Ozone episodes

Bilger has documented ozone and other oxidant measurements in Australia and compared them with those in other cities. Table 4-6 shows the portion of hours during which threshold concentrations were exceeded in Sydney in 1971, 1972, and 1973. Low concentrations were recorded before 1970, probably because of the proximity to nitric oxide emission sources in the central portion of the city. It is also noteworthy that, despite the calm conditions and strong inversion in the winter months (in the Southern Hemisphere), high-oxidant days were relatively infrequent. Figure 4-8 outlines this seasonal variation in oxidant concentration. In Melbourne, Australia, however, a high-ozone episode was observed during... 

Peleg, M M. Luria, G. Sharf, A. Vanger, G. Kallos, V. Kotroni, K. Lagouvardos, and M. Varinou, Observational Evidence of an Ozone Episode over the Greater Athens Area, Atmos. Environ., 31, 3969-3983 (1997). 

Acidic deposition smog (for example, ground-level ozone episodes) ... 

The normal-ozone daily maxima of UV-ERY irradiance may be exceeded in extremely low (Q < A-2S) total ozone episodes during time period longer than 214 hours (local noon V 80 minutes) and the UV-ERY maximum exceeds the normal-ozone maximum by about 25% in this situation. 

Sillman S., Logan J. A., and Wofsy S. C. (1990) The sensitivity of ozone to nitrogen oxides and hydrocarbons in regional ozone episodes. J. Geophys. Res. 95, 1837-1851. 

During regional scale ozone episodes, elevated concentrations become widespread across Europe [20]. Transboundary transport is an important feature of the problem. The concentrations exceed air quality guidelines set to protect human health [22] and critical levels set to protect crops and trees firom ozone damage. To illustrate the approach, the target ecosystem is taken to be human health so that the sensitive ecosystems can be located in the major urban centres of London, Paris, Brussels, Bonn, Amsterdam, Copenhagen, Stockholm and Oslo. For these ecosystems, the maximum hourly mean in a worst-case episode is the most appropriate index of harm. 

S Beaver and A Palazoglu. A cluster aggregation scheme for ozone episode selection in the San Francisco, CA Bay Area. Atmospheric Environment, 40 713-725, 2006. 

Grigorieva, V., S.Kolev and M.Mihalev Investigation of correlations between the high surface ozone episodes and the stratospheric intrusion events, Proc. SPIE Int. Soc. Opt. Eng. (in press). 

Figure 6.4 Illustration of comparative sources which contribute to an ozone episode in Northern Europe.

Figure 6.6 Contribution to non-methane VOC. (a) By mass, (b) POCP weighted. NB These charts are for annual emissions. The natural emissions coincide with the summer ozone episode season. During the critical period, natural emissions may represent 60% or...

The maximum acceptable level for ground-level ozone in Canada is set at 82 ppb over a 1-h period (see Fig. 0-11). An episode occurs when the average ozone concentration exceeds 82 ppb for 1 h or more. Ozone episodes in Canada t3q)icaUy last from one to a few days. It is considered that natural levels of ozone in unpolluted conditions would range between 15 and 25 ppb. 

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