@@1. Introduction The adverse effects of tropospheric ozone (O3) on vegetation, especially at high concentration levels, are now widely admitted. A lot of evidences have been reported over recent years describing the damaging effects of ground level O3 to vegetations in Europe and USA (Fumagalli et al., 2001; Pleijel et al., 2004). Field experiments, for example, the National Crop Loss Assessment Network (NCLAN) experimental studies in the US in the early 1980s and the European Open-Top Chamber (EOTC) studies in 1987-1991, found that elevated surface O3 concentrations can substantially reduce grain yields. Based on the NCLAN results, the US EPA estimated that due to ambient O3 concentrations, the yields of about one third of US crops decreased by 10 % (EPA, 1996). Exposure to ambient O3 was estimated to have reduced US soybean production by 10% on a national average in 2005 (Tong et al., 2007). In some areas such as California, the losses were likely higher. Much of the European Union could be losing more than 5% of their crops yield due to exposure to O3 (Simpson et al., 2007).
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