All of the PRIMENet sites currently monitor ground-level ozone.
Data available at http://www2.nature.nps.gov/ard/gas.
*Virgin Islands NP was not presented in Figure 3 because it was not in operation in 1997.
*Only sites with continuous data for 1997, Big Bend, Canyonlands, Glacier, Rocky Mountain, Sequoia/Kings Canyon, and Shenandoah NPswere included in Figures 5 and 6.
*Theodore Roosevelt and Virgin Islands NPs were not included in Table 1 because they were not in operation in 1997.
Two summation methods have been used to describe how cumulative ozone exposure relates to effects on vegetation during the growing-season, May through September. The SUM60 statistic is a sum of all hourly ozone concentrations equal to or exceeding 60 parts per billion (ppb). A second method called W126 is a sum of all hourly ozone concentrations where the concentration is weighted by a function that gives a greater emphasis to concentrations above 60 ppb.
The following graphs shows the SUM60 and W126 statistics for each of the PRIMENet sites during the 1997 growing-season. Only one year of data is presented because the operation dates of each monitor were highly variable and these indices are difficult to average in a meaningful way. The disadvantage of presenting one year of data is that inter-annual variation is ignored. However, these spatial patterns tend to remain consistent from year to year.
Ozone injury to sensitive vegetation can occur above 25 ppm-hr for a three-month average of SUM60 and has been documented in Sequoia/Kings Canyon, Great Smoky Mountains, and Shenandoah NPS. These parks are likely to exceed the new 8-hour National Ambient Air Quality Standard (NAAQS) which is subject to court remand. The standard is based on human health effects and is set at 80 ppb ozone averaged over three years. Parks with large elevation gradients are particularly susceptible to ozone exposure. High elevation sites report 2-3 times more ozone than low elevations. This is illustrated by the two sites in Great Smoky Mountains NP, where the difference between Cades Cove (CC) at 564 m and Cove Mountain (CM) at 1243 m is a SUM60 factor of four. Ozone exposure at Olympic, Glacier, Denali, and Everglades NPs was very low in 1997.