*W126 is an index of cumulative ozone exposure that relates to vegetation injury and damage. It preferentially weights high ozone exposures but also reflects some influence from relatively low ozone values.
**N100 is the number of hours that ozone has met or exceeded .100ppm. Peak ozone values are also important when judging potential harm to vegetation.

To learn more about the effects of ozone on vegetation visit the EPA Web site for Air and Radiation - http://www.epa.gov/oar/sect812/appen_f.pdf