Lot of vehicles pass through a crowded crossing. These vehicles, emit harmful gases in the form of smoke. Due to which, the concentration of harmful gases and dust particles increases in such places. The policemen have to stand in this polluted air for long period of time and regulate traffic. Inhaling this air for prolonged period of time may affect their health. The masks help filter the polluted air. Hence, policemen regulating traffic at crowded crossing wear masks.