Mexico City may resort to unproven technology in an attempt to cleanse the city's heavily polluted air. An antenna system designed to alter local rainfall and wind patterns is being tested in the city, despite the scepticism of experts.
Physicists Lev Pokhmelnykh of the Mexican company Electrificacian Artificial de la Atmosfera and Gianfranco Bisiacchi of the National Autonomous University of Mexico are testing an antenna that is designed to ionise the atmosphere, creating nuclei on which water vapour can condense. The researchers expect the air to be warmed by the heat released during condensation, causing the intensity and direction of air currents to change.
By using an array of antennae to either create or neutralise ions, they hope to influence local wind patterns and rainfall. Since most of Mexico City lies within a valley, wind and rain can help to disperse air contaminants that often reach high concentrations within the confines of the surrounding mountains.
But Sherwood Rowland of the University of California at Irvine, who won a Nobel prize for his work on atmospheric chemistry, says that natural radioactive materials continually decay and ionise the air. Within a cubic centimetre of atmosphere, about 3000 free electrons are generated every second. So any attempt to alter the natural level of ionisation would require the addition or removal of an enormous number of electrons.
Dionisio Moreno, a physicist in Mexico's environment department, says a government committee evaluating the project -- of which he is a member -- remains sceptical. He says they are still unable to detect a clear change in the intensity or direction of any winds produced by the antenna. "Preliminary results are insufficient," he says. More recent results, presented by Bisiacchi and Pokhmelnykh on 15 January, are still being analysed.
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