Dirt roads = Air pollution?

[Numpty Dumpty 17]

For a good while, I've been slowly building one of my best cities yet (and its still only at 2030 population, small changes can take days to actually make an impact I've found in this game), but I was bugged to death by random pockets of air pollution that seemed to just appear out of the blue and all my sims would complain about germs and how the whole city was unhealthy.

 

So yesterday I decided to upgrade some of the dirt roads that see most of the traffic to paved roads and.....random pollution has subsided quite a bit.

 

There are still smaller pockets around, but it seems that heavily used dirt roads kick up a lot of air pollution and are unhealthy. Keep in mind that when I say "heavily" I have a population of 2k and most of my sims walk to work.

[TuPhat 27]

Sewage will leak through dirt roads, but not paved.   It is possible that some of your 'germs' are caused by this leakage.  

 

Also, you will generally receive random pockets of air pollution blown in from other areas of the map, so if you have other cities that are upwind and producing lots of pollution, this will effect your other cities.