Assessment of tropospheric ozone effects on citrus crops using passive samplers in a western Mediterranean area

This work assesses the effects caused by tropospheric ozone on citric crops in “La Plana de Castellon”, a western Mediterranean area rich in orange orchards. Passive ozone samplers were used as an alternative tool to monitor the ozone levels, to assess the effects of ozone levels on citrus crops, and to estimate the percentage of losses in harvest crops. Measurements were taken during the 3-month periods of higher ozone levels in the summers of 2001, 2002 and 2003. Measurement campaigns were divided into sampling periods of 1 week. Twenty samples were collected during each sampling period to cover an area of 8000 km2. Summer weekly ozone levels ranged between 40–44 μg/m3 in 2001, 54–70 μg/m3 in 2002 and 34–44 μg/m3 in 2003. To assess the effects on orange and lemon trees, a linear equation which described the relationship between ozone concentrations and citrus trees yields was employed. There was an estimated 8% reduction in orange and 11.5% reduction in lemon yields in the year 2003 due to the average ozone levels in the year 2001, a 10% reduction in orange and 14.2% reduction in lemon yield in the year 2004, due to the average ozone levels in the year 2002 and an estimated 7% reduction in orange and 9.8% reduction in lemon yield in the year 2005 due to the average ozone levels in the year 2003. These yield losses may negatively affect the local economy of the area. Passive samplers also proved to be a useful tool for assessing the response of citrus trees to environmental photochemical stress due to tropospheric ozone.