What is the primary cause of smog?

The primary cause of smog is the combination of carbon monoxide and sulfur dioxide. Smog is a type of air pollution that typically results from the interaction of sunlight with pollutants in the atmosphere, particularly when particulate matter and gaseous emissions are involved. Carbon monoxide is a byproduct of combustion processes, such as those produced by vehicles and industrial operations, while sulfur dioxide is commonly released from burning fossil fuels like coal and oil. When these pollutants interact with other atmospheric components, especially under specific weather conditions, they contribute to the formation of smog, which can have significant health and environmental impacts.

Other options refer to conditions that do not directly lead to the formation of smog. Excessive rainfall can help clear air pollutants, while high levels of oxygen and low humidity do not create the chemical reactions necessary for smog formation. Therefore, recognizing the specific pollutants that contribute to smog is crucial for understanding its causes and developing strategies to mitigate its impact.