Air pollution research. Information sign and gas supply tanks (white) at the FACE (Free-Air CO2 and O3 Enrichment) project. This studies the effects of ozone (O3) and carbon dioxide (CO2) pollution on plants. A system of pipes (not seen) supply O3 and/or CO2 to plants in the open air. Ozone is a gas formed by chemical reactions between oxygen and pollutants in the lower atmosphere. Carbon dioxide is formed by burning fossil fuels. Levels of both pollutants are predicted to rise. Carbon dioxide increases plant growth, but ozone reduces it. The FACE site, which started 1989, is located in Wisconsin, USA.
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