Ozone and NO2 exchange to fruit orchards

Critical levels proposed for ozone to protect sensitive plant species including cereal and fruit crops are exceeded throughout the rural U.K. in most summers. Negative growth rates can occur in ozone polluted air. Predictions of future crop yields based on pollution scenarios require information on the deposition rates of the various pollutants. In this paper we present canopy scale measurements of ozone and NO2 deposition to a fruit orchard, apple (Pyrus Coronaria) in a semi-rural environment. Daytime deposition velocities for ozone were found to vary from 3 to 5 mms-1 while nocturnal values varied from 0.5 to 2 mms-1. Canopy uptake of ozone was primarily under stomatal control. NO2 deposition velocities were variable but could reach high values of up to 6 mms-1 probably due to soil uptake beneath the orchard canopy rather than by canopy stomatal uptake. There was evidence for a canopy NO2 compensation or equilibrium point, CCP(NO2), of approximately 4 ppbv consistent with model predictions of the bidirectional NO2 flux if an alpha value of 0.9 is used.