The correct answer is the Presence of many air pollutant resources.Smog is a mixture of smoke + fog caused by the burning of large amounts of coal, vehicular emission, and industrial fumes (Primary pollutants).Smog contains soot particulates like smoke, sulfur dioxide, nitrogen dioxide, and other components. Hence, option 3 is correct.The main cause of having dense smog in winter is the presence of high levels of all suspended particles.Increased levels of CO2 can lead to the warming of the earth's atmosphere and thereby can lead to global warming.