Daily ozone patterns and AOT40 index on the East Coast of the Iberian Peninsula

The results from the Valencian Community air quality network show that with in a natural pathway of air mass transport (e.g. a valley) three different O-3 diurnal patterns are clearly distinguished: high elevation (I-IE), mid- elevation (ME) and coastal sites (CE). HE are characterised by maintaining an almost constant high O-3 level throughout the day (no diurnal cycle). CE have maximum levels coinciding with daylight hours and close-to-zero O-3 l evels at night (diurnal cycle). At ME the maximum values occur in the dayli ght hours; however, O-3 levels never drop to zero. These different patterns occur within a spatial range of 50 to 60 Km,which implies a huge spatial v ariability in the area, and may strongly affect the values of several indic es, e.g. the AOT40. Thus, AOT40 indices for 3 months are calculated as a ru nning value through the year and compared for the different O-3 patterns. A lso, several daylight windows have been applied in the AOT40 calculations i n order to check the sensitivity of the index to the daylight window choice and to the different daily ozone patterns, compared to the AOT40 calculate d for hours with radiation>50W/m(2) (real daylight period) and to the total exposure dose (TED, 24 h). It has been concluded that most windows estimat e up to 90% of the TED in CE, and the estimations drop below 50% of the TED in non-diurnal cycle sites. This could be of importance for species whose period of stomatal conductance do not correspond to the daylight hours. (C) 1999 Elsevier Science Ltd. All rights reserved.