Figure from a great website by Dr. Wilson from Duke University, with lots of information.
The overall amount of this pollution can be modelled:
Its important to put this into perspective: human (anthropogenic) emissions of VOCs can be 40 times greater than the highest modelled biogenic emissions. But the compounds plants produce may be more effective in generating hazardous compound Ozone. Atmospheric chemistry is complex, and it is ironic that the highest biogenic pollution emissions occur in the same areas that high anthropogenic pollution also occurs, compounding the problem.