Characterizing surface ozone concentrations in Norway

Abstract

This paper focuses on 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 experienced at the monitoring sites were below 0.10 ppm and, in most cases, sites experienced fewer than 5% of their hourly average concentrations ⪖0.06 ppm. The lowest maximum hourly average concentrations occured 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 occurences of hourly average concentrations ⪖0.06 ppm were reflected in the absolute values of the exposure index that summed the hourly average concentrations ⪖0.06 ppm (SUM06). In most cases, values for 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 affecting vegetation. For most of the sites, the long-term 7 h (0900–1559 h) and 12 h (0700–1859 h) seasonal average concentrations were in the range of 0.030–0.040 pp. 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 occurence of repeated high hourly average concentrations. There was a large number of daily 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 potentialm fof ozone concentrations to affect vegetation.