Which of the following contributes most to ground-level ozone formation?

Vehicle emissions are the primary contributor to ground-level ozone formation due to the release of nitrogen oxides (NOx) and volatile organic compounds (VOCs) during fuel combustion. When these pollutants interact with sunlight, they undergo chemical reactions that lead to the formation of ozone. This process is most prevalent in urban areas where vehicle traffic is dense, making it a significant concern for air quality and public health.

In comparison, while industrial processes and agricultural activities also release pollutants that can contribute to ozone formation, vehicle emissions are typically a more significant source due to their volume and the concentration of NOx and VOCs emitted in many regions, especially those with high traffic. Forestation does not contribute to ground-level ozone formation; rather, it can help improve air quality by absorbing carbon dioxide and providing oxygen, though it doesn't directly influence ozone levels.