We perform the same bias-correction here
for our year 2030 analysis: we divide simulated O3 exposure in the
U.S. as calculated by the metrics defined in Section 2.2 over each
crop growing season by the ratio of modeled:observed O3 in the
same grid cell where measurement data exist from 1998 to 2002
(where multiple observation sites exist in a single grid cell, we use
the average of the measurements to correct simulated values).