Protecting agricultural crops from the effects of tropospheric ozone exposure: Reconciling science and standard setting in the United States, Europe,and Asia

Ozone (O-3) is well documented as the air pollutant most damaging to agricu ltural crops and other plants. Most crops in developed countries are grown in summer when O-3 concentrations are elevated and frequently are sufficien tly high to reduce yields. This article examines the difficulties in scient ifically determining the reduction in yield that results from the exposure of agricultural crops to surface O-3 and then transforming that knowledge i nto efficient and effective regulatory standards. The different approaches taken by the United States and Europe in addressing this issue as well as t he few studies that have been conducted to date in developing countries are examined and summarized. Extensive research was conducted in the United St ates during the 1980s but has not been continued. During the 1990s, the Eur opean community forged ahead with scientific research and innovative propos als for air-quality standards. These efforts included the development of a ''critical level''or O-3 based on a cumulative exposure above a cutoff conc entration below which only an acceptable level of harm is incurred. Current research focuses on estimating O-3 dosage to plants and incorporating this metric into regulatory standards. The US regulatory community can learn fr om current European scientific research and regulatory strategies, which ar gue strongly for a separate secondary standard for O-3 to protect vegetatio n. Increasing impacts Of O-3 on crops are likely in developing countries as they continue to industrialize and their emissions of air pollutants incre ase. More research is needed on surface O-3 concentrations in developing co untries, on their projected increase, and on the sensitivity that crop cult ivars used in developing countries have to O-3. The threat of reduced agric ultural yields due to increasing O-3 concentrations may encourage developin g countries to increase their energy efficiency and to use different energy sources. This could simultaneously achieve a local benefit through improve d regional air quality and a global benefit through a reduction in the emis sion of greenhouse gases.