Air pollution control is the use of devices to limit or prevent the release of substances that cause pollution in the atmosphere. In a wider sense, air pollution control involves identifying the sources of contamination, and developing improved or alternative technologies and sources of raw materials, and persuading individuals and industries to adopt these. Automobile emission has been, and continues to be, a key area for research, exploring avenues such as recycling and thorough oxidation of exhaust gases; and the production of lead-free gasoline, and the development of alternatives to the conventional internal-combustion engine. On the industrial front, flue-gas cleansing using catalytic conversion or centrifugal, water-spray, or electrostatic precipitators has becoming increasingly widespread. The matching of smokestack design to local meteorological and topographical conditions is important for the efficient dispersal of remaining pollutants.