A numerical analysis of the combined open-top chamber data from the USA and Europe on ambient ozone and negative crop responses

Statistical analysis was performed using selected sets of combined data from the US National Crop Loss Assessment Network and the European Open-Top Chambers Programme to examine the relationships between the occurrences of hourly ambient ozone (O-3) concentrations and adverse crop yield responses. The results suggest that the frequency of occurrences of relatively low hourly O-3 concentrations (similar to < 35 ppb) are not as important as moderate to higher concentrations in eliciting negative crop biomass responses. They also suggest that daily peak (highest) hourly O-3 values (similar to > 90 ppb) may not be as critical, most likely because they frequently do not occur during time periods when conditions that promote atmospheric conductivity (O-3 deposition) and plant uptake (O-3 absorption) are in coherence. (C) 1998 Elsevier Science Ltd. All rights reserved.