THE CHARACTERIZATION OF OZONE EXPOSURES IN RURAL WEST-VIRGINIA AND VIRGINIA

Ozone (O-3) is suspected of being the most significant air pollutant a ffecting vegetation in the United States, Ozone concentrations measure d at Bearden Knob and Parsons, located in a remote forested region of northcentral West Virginia, were characterized and compared with expos ures experienced at other sites in the region. From 1988 to 1992, 1988 was one of the highest O-3 exposure years in the region, while 1992 w as the lowest. At almost all sites in 1992, few hourly average concent rations were greater than or equal to 0.10 ppm, while in 1988 several sites had more than 100 hourly average concentrations greater than or equal to 0.10 ppm. These instances occurred at both high- and low-elev ation sites. In 1992, the high-elevation Bearden Knob site experienced a flat-type diurnal pattern, while the nearby low-elevation Parsons s ite experienced a changing diurnal pattern, indicative of scavenging, Using several indices, O-3 exposures at Parsons were less than those a t Bearden Knob. Evaluation of hourly averaged data for all sites in th e region from 1988 to 1992 showed that Horton Station experienced the highest W126 O-3 exposures. Horton Station is a high-elevation site in the mountains of southwestern Virginia. Square-wave exposures have be en used under artificial conditions in vegetation experiments. If squa re-wave exposures are observed under ambient conditions, then the vege tation data collected under artificial conditions may be relevant for predictive purposes. Square-wave exposures were characterized for two high-elevation sites. In 1992, Horton Station experienced 25 episodes for which the hourly average concentrations remained near 0.05 ppm for eight hours or longer; there were 18 episodes for which the hourly av erage concentrations remained near 0.06 ppm, and three episodes for wh ich the concentrations remained near 0.07 ppm. Bearden Knob experience d 31 episodes of eight hours or longer for hourly average concentratio ns near 0.05 ppm, 13 episodes at or near 0.06 ppm, and three episodes at or near 0.07 ppm. Until experiments are performed to determine the relative importance of hourly average concentrations above 0.03 ppm fo r assessing vegetation effects, using single-parameter exposure indice s to predict effects may produce inconsistent results.