold is proven to be a cause of illness, even loss of life time (10 years near an airport, if I recall correctly, but airport noise is getting better while machines become more fuel-efficient).

To answer your question one would have to look at every single factor. Lead accumulates in bones and destroys your brain. I just see Brazil banned it too in the 80's so this one killer is no more.

http://en.wikipedia.org/wiki/Tetraethyllead

I have found a meta-study that reviews about 80 papers on the subject, especially the Sao Paulo studies, so this should fit exactly your questions:
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3093800/