Urban pollutions are a major environmental issue in many cities around the world. One of the most common forms of urban pollution is smog, which is a combination of smoke and fog created by the burning of fossil fuels. Smog is a major contributor to air pollution and can cause a variety of health problems. It is also a major contributor to global warming, as it traps heat in the atmosphere. Smog is a five-letter word, and is one of the most common forms of urban pollution.