Turns out we have managed to exceed the critical tropospheric ozone levels over our agricultural belt. We generate ozone in this lower atmosphere by our industrial and transport emissions-an Urban problem? Well its supposed to affect crop yields, threateningly, although it might really be fun to figure out that data. [edits on July31,2009: I find some reliable data here] How about a little Asthma for rural India? Then you take your harmless corticosteroids and kill your hippocampal neurons. By the time we start feeling the effect we will probably figure out how the US had tackled this problem, or, did they?
Here, you can visualize the global ozone column(from the ground to the top of the atmosphere) in near real time (within 3h of actual observation). The data is collected by spectrometers on a satellite launched by the European Space Agency. At this NASA site you'll find some more nice images of tropospheric ozone.
Our industrial and transport emissions are nitrogen oxides, carbon monoxide and hydrocarbons and these get converted into ozone in the atmosphere in the presence of sunlight. Lightning will also help. Incidentally, we had a very intense and frequent lightning period during the end of summer in Kolkata. These ozone precursors can also be tracked to determine intercontinental pollution spread.