I want to know about the applications of CFD these days in urban
pollution and its control.

well, now-a-days, dispersion of pollutants from any source (point,
line, etc) can be predicted and/or traced. this can easily be
simulated using the commercial software Fluent. on the other hand, if
you actually want to come up with your own code, then you will most
likely require the lagrangian formulation, which is not that easy.

I'm very happy to see a CFD question on this website. However, CFD is
such a large and complicated field, even in the field of pollution
propogation and control, that I think your question should be more
specific. Do you wish to have examples of applications for catalytic
converters? Or perhaps you want to know how chemicals disperse in the
atmosphere? Maybe you wish to know about the contamination of
waterways? Or perhaps you wish to know how CFD has helped lower
emissions from aircraft engines through combustion modeling? What I'm
trying to say, is that the widely varied mathematical models/methods
and the highly varied applications of CFD are so numerious that you
could write many books and journal articles on the subject, and spend
a career doing it.

In other words, I think that you should ask a very specific question,
especially since many people do their PhD's on very specific areas of
this complicated field.

Finally, nezir-ga, brings up a good point. If you wish to perform a
calculation yourself please invest in a commercial code (like Fluent
for example, or StarCD) or contract an engineering firm to perform the
analysis. However, since you have not told us something about your
background, I don't think comments or researchers will know what level
of technical expertise you wish to have your question answered in.

I wish you luck in finding out more about CFD and pollution control.