need an example to understand how topographical factors intensify air pollution and how they can help pollution?

Question

Since this is not my area of expertise, I searched Google under the key words "topography 'air pollution'" to get these possible sources:

(Broken Link Removed)
http://www.pscleanair.org/airq/basics/weather/default.aspx
http://www.valleyair.org/newsed/apvalley.htm
http://www.arb.ca.gov/knowzone/students/airpollu/airpolpage/whyis.htm
http://www.metroactive.com/papers/metro/09.25.03/smog-0339.html
http://encarta.msn.com/encyclopedia_761577413/Air_Pollution.html

I hope this helps. Thanks for asking.

What is found on the inland side of a mountain range