Ozone is an allotrope of oxygen, and ozone is formed when visible light (violet to more energetic like UV-A) strikes NOx in the presence of VOC. When ozone is found in the air we breathe, it is considered a pollutant. In the upper atmosphere, ozone is formed a different way, and is beneficial. Ozone does not survive long enough to go from Earth's surface to the lower stratosphere (where the ozone layer is)... it is too unstable.
Smog is usually comprised of photoactivated NOx or VOCs. These compounds are emitted by most combustion processes, although even methane counts as a VOC. Smog is pollution, its constituents are considered pollutants.
NOx = oxide of nitrogen
VOC = volatile organic carbon