Final answer:
Vog consists of acidic aerosols formed from sulfur-based gases emitted by volcanoes, while urban smog is composed of hydrocarbon emissions from vehicles.
Step-by-step explanation:
The main difference between volcanic fog, or vog, and urban smog is their composition. Vog consists of acidic aerosols formed from sulfur-based gases, specifically sulfur dioxide (SO₂), which is emitted by volcanoes. On the other hand, urban smog is composed of hydrocarbon emissions from vehicles, such as nitrogen oxides (NOx) and volatile organic compounds (VOCs).