I hated ordinances! Why? Because deep inside I didn't believe they worked! Because it's hard to see the "before" and "after" effect since they take
ages to work and since in that time your population etc increases and your city spreads so it doesn't provide an accurate picture. But look, i'm sure they did work I was just saying I felt like I was just ticking a box with no end result to prove it worked
I really think Cities XL 2011 did a
fantastic job in making pollution accurate. What do I mean? Well simply, I have 2 islands very close to each other seperated only by a tiny river. One island is
all factory and industrial, and the other is my offices/residents etc. I had a click to show "pollution" and I noticed the pollution (which goes from green-->orange-->red depending on how polluted the sky is) was made so that where my
factories are there is actually a green circle, with the bulk of pollution being away from the factories as you go further out.
I have attatched an image to show what I mean
The image is of the ozone layer, but see where Antarctica is? The purple is where my factories are (and it was green colour= low pollution) and the red and orange is where my city is (away from the factories) but pollution there was the highest.
So the developers made it more realistic and complete opposite to SC4 (where pollution was highest where the factories are, and got progressively less as you went further away). I like the new approach because pollution tends to spread due to wind further away.
I too wish we could place trees or something to reduce pollution in the game, strange why that was left out? But then again planting a tree like in SC4 shouldn't be able to reduce air pollution lol, I don't think that's scientifically possible

do trees "clean" the air, or just provide oxygen

i'm not sure.