Atmospheric Environment Vol. 28, No. 1, pp. 89-101, 1994. 1352-2310/94 $6.00+0.00 Printed in Great Britain. © 1993 Pergamon Press Ltd CHARACTERIZING SURFACE OZONE CONCENTRATIONS IN NORWAY ULF PEDERSEN Norwegian Institute for Air Research, P.O. Box 64, 2001 LiUestrom,Norway and ALLEN S. LEFOHN A. S. L. & Associates, 111 North Last Chance Gulch, Helena, Montana 59601, U.S.A. (First received 15 January 1993 and in final form 22 April 1993) Abstraet--This paper focuseson characterizing the hourly ozone concentrations in Norway in a form that is helpful for quantifying the potential for surface ozone concentrations to affect vegetation. In general, the maximum hourly average concentrations experiencedat the monitoring sites were below 0.10 ppm and, in most cases, sites experiencedfewer than 5% of their hourly average concentrations/>0.06 ppm. The lowest maximum hourly average concentrations occurred at the two remote Spitzbergen sites, Ny Alesund and Zeppelin (0.061 and 0.059 ppm, respectively).At the Nordmoen, Birkenes, Haukenes, and Valle sites, the maximum hourly average concentrations were 0.091, 0.099, 0.115, 0.086 ppm, respectively.The infrequent occurrences of hourly average concentrations />0.06ppm were reflected in the absolute values of the exposure index that summed the hourly average concentrations t> 0.06 ppm (SUMO6). In most cases, values for the sigmoidally-weighted cumulative exposure index (W126) were below 10 ppm-h however, the Jeloya and Drotningborg sites experienced values of 34.6 and 24.2 ppm-~h, respectively.The cumulative exposure index that summed all the hourly average concentrations (SUMO) did not adequately focus on the important components of the ozone exposure regime that appear to be responsible for affectingvegetation. For most of the sites, the long-term 7 h (0900-1559 h) and 12 h (0700-1859 h) seasonal average concentra- tions were in the range of 0.030-0.040 ppm. The magnitude of the long-term average concentrations was associated more with the lack of low hourly average concentrations near minimum detectable levels than with the occurrence of repeated high hourly average concentrations. There was a large number of dally occurrences when the maximum 8 h average concentration exceeded 0.03 ppm. For the two remote Spitzbergen sites, Ny Alesund and Zeppelin, 71 and 109 daily occurrences were registered, respectively. However, given the interest on focusing on the occurrences of the higher hourly average concentrations, calculating the number of exceedences greater than 0.03 ppm for the daily maximum 8 h average concentration may not be the most appropriate way to assess the potential for ozone concentrations to affect vegetation. Key word index: Surface ozone, vegetation effects, cumulative exposure index, Norwegian ozone data, SUMO6 exposure index, W126 exposure index, ambient air quality. INTRODUCTION In Norway, photochemically generated ozone is not generally associated with local sources; concentra- tions are mostly associated with regional generation and dispersion of ozone and precursors from sources located in northwestern Europe (Schjoldager, 1984). Concern has been expressed in Norway as well as in other countries that ozone concentrations may be superimposed on a background level that is slowly increasing. Although there is some disagreement concerning the absolute level of the average concen- trations experienced during the last century, there appear to be indications that ozone concentrations are increasing (Feister and Warmbt, 1987; Attmannspa- cher et al., 1984; Hov et al., 1986; Low et al., 1990). Historical records of ozone measurements have been used to characterize concentrations in the last part of the nineteenth century in Europe and North America. Bojkov (1986, 1988) and Volz and Kley (1988) have indicated that ozone concentrations were only about half the mean of surface ozone measure- ments collected in the same region during the last 10-15 years. Bojkov (1986) has reported that Eu- ropean measurements made between the 1850s and 1900 were mostly in the range of 0.017-0.023 ppm. However, other evidence indicates that not all re- gions in Europe were exposed to similar low concen- tration levels. For the period 1889-1900, Lisac and Grubigi~ (1991) have reported higher concentrations for Zagreb, Croatia. The authors reported that for the period 1893-1900, ozone concentrations were approx- imately 0.036 ppm for the average daytime period and 0.030 ppm for the average nighttime period. Lisac and Grubi~i~ (1991) caution that the Zagreb data might be underestimated because the calibration method ne- glected the variation in relative humidity. Similarly, Cartalis and Varotsos (1993) have reported that ozone concentrations measured at Athens, Greece for the 89