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Measurements of air volatile organic compounds (VOCs) and ozone concentrations in different rural sites of Catalonia (NE Spain) were conducted during 1995 and 1996, and the effects of ozone concentrations on biogenic emissions of Mediterranean plants were studied in open topchambers. A significant positive relationship was found between tropospheric ozone and VOC concentrations, which followed seasonal (maximum in early summer and minimum in early winter) and geographical (slightly larger concentrations in interior than in coastal sites) patterns. Results in the open top chambers fumigation experiments showed species-specific responses. There was no significant effect of ozone onVOCs and terpene emission by Aleppo pines, Pinus halepensis L., but there was an order of magnitude increase in VOC emission with increasing tropospheric ozone concentrations (plus 40 nl L-1) in tomatoes, Solanum lycopersicum L. var. Tiny Tim. This response of tomato plants thus opens the possibility of a positive feedback for tropospheric ozone formation. [ABSTRACT FROM AUTHOR]

This paper describes results of experiments carried out by participants of the UN/ECE ICP-Crops to investigate the dose response of plants to long-term ozone exposure. The data were analyzed to determine the influences of climatic and geographical factors upon this dose response. Members of the ICP-Crops carried out experiments at 12 sites inEurope, covering a geographical range from Jokioinen, Finland, to Milan, Italy, to generate the database used in this study. The effects of ozone were determined using N-(2-(2-oxo-1-imidazolidinyl)ethyl)-N'phenylurea (ethylene diurea; EDU) as a protectant against ozone damage. Thus, the ratio of biomass in EDU-treated plants to untreated plants indicated the severity of ozone damage. Simple linear regression produced a low r2 of 0.16 for the dose response. Analysis of the residuals identified three groups in the data depending on their mean residual values. Re-plotting the data into separate dose responses for these three groups produced improvements in the r2 values to 0.33, 0.36 and 0.36, for Groups 1 to 3, respectively. Thedata were subsequently used to train artificial neural network (ANN)models to determine the factors that caused the scatter within the dose response. Vapor pressure deficit and temperature were found to beimportant influences on the dose response whereas longitude, year and altitude were weaker influences. Inclusion of these factors in the ANN model increased the r2 of the model to 0.79. [ABSTRACT FROM AUTHOR]