Account for the following : Electrical precipitation of smoke.
Electrostatic smoke precipitators work by driving polluted flue gas (the gas exiting from a chimney) past two electrodes (electrical terminals) inside a pipe or smokestack, which can be metal wires, bars, or plates. A very high negative voltage is applied to the first electrode. The dirt particles pick up a negative charge as they pass by. A second electrode, made out of metal plates charged to a high positive voltage, is located higher up the pipe (or further along if it's a horizontal pipe). Because opposite charges attract, negatively charged soot particles are drawn to positively charged plates and adhere to them. The collecting plates must be shook from time to time to empty the soot; this can be done manually or automatically.
