3.3. Ozone impacts
The impact on ozone concentrations is related to the atmospheric
concentrations of VOC and NOx. Fig. 3 shows the average
daily maximum concentration of ozone attributable to road transportation
emissions. Daily maximum ozone is temporally averaged
only during the ozone season (ApreSep), consistent with EPA
practice. Road mobile emissions induce a domain-wide increase in
daily maximum seasonal ozone concentrations, except for some
major urban areas (e. g. Miami), where the high background NOx
concentrations account for a decrease in the ozone concentrations
due to the additional NOx emitted by road vehicles.
Road transportation provides the most significant impact over
ozone exposure among the combustions emission sources considered
in this study. From Table 3, the population-weighted mean
daily maximum ozone concentration due to vehicle emissions is
6.90 ppb, about three times larger than the population-weighted
concentration change due to electric generation (2.15 ppb) and
industry (2.06 ppb). Commercial/residential activities, as well as
shipping and rail emissions, have an impact on the mean daily
maximum ozone concentration below 1 ppb.