Retired jet engines could help clear the smog that smothered big cities.
To land at Indira Gandhi Airport is to descend from clear skies to brown ones. New Delhi's air is poisonous. According to the World Health Organization, India's capital has the most polluted atmosphere of all the world's big cities. The government is trying to introduce rules that will curb emissions-allowing private cars to be driven only on alternate days, for example, and enforcing better emissions standards for all vehicles.
But implementing these ideas, even if that can be done successfully, will change things only slowly. A quick fix would help. And Moshe Alamaro, a researcher at the Massachusetts Institute of Technology, thinks he has one. His idea is to take a jet engine, put it next to one of India's dirty coal-fired power plants, point its exhaust nozzle at the sky and then switch it on. His hope is that the jet's exhaust will disrupt a meteorological phenomenon known as "inversion", in which a layer of warm air settles over cooler air, trapping it, and that the rising stream of exhaust will carry off the tiny particles of matter that smog is composed of. Inversion exacerbates air pollution in Delhi and in many other cities, from Los Angeles to Tehran. A particularly intense example caused the Great Smog of London in 1952, when four days of air pollution contributed to 12,000 deaths.
Dr Alamaro thinks a jet engine could punch through the inversion layer to create a "virtual chimney" which would carry the trapped pollution above it, so that it could be dispersed in the wider atmosphere. He calculates that all the emissions from a gigawatt coal-fired power plant could be lifted away using a single engine with a nozzle speed of 460 metres a second.
However, he has not calculated whether a jet engine could disrupt the inversion layer and allow the pollution to escape the city-so he is now going to test that hypothesis. Within eight months, Dr Alamaro plans to put one of his updrafters next to a coal-fired power plant and monitor what happens using a fleet of drones. He is in discussions with Tata Group, a conglomerate with an electricity-generating arm, to run it next to one of the firm's power stations.
