Previous research based solely on laboratory experiments indicated crop yields were unlikely to be affected by ozone because plants in the study showed no visible signs of foliage damage. For rape, the quality of the seed was detrimentally affected by ozone, again inferring the pollutant may be having 'invisible' effects on agricultural production. Ground-level ozone is created when nitrogen oxide emissions, primarily from automobiles and power plants, react with oxygen in the air. Although controls exist in the UK for emissions of ozone precursor gases such as nitrogen oxide from vehicles and industrial plants, pollutants still manage to travel far and wide, damaging crops and impacting human health in rural areas. Ground-level ozone interferes with a plant's ability to produce and store food, so that growth, reproduction and overall health are compromised.
Plants exposed to ozone are more susceptible to disease, pests and environmental stresses.
In the United States, smog has been shown to reduce agricultural yields for vital crops such as soybeans, kidney beans, wheat and cotton. There are options to help lessen ozone's insidious effects, according to Lyons. They include resistant crop varieties, chemicals specially developed to protect crops from ozone, conventional breeding programs and transgenic technology to develop more ozone resistant plants. In the study, crops grown in field plots on University of Newcastle land were exposed to controlled doses of ozone. While there was no visible damage to the crops, researcher John Ollerenshaw found that in oilseed rape, for example, the number of flowering branches produced by individual plants fell by 38 percent.