The effect of smog on life expectancy

Does living in badly polluted cities reduce life expectancy? Would, for example, a Los Angeles resident expect not to live as long as someone living in a rural area, all other things being equal?

I have heard this is true, and read articles backing this up, such as this one:
http://news.bbc.co.uk/1/hi/health/2502283.stm
But, in general, is there a significant difference? Is it comparable to smoking cigarettes in any way or do I have the wrong idea?

I’ve tried to get information on this, but I can’t find anything useful.