Ozone Biomonitoring with Bel-W3 Tobacco Plants in the City of Valencia (Spain) Vicent Calatayud & María José Sanz & Esperanza Calvo & Júlia Cerveró & Wolfgang Ansel & Andreas Klumpp Received: 23 November 2006 / Accepted: 16 February 2007 # Springer Science + Business Media B.V. 2007 Abstract A biomonitoring study using the ozone- sensitive bioindicator plant Nicotiana tabacum cv. Bel-W3 was conducted in the city of Valencia (eastern Spain) and surrounding areas in 2002. Plants were exposed to ambient air at seven sites, including four traffic-exposed urban sites, a large urban garden and a suburban and a rural station, for six consecutive 2-week periods using highly standardised methods. Foliar injury was registered at all stations in at least one of the exposure periods. The urban stations submitted to intense traffic showed lower ozone injury than the less traffic-exposed stations. Strong changes in the intensity of ozone injury were observed for the different exposure periods. Leaf injury was significantly related to both mean ozone values (24 and 12 h means) and cumulative exposure indices (AOT20, AOT40). However, correlation strength was moderate (r s =0.39 to 0.58), suggesting that the plant response to ozone was modified by environmental factors. The use of sensitive bioindi- cators like tobacco Bel-W3 in cities provides com- plementary information to that of continuously operating air quality monitors, as the impact of ambient ozone levels is directly measured. Keywords Air quality . Bioindicators . Tobacco Bel-W3 . Urban air pollution 1 Introduction Ozone is a major component of photochemical smog and is formed through complex photochemical reac- tions involving hydrocarbons and nitrogen oxides as precursors (Chameides and Lodge 1992). The Med- iterranean area is characterized by intense solar radiation, high temperatures, and re-circulation of polluted air masses (Millán et al. 1997, 2000; Sanz and Millán 1998) favouring the formation of this secondary pollutant. In some parts of this area, ozone levels are high enough to cause phytotoxic effects both in crops (Fumagalli et al. 2001) and in native sensitive plant species (Sanz and Millán 2000). Several plant species that develop visible injury have been used as bioindicators of ozone. Among them, ozone-sensitive tobacco cv. Bel-W3 is the most commonly used worldwide, and its response to ozone is the best described. In Europe, this tobacco cultivar has been used in biomonitoring studies at different Water Air Soil Pollut DOI 10.1007/s11270-007-9376-2 V. Calatayud (*) : M. J. Sanz : E. Calvo : J. Cerveró Fundación CEAM, Parc Tecnològic, c/ Charles Darwin 14, 46980 Paterna, Valencia, Spain e-mail: vicent@ceam.es W. Ansel : A. Klumpp Institute for Landscape and Plant Ecology and Life Science Center, University of Hohenheim, 70593 Stuttgart, Germany